Adaptation to muscle injury from low stimulus non-eccentrically biased acute exercises

The purpose of this study was to investigate whether low stimulus non-eccentrically biased acute aerobic exercises result in adequate adaptation in skeletal muscles. Thirty healthy subjects were randomized into three groups: (a) the low stimulus down-hill treadmill exercise group (LSDTEG); the low stimulus up-hill treadmill exercise group (LSUTEG); and the low stimulus level treadmill exercise group (LSLTEG). The three groups performed acute exercises (bout 1) and a repeated exercise (bout 2). In the acute exercises, all the groups exercised at 50% of heart rate reserve (HRR) for 30 min. Two weeks after the acute exercises, the subjects performed a repeated exercise bout at 80% of HRR for 45 min. Creatine kinase (CK), total white blood cells (TWBC), and perceived muscle soreness (SOR) before and 1, 24, and 48 hrs post-exercise were assessed as markers of muscle injury and adaption. The results showed that muscle injury was significantly higher in the LSDTEG than LSUTEG and LSLTEG in the acute exercises. However, there were no significant differences in mean CK, TWBC, and SOR among the groups in the repeated exercise. The extent of muscle adaptation was similar in all three exercise groups. Thus, acute exercises by sedentary individuals can be of low stimulus and non-eccentrically biased to reduce muscle injury while inducing adequate muscle adaptation.