The Nature of the Training Response; Peripheral and Central Adaptations to One-Legged Exercise

13 male subjects were studied and placed in 3 groups. Each group exercised one leg with sprint (S), or endurance (E) training and the other leg oppositely or not at all (NT). Oxygen uptake (Vo₂), heart rate and blood lactate were measured for each leg separately and for both legs together during submaximal and maximal bicycle work before and after 4 weeks of training with 4–5 sessions per week. Muscle samples were obtained from the quadriceps muscle and assayed for succinate dehydrogenase (SDH) activity, and stained for myofibrillar AT Pase. In addition eight of the subjects performed after the training two-legged exercise at 70% Vo₂ max for one hour. The measurements included muscle glycogen and lactate concentrations of the two legs as well as the blood flow and the a-v difference for O₂, glucose and lactate. The improvement in Vo₂ max, the lowered heart rate and blood lactate response at submaximal work levels were only found when exercising with a trained leg (E or S). Part of the variables studied were markedly more changed with E as compared with S-training. Although muscle fibre composition did not change a pronounced muscle adaptation took place with the training with enhancement of the SDH activity of the S and E legs while the NT-leg did not change. Blood flow and oxygen uptake were similar in NT and S–E legs while femoral vein oxygen content was slightly lower in the trained as compared to the NT-leg. Glycogen utilization was lowest in the trained leg with similar glucose uptake in all legs regardless of training status. Moreover, lactate was only continuously released from the NT-leg. It is concluded that training induces marked local adaptations which not only affects the metabolic response to exercise but also are of importance eliciting an improved cardiovascular function.