2020年度は、骨格筋3特性(筋機能特性・筋形態特性・筋材質特性)の相互関係とその変容を、マラソン大会に参加する一般健常ランナーにおける腓腹筋の硬度変化を検証することで明らかにする計画であった。しかしながら、エントリーしていたマラソン大会が、COVID-19の影響により大会直前で中止となったため、研究の骨組みはそのままに運動課題のみラボベースで実施可能な骨格筋の質的変化の基礎研究にシフトし、その成果を報告した論文が採択された。具体的には、組織に照射された超音波のせん断速度の組織的差異から生体内での"硬さの位置情報"を取得できる超音波エラストグラフィと、古くから使用されている簡便で汎用性の高い押し込み式の筋硬度計の関係から各特性の相互作用を検証することとした。21名の男性健常者を対象に、肘関節屈曲角度30・60・90°のいずれかの角度で最大の15・30・45・60・75・90%の筋力を発揮した際の上腕二頭筋の硬さを、押し込み式筋硬度計(E)または超音波エラストグラフィのひずみ係数(strain ratio: SR)およびYoung's modulus(YM)にて測定した。その結果、Eと対数変換されたSR(logarithmical transformed SR: LTSR)の間にはr=−0.626(p<0.01)の強い相関関係が、EとYMの間にはr=0.615(p<0.01)の強い相関関係が認められた。さらに、最大筋力の90%まで出力した際のEは脱力時の9倍にまで増加し、LTSRとの間にはr=−0.732から−0.880の強い相関関係(p<0.01)が、YMの間にも同様にr=0.599から0.768の強い相関関係(p<0.01)が認められた。以上の結果より、スポーツ競技現場や医療現場などで簡便に使用可能な押し込み式筋硬度計を使用しても、超音波エラストグラフィ類似した信頼性の高い値を取得可能であることを示唆するものであるとともに、筋材質特性は形態特性の影響を受けることが理解された。
In 2020, it was planned to clarify the interrelationship of the three skeletal muscle properties (muscle function, muscle morphology, muscle mechanical property) and their alteration in examining changes in the muscle hardness of the gastrocnemius muscles of general healthy runners participating in the marathon event. However, the marathon event in which the target subjects were scheduled to participate was canceled just before the event due to the influence of COVID-19. Therefore, keeping the framework of the research, the exercise task was shifted to the basic research of qualitative changes in skeletal muscle that can be done on a laboratory basis, and the paper that reported the research results within the 2020 season was accepted. Specifically, we decided to examine in detail the relationship between the simple and versatile push-in mater that has been used for a long time and the ultrasound elastography that can acquire "hardness position information" in the living body from the difference in the strain rate of ultrasound waves applied to the tissue. Finally, this study investigated the relationship between push-in meter (PM) and ultrasound strain elastography (USE) for biceps brachii (BB) muscle hardness. BB hardness of 21 young men was assessed by PM and USE during rest and isometric contractions of six different intensities (15, 30, 45, 60, 75, 90% of maximal voluntary contraction: MVC) at 30°, 60° and 90° elbow flexion. Muscle hardness (E) was calculated from the force–displacement (muscle thickness) relationship in PM, and strain ratio (SR) between an acoustic coupler and different regions of interest (ROIs) in BB was calculated and converted to Young's modulus (YM) in USE. A significant (p<0.01) correlation was evident between E and logarithmical transformed SR (LTSR) for the ROI of whole BB (r=−0.626), and E and converted YM (r=0.615). E increased approximately ninefold from resting to 90% MVC, and E and LTSR (r=−0.732 to −0.880). These results suggest that muscle hardness values obtained by PM and USE are comparable. The findings of this study suggest that it is possible to obtain highly reliable values similar to ultrasound elastography even when using a push-in mater in sports competition sites and medical sites, and was understood that mechanical properties are influenced by morphological property (muscle thickness).
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