Abstract
Integrated electromyographic (IEMG) activity of the vastus lateralis and vastus medialis
muscles were recorded when normal male subjects performed isolated concentric and
eccentric exercises on a special “sledge” apparatus, which was connected to a force
plate. Four different submaximal energy levels were investigated in both exercise
types. A single set of exercise included 80 contractions. The net mechanical efficiency
was computed from the force plate record (mechanical work) and from the analysis of
expired air (energy expenditure). The results indicated that IEMG activity increased
with increasing knee angular velocity or mechanical work in concentric exercise, but
in eccentric exercise IEMG stayed at very low levels at all energy levels. The net
mechanical efficiency of concentric exercise was on the average 19.4% ± 2.8%, and
it did not change much with change in the narrow range of peak angular velocities.
In eccentric exercise, however, mechanical efficiency increased in all subjects with
increasing mechanical work or stretch velocity reaching in many instances values over
100%. This increase in mechanical efficiency was characterized by very low IEMG activity,
which stayed approximately the same at all efficiency levels. In concentric exercise
IEMG, energy expenditure and mechanical work changed in parallel when exercise intensity
was increased.
Key words
electromyography - mechanical efficiency - eccentric exercise - concentric exercise
