Effect of submaximal contraction intensity in contract-relax proprioceptive neuromuscular facilitation stretching

Objective: To determine if submaximal contractions used in contract-relax proprioceptive neuromuscular facilitation (CRPNF) stretching of the hamstrings yield comparable gains in hamstring flexibility to maximal voluntary isometric contractions (MVICs). Method: Randomised controlled trial. A convenience sample of 72 male subjects aged 18 - 27 was used. Subjects qualified by demonstrating tight hamstrings, defined as the inability to reach 70degrees of hip flexion during a straight leg raise. Sixty subjects were randomly assigned to one of three treatment groups: 1, 20% of MVIC; 2, 60% of MVIC; 3, 100% MVIC. Twelve subjects were randomly assigned to a control group ( no stretching). Subjects in groups 1 - 3 performed three separate six second CRPNF stretches at the respective intensity with a 10 second rest between contractions, once a day for five days. Goniometric measurements of hamstring flexibility using a lying passive knee extension test were made before and after the stretching period to determine flexibility changes. Results: Paired t tests showed a significant change in flexibility for all treatment groups. A comparison of least squares means showed that there was no difference in flexibility gains between the treatment groups, but all treatment groups had significantly greater flexibility than the control group. Conclusion: CRPNF stretching using submaximal contractions is just as beneficial at improving hamstring flexibility as maximal contractions, and may reduce the risk of injury associated with PNF stretching.