Cadigan Edward W J, Collins Brandon W, Philpott Devin T G, Kippenhuck Garreth, Brenton Mitchell, Button Duane C
Human Neurophysiology Laboratory, School of Human Kinetics and Recreation, Memorial University of NewfoundlandSt. John's, NL, Canada.
BioMedical Sciences, Faculty of Medicine, Memorial University of NewfoundlandSt. John's, NL, Canada.
Front Physiol. 2017 Sep 20;8:707. doi: 10.3389/fphys.2017.00707. eCollection 2017.
Transcranial magnetic (TMS) and motor point stimulation have been used to determine voluntary activation (VA). However, very few studies have directly compared the two stimulation techniques for assessing VA of the elbow flexors. The purpose of this study was to compare TMS and motor point stimulation for assessing VA in non-fatigued and fatigued elbow flexors. Participants performed a fatigue protocol that included twelve, 15 s isometric elbow flexor contractions. Participants completed a set of isometric elbow flexion contractions at 100, 75, 50, and 25% of maximum voluntary contraction (MVC) prior to and following fatigue contractions 3, 6, 9, and 12 and 5 and 10 min post-fatigue. Force and EMG of the bicep and triceps brachii were measured for each contraction. Force responses to TMS and motor point stimulation and EMG responses to TMS (motor evoked potentials, MEPs) and Erb's point stimulation (maximal M-waves, M) were also recorded. VA was estimated using the equation: = (1-/) × 100. The resting twitch was measured directly for motor point stimulation and estimated for both motor point stimulation and TMS by extrapolation of the linear regression between the superimposed twitch force and voluntary force. MVC force, potentiated twitch force and VA significantly ( < 0.05) decreased throughout the elbow flexor fatigue protocol and partially recovered 10 min post fatigue. VA was significantly ( < 0.05) underestimated when using TMS compared to motor point stimulation in non-fatigued and fatigued elbow flexors. Motor point stimulation compared to TMS superimposed twitch forces were significantly ( < 0.05) higher at 50% MVC but similar at 75 and 100% MVC. The linear relationship between TMS superimposed twitch force and voluntary force significantly ( < 0.05) decreased with fatigue. There was no change in triceps/biceps electromyography, biceps/triceps MEP amplitudes, or bicep MEP amplitudes throughout the fatigue protocol at 100% MVC. In conclusion, motor point stimulation as opposed to TMS led to a higher estimation of VA in non-fatigued and fatigued elbow flexors. The decreased linear relationship between TMS superimposed twitch force and voluntary force led to an underestimation of the estimated resting twitch force and thus, a reduced VA.
经颅磁刺激（TMS）和运动点刺激已被用于确定自主激活（VA）。然而，很少有研究直接比较这两种刺激技术来评估肘屈肌的VA。本研究的目的是比较TMS和运动点刺激在评估非疲劳和疲劳肘屈肌VA方面的差异。参与者进行了一项疲劳方案，包括12次持续15秒的等长肘屈肌收缩。参与者在疲劳收缩前、疲劳收缩后3、6、9和12分钟以及疲劳后5和10分钟，以最大自主收缩（MVC）的100%、75%、50%和25%完成一组等长肘屈肌收缩。测量每次收缩时肱二头肌和肱三头肌的力量和肌电图。还记录了对TMS和运动点刺激的力量反应以及对TMS（运动诱发电位，MEP）和Erb点刺激（最大M波，M）的肌电图反应。使用公式：VA = (1 - MEP/M) × 100来估计VA。直接测量运动点刺激的静息抽搐，并通过叠加抽搐力和自主力之间的线性回归外推来估计运动点刺激和TMS的静息抽搐。在整个肘屈肌疲劳方案中，MVC力量、增强的抽搐力量和VA显著（P < 0.05）下降，并在疲劳后10分钟部分恢复。与运动点刺激相比，在非疲劳和疲劳肘屈肌中使用TMS时，VA显著（P < 0.05）被低估。与TMS相比，在50%MVC时运动点刺激的叠加抽搐力量显著（P < 0.05）更高，但在75%和100%MVC时相似。随着疲劳，TMS叠加抽搐力量和自主力之间的线性关系显著（P < 0.05）下降。在100%MVC的整个疲劳方案中，肱三头肌/肱二头肌肌电图、肱二头肌/肱三头肌MEP幅度或肱二头肌MEP幅度没有变化。总之，与TMS相比，运动点刺激在非疲劳和疲劳肘屈肌中对VA的估计更高。TMS叠加抽搐力量和自主力之间线性关系的下降导致估计的静息抽搐力量被低估，从而VA降低。
