Bosco C, Rusko H
Acta Physiol Scand. 1983 Nov;119(3):219-24. doi: 10.1111/j.1748-1716.1983.tb07331.x.
The enhancement of performance in stretch-shortening exercises has been attributed to the recoil of elastic energy stored during the stretching phase. If the time between stretching and shortening (coupling time) is too long the stored elastic energy can be wasted. In the present study, coupling time was increased by asking ten male subjects to run on a treadmill at different speeds (2.2-5.2 m X s-1) using special soft shoes in addition to normal shoes. The results indicated that running with soft shoes required greater energy consumption than running with normal shoes except at slow speed (2.2 m X s-1). When the running speed was increased the extra energy consumed using soft shoes was parallelly enhanced (0.4 J X kg-1/step at 5.2 m X s-1). It was suggested that the effect of coupling time as limiting factor for recoil of elastic energy was relevant in fast twitch (FT) fibers, which were progressively recruited when the running speed was increased. This is consistent to the fact that cross-bridge life time in FT fibers is very short, and therefore more sensitive to coupling time. At slow running speed (2.2 m X s-1) only slow twitch (ST) fibers were recruited and the enhancement of coupling time was not long enough to provocate detachment of cross-bridges of ST fibers, which possess a long cross-bridge life time. It was concluded that the different recruitment of ST and FT fibers influenced the pattern of recoil of elastic energy which was dependent on the running speed.
在拉长-缩短练习中，运动表现的提升归因于拉伸阶段储存的弹性能量的回弹。如果拉伸和缩短之间的时间（耦合时间）过长，储存的弹性能量就会被浪费。在本研究中，通过让10名男性受试者除了穿普通鞋子外，还穿着特殊软鞋以不同速度（2.2 - 5.2米×秒⁻¹）在跑步机上跑步，来增加耦合时间。结果表明，除了低速（2.2米×秒⁻¹）外，穿软鞋跑步比穿普通鞋跑步需要更多的能量消耗。当跑步速度增加时，穿软鞋消耗的额外能量也相应增加（在5.2米×秒⁻¹时为0.4焦耳×千克⁻¹/步）。有人提出，耦合时间作为弹性能量回弹的限制因素，在快肌纤维（FT）中是相关的，当跑步速度增加时，快肌纤维会逐渐被募集。这与FT纤维中横桥寿命非常短，因此对耦合时间更敏感这一事实是一致的。在低速跑步（2.2米×秒⁻¹）时，只募集慢肌纤维（ST），耦合时间的增加不足以引发具有长横桥寿命的ST纤维横桥的分离。得出的结论是，ST纤维和FT纤维的不同募集影响了依赖于跑步速度的弹性能量回弹模式。
