Skeletal muscle adaptation: training twice every second day vs. training once daily

Low muscle glycogen content has been demonstrated to enhance transcription of a number of genes involved in training adaptation. These results made us speculate that training at a low muscle glycogen content would enhance training adaptation. We therefore performed a study in which seven healthy untrained men performed knee extensor exercise with one leg trained in a low-glycogen (Low) protocol and the other leg trained at a high-glycogen (High) protocol. Both legs were trained equally regarding workload and training amount. On day 1, both legs (Low and High) were trained for 1 h followed by 2 h of rest at a fasting state, after which one leg (Low) was trained for an additional 1 h. On day 2, only one leg (High) trained for 1 h. Days 1 and 2 were repeated for 10 wk. As an effect of training, the increase in maximal workload was identical for the two legs. However, time until exhaustion at 90% was markedly more increased in the Low leg compared with the High leg. Resting muscle glycogen and the activity of the mitochondrial enzyme 3-hydroxyacyl-CoA dehydrogenase increased with training, but only significantly so in Low, whereas citrate synthase activity increased in both Low and High. There was a more pronounced increase in citrate synthase activity when Low was compared with High. In conclusion, the present study suggests that training twice every second day may be superior to daily training.