Ørtenblad Niels, Nielsen Joachim, Boushel Robert, Söderlund Karin, Saltin Bengt, Holmberg Hans-Christer
Department of Sports Science and Clinical Biomechanics, SDU Muscle Research Cluster, University of Southern Denmark, Odense, Denmark.
School of Kinesiology, University of British Columbia, Vancouver, BC, Canada.
Front Physiol. 2018 Aug 2;9:1031. doi: 10.3389/fphys.2018.01031. eCollection 2018.
As one of the most physically demanding sports in the Olympic Games, cross-country skiing poses considerable challenges with respect to both force generation and endurance during the combined upper- and lower-body effort of varying intensity and duration. The isoforms of myosin in skeletal muscle have long been considered not only to define the contractile properties, but also to determine metabolic capacities. The current investigation was designed to explore the relationship between these isoforms and metabolic profiles in the arms () and legs () as well as the range of training responses in the muscle fibers of elite cross-country skiers with equally and exceptionally well-trained upper and lower bodies. The proportion of myosin heavy chain (MHC)-1 was higher in the leg (58 ± 2% [34-69%]) than arm (40 ± 3% [24-57%]), although the mitochondrial volume percentages [8.6 ± 1.6 (leg) and 9.0 ± 2.0 (arm)], and average number of capillaries per fiber [5.8 ± 0.8 (leg) and 6.3 ± 0.3 (arm)] were the same. In these comparable highly trained leg and arm muscles, the maximal citrate synthase (CS) activity was the same. Still, 3-hydroxy-acyl-CoA-dehydrogenase (HAD) capacity was 52% higher ( < 0.05) in the leg compared to arm muscles, suggesting a relatively higher capacity for lipid oxidation in leg muscle, which cannot be explained by the different fiber type distributions. For both limbs combined, HAD activity was correlated with the content of MHC-1 ( = 0.32, = 0.011), whereas CS activity was not. Thus, in these highly trained cross-country skiers capillarization of and mitochondrial volume in type 2 fiber can be at least as high as in type 1 fibers, indicating a divergence between fiber type pattern and aerobic metabolic capacity. The considerable variability in oxidative metabolism with similar MHC profiles provides a new perspective on exercise training. Furthermore, the clear differences between equally well-trained arm and leg muscles regarding HAD activity cannot be explained by training status or MHC distribution, thereby indicating an intrinsic metabolic difference between the upper and lower body. Moreover, trained type 1 and type 2A muscle fibers exhibited similar aerobic capacity regardless of whether they were located in an arm or leg muscle.
作为奥运会中对体能要求最高的运动项目之一，越野滑雪在不同强度和持续时间的上下肢联合用力过程中，在力量产生和耐力方面都带来了相当大的挑战。长期以来，骨骼肌中的肌球蛋白同工型不仅被认为可以定义收缩特性，还能决定代谢能力。本研究旨在探讨这些同工型与手臂（）和腿部（）代谢特征之间的关系，以及上肢和下肢训练水平相当且极高的精英越野滑雪运动员肌肉纤维的训练反应范围。腿部肌球蛋白重链（MHC）-1的比例（58±2%[34 - 69%]）高于手臂（40±3%[24 - 57%]），尽管线粒体体积百分比[腿部为8.6±1.6，手臂为9.0±2.0]以及每根纤维的平均毛细血管数量[腿部为5.8±0.8，手臂为6.3±0.3]相同。在这些训练水平相当的腿部和手臂肌肉中，柠檬酸合酶（CS）的最大活性相同。然而，腿部肌肉中3 - 羟基 - 酰基辅酶A脱氢酶（HAD）的能力比手臂肌肉高52%（<0.05），这表明腿部肌肉中脂质氧化能力相对较高，而这无法用不同的纤维类型分布来解释。对于上下肢综合来看，HAD活性与MHC - 1的含量相关（=0.32，=0.011），而CS活性则不然。因此，在这些训练有素的越野滑雪运动员中，2型纤维的毛细血管化程度和线粒体体积至少可以与1型纤维一样高，这表明纤维类型模式与有氧代谢能力之间存在差异。具有相似MHC特征的氧化代谢的显著变异性为运动训练提供了新的视角。此外，训练水平相当的手臂和腿部肌肉在HAD活性方面的明显差异无法用训练状态或MHC分布来解释，从而表明上肢和下肢存在内在的代谢差异。而且，训练有素的1型和2A型肌肉纤维，无论位于手臂还是腿部肌肉，都表现出相似的有氧能力。
