Dynamics of Locomotor Fatigue during Supra-critical Power Exercise.

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 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.