The energy consumption associated with unilateral nonweight-bearing (three-point) crutch ambulation was evaluated in a group of 25 newly injured fracture patients immobilized in a long or short leg cast. After 5 min of crutch ambulation, the rate of oxygen uptake was 32% greater than the value for normal walking (averaging 15.7 ml/kg-min); the heart rate was 53% greater than normal (averaging 153 beats/min); and the respiratory quotient was markedly elevated (averaging 1.03). In those subjects able to ambulate for 10 min, these values averaged 17.6 ml/kg-min and 173 beats/min, approaching the peak values for maximal upper extremity exercise. The prescription of three-point crutch ambulation is a severe exercise challenge requiring strenuous arm and shoulder exertion under anaerobic conditions. These findings account for the common clinical experience that the newly injured fracture patient, unable to weight bear on an injured limb and requiring crutches, is a severely restricted ambulator.