fp^r^l 1 25-36.1987

a?byl,fl.A.F.

DISCUS THROW: RESULTS OF A BIOMECHANIC STUDY

Jan Stepanek, Petr Susanka

^^ This is an extract from the "Scientific Report ofthe IAAF Biomechanic Research on the first World Junior Championships'". The authors analyze the performances of fhe junior di.scus throwers and compare them to the performances of senior athleles recorded at the Helsinki World Championships in J983.

yy

1. Introduction The performance deveiopmeni pro­

files in the Junior Discus Throw show a lendency similar to that for Senior athleles, A slight decline in the increas­ing tendency can be observed after 1974 when compulsory drug tesling was introduced. Another reason for this apparent decline could be the out­standing Junior results in 1974 of even­tual 1976 and 1980 Olympic gold medallist Schlaak - Jahl (GDR) or the 1973 performance of 1976 Olympic silver medallisi Schmidt (GDR).

A slightly retarded development with a sharper rise in performance can be observed for Junior women. In 1964 the difference between the perfor­mances of the best Junior man and the best Junior woman was 7.41 metres. Later, the performance level evened up, and. since 1979, the Junior women have been achieving longer marks than their male counterparts, ll musl be noted that the difference in the mass belween the men's and women's imple- 25

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i 1 ^ tt. 0 ceo-

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D I S C U S T H R O W - M E N

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Cordenkroni A Hor^dth Schnudl / \ / \ /

/ \ / A \ / /

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l( X \ ' \ \ / > " " /

/ \ /y V -^ - / vA f\r'^''^^^'' v/^'~^

_,-''\\ i X " ^ ^^ ' ' fro|resj(On m the Olympic Cyot J J - T T /S. / 5cjt worfrfs performonce of the yeor

A// . \ 7 — s of 3 bejt performoncei / ^ \V' ' " s of K) l>e»t performoncei

- , {/ / \ * / 7

ir 1 , . • . 1 • . . 1 • . . , . .

tOea 72 76 »O B4 YEAR

t ig . 1

D I S C U S T H R O W - W O M E N Mtszir^ika

ichtok- iohl

Haupt

~-^ Progression in the Olympic cycle • Beit worlds performance of the year

* of J best performoncei Jt of 10 bf i t performancti

- T — I — 1 -

loes ra -I—>—r

76 - I 1 1 1 1 1 • T-T

eo • 4 YEAR

26 FiR. 2

Table 1

1,

2.

3,

4.

Men

Boys

Women

Girls

I,

fi.'i,47

57,21

fi5.. 4

.53.57

2.

6.s.y'j

.SH.SO

69.6«

55.95

3.

fiS,45

f'H.l'-J

69,04

55.95

4.

-z.ys

-l.US

-.1.50

-2.3S

5.

-3,52

-l..';9

-4.14

-2..38

6.

26,5

18,8

27.3

17,5

7.

192/114

194/106

182/93

IS2/86

1 - besi performance p( World Champion.ships 2 - personal be-il performance 3 - personal best perft»rmance in Championship year 4 - difference between 1-3 5 - dilTerence between 1-2 6-age 7 - heighl/weighl

ments is 50%. while the difference in tests of physical potential between men and women is much smaller. Another reason for the better marks of the junior women may be the better aerodynamic properties of the women's discus (linger 1977). Its sur­face area is only about 65% of the sur­face area of the men's discus with the difference in mass mentioned above (Bartonietz 1984),

Table I shows the average values of the performance dala for the finahsts at the 1st World Championships for both Seniors and Juniors.

The average age of the best Senior discus throwers is 27 years. That, appa­rently, is an age when the potential of developing slrength culminates. The level of technique and the experience that make it possible lo achieve top performances in competitive events improve with age as well. For this reason, the extreme performances of the Junior male athletes Gardenkrans (SWE) 1974, Hartmann (FRG) 1978, Horvath (HUN) 1985 or the junior women Meszynski (GDR) 1980 and Haupt (GDR) 1984 musl be consi­

dered exceptional. Biochemistry made a strong impact

on iraining and performances in the throwing events after 1960 but has, at the same time, had a negative effect on the health ofthe athlete (i.e. toxic ef­fects on metabolism and the hormone system). A better use of the know­ledge obiained by applied bio­mechanies should, therefore be seen as the only permitted way of improving technique, performance and competi­tion resuhs in the future.

2. Theoretical Considerations

Owing to the shape of the discus, its motion in space (unlike the motion of the shot) musl be judged on the basis of six degrees of freedom (Soong 1982). The theoretical distance of the discus night (1) is influenced by the basic con­ditions that hold for the oblique pul. i.e. velocity of release (VJ . height of release ( h j , angle of release (a„) and gravity (g), as well as by aerodynamic condilions. The angle of release (a„) is defined as the difference between the vector of release velocity and the hori- 27

zontal. The angle of the discus inclina­tion (ß„) is defined as the difference be­tween the longitudinal axis of the dis­cus and the horizontal. The atigle ofat-lack is defined as the difference bet­ween the angle of release (o„) and the angle of the discus inclination (ß„). To­gether with wind force and direction (± w). the angle of attack determines the point of application of the lifiing force. At the moment of release, the athlete imparts a rotary motion lo the discus, which then rotates in flight around its shorter axis.

In actual competition, these data are hard to ascertain. A number of authors (Unger 1977. Soong 1982. Bartonietz 1984) quote similar figures arrived at on the basis of iheoretical siudies. They are unanimous in stating that the velocity of release is the crucial factor that determines the quality of perfor­mance (for performance beyond 65m: V. = 25m/s). An increase of V„ from 24.5 to 25.5 m/s (with all other parameters maintained) will improve the performance by 4.8m. The influ­ence of the height of release is negligi­ble. Increasing h„ from 1.5m to I.Om will improve performance by 0.4m. The optimum angle of release is usually put at 30"-37" (Schmolinski 1978).

The kinematic analysis of the discus throw at the 1984 Olympic Games (Gregor. Whiting and McCoy 1985) produced the following average values of the medallists: Men - 1. 65.59 m: V^ = 24.8 m/s; a, = 35.6"; h„ = 1.73 m Women - 1. 63.50 nr, V„ ^ 25.0 m/s; a„ = 34.7"; h — 1.48 m. Bartonniez (1984) gives a„p, as 35"-37' and the angle of inclination W 20"-25".

Soong (1982) established a connec­tion between the relation of the two angles and wind direction and speed.

28 In calm wealher: a.,,,, = ß p, = 33"; with

a following wind w = -i- 5 m/s a,,„ = ß„„, = 35": into a headw ind w ± 5 m/s a .^ = 35" |5„|„ = 25"; into a headwind, which he considers to be optimal, = - 10 m/s ot.>p. = 35" ß,, , = 20". These data are given for a 2 kilogram discus, with V„ = 25.5 m/s and rotations of 36.9,|„. In a headwind, performance improves. The stronger the wind the more acute the angle of discus inclination: for a varia­tion range of 1 (65-68 m), the angle should be between 35" and 20'\ Simi­larly, increased rotation of the imple­ment improves the stabilily and flighi properties of the discus. Performances are thus improved aswell. IS rps is usu­ally considered the minimum value while 37 rps is considered to be the op­timum.

This kind of information is certainly useful. The question is, though, will an athlete be able, in top-level interna­tional compeiition, lo estimate the wind force and be able to determine the angle of inclination of the discus within a range of less than 5 degrees? The experience necessary for the abil­ity to do this may explain the fairly ad­vanced age of the best adult discus throwers and the markedly poorer per­formance of Junior throwers in lop-level contests.

The athletes in our analyses were filmed simultaneously by two syn­chronized high-speed cameras in the direction of the discus tlight and per­pendicular to it respectively. The di­gitizing of the film, the methods used in the computer processing and the re­sulting three dimensional reconstruc­tion of the action is described in the complete Scientific Report from the 1st World Junior Athletics Champion­ships. Aerodynamic conditions are dif­ficult to ascertain, and are not dealt wilh here.

The technique of discus throwing has undergone a complicated development from Greek Antiquity to the present (Grieser 1983). The changing rules and the resulting changes in lechnique have been accompanied by an effort lo pro­vide the optimum condilions for ex-lending Ihe path along which the discus could be accelerated in the delivery phase.

The level of lechnique cannol be evaluated unless the complex of move­ments of the athlele is separated into partial sections or phases. The phases are characterised by the position of the athlete's body or that of the imple­ment. These so called crucial moments are determined, mostly, on the basis of the contact between the feet and the ground.

The introductory swings and the pre­paratory phase - from the moment when the discus reaches the extreme position before the start of the throw (marked Z max. I) until the righl fool rises from the ground (R 'f) - is a phase nol dealt wiih here, being unimpor­tant. The following action is probably not influenced by this phase at all. The turn is separated by the following three phases: Start (R 4 - L | ) . Fliglii (L +-R+) and Transilion (R i - L I). The final phases of the delivery (from the lefl foot landing- L luntil the release) falls into two parts, separated by the lowesi point on the discus path (Z min. 2). In an effort to exiend the duration of the imparting of an acceleration force to the discus in the final phase of the delivery some athletes perform a jump. A premature engaging of the lifting force of the leg muscles causes a gradual loss of contacl with the ground before the release - usually with the right foot losing contacl first (R + )and the left fool afterwards (L | ) . Obser­

vations (Vrabei 1982, Gregor 1985) in­dicate that this method of delivery is used less frequently by women than by men.

The liming of the World Champions is shown in Table 2 using examples from the 1st World Championships in Athlelics - Helsinki 1983 and the Worid Junior Alhlelics Champion­ships-Athens 1986.

Thc duration of the preparatory phase is an indirect pointer to the scope of the reach of the arm before the body is launched inlo the turn. This phase does not perceptibly influence the re­suUing performance and is considered unimportant here. The time sequence of the turn (R • - L +) seems lo con­firm the findings of other authors (Vra­bei 1982. Gregor el, al. 1985). Men make a more dynamic launch into the turn than women, which is why their flight phase is slightly longer and the double support phase is taken up fas­ter. The shorter average duralion of the turn in men (0.613 sec.) corres­ponds lo the mass ratio of the alhlele-implemenl (57 : I). Women, with a more favourable mass ratio (93 : 1) can perform the lurn in a slower way (0.750 sec) , thus allowing for more ef­ficient delivery. The duration of the de­livery (L 1-0) should be judged on the basis of the length ofthe respective sec­tions of the discus path.

3. Re.sults of analysis: Ist World Championsliips in Athletics - Helsinki 19K3

The shape of the discus path, with the crucial moments, is shown in the three-dimensional reconstruction (Fig. 3, 4). Figures 3 and 4 and Table 2 indi­cate that iherangeand the length of the discus palh in the turn and in the dcliv- 29

ery is greater for men. The delivery phase is the most interesting from the point of view of the timing of the action in relation lo the length of the discus path sections. In this phase. Opitz handles the discus for a longer time along a palh 6 cm shorter than Bugar's. Poor timing of the take-off for the re­verse jump caused Upilz to lose con­tacl with ihe ground (R +) 0.06 sec. be­lbre the release with the right foot and (L •) 0.02 sec. before release with the left fool. The effective lenglh of the discus path that can be utilised for ac­celerating the implement is thus re­duced lo 2.13m and 1.46m. respec­

tively. Bugar maintains a firm double-support posiiion unlil the moment of release. One of the crileria of correct technique is the reduction ofthe flight phase with a timely landing ofthe lefl foot (L | ) in a double-support posi­tion. The length of the discus path in the flight and transition phases should be as short as possible, since it has no effect on the subsequenl acceleration of the discus movement. In these ph­ases, Opitz's lechnique is more effi­cient (s = 1.72m; Bugar: s = 2,30m). That is why her legs, hip and shoulders are well ahead of the movemeni of the discus. The angle of the shoulder axis

30 Fig. 3

Fig. 4

»

10

0

BUGAR 66,V4 m

^ ^ "

qi

> >1

u»

t •1 ,

a,,.i a*t •• q u L> V • • ( 1* l l !>,<! 0

Fig. 5 31

OPITZ 6a.94n)

A, 'J!J .

n" Bfii 4«« o.ai

32

Fig. 6

and the stretched throwing arm should be widest close to the lowest point of the discus path (Z min 2) before release (e.g. Valent 225" with a resulting per­formance of 66.08m). The funclional course of the discus velocity (Fig. 5.6) makes it clear that the final and deci­sive phase of the delivery (L '^- 0) is less efficient whh Opitz.

Bugar. after the left foot landing (L I), accelerates the discus more fluently achieving a greater release vel­ocity (VJ. The longer performance of Opitz (2m). with poorer delivery technique than found with Bugar may be caused by the better fiight proper­ties of the women's discus mentioned above.

4. Results of analy.sis: 1st World Junior Alhletic Championships - Athens 1986

In discussing the performance of the best Junior alhletes. an all out effort

was made to use the same methods and approach to data collection, analysis and interpretation as those used in studying the results of the Ist World Championships in Athletics.

The timing of the action is shown in Table 2. just as it is in the adults" case. The winner of the Junior Men's event. Bakiarov. begins the aclion at a slower speed, both in the preparatory and the starting phases. The turn is longer than Bugar as well (0.62 sec) . The fiight phase is rcduced lo a minumum and the touchdown for the delivery phase is timely. The final phase of thc delivery (descending and ascending) has a longer duration: wilh the path practi­cally identical in length. This results in a lower release velocity, with a corres­pondingly lower performance.

Wyludda makes an even slower start of the throw: turn duralion is 0.84 sec. She accelerates in the decisive phase of the delivery, achieving a substantially higher discus velocity al release.

Table 2 - Timing of the aclion and length of Ihe diücus path in the different phases in relation lo some delivery - phase dala

rhmic

PREPARATORY

TURN Sian Right Tnmsiiion

DELIVERY Dc'scenihng Ascending .Angle of release Hcighi of release Release velocity

CRM JSvmbols/

ajol

hjml vjml^

t 'RM - Crucial momenis

Z-"" ' -Rt

R t - L + L, t - R I

R4-U

L t - Z " " " ' Z""" Hi

UuBarWi.'Wm 1 Wr-HeLsinkiai

t/s/

(1,46

0.33 O.IW 0.19

0,06 0.09 .Ih"

1.65 m

25,4 m/s

sJmi

2,36

3.01 0.67 1.71

1,08 1.43

Opitz <>S,*tm 1 WC Helsinki to

Ui/

0,56

0,45 0,04 0,24

0.111 0,10 3fr

l.57m 24.7 m/s

sfm/

1.81

2.68 0,26 1.46

1.01 1.44

Biikluriiv Wi,«lm I.WCJAihcnsf*

Vsl

0.60

0,40 0,06 0,16

0,10 0,08

35"

s/m/

2.04

2.64 0.58 t..35

1,03 1.5

l.64m 23,5 m/s

WyliKlJ» M,02m I .Wa Athens Sft 1

\JsJ

1,12

0,49 0,14 0,21

0,(17 0.09

37

s/m/

1.27

1.98 0.77 1.01

0.55 1,53

" l.S3m

24,7 m/s

ng. 7 i3

Figures 7 and 8 show the three di­mensional reconstruction of the discus path and the crucial momenis seen from two angles.

The greater scope of discus move­ment in Bakiarov can be seen. In this

way he achieves longer path sections in the different phases, mainly the deliv­ery phase.

The functional course of the cir­cumferential velocity of the discus (Fig. 9) shows that, throughoul the

34 Fig. 8

> »-G O 2 0 -

15-

10-

•max 1

BAKIAROV 60.60

\s TIME[«

V//////////////A V//////. Rt Lt R« l« I O

^mln,2

Fig. 9

E 2 4 -

>-

Ul

> 1 6 H

12-

8 -

4 -

1

c

Zr

1 >

n«x,l

^

0,4

WYLUDDA

- ^ ^ ^ - ^ -

o,e

64,02 m J

/

/

/

/

/• / 1 1 1 1 1 1

1,2 1,6 2,0

^m/////////////A ^,,y., ^ H Rt I t R* U I

^min

T r M E [ i ]

o 1

Fig. 10 35

throw. Bakiarov maintains a higher speed. In the fiight phase and particu­larly, the transition phase (before the left foot landing), the speed is reduced slightly. Wyludda (Fig. 10) in contrast, accelerates ihe discus less in the firsl part of the throw with a more signific­ant speed reduclion in the transition phase which is a consequence of a late landing of the lefl foot. In that period, the discus covers the path belween points R I - L ^which cannot he used for accelerating the implement. This means a shortening of the discus path mainly in thc descending pari in the de­livery phase, which is crucial for ac­celerating the discus. Higher discus speed at release and a preceding

steeper rise of the discus speed can be seen in Upitz as well. This characteris­tic of the funclional course ofthe veloc­ity is probably made possible by the lighter women's discus.

The analyses of the technique of the 1st World .lunior Athietics Champions have shown that the coaches ofthe best young alhletes are aware of the neces­sity of laying the foundations for out­standing future performances, not only by stimulating the development of their physical potential, but mainly by applying modern knowledge from the field of applied biomechanies in teach­ing and improving techniques.

a

36

REFERENCES

BARTONIETZ. K, (WW): Die aerodynamis­chen Eigenschaften von .Speer und Diskus besser nutzen! Der Leichlathlei. 7, 7-1(1. GREGOR. R.J,. WHITING, W.C. & MC COY. R-W, (1985), Kim-miuic Analysis of Olvmpic Di.'iciis Throwers. Iinernational Journal of Spon Biiimochanics. I. 131-138. GRIGALKA. O, (1985): Metanije diska. Leg-kiijiiatk'lila. 8. S-n, GRIESER. M, (198-^): S5 Jahre Diskus-drechiin^ Der I.eichtalhlet. 7. 7-10. SCHMOLINSKI. G. (1978): Track and Field. Berlin: Sportwerlag,

SOONG. T, - CH, (1982): Biomechatucs lanidvses and uppUcaiionsi ofshoiptu and discus und javelin throws. Ill D.N, Ghista. Human body dvnamics (pp, 462-498). O.xford: Clarciidun Press.

UNGER. J, (1977): Throwing in the wind. Mod­ern aihlele and coacll. 4. LS,

S U S A N K A . P . . S T E P A N E K . J . . T S A ­R O U C H A S . E, (1983): Shot piu and Uuowing. In Series of ihe films; Champions Style It, Alhens. 82. Praha: Kratky film.

S U S A N K A , P.. STEPANEK. J.. VRABEL, J. (1984): Di.uiis throw. hi Series of Biomechanical analysis: Champion's slyle III. Helsinki 83. Praha: Kratkv film.