雄性激素受體對於肌肉肥大之影響：敘述性文獻回顧

研究對於運動引起肌肉肥大（muscle hypertrophy）的背後機制在過去幾十年裡主要圍繞在合成性賀爾蒙的濃度變化，尤其是睪固酮（testosterone）受到最多關注。然而睪固酮必須先與雄性激素受體（androgen receptor, AR）結合，才能夠進入細胞核內展開後續一連串的肌肉蛋白生合成反應。因此AR在調節肌肉增長上扮演著至關重要的角色。本文章的目的是要去探討AR究竟是如何去影響運動引起肌肉肥大的過程。經文獻回顧後發現，無論合成性賀爾蒙的濃度為何，AR的增加與肌肉增長之間均呈顯著正相關，這是因為AR對睪固酮的親和力並不受睪固酮濃度所影響，所以增加AR是唯一能夠提升肌肉對睪固酮敏感性的方式，但是若是抑制AR大部分的肌肉肥大效果就會被抵消。此外，AR在肌肉中還具有選擇性增加、調節肌纖維類型與影響肌肉細胞增生的能力，透過攝取不同營養素以及阻力訓練的方式有利於身體製造更多AR，增加血液睪固酮的利用，而人工合成的AR調節劑的出現也代表只要合成的配體能與AR結合，肌肉蛋白的生合成反應就能被開啟，因此AR可以說是整個肌肉增長機制中最關鍵的因子之一。綜合這些研究，我們認為想要增長肌肉就必需先提高AR的濃度。未來還需要更多研究去探討其他能夠增加AR或是改變AR活性的方式。

Researches on the mechanism behind exercise-induced muscle hypertrophy have been predominantly revolving around variations in the concentration of anabolic hormones, with testosterone drawing the most attention, in the past decades. However, testosterone proposed to enter nucleus activating series of muscle protein synthesis reactions only via binding with androgen receptors (AR). Therefore, AR may play a crucial role in mediating muscle growth. The purpose of this review is to explore how AR influences the process of exercise-induced muscle hypertrophy. After conducting a literature review, it has been found that regardless of the concentration of anabolic hormones, there is a significant positive correlation between the increase in AR level and muscle growth. The affinity of AR to testosterone is independent from the concentration of testosterone. Hence, the only way to enhance muscle sensitivity to testosterone is by increasing AR. On the other hand, inhibiting AR may largely counteract the effect of muscle hypertrophy. Furthermore, AR in muscles also demonstrates the ability of increasing selectively, regulating muscle fiber types and influencing muscle cells proliferation. Through consuming different nutrients and resistance training, the body is able to produce more AR to increase the utilization of testosterone in blood. The arrival of artificially synthesized AR modulators indicates that as long as the synthesized ligand is able to bind with AR, the muscle protein synthesis reactions can be initiated. Thus, AR is considered one of the most critical factors in the entire mechanism of muscle growth. Based on the studies included in this review article, it is believed that elevating the concentration of AR in precedence is essential for muscle growth. Further research is much in need to investigate additional methods capable of increasing AR level or modifying AR activity.