The stretch shortening cycle is a form of movement in skeletal muscle where it lengthens and then immediately contracts. This appears to provide more strength and power for activities like throwing and jumping. Some human movements naturally exhibit a stretch shortening cycle, and it can also be seen in specific techniques used in sports to increase power for athletic performance. Researchers explore how the phenomenon works, using both human and animal models to learn more about the function of skeletal models.
Initially, the stretch shortening cycle involves an eccentric movement, where the muscle lengthens and stretches out. An example can be seen in the wind-up used before throwing a ball in some sports. After the muscle stretches, it immediately shortens in a concentric motion, generating power for a push, throw, or other movement. One theory about this type of movement is that it essentially turns the muscle into a spring.
Concentric movements alone tend not to be as powerful as a movement in the stretch shortening cycle. Someone who simply tosses a ball, for example, may not have as much power as a pitcher who has performed a wind-up first. Athletes may be taught to incorporate this cycle to their advantage in training, and use a variety of tools to develop strong, flexible muscles capable of large extensions and fast, powerful contractions. The active stretch prior to movement can be seen in a number of sports.
Natural human movements also show evidence of the stretch shortening cycle. Walking and running, for example, both incorporate a degree of extension and stretching before a contraction to push the foot off the ground. The articulation of the bones in the leg facilitate this, adding power to the stride. Jumping also uses a similar cycle, with people stretching the legs and then crouching to push themselves off the ground. Athletes may refine this with exercise to develop their leg muscles, making their strides longer and their gait more explosively powerful.
Research on this phenomenon can help scientists understand how skeletal muscle works. This can be valuable for activities like developing better athletic training tools and assisting patients with physical therapy, where muscle weakness may make it hard to control movements. Studies on muscle fatigue can also explore the stretch shortening cycle to learn more about how it contributes to the development of tiredness and strain, with the goal of finding new ways to limit fatigue in settings where endurance is critical, like marathons.