To examine the cross-training effects of a proprioceptive neuromuscular facilitation training (PNF) program on peak torque and endurance.Factorial design.Twenty-three males were assigned to a PNF group (n=12) or a control group (n=11).The PNF program included training of the knee extensor and flexor muscles for a period of 8 weeks, exercising three times a week. PNF training included performance of knee movements through range of motion against manual resistance.Isokinetic torque and fatigue of the knee flexors and extensors at 60, 180 and 300°s −1 were assessed prior to and immediately after the training period.Analysis of variance designs indicated that the PNF group demonstrated significant gains (9.9%) in knee extension torque of the contralateral leg. In contrast, no cross-training effects on peak flexion torque was observed.Cross-training effects after PNF exercise were restricted to the knee extensor muscles. Such effects may be important when the aim of a rehabilitation program is to improve the knee extensor muscle function of an immobilized contralateral leg.