Nakagawa Yoshinao, Ratkevicius Aivaras, Mizuno Masao, Quistorff Bjorn
NMR Centre, Department of Medical Biochemistry and Genetics A, Panum Institute, University of Copenhagen, Copenhagen, Denmark.
Med Sci Sports Exerc. 2005 Jun;37(6):937-43.
The aim of this study was investigate ATP economy of force maintenance in the human tibialis anterior muscle during 60 s of anaerobic voluntary contraction at 50% of maximum voluntary contraction (MVC).
ATP turnover rate was evaluated using P magnetic resonance spectroscopy (P-MRS). The total volume of ankle dorsiflexor muscles was assessed by H magnetic resonance imaging (MRI) (H-MRI), and the fiber type composition of the tibialis anterior muscle was evaluated using histochemical analysis of muscle biopsies.
The tibialis anterior muscle occupied 59.7 +/- 0.6% (mean +/- SEM) of the total ankle dorsiflexor muscle volume, which was 267 +/- 10 cm. Relative cross-sectional areas occupied by Type I, IIA, and IIB fibers in the tibialis anterior were 69.3 +/- 2.2, 27.4 +/- 2.76, and 3.2 +/- 1.0%, respectively. ATP economy of force maintenance did not change significantly during the 60-s contraction. It averaged at 4.81 +/- 0.42 N.s.micromol-1, and correlated with the relative cross-sectional area of the muscle occupied by Type I fiber (r = 0.73, P < 0.01). For the second half of the contraction, subjects dropping in force showed lower ATP economy compared with those maintaining the force (3.7 +/- 0.6 vs 5.3 +/- 0.6 N.s.micromol-1; P < 0.05).
It is argued that the unchanged ATP economy of force maintenance during the voluntary contraction could be due to an increase in the ATP economy of contracting muscle fibers offsetting the effects of increased temperature and low ATP economy of Type II fibers. Mechanical interaction between motor units could also act to improve ATP economy of force maintenance.
本研究旨在探究在最大自主收缩（MVC）的50%下进行60秒无氧自主收缩期间，人体胫骨前肌力量维持的三磷酸腺苷（ATP）经济性。
使用磷磁共振波谱（P-MRS）评估ATP周转率。通过氢磁共振成像（H-MRI）评估踝背屈肌的总体积，并使用肌肉活检的组织化学分析评估胫骨前肌的纤维类型组成。
胫骨前肌占踝背屈肌总体积的59.7±0.6%（平均值±标准误），总体积为267±10立方厘米。胫骨前肌中I型、IIA型和IIB型纤维所占的相对横截面积分别为69.3±2.2%、27.4±2.76%和3.2±1.0%。在60秒的收缩过程中，力量维持的ATP经济性没有显著变化。其平均值为4.81±0.42牛顿·秒·微摩尔⁻¹，并且与I型纤维所占肌肉的相对横截面积相关（r = 0.73，P < 0.01）。在收缩的后半段，力量下降的受试者与力量维持的受试者相比，ATP经济性较低（3.7±0.6对5.3±0.6牛顿·秒·微摩尔⁻¹；P < 0.05）。
有人认为，自主收缩期间力量维持的ATP经济性不变可能是由于收缩肌纤维的ATP经济性增加抵消了温度升高和II型纤维ATP经济性降低的影响。运动单位之间的机械相互作用也可能起到改善力量维持的ATP经济性的作用。
