Duffell Lynsey D, de N Donaldson Nick, Newham Di J
Division of Applied Biomedical Research, King's College London, SE1 1UL London, UK.
IEEE Trans Neural Syst Rehabil Eng. 2009 Jun;17(3):263-9. doi: 10.1109/TNSRE.2009.2016199. Epub 2009 Feb 27.
The potential benefits of functional electrically stimulated (FES) cycling for people with spinal cord injury (SCI) are limited by the power output (PO) attainable. To understand why PO and metabolic efficiency are low, it is helpful to distinguish the effect of the SCI from the effects of electrical stimulation. The purpose of this study was to determine the performance of electrically stimulated (ES) muscle under simpler conditions and in able-bodied people in order to answer two questions about the causes of the poor efficiency in FES cycling. Fifteen able-bodied subjects (26.6 years, six male) performed 5 min of intermittent isometric quadriceps contractions at 40% maximum voluntary contraction during both voluntary and ES activation. Subsequently, nine of them performed 5 min of ES intermittent concentric contractions at the same intensity. This intermittent quadriceps activation imitated the muscles' activity during FES cycling at 35 rpm. Metabolic measurements were recorded. Input power relative to the integral of torque produced (W/Nm x s) was significantly higher during ES than voluntary isometric contractions. Efficiency of ES concentric contractions was 29.6 +/-2.9%. Respiratory exchange ratio was high during ES (1.00-1.01) compared with voluntary (0.91) contractions. ES is less economic than voluntary exercise during isometric contractions, probably due to the greater activation of fast muscle fibres. However, during ES concentric contractions, efficiency is near to the expected values for the velocity chosen. Thus there are additional factors that affect the inefficiency observed during FES cycling.
功能性电刺激（FES）骑行对脊髓损伤（SCI）患者的潜在益处受到可达到的功率输出（PO）的限制。为了理解为什么功率输出和代谢效率较低，区分脊髓损伤的影响与电刺激的影响是有帮助的。本研究的目的是在更简单的条件下以及在健全人群中确定电刺激（ES）肌肉的表现，以便回答关于FES骑行效率低下原因的两个问题。15名健全受试者（26.6岁，6名男性）在自主激活和电刺激激活期间，以最大自主收缩的40%进行了5分钟的间歇性股四头肌等长收缩。随后，其中9人以相同强度进行了5分钟的电刺激间歇性向心收缩。这种间歇性股四头肌激活模仿了FES骑行时以35转/分钟的速度肌肉的活动。记录了代谢测量值。相对于产生的扭矩积分的输入功率（瓦/牛顿米×秒）在电刺激期间显著高于自主等长收缩。电刺激向心收缩的效率为29.6±2.9%。与自主收缩（0.91）相比，电刺激期间呼吸交换率较高（1.00 - 1.01）。在等长收缩期间，电刺激不如自主运动经济，可能是由于快肌纤维的更大激活。然而，在电刺激向心收缩期间，效率接近所选速度的预期值。因此，存在其他因素影响在FES骑行期间观察到的低效率。
