IEEE Trans Biomed Eng. 2021 Apr;68(4):1409-1416. doi: 10.1109/TBME.2020.3035838. Epub 2021 Mar 18.
The purpose of this study was to assess whether accelerometry effectively reflects muscle vibrations measured with ultrafast ultrasonography.
Vibration characteristics initiated on the vastus lateralis muscle by an impactor were compared when assessed with accelerometry and ultrasonography. Continuous wavelet transforms and statistical parametric mapping (SPM) were performed to identify discrepancies in vibration power over time and frequency between the two devices.
The SPM analysis revealed that the accelerometer underestimated the muscle vibration power above 50 Hz during the first 0.06 seconds post impact. Furthermore, the accelerometer overestimated the muscle vibration power under 20 Hz, from 0.1 seconds after the impact. Linear regression revealed that the thicker the subcutaneous fat localized under the accelerometer, the more the muscle vibration frequency and damping were underestimated by the accelerometer.
The skin and the fat tissues acted like a low-pass filter above 50 Hz and oscillated in a less damped manner than the muscle tissue under 20 Hz.
To eliminate some artifacts caused by the superficial tissues and assess the muscle vibration characteristics with accelerometry, it is suggested to 1) high-pass filter the acceleration signal at a frequency of 20 Hz, under certain conditions, and 2) include participants with less fat thickness. Therefore, the subcutaneous thickness must be systematically quantified under each accelerometer location to clarify the differences between subjects and muscles.
本研究旨在评估加速度计是否能有效反映超快速超声测量的肌肉振动。
当使用加速度计和超声评估撞击引发的股外侧肌的振动特征时，对两种设备的时间和频率上的振动功率差异进行连续小波变换和统计参数映射（SPM）分析。
SPM 分析显示，在撞击后最初的 0.06 秒内，加速度计低估了超过 50 Hz 的肌肉振动功率。此外，在撞击后 0.1 秒，加速度计高估了低于 20 Hz 的肌肉振动功率。线性回归显示，加速度计下定位的皮下脂肪越厚，肌肉振动频率和阻尼的低估程度越大。
皮肤和脂肪组织在 50 Hz 以上充当低通滤波器，在 20 Hz 以下的振动阻尼比肌肉组织小。
为了消除由浅层组织引起的一些伪影，并使用加速度计评估肌肉振动特征，建议 1）在某些条件下，将加速度信号在 20 Hz 的频率处进行高通滤波，以及 2）纳入皮下脂肪厚度较小的参与者。因此，必须在每个加速度计位置下系统地量化皮下厚度，以明确不同个体和肌肉之间的差异。
