Anaerobic threshold (AT) as determined by VO2max and VLAmax of the working muscle

mass of the human body -an update of the theoretical concept

Institute for Cardiology and Sports Medicine German Sport University Cologne,

Cologne Germany

A. MADER

European Congres Sports Science Rom 1998

Basic assumptions• About the 30% of body mass are involved in running.• Therefore the energy metabolism in the working muscles

is the main cause for the dynamic changes of the measurable parameters which are related to energy supply from oxidative phosphorylation (VO2ml/min*kg) and glycolysis (VLa mmol/l*s).

• Glycolysis and oxidative phosphorylation are activated as a function of the cytosolic phosphorylation state of the high energy phosphate system ([ATP] + [PCr]).

• As the mechanical power output of the muscle cell decreases the phosphorylation state this activates the metabolic reactions at different levels of the state dephosphorylation.

• The lactate distribution space is less than 50% of the body volume.

Human body lactic acid distribution space

Activemusclespace Cla(M)

PassivelactatespaceCla(B)

Non H2O

space

100%65%48%30%

Lactate space

H2Ospace

in % body volume

1) Lactate production in the active space2) Elimination of lactate in both spaces

Non lactate space

CLass Vol.rel

VLass

VLass

VLaOXss

Lactate elimination

I

II

Log/lin. steady state activity of oxidative phosphorylation and glycolysis VO2MMK = Michaelis-Menten-Kinetik

VO2

VLa

PCr

VO2MMK pH=6,4

pH=6,6

pH=6,8

pH=7,0

ATP

-DGATP

rest exhaustion

Protonleak

Cha

nce

pH=6.2

pH = 7.4

Sta

ge

of

an

aero

bic

th

resh

old

VO2

VL

ass

Oxidative steady state

Non steady state

The steady state assumption

• As oxidative phosphorylation and glycolysis are regulated as a function of the cytosolic [ADP] “gross lactate formation” (Vlass) is a function of the relation between VO2max versus VO2ss.

• The rate of glycolysis is

VLamax

(1 +ks2((VO2max-VO2ss)/ks1*VO2ss)3/n)

Vlass = + VLaRest

ks1 0.035 mmol/l [ADP]

ks2 0.2 mmol/l [ADP]

Measured rate of lactate oxidation, trained and untrained rats (results from DONNOVAN and BROOKS (1983))

• Necessary fuel for maintaining

mitochondrial oxidation: • VLaOXmax (mmol/l*min) =

(0.035)* VO2ss(ml/min*kg)• Real carbohydrate (lactate)

oxidation is a function of the lactate concentration:

• VLaOXss (mmol/l*min) = VLaOXmax/(1+ kel/[CLa]2)

• CLa(mmol/l) is the blood lactate concentration

• The 50% activity constant kel can be estimated from tracer experiments of DONNOVAN & BROOKS

Blood lactate(mmol/l)

Best fit kel = 2.0

VLaOXmax= f(VO2ma,x, Cla >> 20 mmol/l)

kel

OSS => VLaOXmax > VLass

(OSS = oxidative steady state)

Consequence• The 50% activity constant kel (CLa) reflects the

sentivity of the pyruvate dehydrogenase (PDH).

• If CLa or CLaSS determines the carbohydrate combustion then “fat combustion” can only take place if there is a “lack of pyruvate production”.

• The lack of pyruvate expressed as VLass - equivalent is

• In this case the mRQ can be recalculated from CLaSS or Cla(B):

V(LackPyr) = VLaOXmax - VLaOXss

---> %VLaOXss = 100/(1+kel/[CLaSS]2)

---> mRQ = ((100 - %VLaOXss)*0.7 + VLaOXss)/100

---> for CLaSS = 4.0 mmol/l the mRQ is ~ 0.97

Way of calculation under the “steady state” assumption

• It is assumed that under all conditions included the complete depletion of PCr the the rectangular area from start to peak VO2 (~ VO2ss) is covered by oxygen uptake and PCr-depletion.

• This is associated with a certain rate of glycolytic energy sup-ply VLass.

Oxidative + alactic power

VO2ss

VO2tot(ml/min*kg) = VO2ss + 2.7 * VLass(mmol/l*min)

CLaVLAss

The problem of the diagnostic of an athletes metabolic capacities ?

• How can be the aerobic capacity (~ aerobic power related to VO2max (ml/min*kg b.w.)) measured or estimated ?

• How can be the glycolytic power - defined as “maximal lactate formation rate” (VLamax (mmol/l*s) - determined or estimated ?

• Does the extent of each of the two powers influence the appearance of the other ?

• How is the appearance of the so called “anaerobic threshold” (AT) related to the extent of the aerobic and the glycolytic power of an athlete ?

Low endurance, female 400/800m runner

2 x 300m

Energy demand

VO2ss

= VO 2tot

Alactic+ oxydat.energy

glycolytic

2 m

inm

ax.

test

treadmill

AT

Measured VO2max

Low endurance Glycolytic power ?

Low endurance, female 400/800m runner measured VO2max = 58 ml/min*kg glycolytic power ?

measuredVO2max

74%VO2max

2Min

.M

ax.t

est

2 x 300m

MeasuredRQ

Calcul.mRQ

CLa

CLa

AT

400m

Metabolic Profile: Low endurance, female 400/800m runner

estimated VO2max = 62 ml/min*kg; glycolytic power = 0.8 mmol/l*s

2 x

300m

300m

400m

600m

800m

MeasuredRQ

trea

dm

ill

VO2ss

VLaOXmax

AT

%fat com

b

VL

anet

Class

Energy demand: Highly endurance trained runner: 4mmol speed =5.65 m/s, VO2max measured = 76, estimated = 80 m/min*kg BW

V4

86%VO2maxmuscle

Range of Endurance

1500mCompetition

Next slide will appear

VO2ss

2 m

in m

ax. t

est

Energy demand

VLass

Long distance runner, high endurance trained

V4

AT

Measured VO2max

vent. RQmeasured

CalculatedmRQ

d

High endurance trainend: VO2max measured 76 ml/min*kg estimated: 80 ml/min*kg, VLamax~ 0.25 mmol/s*l

V4

% Fat combustion

2 m

in

100m

VO2maxmeasured

CLa

1500

m

Measured R

Q

Metabolic RQ

Low anaerobic

Extended range of endurance

VO2

Maximum

Max

test

100m

2Min

VLaOXmax

VLass

High endurance trained

Measured RQ

%Fat oxidation

100m

AT60

0m

VLassLack of pyr

Fat

Extensive endurancetraining CLa < 1.25mmol/l

1500

m

VO2ss

- It seems to be possible to recalculate the metabolic pattern according to various test results using spiroergometry and measurement of lactate con-centration after short intensive loads.

Conclusions:

- The main variables which characterize the athletes metabolic capacities are the estimated maximal oxygen uptake (VO2max) and the maximal rate lactate production (VLAmax).

Thank you for your patience and your

attention