With aging, the skeletal muscles of humans sustain decreases of ~30% in mass and maximum force. Contraction-induced injury may contribute to these declines. When a 225 lengthening contraction protocol (LCP) was administered to small, non-weight bearing muscles of mice, muscles of young/adult mice recovered completely, whereas those of old mice sustained permanent deficits of 20% in muscle mass and maximum force. Despite these observations, whether a large, frequently-recruited, weight-bearing muscle sustains such permanent damage is not known. The hypothesis tested is that following a severe contraction-induced injury, large, weight-bearing muscles of old mice sustain permanent reductions in mass and force. The LCP was administered to plantarflexor muscles of adult and old, male C57BL/6 mice. At 3 days, 1 month, and 2 months following the LCP, maximum isometric forces were measured, anesthetized mice were euthanized, and muscles were removed and weighed. Two months following the LCP, the muscles of the adult mice regained control values of mass and force, whereas the muscles of old mice sustained decreases of 24% in mass and 32% in maximum force. We conclude that a severe contraction-induced injury to large, weight-bearing muscles of old animals causes permanent deficits in mass and force.