九、肌 肉
氧运输到肌肉的最后一步，是毛细血管中的血红蛋白将氧运载至肌细胞线粒体。高海拔原住民的肌肉肌纤维类型和正常毛细血管密度与高加索人相似，而肌纤维截面积减少；后者可增强肌纤维收缩时对流和扩散的氧流量[79]。Gelfi等人（2004）用蛋白质组学法，比较了世居高海拔藏族人和生长在低海拔藏族人的肌肉差异，与低海拔组相比，生长在高海拔的藏族人体内对清除自由基有重要作用的化合物更多。高海拔组的机体通过特定的代谢适应来避免活性氧诱导的组织损伤[80]。与蜂鸟飞行肌相似，夏尔巴人的丙酮酸激酶和乳酸脱氢酶的肌比高达1.4，更好地保证了丙酮酸在线粒体中的代谢，因为该组织需要特别高的三磷酸腺苷（Adenosine triphosphate，ATP）转换率[81]。
研究者将居住在海拔3 000 m、3 700 m和4 500 m处藏族人的肌肉肌红蛋白基因多态性与平原人进行了比较，发现藏族人肌红蛋白79A等位基因的频率高于海平面居民[82]。然而，由于藏族人等位基因频率与海拔梯度研究没有关联，79A等位基因是否与海拔适应优势有关仍有待研究[83]。
总的来说，在高海拔地区，藏族人和夏尔巴人确实比平原人拥有更好的有氧运动能力，这一点可以通过生理调节来解释，生理上的调节使他们在低氧环境仍能维持较强的有氧能力。藏族和夏尔巴人这一优势是基于不同的低氧通气调节、较低的低氧肺血管收缩反应、更好的肺功能、更高的最大心输出量、更高水平的血氧饱和度以及更好的睡眠质量。这些差异明显建立在遗传基础上，不过其机制仍有待进一步解释。
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