THE ‘ANAEROBIC’ THRESHOLD: PHYSIOLOGY AND IDENTIFICATION

THE ‘ANAEROBIC ’ THRESHOLD: PHYSIOLOGY AND IDENTIFICATION

Susan A. Ward DPhil

Human Bio-Energetics Research Centre

Crickhowell, Powys, United Kingdom

[email protected]

The term “Anaerobic Threshold”

seems to polarize investigators into

those who believe it to be a milestone

in advancing the understanding of

exercise bioenergetics ....

and those who believe it to be a millstone.

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Whipp BJ. Unpublished Susan A. Ward

Anaesthesia, 2011, 66, pages 111–123 doi:10.1111/j.1365-2044.2010.06604.x....................................................................................................................................................................................................................

REVIEW ARTICLE

Controversies in the physiological basis of the ‘anaerobicthreshold’ and their implications for clinicalcardiopulmonary exercise testing

J. G. Hopker,1 S. A. Jobson2 and J. J. Pandit3

1 Lecturer, 2 Research Fellow, Centre for Sports Studies, University of Kent, Chatham Maritime, Chatham, Kent, UK3 Consultant Anaesthetist, Nuffield Department of Anaesthetics, Senior Lecturer, Nuffield Department of ClinicalNeurosciences and Fellow of St John’s College, Oxford, UK

B. J. Whipp and S. A. Ward

Human Bio-Energetics Research Centre, Crickhowell, Powys, U.K.

The physiological basis of the 'anaerobic threshold' and implications for clinical cardiopulmonary exercise testing

LETTER TO THE EDITOR

Anaesthesia 2011 66 pages 1048-1049 http://www.respond2articles.com/ANA/forums/thread/876.aspx

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“ANAEROBIC”:

a) Yes (O2 not used in the lactate formation)

b) No (PCr decreases at all work rates)

c) Maybe (Are there regions in the contracting

muscles where the PO2 is “critical”? -

no definitive resolution at present)

THE “ANAEROBIC” THRESHOLD

(lactate; lactic acidosis; ventilatory; gas exchange; …)

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The “Lactate Threshold” (estimated from pulmonary gas

exchange indices) is currently used for:

Assessing the normalcy, or otherwise, of an individual’s

integrative systemic function;

Optimising race pace strategy in athletes;

Optimising the intensity of training and rehabilitative

work rates;

Judging an individual’s appropriateness to undergo major

thoracic or abdominal surgery;

Triaging a patient post-operatively to “the ward” or to an

intensive care facility; and

As an index of life expectancy in patients with heart

disease.

Contributors to buffering

But do not yield CO 2

pH = pK 1 + log [HCO 3-] = pK 2 + log [NaPO 4

-] = pK 3 + log [Pr -] = pK 4 + log [org]

[H2CO3] [H2PO4-] [HPr] [ H org]

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Modified from Handbook for Fellows . Div. Resp. Med., Harbor General Hospital. 1967

THE METABOLIC ACIDOSIS OF EXERCISE

* * **

∝

* *

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LACTATE THRESHOLD ESTIMATION

Whipp BJ. Unpublished Susan A. Ward

θL

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θL lactate threshold

RCP respiratory compensation point

ICB isocapnic buffering

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

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

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supplementalCO2 load

.

.

.

Whipp BJ. Unpublished. Susan A. Ward

VE increases out of proportion to VO2

(hyperventilation relative to O2),but matched to VCO2

(no hyperventilation relative to CO2)

. .

. .

1: supplementalCO2 load

2: hyperventilationrelative to O 2

Henson et al. Eur J Appl Physiol 59:21-28, 1989.bfe

Region of Interest

Sources of “Excess” CO2 Output

during Ramp Exercise

1) Accelerated aerobic substrate catabolism

2) Pulmonary hyperventilation, with a fall in alveolar (end-tidal) and arterial PCO2?

3) Bicarbonate buffering:

(NaHCO3 in blood and KHCO3 in muscle)

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TONACDONOHOTONACDONOHO

ThresholdOf

NonAerobic

CarbonDioxide

OutputNot

OfHyperventilatory

Origin

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θ̂L

1: supplementalCO2 load

2: hyperventilationrelative to O 2but not CO2

bfe Whipp BJ & Ward SA. Unpublished

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Sue et al. Chest 94:931-938, 1988

S=1

θLˆ

Whipp BJ. Unpublished Susan A. Ward

Some Some ““Be Be CarefulsCarefuls””!!

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V-slope graph scaling

Work Rate (Watts)

VO2

(ml/min)VCO2

(ml/min)R ΔVCO2/

ΔVO2

“0” 500 400 0.8

50 1000 950 0.95

Δ = 50 Δ = 500 Δ = 550 S1 = 1.1

VCO2 - VO2 Relationship: S1 > 1.0?. .

. . .

.

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S=1.0

S >1.0

Modified from Wasserman et al. “PETI”, 2005Fig 10-12-3

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Modified from Wasserman et al. “PETI”, 2005. Fig 10-12-3 bfe

But:

VCO2 can begin to increase faster than VO2 :

not just because it begins to be “produced” faster,

but also because its rate of “storage” begins to

slow or stop!!

2OV&

2COV&

. .

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bfeOzcelik et al., 1999

CONTROL PRIOR HYPERVENTILATION

THRESHOLD DISCRIMINATION:

What to do – and why!

What not to do – and why!

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Brian J. Whipp PhD, DSc.

The Anaerobic Threshold:

Physiology and Identification The Science and the Art

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