Bickel C Scott, Slade Jill M, Warren Gordon L, Dudley Gary A
Department of Exercise Science, The University of Georgia, 300 River Rd, Athens, GA 30602, USA.
Phys Ther. 2003 Apr;83(4):366-73.
The quadriceps femoris (QF) and tibialis anterior (TA) muscles are often activated through the use of electrical stimulation by physical therapists. These 2 muscles are fundamentally different in regard to their fiber-type composition. Whether protocols developed using a given muscle can be applied to another muscle has seldom been questioned, even if they differ in fiber type. The purpose of this study was to test the hypothesis that torque augmentation during variable-frequency train (VFT) stimulation as compared with constant-frequency train (CFT) stimulation in the fatigued state would not differ between these muscles, even though the TA muscle has 50% relatively more slow fibers than the QF muscle relative to each muscle's overall composition.
Ten recreationally active men with no history of lower-extremity pathology participated in the study (mean age=25 years, SD=4, range=19-31; mean height=179 cm, SD=5, range=170-188; mean body mass=80 kg, SD=15, range=63-111).
The subjects' TA and QF muscles were stimulated with CFTs (six 200-microsecond square waves separated by 70 milliseconds) or VFTs (first interpulse interval=5 milliseconds) that evoked an isometric contraction.
After potentiation, the torque-time integral and peak torque were not different for the VFT and CFT stimulation. Rise time was longer for the TA muscle than for the QF muscle and for CFT stimulation versus VFT stimulation (both approximately 40%). After 180 CFTs (50% duty cycle), peak torque decreased 56% overall, with no differences between muscles. Enhancement of the torque-time integral (25%) by VFT stimulation was not different between fatigued QF and TA muscles. Torque augmentation was due to the VFT stimulation evoking 27% greater peak torque and less slowing of rise time than the CFT stimulation (15% versus 30%).
The results indicate that the QF muscle may not necessarily fatigue more than the TA muscle. The results suggest that VFTs augment the force of fatigued, human skeletal muscle irrespective of fiber type.
股四头肌（QF）和胫骨前肌（TA）常通过物理治疗师使用电刺激来激活。这两块肌肉在纤维类型组成方面存在根本差异。即使不同肌肉的纤维类型不同，使用特定肌肉制定的方案是否可应用于另一块肌肉却很少受到质疑。本研究的目的是检验以下假设：尽管相对于每块肌肉的总体组成，TA肌肉的慢纤维比QF肌肉多50%，但在疲劳状态下，与恒频训练（CFT）刺激相比，变频训练（VFT）刺激期间的扭矩增强在这两块肌肉中并无差异。
10名无下肢疾病史的休闲活动男性参与了本研究（平均年龄 = 25岁，标准差 = 4，范围 = 19 - 31岁；平均身高 = 179厘米，标准差 = 5，范围 = 170 - 188厘米；平均体重 = 80千克，标准差 = 15，范围 = 63 - 111千克）。
用CFTs（六个200微秒的方波，间隔70毫秒）或VFTs（第一个脉冲间隔 = 5毫秒）刺激受试者的TA和QF肌肉，引发等长收缩。
增强后，VFT和CFT刺激的扭矩 - 时间积分和峰值扭矩无差异。TA肌肉的上升时间比QF肌肉长，且CFT刺激的上升时间比VFT刺激长（两者均约40%）。在180次CFTs（占空比50%）后，峰值扭矩总体下降56%，两块肌肉之间无差异。VFT刺激对疲劳的QF和TA肌肉扭矩 - 时间积分的增强作用（25%）无差异。扭矩增强是由于VFT刺激引发的峰值扭矩比CFT刺激大27%，且上升时间减慢程度更小（分别为15%和30%）。
结果表明，QF肌肉不一定比TA肌肉更容易疲劳。结果提示，VFTs可增强疲劳的人体骨骼肌力量，而与纤维类型无关。
