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Day 2. Free Communications – Physiology and Nutrition

Fatigue is an exercise-induced impairment in the ability to produce muscular force that can be both central and peripheral in origin. The contribution of central and peripheral processes to fatigue is taskdependent. For self-paced cycling exercise, we recently showed that the magnitude of peripheral fatigue after high-intensity, short-duration bouts was greater than that after lower-intensity, longer-duration bouts, where central fatigue was exacerbated (Thomas et al., in press, Medicine & Science in Sport & Exercise). We hypothesised that these differing profiles of fatigue might be specific to the exercise intensity domain in which the bout is completed. The aim of this study was to test this hypothesis by studying the contribution of central and peripheral processes to fatigue after extreme-, severeand heavy-intensity constant-load exercise. After institutional ethics approval, seven trained male cyclists (mean (s) age: 29 (6) years, mass: 74 (9) kg, V̇O2max, 4.6 (0.2) L · min) completed three constant-load cycling trials to exhaustion at extreme (E, 382 ± 33 W), severe (S, 309 ± 24 W) and heavy (H, 257 ± 22 W) exercise intensities, in a randomised, counterbalanced order. Preand post-exercise twitch responses from the knee extensors to electrical stimulation of the femoral nerve and magnetic stimulation of the motor cortex were recorded to assess neuromuscular and corticospinal function, respectively. Time to exhaustion was 3.2 ± 0.6 min, 10.5 ± 1.0 min and 41.7 ± 9.7 min for E, S and H, respectively. Exercise resulted in significant reductions in maximal voluntary force, with no difference between trials (–18%, – 15% and –13% for E, S and H, respectively, P = 0.53). Greater peripheral fatigue was evident after extreme (–33%) compared to severe (–20%, P < 0.05) and heavy exercise (–10%, P < 0.05). A smaller reduction in voluntary activation measured through motor nerve (–3.2%, –5.8% and −7.6% for E, S and H, respectively) and motor cortical stimulation (–1.4%, – 7.7% and – 8.1% for E, S and H respectively) was observed after extreme intensity exercise that approached significance (P = 0.08). These data demonstrate that the contribution of central and peripheral processes to the fatigue observed after constant-load cycling is influenced by the intensity domain in which the exercise is performed, with exercise in the extreme domain incurring greater peripheral fatigue in comparison with exercise in the severe and heavy domains, where peripheral fatigue is less but central fatigue might be greater.