Effects of Increased Training Volume on the Oxidative Capacity, Glycogen Content and Tension Development of Rat Skeletal Muscle

Abstract

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°, 60 min·d^-1), rats were randomly divided into a normal training volume (NTV) group (N = ll) 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 < 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 < 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 < 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. Glycogen concentrations in the plantaris of the ITV group were greater (P < 0.05) than sedentary controls (50.1 ± 2.7 vs 39.5 ± 1.4 umol·g^-1 w. w., respectively). It was concluded that an increased training load for 6 successive days has no deleterious effects on the oxidative capacity, glycogen content, or tension development of rat skeletal muscle.

Key words

Running - citrate synthase - QO₂ - tetanic tension; liver