lt what does it really mean

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”.