PHYSIOLOGY OF EXERCISE PERFORMANCE

AND LIMITATIONS

Susan A. Ward DPhil

Human Bio-Energetics Research Centre

Crickhowell, Powys, United Kingdom

saward@dsl.pipex.com

bfe

High forcegeneration

High glycolyticcapacity

High oxidativecapacity

SKELETAL MUSCLE

bfeModified from Jones DA & Round JM. Skeletal Muscle in Health and Disease: A Textbook of Muscle

Physiology. Manchester Univ Press, 1990.

“2x”

Constant Work-Rate Exercise

Incremental Exercise

Modified from Maughan R, Gleeson M & Greenhaff PL.Biochemistry of Exercise and Training, Oxford University Press, 1977.

muscular force or work rate

High force-generation;high glycolytic

capacity

Low force-generation; high oxidative

capacity

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Decrd. proportion of Type 1 & incrd. proportion of

Type 2x fibres (with loss of oxidative capacity):

COPD (Whittom et al. Med Sci Sports Exerc 30:1467-

1474, 1998)PAH (Mainguy et al. Thorax

65:113-117, 2010)

IIx

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COPD: ↓ (Gosker et al. EurRespir J 30: 73-79, 2007)

COPD : ↓ (Whittom et al. Med Sci Sports Exerc30:1467-1474, 1998)

(From Hoppeler et al., 1973)

Oxygen Uptake (L/Min)

Modified from Rowell LB. Human Cardiovascular Control

Oxford University Press, New York, USA, 1993.

CARDIOVASCULAR SYSTEM

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Q = 5⋅VO2 + 5••

“Rules of thumb”:

SV = 5⋅∆VO2 /∆HR

Whipp BJ, Higgenbottam MB, Cobb FC. Estimating exercise

stroke volume from the asymptotic oxygen pulse in

humans. J Appl Physiol81:2674-2679, 1996.

•

HR Reserve(HRmaxpred – HR peak)

NL ~ 0

Premature cessation of test:(e.g. Resp Dis)

(HRmaxpred > HR peak)HRR > 0

●

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00

500

1

3

2

4

5

VO

2(L

/min

)

5 10 15 20 25 30

Q (L/min)

●

●

●

●

●

VO2 = Q(CaO2 - CvO2)• •

•

•

VO2/Q = (CaO2 - CvO2)• •

↑

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Fick Equation:

linear

-

-

Whipp BJ. Unpublished Susan A. Ward

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0

0

500

21 3 4 5

VO2 (L/Min )

C(a

-v)O

2(m

L/dL

)

5

10

15

20

25

6

●

●

●

●

●

●

C(a-v)O2 (mL/dL)

= 20VO2/(1+VO2)•

•

-

-

•

“Rule of thumb”:

hyperbolic

bfeWhipp BJ. Unpublished

Susan A. Ward

VO2 = Q(CaO2 - CvO2)• •

Fick Equation

“Oxygen Pulse”

VO2/HR = SV(CaO2 - CvO2)

VO2 = HR.SV(CaO2 - CvO2)

Yandell Henderson & Alexander Prince,The Physiological Laboratory of the Yale Medical Sc hool THE OXYGEN PULSE AND THE SYSTOLIC DISCHARGE

“... the oxygen pulse which more than any other fac tor determines the total energy which a man can command for the most strenuous mome nts of life. Its maximum value

depends upon the haemoglobin index and the tidal vo lume of the heart.”(Am J Physiol 35:106-116, 1914)

•

•

bfeWhipp BJ. Unpublished

Susan A. Ward

-

-

-

linear

hyperbolic

VO2/HR = O2-P = SV(CaO2 - CvO2)•

bfe

-

Modified from Whipp BJ. Clinics in Chest Med. 15:17 3-192, 1994.

Whipp BJ. Unpublished. Susan A. Ward

Substrate Free Energy

ATP Energy Yield

Work of Muscular Contraction

Work of Task Performance

(Phosporylative Coupling)

(Contraction Coupling)

(Skill)

“Work Efficiency”

ηpc ≈ 50%

ηcc ≈ 50%cycle

ergometry25-30%

bfeWhipp BJ & Ward SA. Unpublished

Susan A. Ward

ENERGETICS

1/ηw = 1/ηpc + 1/ηcc

100 watts ≈ 1L/min

O2 Deficit:creatine phosphatepreviously-stored O2anaerobic glycolysis

∆ VO2

.

Response “Gain”: ∆VO2/∆WR ≈ 10 ml/min/watt.

bfeModified from Whipp BJ, Mahler M. In: Pulmonary Gas Exchange, Vol. II.

Ed.: West JB. New York: Academic Press, pp 33-96, 1 980.

exponential[time constant ( τ) = time to

reach 63% of steady-state response]

O2 DEFICIT

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Modified from Nery LE, Wasserman K, Andrews JD, Hunt sman DJ, Hansen JE, Whipp BJ. Ventilatory and gas exchange kinetics during exerci se in chronic obstructive pulmonary disease.

J Appl Physiol 53:594-1602, 1982.

(modified from Fukuoka et al. 2002)

1000

Figure 1

-4 -2 0 2 4 6200

400

600

800

1000

VO

2 (m

l · m

in -

1 )

τ = 96.8 s

τ = 71.0 s

(modified from Puente-Maestu et al. 2002)

-4 -2 0 2 4 6200

Time (min)

Healthy Elderly

COPD

bfe

bfeModified from Whipp BJ, Mahler M. In: Pulmonary Gas Exchange, Vol. II.

Ed.: West JB. New York: Academic Press, pp 33-96, 1 980.

Modified from Wasserman K, Van Kessel AL & Burton GC. J Appl Physiol 22:71-85, 1967.

MODERATE INTENSITY

bfeModified from Whipp BJ, Mahler M. In: Pulmonary Gas Exchange, Vol. II.

Ed.: West JB. New York: Academic Press, pp 33-96, 1 980.

Modified from Wasserman K, Van Kessel AL & Burton GC. J Appl Physiol 22:71-85, 1967.

> Lactate Threshold

HEAVY INTENSITY

●

●

●

●

bfeModified from Whipp BJ, Mahler M. In: Pulmonary Gas Exchange, Vol. II.

Ed.: West JB. New York: Academic Press, pp 33-96, 1 980.

Modified from Wasserman K, Van Kessel AL & Burton GC. J Appl Physiol 22:71-85, 1967.

Maximum VO 2

.VERY-HEAVY INTENSITY

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THE RAPID RAMP/INCREMENTAL EXERCISE TEST

Whipp BJ. Unpublished Susan A. Ward

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x

x

x

x

x

x

“0” 1 2 3 4 5 6 7Time (min)

“0”

25

50

75

100

125

150

175

Wor

k R

ate

(Wat

ts)

“R”

2.25

2.0

1.75

1.25

1.5

1.0

0.5

0.75

VO

2 (L

/min

)

● ● ● ● X

bfe

Whipp BJ. Unpublished Susan A. Ward

.

Oxygen Uptake Response Profiles

t1/2 = 1 min

Half-time (t 1/2) = time to reach 50% of steady-state response

[τ = 1.44 t1/2]

-WRGain(ss) = ∆VO2 / ∆WR = Gain(ramp).

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onset ofmetabolic (lactic) acidosis

VO2peak.

τ

Whipp BJ. Unpublished Susan A. Ward

* * **

* *

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Whipp BJ. Unpublished Susan A. Ward

FACO2 = VCO2 (STPD) or P CO2 = 863 x VCO2 (STPD)VA (STPD) VA (BTPS)

but as VA = VE (1 - VD/VT)

PaCO2 = 863(VE/VCO2) x (1-VD/VT)

PaCO2 is therefore determined by two composite variables:(a) ventilatory equivalent for CO 2(b) physiological dead space fraction of the breath

..

..

..

. .

Fick Principle: VCO 2 = VA x FACO2

CONTROL EFFICIENCY

A

. .

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VENTILATORY REQUIREMENTS

Whipp BJ. Unpublished Susan A. Ward

linear hyperbolic

bfe Modified from Whipp BJ. Clinics in Chest Med. 15:173-192, 1994.

*

Whipp BJ & Ward SA. Unpublished. Susan A. Ward

Ventilatory Control

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00

100

200

300

400

500

21 3 4 5VT (L)

VD

(ml)

VD/VT

0.2

0.1

0.13

Gas Exchange (In)efficiency

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Whipp BJ. & Ward S.A. Unpublished Susan A. Ward

θL

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θL lactate threshold

RCP respiratory compensation point

ICB isocapnic buffering

Modified from Wasserman et al. “PETI”, 2005, p 246

Why doesn’t the respiratory compensation for the metabolic acidosis of exercise occur at the lactate threshold – i.e. when arterial pH first starts to fa ll?

The Respiratory Compensation Point

ICB

RCP

(≈ 40 x FEV1)

MVV = Max voluntary ventilationBR = Breathing reserve

= MVV - VEpeak

COPD

Modified from Whipp BJ, Pardy R. In: Hbk Physiol, Resp (Pulmonary Mechanics). Eds: Macklem P, Mead J. Washington DC: Amer Physiol So c, pp 605-629, 1986.

Ventilatory Limitation

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↑VD/VT↓PaCO2

.

The contemplation of those things which are normal is physiology,

and it is the first thing to be learned by medical men.

For that which is normal is right

and serves as a criterion for both itself and the a bnormal.

(William Harvey)

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