Dudley-Javoroski Shauna, Littmann Andrew E, Iguchi Masaki, Shields Richard K
The Univ. of Iowa, Iowa City, IA 52242, USA.
J Appl Physiol (1985). 2008 Jun;104(6):1574-82. doi: 10.1152/japplphysiol.00892.2007. Epub 2008 Apr 24.
With long-term electrical stimulation training, paralyzed muscle can serve as an effective load delivery agent for the skeletal system. Muscle adaptations to training, however, will almost certainly outstrip bone adaptations, exposing participants in training protocols to an elevated risk for fracture. Assessing the physiological properties of the chronically paralyzed quadriceps may transmit unacceptably high shear forces to the osteoporotic distal femur. We devised a two-pulse doublet strategy to measure quadriceps physiological properties while minimizing the peak muscle force. The purposes of the study were 1) to determine the repeatability of the doublet stimulation protocol, and 2) to compare this protocol among individuals with and without spinal cord injury (SCI). Eight individuals with SCI and four individuals without SCI underwent testing. The doublet force-frequency relationship shifted to the left after SCI, likely reflecting enhancements in the twitch-to-tetanus ratio known to exist in paralyzed muscle. Posttetanic potentiation occurred to a greater degree in subjects with SCI (20%) than in non-SCI subjects (7%). Potentiation of contractile rate occurred in both subject groups (14% and 23% for SCI and non-SCI, respectively). Normalized contractile speed (rate of force rise, rate of force fall) reflected well-known adaptations of paralyzed muscle toward a fast fatigable muscle. The doublet stimulation strategy provided repeatable and sensitive measurements of muscle force and speed properties that revealed meaningful differences between subjects with and without SCI. Doublet stimulation may offer a unique way to test muscle physiological parameters of the quadriceps in subjects with uncertain musculoskeletal integrity.
通过长期电刺激训练，瘫痪肌肉可作为骨骼系统有效的负荷传递介质。然而，肌肉对训练的适应性几乎肯定会超过骨骼的适应性，使参与训练方案的人面临更高的骨折风险。评估慢性瘫痪股四头肌的生理特性可能会给骨质疏松的股骨远端传递高到不可接受的剪切力。我们设计了一种双脉冲策略来测量股四头肌的生理特性，同时将肌肉峰值力降至最低。本研究的目的是：1）确定双脉冲刺激方案的可重复性，2）比较该方案在脊髓损伤（SCI）患者和非脊髓损伤患者中的情况。8名SCI患者和4名非SCI患者接受了测试。SCI后双脉冲力-频率关系向左移动，这可能反映了瘫痪肌肉中已知存在的单收缩与强直收缩比率的增强。SCI患者的强直后增强程度（20%）高于非SCI患者（7%）。两组患者均出现收缩速率增强（SCI组和非SCI组分别为14%和23%）。标准化收缩速度（力上升速率、力下降速率）反映了瘫痪肌肉向快速疲劳肌肉的众所周知的适应性变化。双脉冲刺激策略提供了对肌肉力量和速度特性的可重复且敏感的测量，揭示了SCI患者和非SCI患者之间的有意义差异。双脉冲刺激可能为测试肌肉骨骼完整性不确定的受试者的股四头肌生理参数提供一种独特的方法。
