The following article is founded on research conducted at the Division of Sports therapy & Rehabilitation at the University of Bedfordshire, Luton, LU1 3JU. The full Research article is available to view under Student Centre/Learning Resources on this website.
Sheard PW, Paine TJ. Optimal contraction intensity for maximized range of motion following proprioceptive neuromuscular facilitation. Journal of Strength & Conditioning Research..
During the teaching and practise of applying PNF techniques we conducted experiments to compare varying levels of muscle contraction to determine what intensity would achieve the greatest gains in joint range of movement. It was already well established that PNF is a widely used and highly effective means of stretching and that post-isometric relaxation (PIR) achieves great results. Research has been conducted into the efficacy of this technique under various names including P.I.R. and Muscle Energy Techniques and although there is universal agreement that substantial increases in muscle length can be made, the optimal intensity to ask the subject to contract to remained unclear.
We chose to target and compare muscle contraction intensities at 20%, 50% and 100% of the maximum each subject could achieve. The target muscle group for stretching, and therefore contracting, was the hamstrings through hip extension with the knee fully extended. Once each subject had been tested and their maximal voluntary contraction (MVC) recorded, they were invited on 3 further occasions to receive massage and PNF P.I.R. at the different contraction levels described above.
Our results showed a wide range of muscle intensities achieved and after analysing all the data from 37 subjects it was found that a peak increase of 13 degrees in joint range was achieved at an average contraction intensity of just under 65%. It was also noted that contractions intensities were generally underachieved when contraction intensity was higher. Because of this, we encourage the use of a 70% target contraction intensity which will generally produce the desired ~65% contraction.
This study underpins our chosen method when practicing PNF P.I.R. techniques, where we encourage the client to build from 30% to a target of 70% of their estimated maximal contraction. Later we conducted further experiments to discover how to help subjects reach this contraction intensity without the use of equipment providing feedback to help them achieve the target intensity. This will be reported in a later article.
Getting the best flexibility gains using PNF
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