The interplay between peripheral and central factors in the adaptive response to exercise and training.

(1) Local adaptation of skeletal muscles (fibers) only occurs in the extremity involved in the training. (2) Work performance and maximal oxygen uptake were significantly increased only in the trained leg, and the "transfer" to the untrained leg was very small. (3) The classical sign of a training effect with a lowered submaximal heart rate response could only be elicited when exercising the trained leg. Lactate concentration and release of lactate were also lower when the trained leg performed the exercise. (4) The present results suggest that the local adaptation of skeletal muscle to training is of primary importance for enhancing work capacity and oxygen uptake. (5) The results also indicate that there may exist a peripheral factor in the regulation of the heart rate response during exercise. Moreover, the data favor the hypothesis of a chemical receptor playing a role in such a peripheral control system.