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Research: Effects of PNF on Knee Movement Sensation

Submitted by on June 5, 2010 – 5:31 amNo Comment

In the April, 2010 issue of Strength and Conditioning Research, researchers evaluated the ability of the test subjects to identify the change in passive flexion or extension to their knee after a session of either PNF stretching (two repetitions of a contract-relax muscle energy technique for a 30-second hold) or a placebo group who had their legs moved passively without stretching.  In testing, they subjects were blindfolded with earplugs and headphones, so they see or hear when their knees were moved.  Their test findings after stretching showed that the PNF group had a significant latency (delay) in identifying passive movement of their knee, while the control group did not show any change in pre- and post-testing.

Streepey, JW, Mock, MJ, Riskowski, JL, VanWye, WR, Vitvitskiy, BM, and Mikesky, AE.  Effects of Quadriceps and Hamstrings Proprioceptive Neuromuscular Facilitation Stretching on Knee Movement Sensation.  J Strenth Cond Res 24(4): 1037-1042, 2010.

I found this to be a very interesting study, as most previous studies on the effects of stretching focused on its effect on the muscle’s ability to contract or generate power.  As this study shows a decrease in the proprioception of the knee position, it shows a potentially dangerous effect of static stretching before sports involving rapid start and stop or lateral movements, as the muscles must be able to sense and control the joint position to prevent damage to the joint structures.

However, the authors of the study do note that the proprioception was tested with the subject’s leg hanging in a non-weight bearing position, where in a weight-bearing situation, the quadriceps and hamstrings would be actively contracting and not completely relaxed.

So, further testing needs to be performed to identify a true risk, but the study did show a slowed response of the body to identify a change in position of the joint angle following a contract-relax PNF stretch, and shows another reason to avoid holding a stretch for long periods before athletic activity.

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