Neuromuscular Fatigue Following Cycling To Task Failure In Different Exercise Intensity Domains

Abstract

Neuromuscular (NM) fatigue can vary according to exercise intensity and duration; however, fatigue responses across the full spectrum of exercise intensities to task failure remain unclear. PURPOSE: To characterize the central and peripheral NM fatigue responses to cycling to task failure in different exercise intensity domains. METHODS: After a ramp incremental test, 12 healthy, active males (29 ± 5 years) underwent 4 cycling sessions to task failure at 5% below gas exchange threshold (moderate domain; MOD), 5% below the maximal metabolic steady state; HVY), 5% below peak power output (severe domain; SVR), and 120% of peak power output (extreme domain; EXT). At baseline, upon task failure (post), and following 1, 4, and 8 min of recovery, participants performed an NM assessment consisting of a maximal voluntary isometric contraction (MVC) with superimposed and potentiated high frequency doublets (Db100), followed by a low frequency doublet (Db10) and single twitch (QTw). Two-way repeated measures ANOVAs with Bonferroni post hoc examined 4 domains 5 timepoints. RESULTS: MVC declined to the same extent in all domains at post (all p > 0.05) and although not fully recovered at 8 min, the fastest recovery from post was displayed after EXT (+59.5 ± 79.0%) compared to MOD (+9.4 ± 32.0%, p = 0.035), HVY (+17.7 ± 21.8%, p = 0.021), and SVR (+29.8% ± 29.9%, p = 0.016). Voluntary activation at post was lowest after MOD (-11.1 ± 11.6%) compared to EXT (-0.5 ± 4.6%, p = 0.030), and all conditions fully recovered to baseline without differences between domains at 8 min (all p > 0.05). While QTwat post displayed greatest decline in EXT (-50.5 ± 14.7%) and least in MOD (-7.5 ± 28.3%, p = 0.011), EXT (+86.1 ± 69.2%) partially recovered by 8 min to match MOD values (+2.3 ± 17.7%, p = 0.865). Low frequency fatigue (Db10:100) at post was lowest in MOD (-8.6 ± 6.1%) compared to HVY (-18.4 ± 7.9%, p = 0.007), SVR (-22.8 ± 9.3%, p = 0.020), and EXT (-24.8 ± 10.7%, p < 0.001), but all conditions partially recovered from post to match MOD values at 8 min (+2.3 ± 7.2%, all p > 0.05). CONCLUSIONS: Although MVC declined to the same extent following exercise to task failure in all domains, our data confirm that the contribution of central and peripheral factors to this decline differed between conditions. Different NM fatigue recovery patterns were also demonstrated during recovery.