CHANGES IN MECHANICAL OUTPUT AND ELECTROMYOGRAPHY FOLLOWING FATIGUING ISOTONIC AND ISOMETRIC KNEE EXTENSION IN MEN AND WOMEN

Abstract

735 This study determined if surface electromyography (EMG) could be used to index fatigue of the knee extensors in an isotonic extension protocol and a sustained maximal voluntary isometric contraction (MVIC) protocol. Ten males (age = 22.1 ± 3.3 yr, ht = 180.3 ± 5.5 cm, mass 78.7 ± 5.1 kg) and ten females (age = 23.9 ± 4.6 yr, ht = 163.7.3 ± 11.1 cm, mass 63.2 ± 7.4 kg) underwent isometric (120 s MVIC of the knee extensors) and isotonic (120 maximal effort isotonic contractions at a resistance of 25% of the MVIC peak torque determined on the testing day) exercise sessions separated by at least 48 hrs. The EMG signal was collected from the vastus lateralis during both exercise protocols using standard EMG collection techniques. Average peak torque (APT) was calculated from each 3 s window of the 120 s MVIC. The average peak power (APP) of every 3 consecutive contractions was calculated during the dynamic exercise. Both the isometric and isotonic fatigue protocols resulted in significant (p<.05) decreases in APT and APP, respectively. During the isotonic exercise protocol, decreases in APP during contractions 31-54 were significantly greater (p<.05) for males than females. Time-amplitude domain processing of the EMG data demonstrated significant decreases in the root mean square amplitude during the course of isometric exercise (p<.05) but not during isotonic exercise (p>.05). A main effect for gender (p<.05) revealed larger EMG amplitude for females when compared to males during isotonic exercise. These results indicate that gender may be a factor in the development of fatigue and that EMG can index fatigue during a sustained MVIC.