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 (VA) were measured at baseline, 25, 50, 75 and 100% of task-completion. During the initial, baseline visit, and following each constant work rate bout, ramp-incremental exercise was performed, and peak power output and oxygen uptake (V̇O2peak) were determined.
Following 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 90% GET trial. Peak power output and V̇O2peak during ramp-incremental exercise were reduced by 7.0 ± 11.3% and 6.5 ± 9.3%, respectively, following the 110% GET trial relative to the baseline ramp (p ≤ 0.015), with no changes following 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-heavy intensity boundary has implications for performance fatigability, whilst also impairing maximal exercise performance capacity.