Knee extension (quadriceps) strength, peak oxygen consumption, and body composition were measured in 11 orthotopic heart transplant recipients (50 +/- 14 years of age) 18 +/- 12 months after transplantation and 11 untrained sedentary control subjects closely matched (p > or = 0.05) with respect to age, height, and weight. Peak oxygen consumption and absolute knee extension strength in the transplant recipients were 57% and 69% of control, respectively. Leg strength and peak oxygen consumption were not significantly correlated (p > or = 0.05) with months after transplantation. Peak oxygen consumption was significantly (p < or = 0.05) correlated with leg strength in both groups, but the relationship was greater in transplant recipients (r = 0.90) compared with the control group (r = 0.65). These data indicate that a leg-strength deficit persists up to 18 months after transplantation and the decrement in peak oxygen consumption observed in heart transplant recipients is partially explicable by skeletal muscle weakness. Our results underline the importance of progressive resistance training in comprehensive rehabilitation programs.