Effects of increased training volume on the oxidative capacity, glycogen content and tension development of rat skeletal muscle.

This study examined the effects of a short-term sudden increment in training load on the oxidative capacity, glycogen content and tension-generating ability of rat skeletal muscle. After training on a treadmill 5 dwk-1 for 9 wk (30 m.min-1 6 degrees, 60 min.d-1), rats were randomly divided into a normal training volume (NTV) group (N = 11) and an increased training volume (ITV) group (N = 8). The NTV group were sacrificed 24 h after the last bout of exercise, while the ITV group continued to train for further 6 successive days. Training duration for this latter group was increased to 120 min.d-1 for the first 2 d; 240 min.d-1 for the next 2 d; and 360 min.d-1 for the final 2 d; speed and grade were kept constant. Respiratory capacity (QO2) and citrate synthase activity were increased (P less than 0.05) in both the soleus and plantaris muscles, with no change in the white vastus lateralis muscle of the NTV group when compared to age- matched sedentary controls. Glycogen levels were unchanged in these muscles, but liver glycogen content was greater (231.9 +/- 10.1 vs 156.8 +/- 15.3 umol.g-1 w.w. for the NTV vs age-matched sedentary controls, respectively, P less than 0.05). Peak tetanic tension in the gastrocnemius was not changed by training, or the increased training load. Citrate synthase activity (umol.min-1.g-1) was significantly greater (P less than 0.05) in the plantaris (33.3 +/- 1.0 vs 27.0 +/- 1.7) and soleus muscles (40.5 +/- 2.7 vs 28.4 +/- 1.3) in the ITV vs NTV groups.(ABSTRACT TRUNCATED AT 250 WORDS)