Dewhurst Susan, Graven-Nielsen Thomas, De Vito Giuseppe, Farina Dario
Department of Applied Physiology, University of Strathclyde, Glasgow, UK.
Clin Neurophysiol. 2007 Apr;118(4):762-9. doi: 10.1016/j.clinph.2006.12.006. Epub 2007 Feb 20.
To investigate the effect of muscle temperature on force fluctuations during isometric contractions in young and older females.
Fifteen young and 11 older subjects performed 3x30-s long submaximal isometric ankle dorsi-flexions (5%, 10%, and 15% of the maximal force). Tibialis anterior muscle temperature was monitored with an intramuscular probe and manipulated to obtain a cold, control, and warm condition. The coefficient of variation (CofV) and the relative power in the frequency bands 0-3Hz (low), 4-6Hz (middle), and 8-12Hz (high) of the force signal were computed to characterise steadiness. Intramuscular EMG signals were recorded from the tibialis anterior muscle to assess motor unit discharge pattern.
CofV was higher in the older than in the young subjects (P<0.001) in all conditions. In the older group only, CofV increased with cooling with respect to control temperature (P<0.001), whereas in the young group only, relative power of force fluctuations at high frequency decreased with cooling. Motor unit discharge rate and inter-pulse interval variability were not different between groups and across temperatures.
The findings indicate a different effect of temperature on the ability to maintain constant force in young and older subjects.
These results highlight the risk of further impairment to the motor control of older individuals with varying temperature.
研究年轻和年长女性在等长收缩过程中肌肉温度对力量波动的影响。
15名年轻受试者和11名年长受试者进行了3次30秒的次最大等长踝关节背屈（最大力量的5%、10%和15%）。使用肌内探头监测胫骨前肌温度，并通过调节使其处于冷、对照和热状态。计算力量信号在0 - 3Hz（低频）、4 - 6Hz（中频）和8 - 12Hz（高频）频段的变异系数（CofV）和相对功率，以表征稳定性。记录胫骨前肌的肌内肌电图信号，以评估运动单位放电模式。
在所有状态下，年长受试者的CofV均高于年轻受试者（P<0.001）。仅在年长组中，相对于对照温度，CofV随冷却而增加（P<0.001）；而仅在年轻组中，高频力量波动的相对功率随冷却而降低。两组之间以及不同温度下的运动单位放电率和脉冲间期变异性没有差异。
研究结果表明温度对年轻和年长受试者维持恒定力量能力的影响不同。
这些结果突出了温度变化对年长个体运动控制造成进一步损害的风险。
