Abstract
1. The effects of heavy training on a skeletal muscle have been studied in the rat. After denervation of the triceps surae muscle the tendon of the plantaris muscle was implanted into the tuberosity of the calcaneum. It was then possible to demand an unusual performance of the plantaris, the weight of which is only 18 per cent of the weight of the triceps surae.
2. Formation of new muscle fibres was observed after prolonged heavy training. This is incontrast to the opinion of most investigators, who have seen no new fibres formed after training. Degenerative changes followed by regeneration were also seen.
3. The trained muscle could almost double its weight, and treble its force. Paradoxically, the supposedly non-contractile sarcoplasm was seen to have increased after training.
4. Training induced a strong protein synthesis in muscle. In normal muscle protein synthesis can hardly be demonstrated.
5. Connective tissue grew between single muscle fibres in the heavily trained muscle. Its distribution was unequal.
6. Heavy exercise caused marked swelling of an untrained muscle.
7. Functional recovery was satisfactory after the operation. This showed that a muscle can be replaced by one only one-fifth its weight, provided the latter is trained adequately.
8. Not even the most arduous training could inflict permanent damage on the muscle.
