Abstract
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 1st 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 2nd 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 1st period than in the 2nd 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.
Highlights
The mechanism behind the effects of proprioceptive neuromuscular facilitation (PNF) stretching on muscle flexibility still remains partly unclear; an increase in flexibility has been clearly verified [1]
The purpose of this study was to examine 1) whether the subjects could clearly differentiate between three intensities when performing muscle contraction; 2) how close the contraction intensity is to the target intensity; and 3) whether there is a difference in the increase in muscle flexibility upon varying the order of intensity, when the subjects were provided with three different intensities in two orders
There was no significant difference between target and contraction intensity at 75% (p=0.650, 0.775), 50% (p=0.691, 0.955), or 25% of maximal voluntary contraction (MVC) (p=0.334, 0.865) in Group A during the 1st period and 2nd period (Figure 2a) and at 75% (p=0.394, 0.078), 50% (p=0.910, 0.910), and 25% of MVC (p=0.532, 0.496) in Group B during the 1st period and 2nd periods (Figure 2b)
Summary
The mechanism behind the effects of proprioceptive neuromuscular facilitation (PNF) stretching on muscle flexibility still remains partly unclear; an increase in flexibility has been clearly verified [1]. In previous studies where more than two different intensities were used, the method of applying the intensity could be categorized into two types: the stretching may be performed in a randomized order for all intensities within a defined subject [4,6,7,8] or with only one intensity randomly assigned to each subject [3,5,9].
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