Power Output Manipulation from Below to Above the Gas Exchange Threshold Results in Exacerbated Performance Fatigability

Abstract

Performance fatigability is substantially greater when exercising in the severe- versus heavy-intensity domain. However, the relevance of the boundary between moderate- and heavy-intensity exercise, the gas exchange threshold (GET), to performance fatigability is unclear. This study compared alterations in neuromuscular function during work-matched exercise above and below the GET. Seventeen male participants completed work-matched cycling for 90, 110, and 140 min at 110%, 90%, and 70% of the GET, respectively. Knee extensor isometric maximal voluntary contraction (MVC), high-frequency doublets (Db100), low- to high-frequency doublet ratio (Db10:100), and voluntary activation were measured at baseline, 25%, 50%, 75%, and 100% of task completion. During the initial baseline visit and after each constant work rate bout, ramp-incremental exercise was performed, and peak power output and oxygen uptake (V̇O 2peak ) were determined. After the 70% and 90% GET trials, similar reductions in MVC (-14% ± 6% and -14% ± 8%, respectively, P = 0.175) and Db100 (-7% ± 9% and -6% ± 9%, respectively, P = 0.431) were observed. However, for a given amount of work completed, reductions in MVC (-25% ± 15%, P = 0.008) and Db100 (-12% ± 8%, P = 0.029) were up to 2.6-fold greater during the 110% than the 90% GET trial. Peak power output and V̇O 2peak during ramp-incremental exercise were reduced by 7.0% ± 11.3% and 6.5% ± 9.3%, respectively, after the 110% GET trial relative to the baseline ramp ( P ≤ 0.015), with no changes after the moderate-intensity trials ( P ≥ 0.078). The lack of difference in fatigability between the trials at 70% and 90% GET, coupled with the greater fatigability at 110% relative to 90% GET, shows that exceeding the moderate- to heavy-intensity boundary has implications for performance fatigability, while also impairing maximal exercise performance capacity.