Effects of the transition time between muscle-tendon stretch and shortening on mechanical efficiency

Abstract

The net mechanical efficiency of positive work (eta(pos)) has been shown to increase if it is immediately preceded by negative work. This phenomenon is explained by the storage of elastic energy during the negative phase and its release during the subsequent positive phase. If a transition time (T) takes place, the elastic energy is dissipated into heat. The aim of the present study was to investigate the relationship between eta(pos) and T, and to determine the minimal T required so that eta(pos) reached its minimal value. Seven healthy male subjects were tested during four series of lowering-raising of the body mass. In the first series (S (0)), the negative and positive phases were executed without any transition time. In the three other series, T was varied by a timer (0.12, 0.24 and 0.56 s for series S (1), S (2) and S (3), respectively). These exercises were performed on a force platform sensitive to vertical forces to measure the mechanical work and a gas analyser was used to determine the energy expenditure. The results indicated that eta(pos) was the highest (31.1%) for the series without any transition time (S (0)). The efficiencies observed with transition times (S (1), S (2) and S (3)) were 27.7, 26.0 and 23.8%, respectively, demonstrating that T plays an important role for mechanical efficiency. The investigation of the relationship between eta(pos) and T revealed that the minimal T required so that eta(pos) reached its minimal value is 0.59 s.

The Influence of Growth and Maturation on Stretch-Shortening Cycle Function in Youth

“…Additionally, as muscles increase in size during growth, the higher forces during the eccentric phase may result in an increased potential for storage of elastic energy [ 8 ]. More force produced during the eccentric phase may result in the muscle resisting stretch, causing a greater tendinous lengthening [ 8 , 62 ], and resulting in a more efficient elastic energy storage and reutilisation due to the shorter amortisation periods [ 63 ]. The influence of muscle size on the eccentric and concentric phases of the SSC has not been quantified and still needs further research before we can understand how muscle size may influence the underpinning mechanisms of SSC actions.…”

“…Gastrocnemius fascicle length was found to be a positive predictor of RFD during a countermovement jump in adults [ 73 ] and may highlight the potential for improved SSC function throughout childhood and adolescence, should greater fascicle lengths increase their ability to develop force rapidly. Moreover, the ability to develop force rapidly may ultimately enhance SSC performance by reducing ground contact times, leading to an improved mechanical efficiency by the reutilisation of elastic energy [ 63 ]. Additionally, shorter contact times could influence the impact neural potentiation has on the subsequent concentric action, as longer transition times between the eccentric and concentric contraction causes a decay in the magnitude of potentiation [ 74 ].…”

“…It has been hypothesized that because of the indirect line of pull of pennate muscles, a highly pennate muscle will have an increased ability to resist external forces [ 73 ], as the direct tendon force acting on the muscle are dissipated along the aponeurosis. An increased stiffness upon landing could lead to shorter ground contact times and therefore a better reutilisation of elastic energy [ 63 ].…”

A new sledge jump system that allows almost natural reactive jumps

“…The stretchshortening cycle (SSC) can be defined as the stretching of a preactivated muscle-tendon-unit (MTU), immediately followed by a contraction of the muscle (Komi, 1984). The advantage of this type of muscle action compared to a purely concentric one is the higher efficiency, caused by a storage of energy in the elastic elements in the eccentric phase and its release in the following concentric phase (Asmussen and Bonde-Petersen, 1974;Fukashiro et al, 2006;Gollhofer, 1987;Henchoz et al, 2006). During locomotion, especially when running or jumping, most mammals (including man) take advantage of the energy storage in the SSC.…”

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“…However, the more important is that relating SJ and CMJ height we can calculate the elasticity index (Bosco et al, 1986). Due to than the reutilization of elastic energy is greater with a fast stretch-shorten cycle (SSC) (Henchoz et al, 2006), a player with an optimal SJ height and poor elasticity index should based the trainer in plyometric exercises, whereas players with relatively good elasticity index but poor SJ height should achieve the best performance gains thought the use of exercises with slow SSC.…”