lt what does it really mean
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Lactate threshold:what does it really mean?
Andrew R. Coggan, Ph.D.
Cardiovascular Imaging Laboratory
Washington University School of Medicine
St. Louis, MO 63110
Lactate threshold (LT)
• What is it?• How do you measure it?• Why is it important?• What determines it?• How do you train it?
LT – what is it?
Definition• The exercise intensity at which lactate production
exceeds lactate removal, and thus begins to accumulate in muscle and hence in the blood.
Related concepts• OBLA, MLSS, lactate minimum, individual
anaerobic threshold, ventilatory (anaerobic) threshold, critical power, etc.
Lactate threshold: the theory
Lactate threshold: the reality
Smith et al., MSSE 29:654-660, 1997
Blood lactate as a function of time during exercise at a constant intensity
0
1
2
3
4
5
6
0 2 4 6 8 10
Blo
od
HL
a (
mm
ol/L
)
Time (min)
245 W 275 W 310 W 325 W
Time to fatigue @ 310 W: 58 min
Tegtbur, Busse, and Braumann MSSE 25:620-627, 1993
Lactate minimum as an estimate of maximal lactate steady state
LT: why multiple criteria?
• The concept of a lactate “threshold” is really just a convenient way of describing, with a single number, the non-linear relationship between lactate concentration and exercise intensity.
LT – why is it important?
• LT is the single most important physiological determinant of endurance exercise performance.
• Many physiological responses to exercise are more closely related to metabolic fitness (i.e., LT) than they are to cardiovascular fitness (i.e., VO2max).
Relationship of performance to LTwhen VO2max is constant
Coyle et al., J Appl Physiol 64:2622-2630, 1988
Relationship of muscle glycogen useto LT when VO2max is constant
LT – what determines it?
Many factors• Number and/or size of muscle mitochondria• Fiber type/motor unit recruitment• Mode of exercise (muscle recruitment)• Hormonal response
Characteristics of human slow and fast twitch muscle fibers
RAMPLIKE RECRUITMENT OF FIBERS
Fiber type recruitment as a function of exercise intensity
0
20
40
60
80
100
25 50 75 100
% f
ibe
rs r
ec
ruit
ed
at
on
se
t o
f e
xe
rcis
e
% of VO2max
Type I
Type IIa
Type IIb
Total
Vollestad et al. Acta Physiol Scand 125:395-405, 1985
Effect of mode of exercise on LT in trained cyclists
Coyle et al., J Appl Physiol 64:2622-2630, 1988
Training-induced changes in LT over the course of a season in triathletes
Kohrt, O’Conner, and Skinner, MSSE 21:569-575, 1989
+6%+10%
Changes in lactate and epinephrine as a function of exercise intensity
Mazzeo and Marshall, J Appl Physiol 67:1319-1322, 1989
Physiological responses related to LT
• Muscle glycogenolysis• Glucose uptake,
production, & concentration
• Plasma K+
• Plasma NH4+
• Pi/PCr (ADPf)
• Epinephrine• Norepinephrine
• Growth hormone• Cortisol• ß-endorphin• Ventilation• iEMG
• Muscle pO2
• Etc.
LT – how do you train it?
• At least/especially in untrained persons, training at a wide range of intensities and durations will tend to lead to rapid improvements in LT, but
• For trained athletes there may be particular benefit to continuous training at circa-threshold intensities.
Effect of continuous versus interval training on VO2max and citrate
synthase activity
Gorostiaga et al. Eur J Appl Physiol Occup Physiol 63:101-107, 1991
Effect of continuous versus interval training on blood lactate
concentration during exercise
Gorostiaga et al. Eur J Appl Physiol Occup Physiol 63:101-107, 1991
Continuous exercise Interval exercise
Before
training
Same
absolute
intensity
Same
relative
intensity
Before
training
Same
absolute
intensity
Same
relative
intensity
Continuous
training
group
4.7±1.1 2.5±0.4* 2.5±0.3*† 6.2±0.8 4.1±0.3* 5.8±0.8
Interval
training
group
4.8±1.0 3.0±0.7* 5.1±0.9 8.8±1.6 4.3±0.4* 9.0±1.3
0
10
20
30
40
50
60
70
80
90
100
40 50 60 70 80 90 100 110 120 130 140 150
Exercise intensity (% of functional threshold power)
Arb
itra
ry u
nit
s
L1 L2 L3 L4 L5 L6
Physiological strain
Training effect(increase in threshold power)
Maximum duration (volume)
The “sweet spot”?
Key Points
Lactate threshold (LT)
is, at least in theory, the exercise intensity at which lactate production exceeds lactate removal.
can be measured in various ways, all of which provide different, but closely interrelated, values.
is an excellent predictor of endurance exercise performance.
(continued)
Key Points (continued)
Lactate threshold (LT)
provides a measure of a person’s metabolic fitness, as opposed to their cardiovascular fitness (i.e., VO2max).
determines numerous metabolic and neurohormonal responses to exercise.
in turn is determined by numerous factors, but especially muscle respiratory capacity (mitochondrial content).
(continued)
Key Points (continued)
Lactate threshold (LT)
responds rapidly (at least initially) to training at a wide variety of intensities and durations, but
may be particularly improved by continuous training in the “sweet spot”.
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