Affiliations: [a] Department of Exercise and Sport Science, University
of North Carolina-Greensboro, Greensboro, NC, USA | [b] Athletic Training/Sports Medicine Research Laboratory,
Curry School of Education, University of Virginia, Charlottesville, VA,
USA | [c] Childrens Medical Center, University of Virginia,
Charlottesville, VA, USA
Note: [] Address for correspondence: Randy J. Schmitz, Ph.D., ATC, 250
HHP Building, Department of Exercise and Sport Science, University of North
Carolina-Greensboro, Greensboro, NC 27402-6169, USA. Tel.: +1 336 334 3031;
Fax: +1 336 334 3238; E-mail: rjschmit@uncg.edu
Abstract: This study investigated the effects of isotonic and isometric knee
extension exercises on strength, power, and surface EMG in male and female
populations. Using the knee extensors, ten males and ten females performed a
120 s MVIC and 120 maximal isotonic contractions. Prior to each exercise
(t=pre) knee extensor isometric peak torque (strength) and
average peak power (power) were tested utilizing three, 3 s MVIC's and three
maximal isotonic contractions, respectively. Following each exercise, strength
and power were assessed immediately after (t=:00) and at 2.5
(t=:02.5), 5 (t=:05), 10
(t=:10), and 15 (t=:15) minutes. All
strength and power measures were normalized to the respective
t=prevalue. Vastus lateralis surface EMG signals were
collected during all muscle testing and normalized to the respective t=pre
value. Following isometric exercise, both strength and power at
t=:00 (68.7%8.7% & 88.0% ± 8.7%) and
$t=:02.5$ (82.2% ± 17.8% & 95.2% \pm 5.0%)
significantly decreased from t$=$pre (100% ± 0.0%)
p<0.05) with greater decreases in strength at each time
point (p<0.05). EMG analysis revealed a significant EMG
amplitude decrease (p<0.05) att=:00
and t=:02.5 during strength testing with respect to
t=pre. Following isotonic exercise, both strength and power
at t=:00 (68.0% ± 13.2% & 38.8%
± 10.7%) and $t=:02.5$ (84.5% ± 14.9% & 81.6% ± 14.5%)
significantly decreased from t$=$pre (100% ± 0.0%) with a greater power
decrease at $t=:00$ (p<0.05). The EMG amplitude of males was significantly
less at t=:00 than the respective EMG amplitude for females
(p<0.05$) (irrespective of testing condition). We conclude that
muscle performance in the fatigued state is dependent upon the type of exercise
performed.
