Bartlett Jamie L, Kram Rodger
Locomotion Laboratory, Department of Integrative Physiology, University of Colorado, Boulder, CO 80309, USA.
J Exp Biol. 2008 Apr;211(Pt 8):1281-8. doi: 10.1242/jeb.011932.
It has been proposed that muscle-specific factors trigger the human walk-run transition. We investigated if changing the demand on trigger muscles alters the preferred walk-run transition speed. We hypothesized that (1) reducing the demand on trigger muscles would increase the transition speed and (2) increasing the demand on trigger muscles would decrease the transition speed. We first determined the normal preferred walk-run transition speed (PTS) using a step-wise protocol with a randomized speed order. We then determined PTS while subjects walked with external devices that decreased or increased the demand on specific muscle groups. We concurrently measured the electromyographic activity of five leg muscles (tibialis anterior, soleus, rectus femoris, medial and lateral gastrocnemius) at each speed and condition. For this study, we developed a dorsiflexor assist device that aids the dorsiflexor muscles. A leg swing assist device applied forward pulling forces at the feet thus aiding the hip flexors during swing. A third device applied a horizontal force near the center of mass, which impedes or aids forward progression thus overloading or unloading the plantarflexor muscles. We found that when demand was decreased in the muscles measured, the PTS significantly increased. Conversely, when muscle demand was increased in the plantar flexors, the PTS decreased. However, combining assistive devices did not produce an even faster PTS. We conclude that altering the demand on specific muscles can change the preferred walk-run transition speed. However, the lack of a summation effect with multiple external devices, suggests that another underlying factor ultimately determines the preferred walk-run transition speed.
有人提出，肌肉特异性因素会引发人类行走-跑步转换。我们研究了改变对触发肌肉的需求是否会改变首选的行走-跑步转换速度。我们假设：（1）减少对触发肌肉的需求会提高转换速度；（2）增加对触发肌肉的需求会降低转换速度。我们首先使用具有随机速度顺序的逐步方案确定正常的首选行走-跑步转换速度（PTS）。然后，在受试者使用减少或增加对特定肌肉群需求的外部设备行走时，确定PTS。我们同时测量了每个速度和条件下五条腿部肌肉（胫骨前肌、比目鱼肌、股直肌、腓肠肌内侧头和外侧头）的肌电图活动。在本研究中，我们开发了一种辅助背屈肌的背屈辅助装置。一种腿部摆动辅助装置在脚部施加向前的拉力，从而在摆动过程中辅助髋屈肌。第三种装置在质心附近施加水平力，这会阻碍或辅助向前推进，从而使跖屈肌过载或卸载。我们发现，当所测量的肌肉需求减少时，PTS显著增加。相反，当跖屈肌的肌肉需求增加时，PTS降低。然而，组合辅助装置并没有产生更快的PTS。我们得出结论，改变对特定肌肉的需求可以改变首选的行走-跑步转换速度。然而，多种外部装置缺乏累加效应，这表明另一个潜在因素最终决定了首选的行走-跑步转换速度。
