The effect of eccentric and concentric training on the size and strength of human skeletal muscle

The objective of this study was to determine if the high forces generated through eccentric contractions, and the subsequent damage sustained, contributes to greater growth and force increase in human skeletal muscle than other contraction types, and whether damage from eccentric exercise effects the increase in torque and muscle size expected after a progressive concentric strength training program. 20 healthy subjects were split into four groups which participated in 3 different training protocols, with one group serving as the control (C). Groups underwent either concentric training (CT), eccentric damage (ED), or a combination of the two protocols (DC) with the non-preferred biceps over a twelve week period. Isometric and concentric force at 50, 90 and 200°/sec was measured weekly with a Cybex isokinetic dynamometer. Upper arm girth was also measured pre and post training. The CT group displayed the greatest increase in peak torque for both isometric and concentric contractions. The groups undergoing eccentric damage (ED & DC) showed a decrease in the ability to generate force in the weeks following damage, and showed only small torque increases over the twelve weeks with DC improving to a greater extent than ED at higher contraction velocities. Eccentric damage appeared to attenuate the increases in peak torque displayed after concentric training. A hypertrophic response from damage may have resulted in a decrease in muscle strength per unit cross-sectional area, and the failure of DC to respond to training may be due to the inability to generate sufficient intramuscular tension required to elicit an adaptive response