Physical fitness and performance. Fatigue responses during repeated sprints matched for initial mechanical output.
OBJECTIVE
To compare muscle fatigability during two sets of repeated cycling sprints matched for initial mechanical output in a nonfatigued and fatigued state.


METHODS
Eight young men performed 10, 6-s all-out sprints on a cycle ergometer interspersed with 30 s of recovery, followed, after 6 min of passive recovery, by five 6-s sprints, again interspersed by 30 s of recovery.


RESULTS
On the basis of total work (TW), performance in sprint 11 (79.8 +/- 4.8 J.kg) was not significantly different to performance in sprint 4 (80.3 +/- 5.3 J.kg; P = 0.81). The decrease in TW for the five sprints after sprint 4 (i.e., sprints 4 to 8) averaged 14.5% (P < 0.001), which was significantly less than the decrement in TW from sprints 11 to 15 (20.3%; P < 0.05). Despite no significant differences in TW values achieved in sprints 4 and 11, the amplitude of the electromyogram (EMG) signal (i.e., root mean square (RMS)) recorded during sprint 11 (0.398 +/- 0.03 V) was 12.0% lower (P < 0.05) than in sprint 4 (0.452 +/- 0.02 V). In contrast, values of EMG median frequency (MF) recorded during sprint 4 (85.5 +/- 5.5 Hz) and 11 (89.3 +/- 7.2 Hz) were not significantly different (P = 0.33). However, the rate of decrease in EMG activity (i.e., RMS and MF) was similar for the two set of sprints.


CONCLUSIONS
These findings suggest that previous fatiguing repeated-sprint exercise, followed by a rest period, induces greater fatigability during subsequent repeated-sprint exercise, regardless of the initial mechanical output, and that these changes are associated with acute neuromuscular adjustments.
Mendez-Villanueva
Alberto
A
School of Human Movement and Exercise Science, The University of Western Australia, Perth, Australia. amendezvillanueva@yahoo.com
Hamer
Peter
P
Bishop
David
D
D000293:Adolescent; D000328:Adult; D054874:Athletic Performance; D001642:Bicycling / Q000502:physiology*; D004576:Electromyography; D006801:Humans; D008297:Male; D018763:Muscle Fatigue / Q000502:physiology*; D005082:Physical Exertion / Q000502:physiology*; D010809:Physical Fitness; D052097:Quadriceps Muscle / Q000502:physiology