Stretch-Shorten Cycle For Sport
stretch reflex is utilized during many activities because most movements involve two phases of muscular contraction. An eccentric phase which is the muscle lengthening under tension is followed by a concentric phase in which the muscle is shortened. Attaining a pre-stretch of the muscle causes it to be lengthened eccentrically so tension is developed in the muscle like a rubber band. The tension created in the muscle can be used to help increase the strength of the following concentric contraction. The concentric contraction must take place immediately after being stretched or the tension created dissipates as heat (Wilk 1993). An example would be bending down before jumping which allows the quadriceps to be stretched eccentrically so that the following concentric contraction will be stronger. Taking advantage of the elasticity of the muscle and the stretch reflex is referred to as using the stretch-shorten cycle (Bosco et al 1981). It has been shown that the faster the muscle is stretched eccentrically, the greater the force will be on the following concentric contraction (Bosco et al 1980).
History Of The Stretch-Shorten Cycle
During the 1960s, Professor Rodolfo Margaria of Milan was the first to identify the value of the pre-stretch in producing a strong muscular contraction. Margaria’s work looked at muscular movement as a whole. Based on this work, a length tension diagram of the working muscle was developed. This allowed for the comparison of the tension in a muscle that had been pre-stretched and one that had not been pre-stretched. Margaria was able to show that the tension a muscle was able to create was based not only on the muscle length, but also on the previous activity of the muscle. Muscles were able to develop more tension if prestretched. The amount of tension created by stretching the muscle was dependent on the degree and the speed of the muscles’ pre-stretch. This research was used by NASA to develop the most effective way to walk on the moon (Zanon 1989).