EMG activity of the leg extensor muscles with special reference to mechanical efficiency in concentric and eccentric exercise.

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.