McCully Kevin K, Prins Payton, Mistry Kajal, Willingham T Bradley
Department of Kinesiology, University of Georgia, Athens, GA, USA.
Shoulder Elbow. 2018 Apr;10(2):136-143. doi: 10.1177/1758573217726269. Epub 2017 Aug 21.
Symptoms of fatigue and pain are often reported for the trapezius muscle in the shoulder. The present study evaluated endurance in the trapezius muscles of healthy participants using electric twitch mechanomyography (ETM).
Surface electrodes and a tri-axial accelerometer were placed over the left trapezius muscle. Muscles were stimulated for 3 min each at 2 Hz, 4 Hz and 6 Hz. Maintenance of acceleration during muscle twitches was used to calculate an endurance index (EI). Subjects (n = 9) were tested on two separate days to assess reproducibility of the trapezius EI measurements. The endurance measurements were made on the wrist flexor and vastus lateralis muscles for comparison. Near infrared spectroscopy was used to measure muscle oxygenation (HbO) during the stimulation protocol (n = 8).
Mean (SD) EI was 84.9% (8.7%), 63.3% (19.1%) and 41.7% (20.0%) for 2 Hz, 4 Hz and 6 Hz, respectively. The coefficients of variation were 7.4%, 11.3% and 24.0% for 2 Hz, 4 Hz and 6 Hz, respectively. EI values were significantly lower in the trapezius compared to arm and leg muscles (p < 0.05). HbO values were unchanged from resting values with electrical stimulation.
The EI as measured by ETM may provide a reproducible method of evaluating function in trapezius muscles that is not influenced by oxygen saturation.
肩部斜方肌经常出现疲劳和疼痛症状。本研究采用电刺激诱发肌肉抽搐机械肌电图（ETM）评估健康受试者斜方肌的耐力。
将表面电极和三轴加速度计置于左侧斜方肌上。分别以2Hz、4Hz和6Hz的频率对肌肉进行3分钟的刺激。利用肌肉抽搐期间加速度的维持情况计算耐力指数（EI）。受试者（n = 9）在两个不同日期接受测试，以评估斜方肌EI测量的可重复性。同时对腕屈肌和股外侧肌进行耐力测量以作比较。在刺激过程中使用近红外光谱法测量肌肉氧合（HbO）（n = 8）。
2Hz、4Hz和6Hz时的平均（标准差）EI分别为84.9%（8.7%）、63.3%（19.1%）和41.7%（20.0%）。2Hz、4Hz和6Hz时的变异系数分别为7.4%、11.3%和24.0%。斜方肌的EI值显著低于手臂和腿部肌肉（p < 0.05）。电刺激期间HbO值与静息值相比无变化。
ETM测量的EI可能提供一种评估斜方肌功能的可重复方法，且不受氧饱和度影响。
