open access original research physical preparation and ......physical preparation and return to...

Physical preparation and return toperformance of an elite female footballplayer following ACL reconstruction:a journey to the FIFA Women’sWorld Cup

Matt Taberner ,1 Nicol van Dyk ,2 Tom Allen ,3 Neil Jain,4 Chris Richter ,5,6

Barry Drust ,7 Esteban Betancur,8 Daniel D Cohen 8,9

ABSTRACTACL injuries are among the most severe knee injuries in elitesport, with a high injury burden and re-injury risk. Despiteextensive literature on the injury and the higher incidence ofinjury and re-injury in female athletes, there is limitedevidence on the return to sport (RTS) of elite female footballplayers following ACL reconstruction (ACLR). RTS is bestviewed on a continuum aligning the recovery andrehabilitation process with the ultimate aim — a return toperformance (RTPerf). We outline the RTS and RTPerf of anelite female football player following ACLR and her journeyto the FIFA Women’s World Cup, including the gym-basedphysical preparation and the on-pitch/sports-specificreconditioning. We used the ‘control–chaos continuum’ asa framework for RTS, guiding a return above pre-injurytraining load demands while considering the qualitativenature of movement in competition. We then implementedthe ‘RTPerf pathway’ to facilitate a return to team training,competitive match play and a RTPerf. Objective information,clinical reasoning and shared decision-making contributedto this process and helped the player to reach her goal ofrepresenting her country at the FIFA Women’s World Cup.

INTRODUCTIONACL injuries are one of the most severe kneeinjuries in professional sport. While injuryincidence is low, time loss is substantial andthe associated burden is high.1 There isa large body of research examining ACLinjury mechanisms, associated risk factorsand risk reduction in female athletes.2–4 Atthe amateur level, an estimated 32% of femalefootball players do not return to sport (RTS),and those who do return to competition havea high re-injury risk, particularly to the con-tralateral limb.5

Contrary to expectation following ACLinjury, many athletes fail to reach their previouslevel of performance.6 Potentially, this is due tothe over-reliance on traditional time-basedcriteria for rehabilitation progression andRTS, which may overlook individual variation.

Individualised rehabilitation should not onlyconsider the specifics of the injury but shouldalso take into account, and ideally quantify, thevariability between player’s competitivedemands, their cognitive, neuromuscular andmechanical response to the injury, and the con-sequent unloading and the subsequent

To cite: Taberner M, van Dyk N,Allen T, et al. Physicalpreparation and return toperformance of an elite femalefootball player following ACLreconstruction: a journey to theFIFA Women’s World Cup. BMJOpen Sport & Exercise Medicine2020;0:e000843. doi:10.1136/bmjsem-2020-000843

► Supplemental material ispublished online only. To viewplease visit the journal online(http://dx.doi.org/10.1136/bmjsem-2020-000843).

Accepted 22 September 2020

© Author(s) (or theiremployer(s)) 2020. Re-usepermitted under CC BY-NC. Nocommercial re-use. See rightsand permissions. Publishedby BMJ.

For numbered affiliations seeend of article.

Correspondence toMatt Taberner;[email protected]

Key points

► Beginning early in the process, strength and powerdiagnostic tests implemented throughout rehabilitationcan quantify the (1) willingness to load the involvedjoint, (2) effectiveness of progressive ‘optimal loading’targeting individual limb and bilateral performancedeficits and interlimb asymmetries/avoidancestrategies, and (3) status of asymmetries and deficitsrelative to pre-injury data where available, or sports-/phase-specific reference data.

► The ‘control–chaos continuum’ providesa framework to plan progressive sports-specificconditioning, technical skill integration, and returnto the required chronic running load demands, whileconsidering the qualitative nature of movement incompetition.

► The ‘RTPerf’ pathway provides a conceptual modelthat helps guide planning and decision-makingaround player re-integration to the team trainingenvironment, progressive exposure to competitivematch minutes and subsequent RTPerf.

► RTPerf follows RTS and is characterised by multipleindicators — a combination of quantitative; matchcompared to pre-injury outputs, the ability toproduce, and cope with concurrent running loadsand qualitative information; video demonstratingpre-injury playing traits and coaching perspectiveincluding frequent selection for competition. Theplayer’s performances and higher physical outputsin the World Cup and during competition 1-yearpost RTS suggest that in the current case, theplayer’s expectation to return to previousperformance had indeed been achieved.

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response to components of reloading applied during therehabilitation process.7

A performance-based rehabilitation process followingACL injury should aim to identify and resolve deficits inneuromuscular performance, providing conditioning ofsufficient intensity, volume and specificity to prepare anelite athlete for the demands of their sport. A ‘return tofunction’ may therefore not be an appropriate paradigmfor elite sport,8 due to the far higher demands imposedon these athletes. Additionally, sports science and medi-cal practitioners are also under pressure to return athletesearlier thanmight be considered completely safe.9 There-fore, the integration and accumulation of adequatesports-specific loading and the use of objective tools tocontrol and quantify load while monitoring the responseare important means to mitigate the increased risk that isassociated with an accelerated return. A performance-based approach should go beyond returning an athleteto their previous condition or simply integrating condi-tioning to rehabilitate the injury. Physical preparationshould also aim to return the athlete with greater capabil-ities than pre-injury, while recognising certain aspects ofperformance may only fully recover after exposure tocompetition. As such, monitoring of neuromuscular per-formance should extend beyond RTS to characterise anathlete’s response to competition and their journeytowards a return to performance (RTPerf).

10

Currently, there is little published research describingthe RTS or RTPerf process in elite female football playersfollowing ACL reconstruction (ACLR). In this article, weoutline the gym-based physical preparation and on-pitch/sports-specific reconditioning of an elite female footballplayer following ACLR, and her journey towards a RTPerfat the FIFA Women’s World Cup. We used the ‘control–chaos continuum’11 as a framework for sports-specificphysical preparation and RTS. Within the RTScontinuum,12 we also outlined an ‘RTPerf pathway’,13

which aids a progressive return to team training, competi-tion and ultimately, a RTPerf.

CASE SCENARIOThe 24-year-old female player, who gave informed con-sent for the use of her information was a New ZealandInternational central midfielder with 8 years of playingexperience across the US collegiate system (2012–2016),Icelandic league (2016–2017), English Women’s SuperLeague (2017–current) and at International level since2011. She ruptured her left ACL in contact made duringa tackle in an English Women’s Super League match. Shewas unable to play on or weight-bear in the immediateperiod following the injury. AnMRI scan was performed 2days later and revealed a mid-substance full-thickness tearof the ACL (figure 1A), along with a partial tear of thepopliteal attachment of the posterior inferior meniscalpopliteal fascicle (figure 1B) and a partial tear of thepopliteofibular ligament (figure 1C). Ten days later shewas assessed by a consultant Orthopaedic surgeon. Shedescribed no instability or locking symptoms but was

uncomfortable weight-bearing. She also reported no pre-vious injuries or family history of ACL tears.Clinical examination revealed normal lower limb align-

ment, mild quadriceps atrophy and a persistent mildeffusion. There was no joint line tenderness, and menis-cal provocation tests were negative. Her range of move-ment was restricted from 10° to 80° flexion, incomparison with a hyperextension of 5° and flexion to130° on her uninvolved limb. She had mild tenderness topalpation at the origin of the medial collateral ligament,but this was stable on valgus stress testing. Lachman’s andAnterior Drawer tests were positive. The pivot-shift testdemonstrated a positive glide and the dial test was nega-tive. There were no signs of generalised ligamentoushyperlaxity.Sixteen days later (1 month post-injury), the player

underwent ACLR once her effusion was fully resolvedand she had regained full range of motion. Surgery wasperformed under general anaesthetic using a 7.5 mmfour-strand autologous hamstring (semitendinosus andgracilis) graft that was prepared along its length witha #2-Fibreloop suture (Arthrex, Naples, FL, USA).A ligament preservation (single-anteromedial bundle bio-logical augmentation type) technique14 was used for thereconstruction, which preserved about 60% of her origi-nal ACL (figure 1D). Suspensory fixation using a corticalbutton with an adjustable loop was used for femoral fixa-tion introducing the graft into a femoral socket of20 mm×7.5 mm within a total femoral drill length of34 mm. An 8 mm×28 mm tapered biocomposite interfer-ence screw was used for tibial fixation (Arthrex) withina tibial tunnel with a diameter of 7.5 mm. There were noassociated chondral lesions seen at the time of the arthro-scopic surgery, and nomeniscal tears (including root andRAMP tears) were observed following direct visualisationand probing. Post-reconstruction examination underanaesthesia produced a normal pivot-shift test and nor-mal Lachman’s test. It was determined that the knee wasstable and therefore it was not indicated to address thepartial tears of the meniscal popliteal fascicle or popliteo-fibular ligament, with the expectation that these wouldheal non-operatively. Weight-bearing and range ofmotion were permitted immediately following surgery,and no brace was used.The player’s RTS was viewed on a continuum, align-

ing her recovery and rehabilitation (figure 2)12 withthe goal of returning her to full-team training/com-petition and an opportunity to challenge for WorldCup squad selection. The main objectives of early man-agement (0–4 months; figure 2), led by a club phy-siotherapist, were to minimise pain and swelling,resolve arthrogenic muscle inhibition, re-establishrange of motion and limit muscle atrophy throughearly loading.15 Following this, reconditioning wasintegrated based upon the optimal loading concept— to maximise adaptation of the healingstructures,16 while throughout the RTS process beingmindful of the biological healing timeline, pain was

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assessed with a numerical rating scale and joint effu-sion, which were monitored daily.

INFORMING PROGRESSION THROUGHOUT RTSStrength and power diagnostic tests were used to assessand objectively quantify progress in strength and powerqualities.11 17 Global Positioning Systems (GPS) data wereused to plan and provide a quantitative assessment of on-

pitch running load throughout the RTS process, follow-ing a return to on-pitch reconditioning. These were keyelements of objective data that informed decision-makingalongside clinical reasoning and experience.11

The dual-force platform double-leg countermovementjump (CMJ) was our core strength and power diagnostictest, used to characterise changes in specific neuromus-cular qualities represented by eccentric (downwards),

Figure 1 MRI and intra-operative imagining following ACL injury and surgical repair. (1) Post-injury MRI; (A) T2 image showingacute mid substance ACL rupture with associated pivot shift related osseous contusion on the sulcus terminalis and along theposterior margin of the lateral tibial plateau. No osteochondral fracture or step deformity in either contusion region. (B) Acute partialtearing of the popliteal attachment of the posterior inferior meniscal popliteal fascicle. No associated lateral meniscal tear. (C)Acute partial tearing of the popliteofibular ligament. (D) Intra-operative image; pink arrow represents ligament preservation(SAMBBA type) technique used for the reconstruction preserving ~60% of the players original ACL, blue arrow represents ACLgraft. (E) Post-operative (18 months) MRI; T1 sagittal image showing a grossly intact ACL reconstruction with evidence ofligamentisation. SAMBBA, single-anteromedial bundle biological augmentation.

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concentric (upwards) and landing phase force, impulse,velocity, power and centre of mass displacement variablesand was also used to monitor load-response. Asa component of squad preseason and in-season monitor-ing, the player was familiarised with the test, and impor-tantly, her healthy pre-injury ‘benchmark’ data wasavailable. The CMJ phase-specific variables and asymme-tries (figure 3A,B and online supplemental appendix)derived from vertical ground reaction force time dataare not joint-specific but are considered clinicallyrelevant18 19 due to associations with knee kinetic deficitsand function post-ACLR. While significant asymmetriesare observed across the three phases of the bilateral CMJfollowing ACLR and other lower limb injuries, those inthe CMJ eccentric deceleration (countering negativevelocity during the downward phase) and landing(impact load absorption) phases, characterised as com-pensatory strategies to attenuate involved knee loadingare especially persistent and of concern as post-ACL they

are associated with poorer knee function.18 20–23 Theseasymmetries are however reported to be lower followingsemitendinosus-gracilis than patellar tendon autografts.24

We used the CMJ data (individual limb outputs and CMJbilateral performance variables (table 1; figures 4 and 5),referenced to the player’s pre-injury values, to quantifyearly post-surgery deficits/compensatory strategies, thento monitor the response of targeted components of neu-romuscular function to conditioning and to inform pro-gression decisions.11 25 Gathercole26 characterised thejump height, peak power and variables typically reportedin CMJ performance as CMJ-TYP, and those that quantifyphase durations, and rates/or time-limited force, powercharacteristics or CMJmechanics during eccentric and con-centric phases as alternative variables (CMJ-ALT).26 27 It iswell documented that changes in CMJ-ALT variables reflect-ing underlying neuromuscular/biomechanical ‘strategy’alterations may not be expressed in CMJ-TYP and thereforeare more sensitive to both acute and residual fatigue

Figure 2 An overview of the return to performance (RTPerf) of an elite female football player following ACL reconstruction (ACLR).Early rehabilitation phase (0–6 months): early physiotherapy care (0–4 months), gym-based physical preparation (4–6 months)including isometrics (ISO), jump-landing preparation (J-L PREP), dynamic strength training (DYN), blood-flow restriction resistanceexercise (BFR-RE) alongside blood-flow resistance aerobic exercise (BFR-AE) and anti-gravity treadmill running (A-GR). Return toparticipation phase (6–9.5 months); on-pitch/sports-specific reconditioning using the ‘control–chaos continuum’ (on-pitch weeksdisplayed) plus gym-based physical preparation; progressive dynamic strength training (DYN+), BFR-RE+ and J-L PREP+. Withsurgeon discharge and RTS criteria completed the player returned to sport and followed the RTPerf pathway (10–13 months;on-pitch weeks displayed), and progressive optimal loading continued (DYN+, BFR-RE+ and J-L PREP+) until the player reachedthe Women’s World Cup preparation period; optimal loading was then modified due to increased match play and maintainedthrough an RTPerf at the FIFA Women’s World Cup (13–14 months+). During the RTS process, objective measures includedthe countermovement jump (CMJ — Submax; submaximal and Max; Maximal — colour coded in-line with Max test number —figures 4 and 5), isometricmid-thigh pull (IMTP; figure 6B), isometric hip strength (ISOHIP; figure 6A), isokinetic dynamometry (IKD)and DEXA (table 3) were used alongside daily assessment of pain (<2/10 numerical rating scale) and degree of joint effusion. DEXA,dual-energy X-ray absorptiometry; RTS, return to sport.

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Tab

le1

Selec

tedtren

dsin

coun

term

ovem

entjum

p(CMJ)

bilateral,invo

lved

andun

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lved

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tputs,

andinterlimbas

ymmetrie

sco

nsidered

duringthereha

bilitatio

nproce

ss:interpretatio

nan

dinflu

ence

ondec

ision-mak

ing

Pha

seEarly

reha

bilitation(4–6months

)Gym

-bas

edphy

sica

lpreparation

Returnto

participation(6–9.5months

)On-

pitch

reco

nditioning

andgym

-bas

edphy

sica

lpreparation

CMJTes

tsCMJSUB-M

AX

CMJSUB-M

AX→

CMJMAX1

CMJMAX1→

CMJMAX2

CMJMAX2→

CMJMAX4

CMJMAX5

RTSCRITERIA

Wha

twere

theke

ytren

dswe

obse

rved

andho

wwe

interpreted

them

75%

dec

reas

ein

jumphe

ight,

58%

dec

reas

eec

centric

pea

kve

locity

and27

%dec

reas

ein

coun

term

ovem

entd

epth

relativ

eto

pre-injury.

Indicativeof

aco

mbinationof

capac

itydeficits

andstrategies

(dec

reas

edland

ingim

pac

t,dec

elerationdem

andsan

dec

centric

load

ingin

dee

per

knee

flexion

)which

serveto

limit

impac

tand

ecce

ntric

load

s.32

Increa

sesin

ecce

ntric

pea

kve

locity

andco

unterm

ovem

ent

dep

th,w

ithincrea

sedtotal

ecce

ntric

dec

elerationRFD

anda

larger

increa

sein

invo

lved

limb

than

theun

invo

lved

limbou

tput.

Increa

sein

pea

kland

ingforce

(30.2→

61.6

N/kg)

anddec

reas

ein

pea

kland

ingforceas

ymmetry

from

46%

→2%

high

eron

invo

lved

limb.

Tren

dsindicativeof

anincrea

sed

capac

ityan

dwillingn

essto

ecce

ntric

allyload

indee

per

flexion

with

outinv

olve

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avoidan

cean

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senc

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avoidan

cestrategy

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pite

increa

sein

totalp

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ntric

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locity

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→−0.97

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similarec

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both

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itive

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bothinvo

lved

andun

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plyom

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activ

ity,28co

ncurrent

with

anti-

grav

itytrea

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ing

progres

sion

.

Increa

sein

jumphe

ight

(5cm

)alon

gsidedec

reas

ein

indices

oftotalp

eakland

ingforce:

pea

kland

ingforce/bod

yweigh

t(→

48.2

N/kg)

and/ju

mphe

ight

(→10

6N/cm)a

ndan

increa

sein

pea

kland

ingforceas

ymmetry

(from

2%high

eron

invo

lved

to15

%high

eron

uninvo

lved

limb)

due

toalarger

dec

reas

eon

the

invo

lved

limb.

Ove

rall,increa

sesin

capac

ityto

load

onland

ing,

grea

terkn

eefle

xion

inco

unterm

ovem

enta

ndin

estim

ated

knee

flexion

onland

ing;

totalp

eakland

ingforce

indices

now

below

pre-injury

values

with

someload

avoidan

ceev

iden

tontheinvo

lved

limb.

Max

3an

dMax

4testswere

perform

edfollo

wingawee

kof

new

load

ingdem

ands(w

iththe

expec

tatio

nof

residua

lfatigue

affectingva

lues

);wetherefore

cons

idered

Max

2→Max

3an

dMax

3→Max

4se

paratelyto

the

overalltrend

sbetwee

nMax

1→Max

2→Max

5.

Betwee

nMax

2an

dMax

3,large

(15–

18%

)dec

reas

esinforceat

zero

velocity,e

ccen

tric

dece

leratio

nRFD

,con

centric

impu

lse-10

0(selec

tedMax

3an

dMax

4da

tash

ownin

onlinesu

pplemen

tal

appe

ndix).Increa

sedas

ymmetrie

sdu

eto

alarger

decrea

sein

uninvo

lved

than

invo

lved

limb

performan

ce:for

exam

ple,force

atze

rove

locity

Invo

lved

:555

→53

3N;

uninvo

lved

:527

→45

3N;e

ccen

tric

dece

leratio

nRFD

invo

lved

:15

32→13

60N/s;u

ninv

olve

d:

1575

→11

66N/s.

Thetotalforce

atzero

velocity

and

ecce

ntric

dece

leratio

nRFD

tren

ds

sugg

estn

euromus

cularfatigue

25

andfollowed

awee

kwith

3×on

-pitchse

ssions

with

totald

istanc

e:80

40m

(0.8×ga

meloa

d),firs

tex

posu

reto

FWBrunn

ing.

Whilethe

individua

llim

btren

dsin

the

ecce

ntric

pha

seindica

tethatfatig

uewas

asym

metric

al.T

helarger

mag

nitude

offatig

ueon

the

uninvo

lved

limbsu

gges

ting

preferen

tialloa

ding

ofthat

limb/

relativeun

load

ingof

theinvo

lved

limbduringon

-pitc

hrunn

ing

activity.

AtM

ax4des

pite

thetest

performed

followingafurthe

rinc

remen

tin

runn

ingload

;6×on

-pitc

hse

ssions

(totald

istanc

e:20

148m

(1.9×

gameloa

d),the

rewas

some

reco

very

offorceat

zero

velocity

andco

ncen

tric

impulse

-100

but

remaine

dbelow

Max

2ou

tputs.

Thissu

ggestedthat

theplayerwas

beco

mingac

custom

edto

FWB

runn

ing,

adap

tingto

thestim

ulus

andpo

tentially

load

ingless

asym

metric

allyin

on-pitc

htraining

.

Relativeto

Max

2,bilateral

perform

ance

andtotalp

eak

land

ingforceindices

were

relativ

elystab

le,rec

overingafter

thedec

lines

high

lighted

betwee

nMax

2an

dMax

3

Dec

reas

edtotale

ccen

tric

dec

elerationRFD

with

alarger

dec

reas

eon

the

uninvo

lved

than

theinvo

lved

limb,s

uchthat

invo

lved

limb

ecce

ntric

dec

elerationRFD

now

10%

>un

invo

lved

.

Increa

seon

invo

lved

limbpea

kland

ingforce(142

3→16

50N)and

dec

reas

ein

uninvo

lved

limb

(170

2→16

33N)lea

dingto

anas

ymmetry

shift

from

16%

high

eron

uninvo

lved

to1%

high

eron

invo

lved

limb.

Abso

lute

andtren

dsan

d%

asym

metry

indicateagrea

ter

contrib

utionof

theinvo

lved

limb

duringdec

elerationan

dland

ing

load

acce

ptanc

etasks

Tren

dsintotalcon

centric

impulse

show

smallinc

reas

e,with

both

limbsincrea

sing

andasm

all

dec

linein

conc

entric

impulse

asym

metry

to9%

.

While

pre-injury‘ben

chmark’'d

atawereav

ailable

forthe

playe

r,wedid

notc

onsider

ecce

ntric

dec

elerationRFD

asym

metry:1

7%(in

volved

>un

invo

lved

)and

pea

kland

ing

forceas

ymmetry:17%

(uninv

olve

d>invo

lved

)sen

sible

ben

chmarks

toreturn

theplaye

rto.

Instea

d,toqua

lifyhe

rstatus

andprogres

sion

,wewere

guided

bydatafrom

maleEng

lishprofess

iona

lplaye

rswith

outlow

erlim

binjury

intheprio

rse

ason

—ec

centric

dec

elerationRFD

asym

metry:~

10%

,pea

kland

ingforce

asym

metry:~

9%,2021an

dhe

r8-mon

thas

ymmetrie

san

dinvo

lved

limbprogres

sbetwee

n6mon

thsan

d8mon

thsin

theco

ntex

tofv

alue

sin

profess

iona

lmaleplaye

rspos

t-ACLR

(ecc

entricdec

elerationRFD

asym

metry:~

20%

,pea

kland

ingforceas

ymmetry:~

17%

).31

Wealso

cons

idered

thereco

very

ofhe

rab

ility/w

illingn

ess

toec

centric

allyload

atve

locity(ecc

entricpea

kve

locityon

ly1%

less

than

pre-injury).

Weprio

ritised

reco

very

ofec

centric

dec

elerationan

dland

ingload

acce

ptanc

e,bas

edon

eviden

ceof

persisten

ceof

deficits

/avo

idan

cestrategies

inthes

epha

ses1

7192131

andas

sociated

poo

rkne

efunc

tion.

1719How

ever,w

ewere

also

interested

intheprogres

sion

ofov

erallp

erform

ance

andreduc

ingco

ncen

tricim

pulse

asym

metry

which

atRTS

,at

9%was

slightlyab

ovethemea

n+1S

Dof

healthy

uninjuredmaleprofess

iona

lplaye

rs,b

utlower

than

the

~13

%as

ymmetry

inthat

pha

sereportedin

male

profess

iona

lsat

8mon

ths.

31

Relativeto

pre-injuryva

lues

,bilateralp

erform

ance

deficits

forCMJ-TY

Pva

riableswerebelow

10%

;jum

phe

ight:8

%,

conc

entric

pea

kpow

er:3

%,c

once

ntric

pea

kve

locity:1

%.

Deficits

werelarger

forCMJ-ALT

:flig

httim

e:co

ntraction

time:

27%

,con

centric

impulse

-100

:23%

aligning

with

eviden

cethat

thes

edeficits

persist

afterRTC

afterCMJ-

TYPreco

vered21an

dat

leas

tpartly

driv

enbyasu

bstan

tial

chan

gein

coun

term

ovem

entd

epth.

Con

tinue

d

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Tab

le1

Con

tinue

d

Pha

seEarly

reha

bilitation(4–6months

)Gym

-bas

edphy

sica

lpreparation

Returnto

participation(6–9.5months

)On-

pitch

reco

nditioning

andgym

-bas

edphy

sica

lpreparation

CMJTes

tsCMJSUB-M

AX

CMJSUB-M

AX→

CMJMAX1

CMJMAX1→

CMJMAX2

CMJMAX2→

CMJMAX4

CMJMAX5

RTSCRITERIA

Ifan

dho

wthis

inform

ation

influ

ence

ddec

isions

Rathe

rthan

inform

ingdec

isions

,datafrom

thistim

epoint

was

used

prin

cipallyas

apos

t-su

rgery

bas

elineto

guidegy

m-bas

edex

ercise

presc

riptio

n:1)

empha

sising

invo

lved

limb

hypertrop

hyan

dstreng

thdev

elop

men

talong

sidetheir

mainten

aceon

theun

invo

lved

limb2)

progres

sive

integrationof

jump-lan

dingac

tivities

toim

prove

dec

elerationan

dco

ntrol

ofim

pac

tforce

s.

Along

sideothe

rstreng

than

dpow

erdiagn

ostic

s,CMJtren

dsin

bothov

erallp

erform

ance

partic

ularlyin

ecce

ntric

qua

lities

sugg

estiv

eof

apos

itive

resp

onse

toinitial

off-pitc

hco

ndition

ing.

Furthe

rmore,

thes

eresp

onse

swerewith

outm

anife

stingthe

largeav

oidan

cestrategies

/injuredlim

bca

pac

itydeficits

reportedin

profess

iona

lmale

playe

rs6-mon

thspos

t-ACLR

asym

metrie

sof:2

0%inec

centric

dec

elerationRFD

,25%

inpea

kland

ingforcewhilehe

rcon

centric

impulse

asym

metry

was

comparab

leto

the18

%reported

atthistim

epoint.31Th

esetren

ds

gave

usco

nfiden

ceto

progres

sdyn

amic

streng

thtraining

and

jump-lan

dingac

tivities

andto

initiatean

ti-grav

itytrea

dmill

runn

ing.

Intheco

ntex

tofthe

pos

itive

resp

onse

toan

ti-grav

itytrea

dmill

runn

ing,

dyn

amic

streng

thtraining

andincrea

sesin

dec

elerativeload

inginplyom

etric

activ

ities

represe

nted

bythe

substan

tialimprove

men

tsin

bilateralp

erform

ance

across

ecce

ntric

,con

centric

andland

ing

pha

ses,

andthestab

ility

ofec

centric

dec

elerationRFD

asym

metry.T

hiswas

des

pite

increa

sesin

ecce

ntric

pea

kve

locity

andco

unterm

ovem

ent

dep

th,a

ndthelack

ofad

verse

resp

onse

(painor

jointe

ffus

ion)

—indicativeof

thejoint‘co

ping’'

with

load

ingdem

ands,

therefore

wedid

notc

onsider

thepea

kland

ingforceas

ymmetry

increa

sealon

eas

atren

dwhich

warranted

delay

inprogres

sion

toareturn

toon

-pitc

hrunn

ing.

Intheco

ntex

tofreturning

toon

-pitc

hrunn

ing(highco

ntrol)

alon

gsidetheco

ntinue

doff-pitc

hphy

sica

lpreparationan

dab

senc

eof

adve

rsejointres

pon

se,w

eco

nsidered

thedec

lines

insp

ecific

outputsac

ceptable

and

represe

ntativeof

residua

lfatigue

relatedto

thelargeincrem

entin

load

ingdem

andsrather

than

ase

tbac

kto

theproce

ss.

Furthe

rmore,

thes

eva

riables

show

edreco

very

atMax

4des

pite

furthe

rincrea

sesin

runn

ingload

(→20

000m)(P

leas

ereferto

onlin

esu

pplemen

tala

ppen

dix

forfurthe

rdiscu

ssionon

fatig

ue-rec

overy

mon

itorin

gin

reha

bilitatio

n).O

urclinical

riskas

sess

men

twas

that

thes

edatadid

notw

arrant

delay

ing

tran

sitio

nto

themod

erateco

ntrol

pha

se.A

tthisstag

ewith

RTT

(2mon

ths)

andRTC

(3.5

mon

ths)

away

,ens

uringad

equa

teex

pos

ure

toload

ingwas

prio

ritised

over

pea

kperform

ance

.

Theco

ntinue

dim

prove

men

tin

indicatorsof

totald

eceleration

capac

ity/lo

adingwith

outthe

emerge

nceof

invo

lved

limb

avoidan

cestrategies

inco

mbinationwith

theab

senc

eof

pain/jointe

ffus

ionindicated

apos

itive

resp

onse

tothe

asso

ciated

load

ingdem

andsof

early

football-sp

ecificac

tivities

(con

trol

toch

aospha

se)a

ndac

hiev

ingon

-pitc

hrunn

ingload

targets.

Thisga

veus

confiden

ceto

progres

she

rto

mod

erate/high

chao

spha

sesan

dex

pos

ethe

playe

rto

theas

sociated

increa

sesin

volume/intens

ity.

Key

CMJRTS

cons

iderations

includ

edbilateral

perform

ance

progres

s,partic

ularlyindec

elerationca

pac

itywith

oute

xces

sive

avoidan

cestrategies

.Wealso

cons

idered

thegrea

terfle

xion

duringtheco

unterm

ovmen

tan

damoreco

mpliant

land

ingafavo

urab

lesh

iftinstrategy

/ca

pab

ility

inafemaleathletepos

t-ACLR

.33

Asaresu

lt,while

weex

pec

tedfurthe

rincrea

sesin

total

ecce

ntric

dec

elerationRFD

andothe

rec

centric

/SSC

varia

blesduringRTT

andRTC

,wesp

eculated

that

outputs

forthes

eva

riablesmay

notreturnto

pre-injuryleve

lsan

dmight

beco

nsidered

asne

wbas

elines

formon

itorin

g.Figu

res4an

d5doho

wev

ersh

owthefurthe

rreco

very

ofthes

eva

riablesfollo

wingRTC

andareturn

toperform

ance

.

Bilateralp

erform

ance

=co

mbined

limbou

tput

varia

bles.

Thos

eco

nsidered

‘typ

ical’(CMJ-TY

P)(jumphe

ight,c

once

ntric

pea

kpow

er,c

once

ntric

pea

kve

locity),an

dthos

eco

nsidered

‘alte

rnative’

(CMJ-ALT

).CMJ-ALT

varia

bleshe

lpfurthe

ran

dun

derstan

dne

urom

echa

nica

ltrend

sbyqua

ntify

ingch

ange

sin

‘strateg

y’den

otingdurationof

pha

ses(ie

,flig

httim

e:co

ntractiontim

e,ec

centric

/co

ncen

tric

duration)

andin

othe

rtim

e-co

nstraine

dmec

hanica

loutputsac

ross

spec

ificpha

sesan

dsu

bpha

ses(ie

,ecc

entric

dec

elerationRFD

)aswella

sdes

criptors

ofmov

emen

tstrateg

ies(ie

,ec

centric

pea

kve

locity,c

ountermov

emen

tdep

th).2

025262931La

ndingindices

high

lighted

arebod

yweigh

tand

jumphe

ight

relativ

epea

kland

ingforce.

Sev

eralof

thes

eva

riablesan

dco

mpon

ents

aresh

ownin

figure3.

Pleas

ereferto

Figu

re4forco

mplete

dataforpre-injury,

Sub

-max

,Max

1,Max

2,Max

5an

d1-yr

RTS

.See

onlinesu

pplemen

tala

ppen

dixforMax

3an

dMax

4.To

talrefersto

combined

limbva

lues

forava

riable

forwhich

individua

llim

bou

tputsarealso

give

n,forex

ample,total

pea

kland

ingforce=left+rig

htpea

kland

ingforce.

FWB,fullw

eigh

t-bea

ring(run

ning

);ec

centric

dec

elerationRFD

,ecc

entric

dec

elerationrate

offorcedev

elop

men

t;(N/kg,

New

tonper

kilogram

bod

yweigh

t,N/cm,N

ewtonper

centim

etre

ofjump

height);co

ncen

tric

impulse

-100

=(Net)c

once

ntric

impulse

from

thestarto

f100

msof

conc

entric

impulse

;RTC

,returnto

competition

;RTS

,returnto

sport;RTT

,returnto

training

;SSC,s

tretch

-sh

ortening

cycle.

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following competition or high-intensity fatiguingexercise.26 28 Conversely, positive adaptations to trainingmay be detected by CMJ-ALT in the absence of significantchanges in CMJ-TYP.26 29 While CMJ-ALT variables havebeen used to improve the detection of positive or negativeadaptations to load andcompetition (‘load-response’mon-itoring) in healthy athletes, recent evidence and case stu-dies also indicate value in better characterising the status ofthe injured athlete and their response to reconditioningduring the RTS process.10 22 30 31

Baseline bilateral (individual limb outputs) and unilateralstrength and power diagnostic test data were available forthe player (figures 4 and 5). This is important in reducingdependence on interlimb asymmetry as a core indicator ofprogress and for RTS decision-making, potentially mislead-ing due to performance decline in both limbs36 and thedegree of pre-injury asymmetry in healthy players.22 How-ever, if this data is not available, progress should be quanti-fied not only by changes in % asymmetry but considerationof absolute trends in individual limb performance, in thecontext of overall (bilateral) outputs and loading demands— particularly in the eccentric (downward) and landing

phases. Furthermore, frequent and early testing, more thor-oughly quantifying response and progress throughoutreconditioning, can provide greater confidence that theloading has stimulated the desired adaptations and drivenprogress in neuromuscular qualities, particularly in thoseidentified in the literature to be most affected by the injury.

GYM-BASED PHYSICAL PREPARATIONPhysical preparation during early rehabilitation (4–6 months; figure 2), return to participation (6–9.5 months;figure 2) and beyond RTS (10–13 months; figure 2)included a combination of strength training, jump-landingactivities and blood-flow restriction (BFR) training.37 Theconceptual goals of the gym-basedprogrammingwere to (1)restore muscle mass and (2) develop concentric andeccentric strength qualities across the force–velocity spec-trum (figure 6).Prior to beginning the early rehabilitation phase, the

player performed a submaximal CMJ, providing earlyinsights on strategy and willingness to load the knee dyna-mically and as a benchmark to assess the influence ofphysical preparation during the early rehabilitation

Figure 4 Trends in selected countermovement jump (CMJ) bilateral, individual limb variables and asymmetries at selectedtimepoints during rehabilitation and 1-year post RTS. Panels (A and B). Table shows values for selected bilateral CMJ variables forthe player pre-injury (in-season; 2 months prior to injury) and in post-ACLR submaximal (Submax) and in the subsequent monthlymaximal tests (Max1, Max2, Max5). Graph shows percentage change in variables relative to the pre-injury values. For the timing oftests relative to on- and off-pitch conditioning and phases (see figure 2). CMJ bilateral variables refer to variables derived from thetotal vertical ground reaction force data (combined individual limb outputs) during a bilateral CMJ performed on floor-embeddeddual-force platforms, sampling at 1000 Hz (FD4000, Vald Performance, Brisbane, Australia). Panel (C). Absolute left and right limbvalues and interlimb asymmetries (ILAs) for selected variables during the performance of the bilateral CMJs in panels A and B. Theteammean (SD) is ILA%measured at same time point as pre-injury for the player. Positive and negative ILA% refer to higher valueson uninvolved limb or involved limb, respectively. Variables highlighted here are visualised in figure 3. Ecc, eccentric, Con,concentric; RFD, rate of force development; RTS, return to sport.

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phase (table 1; figures 4 and 5). The player also per-formed an isometric mid-thigh pull (IMTP) test (figure7B), but with no pre-injury data for her, this assessmentwas only used to determine trends in the player’s maximalforce-generating capacity and the associated interlimbasymmetries.

Strength trainingIn the early phase of reconditioning (4–6 months;figure 2), we included a combination of overcomingand yielding isometric exercises to develop strength inspecific joint positions — emphasising hip and kneeangles associated with the acceleration and stance

Figure 5 Countermovement jump (CMJ) take-off phase. Force (N)–time, power (W)–time curves (lower panel) and velocity (m/s),centre of mass displacement (cm)–time curves (upper panel) for the at pre-injury, at four time points during rehabilitation and 1-year after RTS (see figure 2 for test timing). Shaded horizontal bars (lower panel) show durations of downward ('eccentric')subphases: unloading (left gradient fill plus small dashed outline)→yielding (centre gradient fill plus medium dashed outline)→deceleration (right gradient fill plus large dashed outline) and the concentric phase (solid fill plus solid outline). Numbers within theshaded bars are the duration of each phase (ms) at each assessment point. Also see figure 3 for an overview of the phases. Thejump with the highest FT:CT is presented, taken from three trials of bilateral CMJ performed on floor-embedded dual-forceplatforms sampling at 1000 Hz (FD4000, Vald Performance, Brisbane, Australia). FT:CT, flight time:contraction time; RTS, return tosport.

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phases of locomotion (figure 8A). Throughout recondi-tioning (4–9.5 months; figure 2), we progressively inte-grated dynamic strength training (figure 9; onlinesupplemental video 1) using predominately closedkinetic chain exercises except for the leg extension —

specifically to isolate eccentric knee extension.38

Strength training biased the involved limb, progressivelyusing a higher volume in unilateral strength exercises(ie, 5:2 sets ratio).15

As neuromuscular performance deficits at joints otherthan the knee are associated with ACL injury risk,39 40 weprogrammed accessory strength exercises (figure 9), andmonitored isometric hip strength (figure 7A). ‘Imperfect

training’ was also integrated into the player's program-ming to challenge joint centralisation and improve neu-romuscular control (online supplemental video 1).

Jump-landing preparationSignificant CMJ eccentric deceleration phase and landingforce asymmetries are observed following ACL and otherlower limb injuries in professional players.22 23 31 41

Furthermore, in female athletes, higher peak landingforces in the drop jump, an indicator of a stiffer (lowerflexion) landing, is a potential risk factor for secondaryACL injury.33 In addition, competitive elite footballdemands repeated high-intensity decelerations.42 Due to

Figure 6 Dynamic strength training and jump-landing preparation approach to restore muscle mass, concentric, eccentricstrength and rate of force development across the force–velocity spectrum following ACL reconstruction. BB, barbell; BR, bandresisted; eccs, eccentrics; RFE, rear-foot elevated; SSB, safety squat bar; SL, single-leg; supramax, supramaximal.

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these injury-, sex- and sport-specific considerations, and thesubstantial variability in the progress of eccentric qualitiesand asymmetries described in professional male playersbetween 6 months and 8 months post ACLR,31 we particu-larly emphasised training to promote recovery of

deceleration and load acceptance qualities, using jump-landing activities and dynamic strength training (4–9.5 months; figures 2 and 8B; online supplemental videos2 and 3). We considered it key to determine if this loadingcombination (figures 8 and 9) was effective in promoting

Figure 8 Isometric strength (A) and (B) jump-landing preparation following ACL reconstruction. Exercises become moredemanding# as you move downwards through each column. #=Exercise demand related to intensity (intent, movement velocity),complexity, joint stress, contractionmode, stability demand (base of support/instability), position of load— therefore, demand canvary through each category based upon these factors. Overcoming=pushing/pulling against an immovable object,Yielding=holding a weight, and preventing it from moving (fixed position), ie, resistance to deformity. CT, contact time; DL,double-leg, ≥ progression; horiz., horizontal; Iso, isometric; Lat, lateral; MVC, maximal voluntary contraction; Med, medial;MTU, muscle-tendon unit; MU, motor-unit; RFD, rate of force development; RFE, rear-foot elevated; reps, repetitions; SL,single-leg; TUT, time under tension.

Figure 7 (A) Isometric hip strength (Ad and Ab) measured using the ForceFrame sampling at 50 Hz (Vald Performance, Brisbane,Australia) in a supine position at 45°, recording the maximum value out of 3×3 s maximum efforts (10 s rest between repetitions).Values within bars are peak force (N), % interlimb (IL) asymmetry for Ad:Abmeasured at 4, 6, 7 and 9months post-surgery (PS). (B)isometric mid-thigh pull (IMTP) measured 4, 6 and 9 months post-surgery using floor-embedded dual-force platforms sampling at1000 Hz (FD4000, Vald Performance, Brisbane, Australia). Values within bars are absolute peak force (N) of the involved anduninvolved limb and relative peak force (Rel. PF, N/kg) is displayed above the bars (summed and expressed relative to bodymass).For reference,mean (SD) for the player’s club first team (n=20): IMTP absolute peak force: 1708N (140N), Rel. PF: 27N/kg (2 N/kg),peak force IL asymmetry: 11% (6%). Ad, adduction; Ab, abduction; ISO HIP, isometric hip strength; RTS, return to sport.

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these adaptations. CMJ trends between Submax andCMJ Max1 indicated a positive response to loadingand improved deceleration qualities (table 1; figures 4and 5) providing confidence in introducing exerciseswith higher deceleration demands and increasing loadon the ACL aimed at developing explosive power.43

These included a combination of stretch-shorteningcycle (SSC) exercises, beginning with ‘slow’ SSC(>250 ms ground contact, eg, single-leg box jumps),progressing to more demanding ‘fast’ SSC derivatives(<250 ms ground contact, eg, single-leg hurdle hops).

BFR trainingWe implemented BFR aerobic exercise during early rehabi-litation (4–6 months; figure 2) and BFR resistance trainingprogressively throughout reconditioning (4–9.5 months;figure 2) using a PTS ii portable tourniquet system withEasi-Fit cuff (Delfi Medical Innovations, Vancouver, BC,Canada). BFRpromotesmuscular hypertrophy and strengthincreases at a lower% of 1RM, amore tolerable format thanheavy-load training in early phases of reconditioning44 alsoaccelerating aerobic improvements.45 BFR resistance

training was implemented in closed kinetic chain exercises,initially with support, which was then removed and externalload progressively added (figure 9; online supplementalvideo 4). BFR aerobic exercise was integrated using staticcycling with the involved limb occluded using 40% arterialocclusion pressure for three to four sets lasting 3–4 min<65%MaxHR (online supplemental video 4).44 45

PROGRESSION TO ON-PITCH REHABILITATION USING THECONTROL–CHAOS CONTINUUMAt 5.5months post-surgery, alongside improvements in CMJdeceleration qualities and performance variables (table 1),the player had achieved one of our criteria for initiatinganti-gravity treadmill running (Alter-G, Fremont, CA, USA)— an interlimb peak force asymmetry of <10% in isometricposterior chain (figure 10A) and IMTP tests(figures 7B and10B).30 Running began at 60% body weight at 13 km/hour(3.6 ms-1), with intervals of three sets of 6 min (2 min activerecovery), covering a distance of 3.5 km, progressing up to90% body weight, at 15 km/hour (4.2 ms-1) (table 2). Largeimprovements in CMJ variables including eccentric decel-eration rate of force development betweenMax1 andMax2

Figure 9 Dynamic strength, blood-flow restriction and accessory strength exercise selection following ACL reconstruction.Exercises become more demanding# as you move downwards through each column. #=Exercise demand related to intensity (%RM,movement velocity), joint stress, contractionmode, stability demand (base of support/instability), position of load— therefore,demand can vary through each category based upon these factors. BFR-RE, blood-flow restriction resistance exercise; BB,barbell; Con, concentric; CSA, cross-sectional area; DB, dumbbell; DL, double-leg; Ecc, eccentric, Early, early rehabilitationphase; End, end rehabilitation phase; Hip Dom, hip dominant; KB, kettlebell; Knee Dom, knee dominant; MB, medicine ball;PR, passive recovery; RDL, Romanian deadlift; reps, repetitions; RFD, rate of force development; RM, repetition maximum;SL, single-leg; STR, strength; W:R, work:rest ratio.

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suggested positive adaptations to progressions in anti-gravitytreadmill running, dynamic strength training and the load/velocity of deceleration and plyometric loading activities(table 1; figures 4 and 5).29

The plan for on-pitch rehabilitation adapted the fivephases of the ‘control–chaos continuum’ (figure 11) topre-injury GPS data, ACL rehabilitation–specific loadconsiderations and ecological validity in relation to theteam training environment (figure 10).11

High controlAt 6 months post-surgery, on-pitch running began,under conditions of high control (weeks 1–4 on-pitch; figure 2). The phase aims are to establisha foundation for gradual increases in running volume(total distance) while minimising explosive distance(distance accelerating/decelerating, ie, from 2 to 4ms-1 <1 s) and to assess the ability to cope with therunning load.

Figure 10 Isometric posterior chain test (A) measured using a portable force platform sampling at 1000 Hz (PS-2141, Pasco,Roseville, CA, USA) in a supine position at 90° hip and knee flexion and isometric mid-thigh pull test (B) measured usingpermanently installed force platforms sampling at 1000 Hz (FD4000, Vald Performance, Brisbane, Australia) with ideal angles of175° at the hip— (replicating a 5° forward lean) and 145° at the knee (measured from head of fibula to lateral malleolus— greatertrochanter).

Table 2 Typical weekly training structure prior to a return to on-pitch running

Time Monday Tuesday Wednesday Thursday Friday Saturday Sunday

AM Injuryspecificationpreparation

Isometricstrength + jump-landingpreparation

Injury specificationpreparation

Dynamic strength +BFR-RE (80% LOP)

Upper bodystrength +stability

Recovery +treatment

Injury specificationpreparation

Isometric strength+ jump-landingpreparation

Injuryspecificationpreparation

Dynamic strength+ BFR-RE (80%LOP)

Upperbodystrength +stabilityRecovery+treatment

Off

PM BFR-AR (Bike)(5×3min— 1minAR) (40% LOP)

Anti-gravitytreadmill running5×3 min at 80% BW13 km/hour

Off BFR-AR (Bike) (5×3min — 1 min AR)(40% LOP)

Anti-gravitytreadmill running5×3 min at 80%BW 13.5 km/hour

Off Off

AR, active recovery; BFR-AR, blood-flow restriction aerobic exercise; BFR-RE, blood-flow restriction resistance exercise; BW, body weight;km/hour, kilometres per hour; LOP, limb occlusion pressure.

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Figure11

Con

trol–ch

aosco

ntinuu

man

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seprogres

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ndition

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eran

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,acc

elerations

;COD,c

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ction;

dec

,dec

elerations

,mag

nitude(acc

/dec

)=intens

ityof

theac

celeratio

n/dec

elerationeffort;E

:R,exe

rcise:restratio

;EXP-D

,exp

losive

distanc

e(distanc

eac

cumulated

acce

leratin

g/dec

elerating,

ie,from

2to

4ms-

1<1s);E

xt,exten

sive

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session=

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dem

ands,

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igh-sp

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playe

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,mob

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lved

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tivity

,poten

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pec

ific=

releva

nceof

othe

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tual

sport/sp

ecifictraining

sessiontype;

RS,

runn

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eed;S

SG,small-sided

games

;TD,totaldistanc

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aveof

attack

.GPS,G

lobalPos

ition

ingSystems(aug

men

ted10

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,StatSports,B

elfast,U

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Running speedswere arbitrarily limited to<60–65%of theplayers pre-injury maximal speed (pre-injury maximalspeed; 7.59 ms-1, 60-65%=4.5–4.9 ms-1), limiting musculos-keletal and mechanical demands, and mitigating elevatedsoft tissue injury risk following prolonged absence. Sessionscomprised of box-to-box runs (17 s) with walking periods tothe edge of the 6-yd box and back as active recovery (13 s).Volume progressively increased from 3×6 repetitions (threesets of 3min duration) to 4×8 repetitions (four sets of 4minduration) with 1.5 min passive interset recovery, buildingprogression into the moderate control phase (figure 11).Between Max2 and Max3, CMJ bilateral variable

trends (table 1; figures 4 and 5, Max3 data shownin the online supplemental appendix) suggested neu-romuscular fatigue, but no pain or joint effusion wasevident. Therefore, our clinical risk assessment wasthat the player was coping, and these CMJ trends didnot warrant delayed transition to the next phase. Thesensitivity of CMJ variables to neuromuscular fatiguemeans that performing an assessment up to 72 hoursafter intense loading can still result in the underesti-mation of the chronic improvements due to super-imposed residual fatigue, potentially leading toa ‘false-negative’ interpretation of progress. However,an assessment may be deliberately timed to capturethis residual fatigue response in terms of bilateraland individual limb (asymmetrical fatigue) to novelloading type, or increments, thereby providing valu-able indirect information on the ‘cost’ of a session orseries of sessions (this approach is described furtherand illustrated by data from Max3 and Max4 assess-ment data in the online supplemental appendix).

Player perspective: “It feels amazing” [to be backon the pitch] “It definitely gives you that lift to keepon going. Every injury is obviously hard on theperson going through it and for the most partI have handled that aspect of it quite well”. “ButI’ve had a big smile on my face being out on thepitch again, and I can’t wait to be enjoying myfootball again.”46

Moderate controlAt 7 months post-surgery (weeks 5–6 on-pitch; figure 2),with the foundation laid for running volume progression,and no pain or swelling, we progressively introducedchange of direction activities and running with the ballto increase movement variability. Within conditioningblocks to develop aerobic qualities, we targeted lowerthreshold high-speed running (HSR) exposure (5.5–6.9ms-1), with session-to-session increments in volume(figure 11) involving embedded linear running withand without the ball in intermittent dribbling lanes. Low-level technical actions were also incorporated in drillcontent.11 Warm-ups integrated running mechanics,acceleration/deceleration and change of direction drills(online supplemental video 5).

Player perspective:The knee has showed really posi-tive signs, no swelling, and has shown it is able tohandle running.46

Control to chaosAt 8 months post-surgery (weeks 7–8 on-pitch; figure 2),we introduced the football-specific weekly training struc-ture with the intention of overloading game-specificdemands.11 We continued the development of accelera-tion and deceleration qualities, programming higher-speed change of direction drills in warm-ups (onlinesupplemental video 5). Within intensive sessions, we inte-grated position-specific acceleration/deceleration activ-ities to replicate the explosive movement demands ofmatch play and ‘pass andmove’ drills to develop technicalactions, progressively including more reactive passingand movement within drills (figure 11). Within extensivesessions, we progressively incorporated HSR, manipulat-ing exercise:rest ratios to target the required energy sys-tems (figure 11).11

Player perspective: (With regards to the impor-tance of support staff in the RTS process) thebiggest thing that an injury teaches you is whothe good people are around you and who is withyou. Those people are huge and will help youget through the injury. In recovery, you don’talways show your true emotions but havingthe right people around you help carry youthrough it. 46

Moderate chaosAt 8.5 months post-surgery (weeks 9–10 on-pitch;figure 2), the player entered the moderate chaos phase.Max5 CMJ data suggested continued improvement in theplayer’s willingness/ability to rapidly load and decele-rate (table 1; figures 4 and 5), trends indicating a positiveresponse to football-specific movements introduced in theprevious phase. This gave us confidence in clearing her foran increased volume of spontaneous football-specificmovements and the associated high-velocity decelera-tion/eccentric loading demands. Inclement weathermeant only two pitch-based sessions were completed inthe phase’s first week. We therefore adjusted the plan,implementing two non-weight-bearing cardiovascular con-ditioning sessions before reverting back to the plannedrunning load progression in the subsquent week. We pro-gressively increased both controlled and chaotic HSRvolume, with increments determined by a combination ofcurrent rehabilitation running loads, chronic rehabilita-tion targets and the players’ gameload (figure 11).11 25 30

We introduced increasing position-specific 'pass andmove' and 'pattern of play' drills, progressing the volumeand intensity of technical actions and integrated supportstaff to challenge visual perception and spatial awareness(figure 11).11 Reactive elements were also introducedinto positional speed drills’ increasing movement

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variability and exposure to higher risk conditions. Wecontinued to place emphasis on the development of aero-bic qualities, eliciting >85% MaxHR for 25–40 min persession, and chronic running loads were now above pre-injury training outputs(figure 11). Pretraining prepara-tion and gym-based conditioning continued alongsideprogression of on-pitch rehabilitation within the players’weekly training structure (table 3).

Player perspective: First and foremost, of course,I want to get back playing for [club team]. Butthere is a big hope and dream that I can play inFrance come June. That keeps me going whenI have those tough days. For me personally, thisinjury is a step back, but it is not the end of theworld. There are plenty of people out there whodeal with career ending injuries or illnesses so thatrealisation has made it easier to deal with.46

High chaosAt 9 months post-surgery (weeks 11–12 on-pitch; figure 2)and in the final phase of rehabilitation, we empha-sised position-specific conditioning and progressiveincrements in running loads beyond pre-injury weeklytraining load outputs (figure 11).11 Conditioningemphasised position-specific speed/speed–endurancedrills, with movement speed dictated by the speed/direction of passing and technical actions integratedinto position-specific contexts, such as attacking anddefending in one-on-one situations. Training dura-tions were above both her pre-injury and the newcoaching team’s typical levels, with finishing practiceadded at the end of sessions ensuring training of high-intensity technical actions.

RTS DECISION-MAKINGThe player was involved in RTS decision-making discus-sions, ensuring she remained central to the process.

Several criteria informed RTS and the return to teamtraining decision (9.5 months; figure 2):1. Absence of pain/swelling.2. Having ‘trained enough’ (completed sufficient on-

pitch rehabilitation to be prepared for team training)and achieving higher training loads than pre-injury(figure 12).

3. Integration of the required level of technical actions(aligned to the current coaching team’s trainingcomponents).

4. Global consideration of strength and power diagnostictest data, including (1) achieving proposed thresholdsof asymmetry for isometric strength and performanceoutputs; (2) consideration of trends in these asymme-tries; (3) CMJ-ALT values in relation to player bench-marks and/or (if benchmark not available) trends inthese variables; (4) phase-specific asymmetries— in thecontext of players pre-injury values, and sports-specificprofiles post-ACLR and in healthy players15 19 20; (5)bilateral CMJ-ALT and individual limb force andimpulse fatigue-recovery response following incrementsin sports-specific loading (see online supplementalappendix).

5. Achieving <5% asymmetry in lower limb muscle mass,and

6. Surgeon discharge.The player reportedminimal pain (<2/10 on the numer-

ical scale), and no signs of joint effusion. Involved limbmusclemass (dual-energy X-ray absorptiometry) was abovepre-injury with an interlimb asymmetry of 3%(table 4).Isokinetic concentric knee extension (@ 600/s) limb sym-metry index was <12%, below the criterion <15%.47 Iso-metric hip strength showed small improvementscompared to 5 months post-surgery in global adduction/abduction strength (3% and 2% limb symmetry indexrespectively; figure 7A) but larger relative improvementin hip abduction (adduction: abduction ratio— 5 monthspost-surgery: 1.2, RTS: 1.0), a desirable outcome for ath-letes returning after ACLR.39

Table 3 Typical weekly training structure during the on-pitch rehabilitation phase — ‘control–chaos continuum’: moderatechaos phase

Time Monday Tuesday Wednesday Thursday Friday Saturday Sunday

AM Injury specificationpreparation

On-pitchconditioning(moderate chaos –

intensive)


On-pitchconditioning(moderate chaos– extensive

Upper bodystrength+stability

Recovery+treatment


On-pitchconditioning(moderatechaos –

intensive)


On-pitchconditioning(moderate chaos– extensive

Upper bodystrength+stabilityRecovery+treatment

Off

PM Isometric strength+jump-landingpreparation

Dynamicstrength+BFR-RE(80% LOP)

Off Isometricstrength+jump-landingpreparation

Dynamicstrength+BFR-RE(80% LOP)

Off Off

BFR-RE, blood-flow restriction resistance exercise; LOP, limb occlusion pressure.

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Figure12

Playe

rreturn

toch

ronicrunn

ingload

sfollo

wingACLreco

nstruc

tionus

ingtheco

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aosco

ntinuu

man

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toperform

ance

(RTP

erf)p

athw

ay.D

ata

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game(m

ean)

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ectiv

etraining

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ncurrent

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lute

andrelativ

eload

(gam

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2×=2ga

mes

).EXP-D

,ex

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e(distanc

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g/dec

elerating,

ie,2

to4ms-

1<1s);H

SR,h

igh-sp

eedrunn

ing(>5.5ms-

1;d

welltim

e0.5s

);HMLD

,highmetab

olicload

distanc

e(distanc

eab

ove25

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-1;s

umof

HSRan

dEXP-D

);TD

,total

distanc

e.Green

=high

control(low

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ity)m

ovingtowardsred=high

chao

s(highintens

ity).Grey

shad

es=RTP

erfpathw

ay;d

arke

stgrey

=return

totraining

:non

-con

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(RTT

-NC),darkgrey

=return

totraining

:con

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(RTT

-C),mid-grey=

return

totraining

:full

integration(RTT

-FI),

light

grey

=return

toco

mpetition

(RTC

)World

Cup

preparation(m

atch

expos

ure)

—thepha

selead

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(FIFAWom

en’s

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),bad

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with

inea

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k.Global

Pos

ition

ingSystems(aug

men

ted10

HzApex

,StatSports,B

elfast,U

K).

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Table 1, figures 4 and 5 outline key CMJ data informingRTS decisions. Theoretically, reconditioning shouldrecover both CMJ-TYP and ALT variables, with the latterrecovering more slowly.22 30 However, the player’s coun-termovement depth was substantially greater than pre-injury, indicative of reduced stiffness and potentiallyrepresenting a positive outcome from a re-rupture riskperspective,33 but also limiting the improvement ineccentric phase kinetic variables indicative of neuromus-cular efficiency/SSC performance including: eccentricduration, eccentric deceleration rate of force develop-ment, eccentric peak power and flight time:contractiontime (see online supplemental appendix for furtherexplanation). It is important to note that in the contextof load-response monitoring in healthy athletes, trendssuch as these, and specifically decreased flight time:con-traction time has been associated with reduced HSRperformance.48 However, these decrements were attribu-table to residual neuromuscular fatigue as opposed toa chronic alteration in jump strategy, which appears tobe the case in the present player. Potentially, this appar-ent reduction in neuromuscular efficiency/SSC was com-pensated for by greater strength capacity, as at RTS theplayer had achieved a new maximal speed (8.2 ms-1; week11 on-pitch; high chaos — session data quality: HDOP0.4/no. of satellites 20), indicating that this CMJ strategychange did not negatively affect her high-velocity runningperformance— a priority of rehabilitation and marker ofRTS success. The CMJ is used to unmask and quantifyavoidance strategies and assess responses to loadingthroughout rehabilitation, while pre-injury CMJ kinetic‘benchmarks’ should be considered alongside potentialstrategy changes and on-pitch performance, rather thanan independent goal of rehabilitation.31

SETTING A PATHWAY TOWARDS RTPERFAt 9.5 months post-surgery, using the ‘RTPerf pathway’ toguide a phased approach to full-team integration,13 the

player returned to team training. Players often experi-ence a ‘trafficking’ effect upon reintegration;a sensation of high cognitive load with little space andtime to manoeuvre following a long period withoutintense interaction with other players.13 49 A period ofneurocognitive re-adaptation is required to re-accustomthe player to these situations (figure 11).13

Player perspective: It has been a hard journey, butthe last 3 months have been really good, and nowI’m actually back with the team.46

RETURN TO TRAININGNon-contactFollowing discussion with the coaching staff, we inte-grated the player back into modified training (weeks13–14 on-pitch; figure 2) emphasising contact avoidanceandmodified training to ensure progressive player inter-action (figure 11).13 Modifications included beinga link-player on the periphery of the small-, medium-and large-sided games, progressing to a ‘floater’ (spareplayer) to increase interaction with other players. This2-week phase involved stable overall running load anda small increment in HSR volume (figures 11 and 12). Aswe anticipated, the players’ internal response (>85%MaxHR) during the first week of her return to trainingwas greater than the final phase of rehabilitation(151 min compared to 117 min) despite a higher run-ning load in week 12 on-pitch. The increasing level ofplayer traffic and associated cognitive load possiblyincreased sympathetic drive, resulting in an increasedheart-rate response.50 51 However, in the second week ofthe player’s return, the increased internal response atte-nuated (103 min), suggesting possible adaptation to theincreased cognitive stimulus.

Player perspective: Now I’m actually back with theteam, so I think that’s the best part about it, you getsick of being by yourself and sick of playing against

Table 4 Anthropometric and dual-energy X-ray absorptiometry information pre-injury, post-surgery, pre-return to sport (RTS),return to training full integration (RTT-FI) and prior to World Cup preparation (pre-WCP)

DateTimephase

Height(cm)

Weight(kg)

WBT score

WBZ score

Fatmass(kg)

Leanmass(kg)

Bodyfat(%)

Leanmassleft leg(kg)

Leanmassrightleg(kg)

Leanmassleftarm(kg)

Leanmassrightarm(kg)

31 January 2018 Pre-injury

161 55.4 1.8 1.8 10.7 39.8 20.6 6.5 6.3 2 2.1

06 June 2018 Post-surgery

161 54.2 1.6 1.6 12.1 37.1 23.8 5.7 6.3 1.9 2

23 January 2019 Pre-RTS

161 56.2 2 2 11.7 39.8 21.9 6.7 6.9 1.8 2

27 March 2019 RTT-FI 161 55 2.3 2.2 10.6 39.7 20.4 6.7 7.3 1.9 211 May 2019 Pre-

WCP161 54.6 2 1.9 10.1 40 19.6 6.9 7.3 1.9 2

Left leg, involved limb; right leg, uninvolved limb; WB, weight-bearing.

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your coach, I’m a bit bored of that now, I’m ready tohave the team involved and to get back playing.52

ContactDuring this phase, we introduced, and progressivelyincreased, exposure to contact (weeks 15–16 on-pitch;figure 2) with subtle training restrictions, for exampleswitching between a 'floater' and full-integration optionsto deliver gradual, controlled full training exposureswithin game-based elements (figure 11; online supplemental video 6).13 Frequent communication with thecoaching staff also ensured that required technical skillswere refined such as ‘pass andmove’ and ‘pattern of play’drills with increasing passing distance and touch numberrestrictions. If not feasible, additional fine-tuning of theseskills was done with the assistant coach, developing theplayer–coach interaction.53

Player perspective: Following the draw for theWomen’s World Cup, the player national team wasdrawn in the same group with some of her team-mates at a club level, this gave her greater incentiveto achieve her goal “We drew the Dutch so there wasa buzz with the likes of [Player 1, Player 2, andPlayer 3],” “So there is a big incentive for me towork hard and return to playing in time for thetournament”46

RETURN TO TRAINING: FULL-INTEGRATIONAt 10months post-surgery (weeks 17–23 on-pitch; figure 2)and 13 weeks from her nation’s first World Cup match,she resumed unrestricted full training (online supplemental video 6). We continued to advise coachingstaff on session parameter manipulation includingpitch dimensions, interval/repetition/set prescriptionalongside inter-set recovery periods to maximise energysystem conditioning and the development of physicalqualities in combination with their technical and tacticalrequirements (figure 11).13 We continued to monitorGPS running loads in real-time and post-session, aimedat targeting session-specific loads, for example within anintensive session, the explosive distance component ofhigh-metabolic load distance (distance above 25 W•kg-1;sum of HSR and explosive distance) (figure 11).The player was selected for an international camp

including two competitive fixtures. We communicatedrecommendations regarding training and progressionof match minutes to the sports science/medical staff ather national team and provided the player with the sameGPS unit used during club training to ensure consistencyin measurements.54 She played 30 min in the first fixtureand 2 min as a second-half substitute in the second.In week 20 of on-pitch training, the player made her

competitive club comeback, playing 2 min as a substitutein aWomen’s Super League match. In the weeks followingthe players’ return from international camp, we implemen-ted some additional aerobic power interval conditioning

within the team training schedule, with the intention tolimit decrements in aerobic fitness during her modifiedreturn to competition.55 We progressively increased ‘con-trolled’ HSR volume (figures 11 and 12), providing anincreased stimulus to develop the player's work capacityin preparation for the pre World Cup camp.

Coach perspective: “It is great to have [the player]fully-fit and available for selection”, “it’s our firstopportunity to see her and we know she has workedvery hard in her rehab since her ACL operation”56

RETURN TO COMPETITION: PROGRESSIVE MATCH EXPOSUREAt 12 months post-surgery (weeks 24-27 on-pitch; figure2) and following the end of the club season, the playerjoined her national team in preparation for the WorldCup. Her two substitute appearances at club-level did notrepresent a ‘true’ return to competition due to a lack ofcompetitive match minutes. Therefore, we communi-cated a plan to progressively increase match minutes inthe build-up to the World Cup with the sports science/medical staff from her national team. In week 24 (on-pitch training), she achieved her pre-injury peakmaximalspeed during a friendly match (figure 13; online supplemental video 7). During the pre-tournament camp, thefrequency and density of training sessions increased andthe player completed the largest volume of explosive dis-tance since returning to on-pitch activities.The player was coping well with the increasing train-

ing load and building a chronic loading capacity inpreparation for the expected concurrent load demandsof the first competitive week of the World Cup. In thesecond friendly match, she played 75 min at a matchintensity above pre-injury outputs, her largest exposureto competitive match minutes since returning to sport.The lack of negative response (pain/joint effusion) alsosuggested she was coping with match demands. Follow-ing this match, the players were given 4 days leave fromcamp during which she performed some 'controlled'interval running as a cardiovascular stimulus and toprevent a large fluctuation in week-to-week runningload volume.After 12.5 months post-surgery (week 27 on-pitch), dur-

ing another friendly match, she played only 22min due totactical decisions. To compensate for the lack of matchexposure, post-match along with the rest of substitutes,the player completed some interval running to top-upHSR volume. In the penultimate week before the tourna-ment, the player played her first full competitive match injust over a year. Total distance and explosive distancematch outputs were higher than pre-injury (figure 13),representative of her ability to perform game-based press-ing actions. Furthermore, concurrent (training plusmatch) explosive distance exceeded pre-injury output,while total distance andHSR were on par with concurrentpre-injury, indicating the player could produce typicalconcurrent load outputs(figure 12). She also displayedelements of her pre-injury playing traits and no

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Figure 13 Final phaseof the return to performance (RTPerf) pathway—progression in return to competitionmatchminutes andRTPerf attheFIFAWorldCup (matchphysicaloutputs).Data representativeofactualmatchdataexpressed inbothabsoluteand relative (comparisonto pre-injury typical match output). EXP-D, explosive distance (distance accelerating/decelerating, ie, from 2 to 4 ms-1 <1 s);HSR, high-speed running (>5.5 ms-1; dwell time 0.5s); HMLD, highmetabolic load distance (distance above 25W•kg-1; sumof HSR and EXP-D); MS, maximal speed; >85% MAXHR, time above 85% maximal heart-rate; Mean, average; ME, matchexposure; RTC, return to competition; RTPerf, return to performance; HDOP, horizontal dilution of precision; TD, totaldistance; No. of, number of Global Positioning Systems (augmented 10 Hz Apex, StatSports, Belfast, UK).

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apprehension towards contact in competition (onlinesupplemental video 7).

RTPERF: THE FIFA WOMEN’S WORLD CUPAt 13 months post-surgery (weeks 28–29 on-pitch;figure 2), the player realised her long-term ambitionplaying 90 min in the first World Cup game, againdisplaying typical pre-injury playing traits such as drivingruns with the ball into the final third of the pitch(online supplemental video 7). Based on this perfor-mance, she was selected to start the second game,again playing 90 min. In a high-pressing game (involvingthe movement of a team in unison to gain ball posses-sion — limiting space, time on ball and passingoptions), the team worked hard to regain ball possessionfor long periods of the game, creating intensive physicalgame demands (figure 13). These demands meant HSRwas below typical output, however explosive distance wasabove her pre-injury gameload, indicating she couldhandle game-specific demands. In the final groupgame, she played 87 min, but the team failed to qualifybeyond the group stages.

Player perspectives: Following elimination from thetournament, the player gave a reflection of herjourney ‘Football gives you it all! The highs of play-ing at my first World Cup and the feeling of walkingout of the tunnel for the first match are momentsI won’t forget. Then the lows of not achieving ourgoal [the team] and leaving this World Cup emptyhanded.’57

“For me, it was always about getting back frominjury, then trying to work my way back into theteam and make it hard for [the manager] to notput me in the starting eleven”.58

SUMMARYRehabilitation following ACLR is complex and like anysuccessful RTS process is most effectively facilitatedwhen objective pre-injury data, informed clinical rea-soning and shared decision-making are combined.With the initial goal of facilitating a return to on-pitch running, progressive optimal loading targetedrecognised post-ACLR neuromuscular deficits and

Figure 14 One-year post return to sport match physical outputs for both domestic club (2×90 min) and national team (64 and75 min). Data representative of actual match-data expressed in both absolute and relative (comparison to pre-injury typical matchoutput). EXP-D, explosive distance (distance accelerating/decelerating, ie, from 2 to 4 ms-1 <1 s); HSR, high-speed running(>5.5 ms-1; dwell time 0.5s); HMLD, high metabolic load distance (distance above 25 W•kg-1; sum of HSR and EXP-D);HDOP, horizontal dilution of precision; MS, maximal speed; RTPerf, return to performance; TD, total distance; No. of,number of. Global Positioning Systems (augmented 10 Hz Apex, StatSports, Belfast, UK).

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avoidance strategies, particularly in deceleration andload absorption qualities. The ‘control–chaoscontinuum’11 and its adjunct, the ‘RTPerf pathway’13

guided progressive on-pitch/sports-specific rehabilita-tion, a return to team training, competitive matchplay and the ultimate goal — a RTPerf.

EPILOGUEAfter the FIFA Women’s World Cup, the player trans-ferred to another English Women’s Super League clubplaying 18 matches across League, domestic cup competi-tions (13×90 min appearances) and 3 internationalfriendly matches prior to COVID-19 curtailing the2019–2020 Women’s professional season. We obtaineda snapshot of match physical outputs 1-year post RTS, high-lighting contextual differences related to her position forclub compared to her country. In her club role, she wasoperating as holding central midfielder, with lower physicaldemands than her wide midfielder role for the nationalteam — tournament data highlighting greater HSR andmaximal speed demands (figure 14). We also obtaineddata from a CMJ assessment at her club 1-year RTS(figures 4 and 5) allowing us to further describe herRTPerf journey. This revealed diverse trends in differentCMJ variables, with positive adaptations likely stimu-lated by match exposure — for the elite footballer com-petitive match play has been highlighted as the mostpowerful stimulus for development of neuromuscularcharacteristics .59 Also, notable was the stability of theincreased countermovement depth (a proxy indicatorof deeper knee flexion) gained during rehabilitationsuggests it has become an embedded strategy. However,her SSC function within her new range continued toimprove, indicated by the large improvements in CMJvariables such as eccentric peak power, eccentric decel-eration RFD and flight time:contraction time. Also, pre-sumably driven by her on-pitch loading demands, the1-year post test revealed a return to her previous patternof kinetic asymmetries, albeit with a reduced magnitudeof peak landing force and eccentric deceleration RFDasymmetry. These data highlight the importance ofongoing neuromuscular monitoring in the period of12–24 months post-surgery not only to quantify progressin the involved limb but also to monitor for detrimentalchanges in the uninvolved limb,10 now at elevated riskof ACL rupture.5 At 18 months post-surgery, an MRI(figure 1E) showed a fully intact graft with evidence ofligamentisation.

Author affiliations1School of Sport and Exercise Sciences, Liverpool John Moores University, Liverpool,UK2High Performance Unit, Irish Rugby Football Union, Dublin, Ireland3Performance and Research Department, Arsenal Football Club, London, UK4The Manchester Institute of Health and Performance, Manchester, UK5Sports Surgery Clinic, Dublin, Ireland6University of Roehampton, London, UK7School of Sports, Exercise and Rehabilitation Sciences, University of Birmingham,Birmingham, UK

8Sports Science Center (CCD), Colombian Ministry of Sport (Mindeporte), Colombia9Masira Research Institute, Universidad de Santander, Bucaramanga, Colombia

Twitter Matt Taberner @MattTaberner, Nicol van Dyk @NicolvanDyk, Tom Allen@tallen_5, Neil Jain @neiljainortho, Chris Richter @ChrisRichterPhD, Barry Drust@BARRYD22 and Daniel D Cohen @daniecohen1971.

Acknowledgements The authors thank Lloyd Parker (Everton FC Sports Nutrition-ist) for providing DEXA scan information and nutritional support to the player, LukeBenstead (Royal Belgian Football Association Performance Analyst) for providingtraining and competition video editing using Coach Paint (Chyronhego, New York,USA), and Chris Difford (Bristol City Women’s FC Physical Performance Coach) forconducting 1-year post RTS CMJ testing.

Contributors NJ surgically operated on the player and assisted with writing themanuscript in relation to the injury pathology and surgical procedure. MT led physicalpreparation and RTS, communicated with the New Zealand Women's national teamsports science/medical staff, planned and wrote the manuscript. DC, NvD, TA, andBD provided guidance and assisted in the writing of the manuscript. EB and CRprovided analysis of strength and power diagnostic testing alongside DC and MT.

Funding This research received no specific grant from any funding agency in thepublic, commercial or not-for-profit sectors.

Competing interests None declared.

Patient consent for publication Obtained (BMJ consent form).

Ethics approval Not required — letter provided by the Universidad de Santander(UDES) ethical committee (data collection as part of employment).

Provenance and peer review Not commissioned; externally peer reviewed.

Data availability statement All data relevant to the study are included in the articleor uploaded as supplemental information.

Supplemental material This content has been supplied by the author(s). It hasnot been vetted by BMJ Publishing Group Limited (BMJ) and may not have beenpeer-reviewed. Any opinions or recommendations discussed are solely those ofthe author(s) and are not endorsed by BMJ. BMJ disclaims all liability andresponsibility arising from any reliance placed on the content. Where the contentincludes any translated material, BMJ does not warrant the accuracy andreliability of the translations (including but not limited to local regulations, clinicalguidelines, terminology, drug names and drug dosages), and is not responsiblefor any error and/or omissions arising from translation and adaptation orotherwise.

Open access This is an open access article distributed in accordance with theCreative Commons Attribution Non Commercial (CC BY-NC 4.0) license, whichpermits others to distribute, remix, adapt, build upon this work non-commercially,and license their derivative works on different terms, provided the original work isproperly cited, appropriate credit is given, any changes made indicated, and the useis non-commercial. See: http://creativecommons.org/licenses/by-nc/4.0/.

ORCID iDsMatt Taberner http://orcid.org/0000-0003-3465-833XNicol van Dyk http://orcid.org/0000-0002-0724-5997Tom Allen http://orcid.org/0000-0001-6286-7433Chris Richter http://orcid.org/0000-0001-6017-1520Barry Drust http://orcid.org/0000-0003-2092-6962Daniel D Cohen http://orcid.org/0000-0002-0899-4623

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