Effects of Progressive Increased Intensity of PNF Stretching on Hamstring Force and Flexibility

In most previous studies of PNF stretching performed at different intensities, the subjects were provided with the intensities in a randomized order. In addition, subjects were aided in maintaining a steady level of contraction force using a dynamometer as visual feedback. However, such a procedure differs from the procedure used in actual clinical settings. This study aimed to examine the effect of the applied order of three different intensities of PNF stretching on the ability to regulate the contraction force and increase muscle flexibility. During the 1 period, three different stretching intensities were applied in the order of 25%, 50%, and 75% of MVC in the group A and in the order of 75%, 50%, and 25% of MVC in the group B. This order was reversed during the 2 period. The contraction force was measured using the strain gauge and hamstring flexibility was measured using active knee extension. There was no significant difference between target and contraction intensity at three target intensities in both groups. Additionally, contraction forces between different intensities clearly were distinguished by subjects in both groups. In Group A, increase in flexibility was significantly higher in the 1 period than in the 2 period. Healthy adults could clearly differentiate and regulate contraction intensity when the intensities were differentially applied at 25% intervals. The higher target intensity compliance and increase in flexibility may be anticipated when progressively increase intensity was applied, compared to the same factors in reverse order.