MUSCLE-CONTRACTION INCREASES THE STRENGTH OF HEALING TIBIAL FRACTURE IN THE RAT

Tibial fractures in 7-week-old rats were fixed with intramedullary nai ls. After 25 days of healing the nails were removed and the tibiae loa ded in vivo with intact soft tissues until refracture. The animals wer e tested in three-point anterior cantilever bending either during musc le contraction (n 8) or with relaxed muscles (n 8). Muscle contraction increased the ultimate bending moment by 84 percent, energy absorptio n by 108 percent, bending stiffness by 21 percent, and ultimate deflec tion by 49 percent.