Training-induced protection and effect of terminated training on exercise-induced damage and water content in mouse...

Muscle swelling in connection with training-induced protection against exercise-induced damage and the disappearance of the protective adaptation after termination of training was studied in male NMRI-mice, aged 8 weeks at the beginning of the experiment. Mice were randomly assigned to several different treatment groups (training, training-exercise, exercise, detraining, detraining-exercise, together with their respective controls). Training and prolonged exercise sessions were performed by running uphill (6 degrees) on a motor-driven treadmill. Muscle damage was estimated by the total activity of beta-glucuronidase and water content from the red parts of m. quadriceps femoris (MQF), m. soleus (MS), m. rectus femoris (MRF), and from m. triceps brachii (MTB). Training-induced protection was observed in MS after only one week of training. In MQF the protection was incomplete after 1 and 4 weeks' training. In MS the protection disappeared already one week after the cessation of training. In MQF the training-induced protection persisted in part for one week but after four-week's detraining no protection was observed. The present results suggest that diminution of muscle swelling forms part of the adaptation of skeletal muscle in resisting exercise damage, and, vice versa, increased susceptibility to exercise damage, which follows the termination of training, is linked to muscle reswelling.