Holmbäck Anna Maria, Porter Michelle M, Downham David, Andersen Jesper L, Lexell Jan
Department of Physical Therapy, Lund University Hospital, SE-221 85 Lund, Sweden.
J Appl Physiol (1985). 2003 Dec;95(6):2416-24. doi: 10.1152/japplphysiol.00517.2002. Epub 2003 Aug 29.
The aim was to investigate determinants of ankle dorsiflexor muscle (DF) strength and size in moderately active young men and women (n = 30; age 20-31 yr). Concentric (Con) and eccentric (Ecc) strength were measured isokinetically. Magnetic resonance imaging was used to determine the muscle cross-sectional area (CSA). Multiple biopsies were obtained from the tibialis anterior muscle to determine total numbers, areas (Area I and II) and proportions (Prop I and II) of type I and II fibers, respectively, and relative contents of myosin heavy chain (MHC) isoforms MHC1, MHC2a, and MHC2x. Women had lower Con and Ecc strength (24 and 27%; P < 0.01), smaller CSA (19%; P < 0.001), lower Ecc DF specific strength (strength/CSA) (10%; P < 0.01), and smaller Area I and Area II (21 and 31%; P < 0.01) than men. Prop I, MHC1, estimated total number of fibers, and Con DF specific strength were similar for both sexes. Con DF strength was up to 72% determined by CSA and Prop I, and Ecc DF strength was up to 81% determined by CSA, Prop I, and sex; variables other than CSA explained at most 9%. Body weight and fiber areas explained >50% of the variation in CSA. In conclusion, CSA was the predominant determinant of DF strength, CSA was to a great extent determined by the body weight and the sizes of muscle fibers, and sex differences in Ecc specific strength require further study.
目的是调查中度活跃的年轻男性和女性（n = 30；年龄20 - 31岁）踝背屈肌（DF）力量和大小的决定因素。等速测量向心（Con）和离心（Ecc）力量。使用磁共振成像确定肌肉横截面积（CSA）。从胫骨前肌获取多个活检样本，分别确定I型和II型纤维的总数、面积（区域I和II）和比例（比例I和II），以及肌球蛋白重链（MHC）亚型MHC1、MHC2a和MHC2x的相对含量。与男性相比，女性的向心和离心力量较低（分别低24%和27%；P < 0.01），CSA较小（低19%；P < 0.001），离心DF比肌力（力量/CSA）较低（低10%；P < 0.01），区域I和区域II较小（分别小21%和31%；P < 0.01）。两性的比例I、MHC1、估计的纤维总数和向心DF比肌力相似。向心DF力量高达72%由CSA和比例I决定，离心DF力量高达81%由CSA、比例I和性别决定；CSA以外的变量最多解释9%。体重和纤维面积解释了CSA变异的>50%。总之，CSA是DF力量的主要决定因素，CSA在很大程度上由体重和肌纤维大小决定，离心比肌力的性别差异需要进一步研究。
