APPS November 2002 Meeting Abstract 126

Uwe Proske¹, David L. Morgan², John E. Gregory¹, Nicholas P. Whitehead¹, Camilla L. Brockett¹, Departments of 1 Physiology, 2 Electrical and Computer Systems Engineering, Monash University, Melbourne, Victoria.

Eccentric exercise leads to sensations of stiffness and soreness the next day, the result of damage to muscle fibres. Two aspects of the damage process which we have been studying are an increase in passive tension and a shift, in the direction of longer muscle lengths, of the optimum length for active tension. The shift in optimum length is attributed to the presence, in damaged muscle fibres, of disrupted, overstretched sarcomeres in series with still-functioning sarcomeres. This acts to increase the muscle's effective series compliance. The rise in passive tension is the result of damaged muscle fibres entering a state of injury contracture, as a result of the uncontrolled movement of Ca²⁺ across torn membranes into the sarcoplasm.

The amount of muscle damage is determined by the length range over which the muscle is stretched while contracting. At the level of the sarcomeres it is the descending limb of their length-tension relation which is the potential region for their disruption. It is a common experience that a second period of eccentric exercise, carried out a week or so after the first, leads to much less stiffness and soreness. This is the adaptation process. Animal experiments suggest that muscle fibres adapt by increasing the number of sarcomeres in series, thereby making it less likely for them to be stretched onto their descending limb. All of this has led to the conclusion that specific, targeted eccentric exercise, as part of a training program, will provide protection against damage and soreness. There is some circumstantial evidence that the damage from eccentric exercise may lead to a major muscle tear. The proposal is, therefore, that athletes at risk of suffering a muscle strain should be subjected to a regular eccentric exercise program.