Pinto Matheus Daros, Silveira Pinto Ronei, Nosaka Kazunori, Blazevich Anthony John
Centre for Human Performance, School of Medical and Health Sciences, Edith Cowan University, Joondalup, AUSTRALIA.
Med Sci Sports Exerc. 2023 Apr 1;55(4):740-750. doi: 10.1249/MSS.0000000000003082. Epub 2022 Nov 8.
Ultrasound-derived echo intensity (EI) has been used as a physiological marker for changes in skeletal muscle "quality" with physical training, disuse, aging, and neuromuscular disorders. However, the methodological and physiological factors influencing EI and its longitudinal change are still unclear. Here, we performed two separate experiments to investigate the effects of muscle temperature and fascicle angle, which are known to influence muscle tissue and sound wave properties and therefore affect EI.
In experiment 1 ( n = 16, 28.0 ± 6.6 yr), vastus lateralis (VL) ultrasonographic images were acquired and intramuscular temperature continuously recorded for 15 min after 20 min of heating to 40.4°C ± 0.7°C using a microwave device. In experiment 2 ( n = 17, 30.2 ± 9.8 yr), VL sonographic images were obtained with the knee both fully extended (0°) and flexed to 90° and EI and fascicle angle measured post hoc . Fascicle movement was tracked during the passive knee flexion to ensure that sonographic images were obtained at the same muscle region. Knee flexion reduced muscle thickness, and we therefore reran analyses calculating EI using identical dimensions to minimize this effect.
EI decreased only immediately after the passive heating, and although a moderate, negative correlation was observed between EI and temperature ( rrm = -0.36), the effect of muscle temperature was small ( β = 0.97 (-1.89 to -0.06) per degree Celsius, P = 0.051). Nonetheless, EI increased as fascicle angle decreased, and a large, negative correlation ( rrm = -0.85) was observed; the effect of fascicle angle on EI was large ( β = 3.0 (-3.8 to -2.2) per degree, P < 0.01), and this was maintained when analyses were performed at a constant depth of the region of interest ( β = 3.5 (-4.4 to -2.7) per degree, P < 0.01).
These findings support the hypothesis that fascicle angle meaningfully affects VL EI but provides weak evidence of a temperature effect in vivo . Thus, acute fascicle angle alterations should be accounted for in studies using EI measurements, and longer-term studies should consider whether changes in EI might be partly explained by a change in fascicle angle.
超声衍生的回声强度（EI）已被用作骨骼肌“质量”随体育锻炼、废用、衰老和神经肌肉疾病变化的生理标志物。然而，影响EI及其纵向变化的方法学和生理因素仍不清楚。在此，我们进行了两项独立实验，以研究肌肉温度和肌束角度的影响，已知这些因素会影响肌肉组织和声波特性，进而影响EI。
在实验1（n = 16，28.0±6.6岁）中，使用微波设备将股外侧肌（VL）加热至40.4°C±0.7°C持续20分钟后，采集VL超声图像，并连续记录肌肉内温度15分钟。在实验2（n = 17，30.2±9.8岁）中，在膝关节完全伸展（0°）和屈曲至90°时获取VL超声图像，并在事后测量EI和肌束角度。在被动膝关节屈曲过程中跟踪肌束运动，以确保在同一肌肉区域获取超声图像。膝关节屈曲会减小肌肉厚度，因此我们重新进行分析，使用相同尺寸计算EI，以尽量减少这种影响。
EI仅在被动加热后立即下降，尽管EI与温度之间观察到中度负相关（rrm = -0.36），但肌肉温度的影响较小（每摄氏度β = 0.97（-1.89至-0.06），P = 0.051）。尽管如此，EI随着肌束角度减小而增加，并观察到高度负相关（rrm = -0.85）；肌束角度对EI的影响很大（每度β = 3.0（-3.8至-2.2），P < 0.01），当在感兴趣区域的恒定深度进行分析时，这种情况仍然存在（每度β = 3.5（-4.4至-2.7），P < 0.01）。
这些发现支持以下假设，即肌束角度对VL EI有显著影响，但为体内温度影响提供的证据较弱。因此，在使用EI测量的研究中应考虑急性肌束角度改变，长期研究应考虑EI的变化是否可能部分由肌束角度变化解释。
