Proceedings of The Physiological Society

Europhysiology 2018 (London, UK) (2018) Proc Physiol Soc 41, C053

Oral Communications

Exercise-induced fatigue is a consequence of exercise intensity and is independent of task power

M. R. Chadwick1, M. J. Davies1, A. P. Benson1, G. N. Askew1, C. Ferguson1

1. School of Biomedical Sciences, University of Leeds, Leeds, United Kingdom.

During constant-power cycle ergometry that exceeds the lactate threshold (LT), exercise-induced fatigue decreases the capacity of the exercising muscles to generate power (Cannon et al., 2011). The magnitude of task-specific, exercise-induced fatigue can be quantified using brief (~6 s) isokinetic measurements of maximal voluntary power before and immediately upon cessation of the exercise task (Cannon et al., 2011). During intermittent exercise, task power (power during work phases) can be dissociated from the exercise intensity (physiological and perceptual stress (Whipp, 1996)) (Davies et al., 2017). Thus, a greater task power can be performed during intermittent than intensity-matched constant-power exercise. As a higher task power likely increases recruitment of fatigue-susceptible muscle fibres (Hodson-Tole & Wakeling, 2008), we aimed to determine whether intermittent exercise increases the magnitude of exercise-induced fatigue compared to intensity-matched constant-power exercise. Eight healthy participants (23 ± 2 yr) performed ramp-incremental cycle ergometry to the limit of tolerance to determine LT and peak oxygen uptake (VO2peak). Participants then completed (1) constant-power exercise and (2) intermittent exercise with work:recovery durations of 10:10 s. Task power for constant-power and intermittent exercise was predicted by a computational model (Benson et al., 2013) to evoke an oxygen uptake (VO2) that was 40% of the difference between LT and VO2peak. Isokinetic maximal voluntary power was measured pre- and post-exercise at 80 rpm to determine the magnitude of the exercise-induced fatigue. Pulmonary gas exchange and heart rate were measured throughout. Blood lactate concentration and subjective ratings of dyspnoea and leg tiredness were obtained every 5 min and at the end of exercise. Task power was greater during intermittent than constant-power exercise (mean ± SD; 296 ± 98 vs. 169 ± 54 W; p < 0.01). There was no difference between constant-power and intermittent exercise: VO2 (2.71 ± 0.69 vs. 2.65 ± 0.62 L/min; p > 0.05), heart rate (171 ± 13 vs. 167 ± 17 bpm; p > 0.05), dyspnoea (6.1 ± 1.4 vs. 5.9 ± 1.5; p > 0.05), leg tiredness (6.6 ± 1.3 vs. 6.4 ± 1.6; p > 0.05) or blood lactate (4.5 ± 1.2 vs. 4.0 ± 1.3 mmol/L; p > 0.05). The reduction in isokinetic maximal voluntary power (i.e. exercise-induced fatigue) was not different following constant-power vs. intermittent exercise (86 ± 45 vs. 86 ± 36 W; p > 0.05). Intermittent exercise allowed for an ~76% increase in task power compared to constant-power exercise for the same physiological (VO2, heart rate, blood lactate) and perceptual (dyspnoea, leg tiredness) stress. Exercise-induced fatigue was not different following intensity-matched intermittent vs. constant-power exercise, suggesting exercise-induced fatigue is a consequence of exercise intensity and is independent of task power.

Where applicable, experiments conform with Society ethical requirements