Affiliations: [a] Department of Exercise and Sport Science, University
of North Carolina -- Greensboro, Greensboro, NC, USA | [b] Athletic Training/Sports Medicine Research Laboratory,
University of Virginia, Charlottesville, VA, USA
Note: [] a
Abstract: {\it Purpose:} The purpose of this study was to determine if surface
electromyography (EMG) could be used to index fatigue during isotonic and
maximal voluntary isometric contractions (MVIC) of the knee extensors in men
and women. {\it Methods:} Ten males (age = 22.1 \pm 3.3 yr, ht = 180.3 \pm 5.5
cm, mass 78.7 \pm 5.1 kg) and ten females (age = 23.9 \pm 4.6 yr, ht = 163.7.3
\pm 11.1 cm, mass 63.2 \pm 7.4 kg) underwent one isometric (120 s MVIC of the
knee extensors) and one isotonic (120 maximal effort isotonic contractions at a
resistance of 25% of the MVIC peak torque determined on the testing day)
exercise session 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 torque (AT) was calculated from each 3 s window
of the 120 s MVIC, and the average peak power (APP) was calculated for every 3
consecutive contractions during the dynamic exercise. {\it Results:} Both the isometric and isotonic fatigue protocols
resulted in significant (p<0.05) decreases in AT and APP, respectively.
During the isotonic exercise protocol, decreases in APP during contractions
31--54 were significantly greater (p<0.05) 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<0.05) but not during isotonic exercise (p>0.05). A main
effect for gender (p<0.05) revealed larger EMG amplitude for females when
compared to males during isotonic exercise. {\it Conclusions:} These results indicate that gender may be a
factor in the development of dynamic fatigue and that EMG can index fatigue
during a sustained MVIC.
