Binder-Macleod S A, Lee S C, Fritz A D, Kucharski L J
Department of Physical Therapy, University of Delaware, Newark, Delaware 19716, USA.
J Neurophysiol. 1998 Apr;79(4):1858-68. doi: 10.1152/jn.1998.79.4.1858.
A muscle does not have a unique force-frequency relationship; rather, it is dynamic and depends on the activation history of muscle. The purpose of this study was to investigate the force-frequency relationship of nonfatigued and fatigued skeletal muscle with the use of both catchlike-inducing trains (CITs) that exploited the catchlike property of skeletal muscle and constant-frequency trains (CFTs). Quadriceps femoris muscles were studied during isometric contractions in twelve healthy subjects (5 females, 7 males). Both the peak force and force-time integrals produced in response to each stimulation train were analyzed. Compared with nonfatigued muscles, higher frequencies of activation were needed to produce comparable normalized peak forces when the muscles were fatigued (i.e., a "rightward" shift in the force-frequency relationship) for both the CFTs and the CITs. When using the normalized force-time integral to measure muscle performance, the CFTs required slightly higher frequencies to produce comparable normalized forces from fatigued muscles, but the CITs did not. Furthermore, when the muscles were fatigued, the CITs produced greater peak forces and force-time integrals than all comparable CFTs with frequencies </=20 pps. In general, the lower the frequency the greater the augmentation produced by the CITs. In addition, the CIT that elicited the greatest force-time integral produced a 25% greater force-time integral than the best CFT. Because the CITs augmented forces across a wide range of physiological relevant activation rates, these results may have important clinical implications when using electrical stimulation to aid patients with paralysis. The results of this study contribute to our understanding of the relationship between the activation pattern of a muscle and the force output produced.
肌肉并不具有独特的力-频率关系；相反，它是动态的，取决于肌肉的激活历史。本研究的目的是利用利用骨骼肌类似强直收缩特性的类强直诱导训练（CITs）和恒频训练（CFTs），研究非疲劳和疲劳骨骼肌的力-频率关系。在12名健康受试者（5名女性，7名男性）进行等长收缩期间，对股四头肌进行了研究。分析了对每种刺激训练产生的峰值力和力-时间积分。与非疲劳肌肉相比，当肌肉疲劳时（即力-频率关系“右移”），对于CFTs和CITs，产生可比的标准化峰值力需要更高的激活频率。当使用标准化力-时间积分来测量肌肉性能时，CFTs需要略高的频率才能从疲劳肌肉中产生可比的标准化力，但CITs则不需要。此外，当肌肉疲劳时，CITs产生的峰值力和力-时间积分比所有频率≤20次/秒的可比CFTs都要大。一般来说，频率越低，CITs产生的增强作用越大。此外，产生最大力-时间积分的CIT产生的力-时间积分比最佳CFT大25%。由于CITs在广泛的生理相关激活率范围内增强了力量，这些结果在使用电刺激辅助瘫痪患者时可能具有重要的临床意义。本研究结果有助于我们理解肌肉激活模式与产生的力输出之间的关系。
