Academic journal article Research Quarterly for Exercise and Sport

Stretch Shorten Cycle Performance: Detrimental Effects of Not Equating the Natural and Movement Frequencies

Academic journal article Research Quarterly for Exercise and Sport

Stretch Shorten Cycle Performance: Detrimental Effects of Not Equating the Natural and Movement Frequencies

Article excerpt

Most movements, such as running, jumping, throwing, striking, and lifting are a result of an eccentric action promptly followed by a concentric action. Such a movement sequence is typically referred to as a stretch shorten cycle (SSC), as the muscle is stretched prior to being shortened. SSC movements are common, because they augment the concentric phase of the activity through a more effective transmission of initial force, the use of elastic strain energy, and additional reflexively induced neural input (Bosco, Tarkka, & Komi, 1982; Komi, 1984; Wilson, Wood, & Elliott, 1991). In maximizing the benefits of using prior stretch, several authors have suggested that the movement frequency of the SSC portion of the action should be matched with the natural frequency of the musculo-tendinous system (Bach, Chapman, & Calvert, 1983; Denoth, 1985; Taylor, 1985; Wilson et al., 1991), because the system then operates in resonance; the authors reported that optimal benefits of the SSC were then achieved.

Bach et al. (1983) performed a study whereby participants were required to perform a cyclical contraction of the calf musculature over a series of movement frequencies which varied in 0.5 Hz steps from 2.5 to 5.5 Hz. These researchers observed that the muscular effort associated with performing oscillations about the ankle joint, at a given force, was minimized when participants performed at their natural frequency (3.3 [+ or -] 0.15 Hz). Further, these researchers re-analyzed several studies and reported that the frequency of the landing impulse of performance by participants in repetitive hopping, jumping, and fatigued running showed close resemblance to the estimated natural frequency of their elastic structures. Cavagna, Franzetti, Heglund, and Willems (1988) observed that, at low speeds of running and in trotting, the apparent natural frequency of the body was practically equal to the freely chosen step frequency. Denoth (1985) designed a mechanical model which demonstrated that the maximal performance in the vertical throw of a shot occurred when the frequency of the movement corresponded to the natural frequency of the series elastic mass system, and, hence, the system was in resonance.

Taylor (1985) observed that participants who hopped utilized a nearly constant movement frequency over a wide range of speeds (0.25-2.2 m [center dot] [s.sup.-1]). Similar observations have also been made with hopping kangaroos (Dawson & Taylor, 1973) and galloping quadrupeds (Heglund, Taylor, & McMahon, 1984). At the preferred hopping frequency Taylor (1985) reported that the role of elastic strain energy was maximized and that of metabolic energy was minimized. Forcing participants to hop at frequencies other than the preferred frequency greatly reduced the use of elastic strain energy in movement. Taylor rationalized the preferred movement frequency as being matched to the natural frequency of the "whole body spring." This author concluded: "The behavior of this system is what would be predicted for a tuned spring with its resonant frequency at the natural hopping frequency." (Taylor, 1985, p. 257).

Wilson et al. (1991) observed that experienced weight trainers performed near maximal bench press lifts that matched the participants' natural and movement frequencies. Consequently their musculo-tendinous systems were in resonance. Because all participants were reported to be operating in resonance, it was not possible to establish the importance of resonance to the performance benefits associated with the SSC.

While the above studies provide some interesting evidence supporting the performance of SSC actions in resonance, it is by no means overwhelming. The present study aims to follow this research and examine the performance benefits derived from prior stretch when upper body SSC movements of varying movement frequency are performed by relatively untrained individuals. In structuring such a study it is conceivable that at least some of the SSC movements may not be performed in resonance. …

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