higher rate of loading), and therefore have a better ability to use the SSC.Īn abundance of research has demonstrated that stronger athletes have a better ability to store elastic energy over weaker individuals (31, 32, 33). It also suggests that athletes’ with higher levels of muscular strength can absorb more force (i.e. This demonstrates the importance of muscle stiffness during the SSC and its ability to improve performance. Failing to stiffen during the eccentric and amortisation phases, means the performance enhancing effect of the SSC will be lost and the joint would likely collapse. This causes the deformation/ lengthening of the tendon and the development of the storage elastic energy.ĭuring the concentric phase of the SSC (often referred to as the ‘positive acceleration’ phase), the muscle is then able to concentrically contract and provide additional propulsive force (2). The muscle must then remain contracted/ stiff during the first two processes of the SSC (eccentric and amortisation phases) in order to transmit the isometric forces into the tendon. This means that the muscle must contract and stiffen prior to the beginning of the SSC during ground contact – known as ‘muscular pre-activity’. Unlike muscles, the tendons cannot be voluntarily contracted, and as a result they can only remain in their state of tension. However, due to the elastic properties of the tendon, it is commonly agreed that the tendon is the primary site for the storage of the elastic energy (29, 30). In humans, this stretch and storage of elastic energy is instead placed upon the muscles and tendons during movement. In other words, the amount of force used to stretch the band, should be equivalent to the amount of force produced by the band in order to return to its pre-stretched state. The amount of stored elastic energy (sometimes referred to as ‘strain’ or ‘potential’ energy) is potentially equal to the applied force and induced deformation (5). When the band is stretched there is a build-up of stored energy, which when released causes the band to rapidly contract back to its original shape. The concept of elastic energy is similar to that of a stretched rubber band. Despite this large list, it is commonly agreed that there are three primary mechanics responsible for the performance enhancing effects of the SSC (2). There are numerous neurophysiological mechanisms thought to contribute to the SSC, some of which include: storage of elastic energy (18, 19, 20, 21), involuntary nervous processes (22, 23), active state (1, 24), length-tension characteristics (25, 26), pre-activity tension (27, 28) and enhanced motor coordination (1, 24). Mechanisms of the Stretch-Shortening Cycle (SSC) Whereas race walking, which has a ground contact time of 270-300 milliseconds is commonly classified as a slow-SSC movement (10). As displayed in Table 1, a long jump is typically classified as a fast-SSC movement as it has a ground contact time of 140-170 milliseconds (9). Table 1 provides some examples of common exercises and their potential SSC classification.
Consequently, the SSC has been separated into two categories based upon the duration of the SSC: walking), there are great differences in the speed of the SSC. As some movements are much faster than others (e.g.
As the limbs are continuously changing direction there is a constant use of the SSC in order to change the direction the limb is moving. For example, during walking, jumping, running, twisting or even lowering and then raising your arm. The SSC does not only occur during single-bout jumping or rebounding movements but also during any form of human movement when a limb changes direction.
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