ONLY FORCE PRODUCTION DECLINES WITH FATIGUE
Kremenic, I. J., Glace, B. W., & McHugh, M. P. (2008). EMG changes during a prolonged bout of cycling. ACSM 55th Annual Meeting Indianapolis. Presentation number 2501.
This study examined EMG amplitude and frequency changes during a bout of fatiguing cycling. Trained cyclists (M = 11; F = 6) cycled for two hours at their ventilatory threshold (~66% VO2max), interspersed with five 1-minute sprints, followed by a 3-km time trial. EMGs of the vastus lateralis, vastus medialis, and rectus femoris were recorded for 30 seconds at 15, 75, and 115 minutes of cycling. Pedal frequency and oxygen consumption [VO2] were measured simultaneously. Maximal voluntary isometric strength was tested before and following cycling to indicate strength losses from fatigue. Maximum amplitude and average frequency for each pedal cycle were averaged for each 30-second measurement period.
Maximal voluntary isometric force declined by 21% after cycling, indicating fatigue. Pedal frequency did not change during the exercise. Rectus femoris EMG frequency decreased over time, which is to be expected with fatigue.
Implication. Contrary to expectations, only rectus femoris EMG frequency was altered with fatigue. There were no other amplitude or frequency changes in the quadriceps muscles in spite of significant fatigue.
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