Muscle contraction increases the structural capacity of the lower leg: an in vivo study in the rat.

A model to study the contribution of muscle contraction to the structural capacity of the rat tibia was developed. The right lower leg was tested to failure in three-point ventral bending during electrically stimulated muscle contraction. The left lower leg was tested without stimulation, as a control. The mean ultimate bending moment for the stimulated legs was 0.603 Nm, compared with 0.492 Nm for the unstimulated legs (p < 0.001). The ultimate energy absorption was 0.313 and 0.188 J in the stimulated and unstimulated legs, respectively (p < 0.01). Fracture strength has been studied nearly exclusively in dissected bone stripped of all soft tissues. The present investigation suggests that studies of dissected bone are incomplete compared with the in vivo situation, as contraction of the muscles substantially increased the fracture strength of the lower leg in rats.