Effects of 8-week static stretch and PNF training on the angle-torque relationship

This study tested the hypothesis that the extent of enhancement in muscle strength following an 8-week program of static stretch (SS) and proprioceptive neuromuscular facilitation (PNF) training would be related to a shift in optimum angle (OA) toward a longer muscle length. Thirty healthy males were randomly assigned into SS, PNF, and control (CON) groups (n = 10 per group). The SS and the PNF groups engaged in flexibility training three times per week for eight weeks, while the CON group underwent no training during this time. Passive range of motion (P-ROM) of the hip and maximal isokinetic concentric strength (ISO) at the angular velocity of 60°/s (i.e, the angle-torque relationship) were measured before and after training for all groups. The results of this study showed that compared to before training, the P-ROM values of both the SS (25°) and PNF (31°) groups were significantly increased (P < 0.05) after training, while those of the CON group remained unchanged (P > 0.05). In addition, after the training, both the SS and PNF groups saw a significant increase in ISO (SS: 13%; PNF: 17%; P < 0.05), and a marked shift of the OA toward a longer muscle length (SS: 9°; PNF: 10°; P < 0.05). The CON group, however, saw no significant change in either of these two variables. There was a positive correlation (P < 0.05) between the increase in ISO and the shift of OA toward a longer muscle length for the SS (r = .69) and PNF (r = .78) groups after training. It was concluded that eight weeks of SS and PNF training can not only effectively improve flexibility, but also increase ISO and cause a shift of OA toward a longer muscle length.