Skeletal muscle recovery after tenotomy and 7-day delayed muscle length restoration

Rabbit extensor digitorum longus (EDL) tendons were cut with the muscle act ive (active tenotomy, AT) or with the EDL at rest (passive tenotomy, PT). O ne, 7, and 21 days after tenotomy, contractile testing was performed. A sec ond experiment was performed in which EDL tendons underwent PT and, after a 7-day delay, muscle-tendon units were restored to their original length. M aximum isometric tension dropped precipitously 1 day after either AT or PT to approximately 50% of normal and continued to decline by day 7. In contra st to PT, where peak tension (P-o) decreased further by 21 days, after AT, P-o partially recovered. Differences in muscle mass, cross-sectional area, fiber type, and sarcomere number did not explain the differential response. One day after length restoration of muscles, P-o rapidly increased by appr oximately 40%. These observations have implications for understanding the o utcome of muscle-tendon unit injury and surgical repair. (C) 2000 John Wile y & Sons, Inc.