D'Antona Giuseppe, Lanfranconi Francesca, Pellegrino Maria Antonietta, Brocca Lorenza, Adami Raffaella, Rossi Rosetta, Moro Giorgio, Miotti Danilo, Canepari Monica, Bottinelli Roberto
Department of Experimental Medicine, Human Physiology unit, University of Pavia, Via Forlanini 6, 27100 Pavia, Italy.
J Physiol. 2006 Feb 1;570(Pt 3):611-27. doi: 10.1113/jphysiol.2005.101642. Epub 2005 Dec 8.
Needle biopsy samples were taken from vastus lateralis muscle (VL) of five male body builders (BB, age 27.4+/-0.93 years; mean+/-s.e.m.), who had being performing hypertrophic heavy resistance exercise (HHRE) for at least 2 years, and from five male active, but untrained control subjects (CTRL, age 29.9+/-2.01 years). The following determinations were performed: anatomical cross-sectional area and volume of the quadriceps and VL muscles in vivo by magnetic resonance imaging (MRI); myosin heavy chain isoform (MHC) distribution of the whole biopsy samples by SDS-PAGE; cross-sectional area (CSA), force (Po), specific force (Po/CSA) and maximum shortening velocity (Vo) of a large population (n=524) of single skinned muscle fibres classified on the basis of MHC isoform composition by SDS-PAGE; actin sliding velocity (Vf) on pure myosin isoforms by in vitro motility assays. In BB a preferential hypertrophy of fast and especially type 2X fibres was observed. The very large hypertrophy of VL in vivo could not be fully accounted for by single muscle fibre hypertrophy. CSA of VL in vivo was, in fact, 54% larger in BB than in CTRL, whereas mean fibre area was only 14% larger in BB than in CTRL. MHC isoform distribution was shifted towards 2X fibres in BB. Po/CSA was significantly lower in type 1 fibres from BB than in type 1 fibres from CTRL whereas both type 2A and type 2X fibres were significantly stronger in BB than in CTRL. Vo of type 1 fibres and Vf of myosin 1 were significantly lower in BB than in CTRL, whereas no difference was observed among fast fibres and myosin 2A. The findings indicate that skeletal muscle of BB was markedly adapted to HHRE through extreme hypertrophy, a shift towards the stronger and more powerful fibre types and an increase in specific force of muscle fibres. Such adaptations could not be fully accounted for by well known mechanisms of muscle plasticity, i.e. by the hypertrophy of single muscle fibre (quantitative mechanism) and by a regulation of contractile properties of muscle fibres based on MHC isoform content (qualitative mechanism). Two BB subjects took anabolic steroids and three BB subjects did not. The former BB differed from the latter BB mostly for the size of their muscles and muscle fibres.
从5名男性健美运动员（BB，年龄27.4±0.93岁；平均值±标准误）的股外侧肌（VL）获取针吸活检样本，这些运动员进行肥大性抗阻训练（HHRE）至少2年，同时从5名活跃但未受过训练的男性对照受试者（CTRL，年龄29.9±2.01岁）获取样本。进行了以下测定：通过磁共振成像（MRI）在体内测定股四头肌和VL肌肉的解剖横截面积和体积；通过SDS-PAGE测定整个活检样本的肌球蛋白重链异构体（MHC）分布；通过SDS-PAGE根据MHC异构体组成对大量（n = 524）单根去皮肌纤维进行分类，测定其横截面积（CSA）、力量（Po）、比力（Po/CSA）和最大缩短速度（Vo）；通过体外运动分析测定纯肌球蛋白异构体上的肌动蛋白滑动速度（Vf）。在BB组中观察到快速纤维尤其是2X型纤维的优先肥大。体内VL的巨大肥大不能完全由单根肌纤维肥大来解释。实际上，BB组体内VL的CSA比CTRL组大54%，而BB组的平均纤维面积仅比CTRL组大14%。BB组的MHC异构体分布向2X纤维偏移。BB组1型纤维的Po/CSA显著低于CTRL组的1型纤维，而BB组的2A和2X型纤维均比CTRL组明显更强。BB组1型纤维的Vo和肌球蛋白1的Vf显著低于CTRL组，而快速纤维和肌球蛋白2A之间未观察到差异。研究结果表明，BB组的骨骼肌通过极度肥大、向更强有力的纤维类型转变以及肌纤维比力增加，显著适应了HHRE。这种适应性不能完全由众所周知的肌肉可塑性机制来解释，即单根肌纤维肥大（定量机制）以及基于MHC异构体含量对肌纤维收缩特性的调节（定性机制）。5名BB受试者中有2人服用合成代谢类固醇，3人未服用。前一组BB受试者与后一组BB受试者的主要区别在于他们肌肉和肌纤维的大小。
