![]() ![]() Two proprioceptors are of most relevance in the SSC. The SSC causes an increased excitability of proprioceptors for an optimal reaction by the neuromuscular system. ( 2) supports this theory, showing that in a countermovement jump, peak force is already closely approached or even reached at the transition point between eccentric and concentric motion (before the concentric phase has even begun). ![]() As a result, developed force and joint moments are greater at the beginning of the concentric phase and more work is produced through the first part of the concentric motion compared to concentric only squat jumps. The slow eccentric phase allows muscles to develop a high level of active state (more attached cross-bridges) before the start of concentric motion. ( 4) determined that in tasks such as maximal effort vertical jumps, in which eccentric-concentric coupling is used compared with purely concentric squat jumps, the performance enhancement in the SSC is likely caused by the eccentric phase, allowing an increased time to develop force. This potentiation effect increases with the speed of the eccentric action and decreases with the amount of transition time between the eccentric and concentric phases ( 2).īobbert et al. These authors suggest that the performance enhancement from the preceding stretch or from the isometric contraction may result from an attainment of a greater level of neural excitation before the concentric movement. ( 32) observed an increase in work output during the concentric phase of squatting exercise when that concentric phase was preceded by a prestretch or by an isometric contraction, in comparison with a purely concentric squatting exercise. It has been speculated that the prestretch in the SSC may enhance the concentric contraction through neural potentiation of the muscle contractile machinery during the eccentric phase, allowing for a greater number of motor units to be recruited during the concentric contraction ( 30). A short transition between the eccentric and concentric phase is necessary for this elastic energy to be used optimally.Īdditional mechanisms of action also have been proposed. Part of this energy is temporarily stored and then reused during the concentric contraction phase of the SSC ( 4). During the eccentric phase, the active muscles are prestretched and absorb energy. ![]() One view has been that the SSC causes an enhancement during the concentric phase attributable to the storage and reutilization of elastic energy ( 7, 16). The SSC appears to be the natural form of muscle function, and it is evident in everyday activities, such as walking and running, as well as in more challenging actions, including throwing and jumping. In real-life situations, exercise seldom involves a pure form of isometric, concentric, or eccentric actions ( 15). The SSC is observed in a wide range of activities. In comparison with purely concentric movements, the SSC allows greater forces to be produced at any given velocity during the concentric phase ( 13). When the force velocity curve is measured during a complex SSC movement involving a number of joints and muscle groups, such as a vertical jump, the use of a preceding eccentric phase shifts the force-velocity curve to the right. This eccentric/concentric coupling of muscular contraction produces a more powerful contraction than that which would result from a purely concentric action alone ( 14). The SSC is a natural type of muscle function in which muscle is stretched immediately before being contracted. ![]()
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