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Dynamics of Locomotor Fatigue during Supra-critical Power Exercise


Medicine & Science in Sports & Exercise: August 2019 - Volume 51 - Issue 8 - p 1720–1726
doi: 10.1249/MSS.0000000000001965

Purpose We aimed to measure 1) the dynamics of locomotor fatigue during constant supra-critical power cycling and 2) the magnitude of any reserve in locomotor power at intolerance to constant and ramp-incremental cycling in recreationally active volunteers.

Methods Fifteen participants (7 women and 8 men, 22 ± 3 yr, 3.34 ± 0.67 L·min−1 V˙O2peak) completed ramp-incremental and very-heavy constant power (205 ± 46 W) exercise to the limit of tolerance. Immediately after intolerance, the ergometer was switched into the isokinetic mode, and participants completed a short (~5 s) maximal isokinetic effort at 70 rpm. The time course of locomotor fatigue during constant supra-critical power exercise was characterized with these short maximal isokinetic sprints at 30, 60, 120, and 180 s and at the limit of tolerance. Each bout was terminated after the isokinetic sprint.

Results Constant power exercise duration was 312 ± 37 s. Isokinetic power production values at 30, 60, 120, and 180 s and at the limit of tolerance (at 312 ± 37 s) was 609 ± 165, 503 ± 195, 443 ± 157, 449 ± 133, and 337 ± 94 W, respectively. Of the total decline in isokinetic power, ~36% occurred within the first minute of exercise, and significant (P < 0.05) reductions in isokinetic power occurred at all time points versus the baseline maximal isokinetic power (666 ± 158 W). In addition, a significant power reserve of 132 ± 74 W (64% of the task requirement) and 119 ± 80 W (47%) was present at the limit of constant power and ramp-incremental exercise, respectively.

Conclusions Locomotor fatigue occurred rapidly during supracritical power exercise with pseudo-exponential kinetics. Instantaneous isokinetic power production at the limit of tolerance exceeded that of the task requirement, regardless of the constant or ramp work rate profile. Thus, the perceptual and physiologic limits were dissociated at the limit of tolerance in recreationally active volunteers.

1School of Exercise and Nutritional Sciences, San Diego State University, San Diego, CA; and

2School of Biomedical Sciences, Faculty of Biological Sciences, University of Leeds, Leeds, UNITED KINGDOM

Address for Correspondence: Daniel T. Cannon, Ph.D., San Diego State University, 5500 Campanile Drive, MC 7251, San Diego, CA 92182; E-mail:

A. R. S. and B. K. contributed equally to this study.

Submitted for publication June 2018.

Accepted for publication February 2019.

Online date: February 27, 2019

© 2019 American College of Sports Medicine