Athletes can safely train through the pain of exercise-induced muscle damage because the damage is not made worse nor recovery delayed by repeated bouts of the same exercise. That's the encouraging conclusion of a Taiwanese study investigating the effects of seven-day eccentric training on muscle damage and inflammation.

The researchers were testing the theory that performing the same bout of eccentric training every day for six days after an initial bout of unaccustomed exercise would exacerbate inflammatory response and muscle injury at an early stage of the repair process and therefore hinder recovery.

Their study involved 22 college-age males, randomly assigned to either an eccentric training or a control group. On the first day of the study, all the subjects performed a bout of maximal isokinetic voluntary eccentric exercise with the elbow flexors of their non-dominant arm on an exercise machine. Subsequently the training group performed exactly the same set of exercises for each of the following six days, while the control group were allowed to rest their aching muscles.
The researchers measured a range of indicators of muscle damage and inflammatory response before and immediately after the first bout of exercise and then every 24 hours for seven consecutive days for both groups.

Surprisingly perhaps, there were no significant differences between the training and control groups in the following indicators:

l Muscle function. Maximal isometric force dropped significantly to about 42% of its pre-exercise value immediately after the first bout of exercise and then started to regain some strength, although it was still not completely restored by the end of the study;
l Range of motion. There was a significant decrease for both groups after the first bout of exercise, followed by a gradual recovery from day 3;

l Muscle soreness. For both groups soreness developed one day after the first exercise bout, was sustained for three days and then gradually diminished so it was almost back to baseline by day 7;

l Arm circumference. This measure of inflammation increased gradually in both groups from immediately after the first bout of exercise to day 5, then started to subside for both groups;
l Biochemical markers of muscle damage, including enzyme and inflammatory responses.

The major finding about the exercise group was that they were unable to work as hard on days 2-7 as they had on day 1. Total work values for days 2-7 were only 69%, 65%, 57%, 70%, 72% and 73% respectively of those on day 1.

The researchers are unable to provide a watertight explanation for their findings, but they speculate that an adaptation takes place in response to the initial injury which then acts to protect the active muscles.

Med Sci Sports Exerc 2001 Oct 33(10), pp 1732-8

Isabel Walker