Bijker K E, de Groot G, Hollander A P
Institute for Fundamental and Clinical Human Movement Sciences, Faculty of Human Movement Sciences, Vrije Universiteit Amsterdam, Van der Boechorststraat 9, 1081 BT Amsterdam, The Netherlands.
Eur J Appl Physiol. 2002 Oct;87(6):556-61. doi: 10.1007/s00421-002-0663-8. Epub 2002 Jul 13.
Delta (delta) efficiency is defined as the ratio of an increment in the external mechanical power output to the increase in metabolic power required to produce it. The purpose of the present study was to investigate whether differences in leg muscle activity between running and cycling can explain the observed difference in delta efficiency between the two activities. A group of 11 subjects performed incremental submaximal running and cycling tests on successive days. The delta efficiencies during running and cycling were based on five exercise stages. Electromyograph (EMG) measurements were made of three leg muscles (gastrocnemius, vastus lateralis and biceps femoris). Kendall's correlation coefficients between the mean EMG activity and the load applied were calculated for each muscle, for both running and cycling. As expected, the mean delta efficiency during running (42%) was significantly greater than that during cycling (25%). For cycling, all muscles showed a significant correlation between mean EMG activity and the load applied. For running, however, only the gastrocnemius muscle showed a significant, but low correlation ( r=0.33). The correlation coefficients of the vastus lateralis and biceps femoris muscles were not significantly different from 0. The results were interpreted as follows. In contrast to cycling, which includes only concentric contractions, during running up inclines eccentric muscle actions play an important role. With steeper inclines, more concentric contractions must be produced to overcome the external force, whereas the amount of eccentric muscle actions decreases. This change in the relative contribution of concentric and eccentric muscle actions, in combination with the fact that eccentric muscle actions require much less metabolic energy than concentric contractions, can explain the difference between the running and cycling delta efficiency.
德尔塔（δ）效率的定义是外部机械功率输出的增量与产生该增量所需代谢功率增加量的比值。本研究的目的是调查跑步和骑自行车时腿部肌肉活动的差异是否可以解释这两种活动中观察到的δ效率差异。一组11名受试者在连续几天内进行了递增亚极量跑步和骑自行车测试。跑步和骑自行车时的δ效率基于五个运动阶段。对三块腿部肌肉（腓肠肌、股外侧肌和股二头肌）进行了肌电图（EMG）测量。计算了跑步和骑自行车时每块肌肉的平均肌电活动与施加负荷之间的肯德尔相关系数。正如预期的那样，跑步时的平均δ效率（42%）显著高于骑自行车时的平均δ效率（25%）。对于骑自行车，所有肌肉的平均肌电活动与施加负荷之间均显示出显著相关性。然而，对于跑步，只有腓肠肌显示出显著但较低的相关性（r = 0.33）。股外侧肌和股二头肌的相关系数与0无显著差异。结果如下解释。与仅包括向心收缩的骑自行车不同，在爬坡跑步时离心肌肉动作起着重要作用。坡度越陡，必须产生更多的向心收缩来克服外力，而离心肌肉动作的量则减少。向心和离心肌肉动作相对贡献的这种变化，再加上离心肌肉动作比向心收缩需要少得多的代谢能量这一事实，可以解释跑步和骑自行车δ效率之间的差异。
