Proprioceptive Neuromuscular Facilitation (PNF) is a type of flexibility exercise which combines muscle contraction and relaxation with passive and partner-assisted stretching. The technique has received considerable attention recently, since it is thought to improve range of motion in the skeletal joints to a greater extent than conventional static stretching.
Another concept new to flexibility training is that of the length-tension relationship of lengthened muscles; the idea is that it is not just the maximal range of motion (ROM) of a joint that matters but also the tension developed within the muscle at its maximal ROM. This is interesting because if there is no muscle tension at the limit of the ROM, there will be little mechanical resistance to further stretching, and it will cause no pain.
Now a pair of German researchers have carried out a study comparing the effects of PNF and static stretch training in relation to both ROM and muscle tension. Their subjects trained each leg separately as follows:
a. with one leg they used a PNF technique involving contraction and then relaxation of the hamstring, with the hamstring stretched during relaxation
b. with the other leg they used a static training technique similar to'touch your toes'.
The subjects held the stretches at maximal ROM for 15 seconds, performing three sets of four stretching cycles on each leg twice weekly for a period of six weeks. Their maximal ROM, and tension at maximal ROM (Tmax), was measured before and after the training programme.
Predictably, the investigators found that the maximal ROM of both legs had increased by the end of the study period. What was more surprising, however, was that there was no apparent difference in the effects of these two very different stretching techniques; both resulted in maximal ROM increases of about 30% - improvements which were still apparent in both legs eight weeks after the training programme had finished.