1992 Volume 37 Issue 1 Pages 87-95
The effects of jump and isometric training on contractile properties (in situ) were studied in the fast-twitch gastrocnemius (GC) and slow-twitch soleus (SOL) muscles of male Sprague-Dawley rats, and the relationship to fiber type composition were determined. Individual fibers in both muscles were classified as fast-twitch glycolytic (FG), fast-twitch oxidative glycolytic (FOG) or slow-twitch oxidative (SO) fibers according to Peter et al. The jump training (JT) consisted of 48 cm vertical jumps at 50 times/day, and the isometric training (IT) consisted of holding on to a vertical grid for 30 min/day. After 6 weeks of training, both JT and IT significantly reduced the isometric twitch contraction time of the SOL, but not that of the GC. Muscle fatigability was tested by the intermittent stimulation (IS) at 40 Hz fof 330 ms each second. No significant differences were observed in the decline of tension developed during IS in all muscles of each group. Fiber type compositions of both muscles were not changed with training. The results of this study suggest that exercise training improves excitation-contraction coupling, rather than the myosin isoenzyme pattern and oxidative enzyme activity which are used as criteria for fiber type classification, and that this induces alterations in mechanical properties.
