What science has to say about the performance benefits of stretching and flexibility exercises
Flexibility training, or stretching, is used in varying forms by practically every coach, athlete and physiotherapist on a regular basis. That is to say, a form of stretching is likely to take place at some point in every training or therapy session. In spite of this, flexibility training is probably the least understood of all the fitness components, in terms of its scientific basis. This article will discuss the latest research findings and recommendations to explain why and how stretching should best be carried out.
What does it mean?
Flexibility is defined as the static maximum range of motion (ROM) available about a joint. The largest limiting factor of static ROM is the structure of the joint itself. Thus, even after endless stretching exercise, there will be a limit as to how much movement is available. In addition, joint structures can vary between individuals, and this must be recognised when assessing flexibility standards in athletes. Most of the variability in static ROM is due to the elastic properties of the muscle and tendons attached across the joints. ‘Stiff’ muscles and tendons reduce the ROM while ‘compliant’ muscles and tendons increase ROM. It is these elastic properties that are altered after stretching exercises. When a muscle is held for some times under tension in a static stretch, the passive tension in the muscle declines, ie, the muscle ‘gives’ a little. This is called a ‘viscoelastic stretch relaxation response’. Passive tension is defined as the amount of external force required to lengthen the relaxed muscle. Obviously, the less external force required, the more pliable the muscle. This increased pliability is maintained for up to 90 minutes after the stretch (Moller et al, 1985).
In the long term, regular static stretching will bring about permanent increase in static ROM, which is associated with a decrease in passive tension. Experimentally, this was shown by Toft et al (1989), who found a 36% decrease in passive tension of the plantar flexors after three weeks of regular calf stretches. The relationship between static ROM and passive tension has been further supported by McHugh et al (1998). These researchers demonstrated that maximum static hip flexion ROM was inversely correlated with the passive tension of the hamstrings during the mid-range of hip flexion. This suggests that the ease with which the muscle can be stretched through the mid-ROM is increased if the maximum static ROM is improved. The concept that increased static ROM results in more pliant mechanical elastic properties of the muscle suggests that static stretching is beneficial to sports performance.