The effects of training status and exercise intensity on exercise-induced muscle damage.

Background: Individuals participating in exercise beyond their level of fitness may be at higher risk for exercise-induced muscle damage, however the impact of training status on muscle damage development is not well understood. The purpose of this study was to measure skeletal muscle damage and soreness after five days of high and low intensity exercise in previously trained and untrained individuals.

Methods: Eighteen males and females (9 trained and 9 untrained) completed five consecutive days of high intensity (HI) exercise and five consecutive days of low intensity (LI) exercise. Blood was drawn at the initial visit and after completion of each exercise intensity period.

Results: CK was elevated post exercise for both groups during both intensities, but was greater in trained vs. untrained (HI: 203.6 vs. 143.4 IU/L and LI: 156.4 vs. 109.3 IU/L; P<0.01). Myoglobin was significantly higher after exercise for both groups (P<0.01) and was higher following high vs. low intensity in trained (P<0.01), but not untrained (P=0.052). Untrained experienced soreness following one day of high intensity exercise vs. after 3 days in trained participants (P=0.04, P=0.02).

Conclusions: The current study suggests that high intensity exercise results in greater muscle damage in both trained and untrained individuals vs. low intensity exercise. However untrained participants experience more pain and with earlier onset and should therefore take caution when beginning exercise programs that require consecutive sessions of high intensity exercise.