Intensity-dependent tolerance to exercise after attaining VO2 max in humans

• Published in: Journal of applied physiology (1985) Vol. 95; no. 2; p. 483
• Main Authors: Coats, Edward M, Rossiter, Harry B, Day, James R, Miura, Akira, Fukuba, Yoshiyuki, Whipp, Brian J
• Format: Journal Article
• Language: English
• Published: Am Physiological Soc 01-08-2003
• ISSN: 8750-7587; 1522-1601
• DOI: 10.1152/japplphysiol.01142.2002

1 Department of Physiology, St. George's Hospital Medical School, Cranmer Terrace, London, United Kingdom;
2 Department of Medicine, Division of Physiology,
University of California, San Diego, California 92093-0623;
3 Department of Exercise Science and Physiology,
Hiroshima Women's University, Hiroshima 724-8558, Japan; and
4 Division of Respiratory and Critical Care Physiology
and Medicine, Harbor-University of California at Los Angeles Medical Center,
Torrance, California 90502
Submitted 11 December 2002
; accepted in final form 25 March 2003
The tolerable duration of high-intensity, constant-load cycle ergometry is a hyperbolic function of power, with an asymptote termed critical power (CP)
and a curvature constant (W') with units of work. It has been suggested
that continued exercise after exhaustion may only be performed below CP, where
predominantly aerobic energy transfer can occur and W' can be partially
replenished. To test this hypothesis, six volunteers each performed
cycle-ergometer exercise with breath-by-breath determination of ventilatory
and pulmonary gas exchange variables. Initially, four exercise tests to
exhaustion were made: 1 ) a ramp-incremental and 2 ) three
high-intensity constant-load bouts at different work rates, to estimate
lactate ( L ) and CP thresholds, W', and maximum oxygen
uptake ( O 2 max ).
Subsequently, subjects cycled to the limit of tolerance (for 360 s) on
three occasions, each followed by a work rate reduction to 1 ) 110%
CP, 2 ) 90% CP, and 3 ) 80% L for a 20-min
target. W' averaged 20.9 ± 2.35 kJ or 246 ± 30 J/kg. After
initial fatigue, 110% CP was tolerated for only 30 ± 12 s. Each subject
completed 20 min at 80% L , but only two sustained 20 min at
90% CP; the remaining four subjects fatigued at 577 ± 306 s, with
oxygen consumption at 89 ± 8%
O 2 max . The results
support the suggestion that replenishing W' after fatigue necessitates a
sub-CP work rate. The variation in subjects' responses during 90% CP was
unexpected but consistent with mechanisms such as reduced CP consequent to
prior high-intensity exercise, variation in lactate handling, and/or regional
depletion of energy substrates, e.g., muscle glycogen.
maximal oxygen uptake; fatigue; gas exchange dynamics
Address for reprint requests and other correspondence: H. B. Rossiter, Dept. of Medicine, Division of Physiology, Univ. of California, San Diego, La Jolla,
CA 92093-0623 (E-mail:
hrossiter{at}ucsd.edu ).