肌酸是一种由肝脏、肾脏和胰腺每日合成约1克的化合物，其中超过95%储存在骨骼肌中，形式为磷酸肌酸，用于再生三磷酸腺苷（ATP）以驱动肌肉收缩、神经信号和蛋白质合成。其余不足5%存在于大脑和睾丸组织中。标准补充剂为肌酸单水合物，每日剂量3至5克，是研究最多、效果最确切且成本最低的形式。其他衍生形式（如盐酸肌酸、柠檬酸肌酸、乙酯肌酸等）未显示任何额外效益。高剂量“加载期”无长期优势，可能增加肾脏负担。临床数据显示，短期与长期使用均安全，仅可能引起短暂性水潴留、轻度腹胀或胃部不适。

肌酸在高强度、短时间的运动中最有效，如短跑、举重与高强度间歇训练。其机制是磷酸肌酸将磷酸基团提供给腺苷二磷酸（ADP），迅速再生ATP，从而提升爆发力。对耐力运动影响较小。研究显示，它还可增加肌肉糖原储备，促进恢复。肌酸不直接促进肌肉生长，但结合抗阻训练与营养摄入可维持肌力与瘦体重，对老年人或受伤康复者尤为重要。女性在围绝经期和绝经期每年流失1至2%的肌肉质量，补充肌酸可帮助延缓肌肉和骨质退化，尤其由于女性基础肌肉量较低，反应可能更显著。

新兴证据表明，肌酸对脑部健康亦具潜在益处，可减少精神疲劳、改善睡眠剥夺或高压环境下的认知表现，并可能通过支持脑能量代谢与增加多巴胺、血清素水平减轻抑郁症状。对于女性在雌激素波动期出现的情绪和认知问题尤为相关。肌酸补充剂的安全性高，但18岁以下人群及肾病患者应避免使用。由于美国食品药品监督管理局不监管膳食补充品的纯度，建议选择经过第三方检测的品牌，如Thorne（5克/份，四重检测）、Nutricost（100份装，5克/勺）及Peach Perfect（每份5克肌酸+1克胶原+1克BCAA）。

Creatine is a compound synthesized by the liver, kidneys, and pancreas at about 1 gram per day, with over 95% stored in skeletal muscle as phosphocreatine for regenerating adenosine triphosphate (ATP), the molecule driving muscle contraction, neural signaling, and protein synthesis. Less than 5% resides in brain and testicular tissue. The standard supplement form, creatine monohydrate, is the most studied, effective, and inexpensive, typically taken at 3–5 grams per day. Other variants (e.g., hydrochloride, citrate, ethyl ester) show no added benefit. High-dose “loading” offers no sustained gain and may burden the kidneys. Clinical trials confirm safety over both short and long durations, with minor side effects limited to transient water retention, mild bloating, or stomach discomfort.

Creatine most benefits short, high-intensity efforts such as sprinting, weightlifting, and high-intensity interval training, where phosphocreatine donates phosphate to adenosine diphosphate (ADP) for rapid ATP regeneration and power output. It has limited relevance for endurance sports. Studies suggest it increases muscle glycogen storage, aiding recovery. While it doesn’t directly grow muscle, combined with resistance training and adequate nutrition, it maintains strength and lean mass, especially important for aging adults or during rehabilitation. Women in perimenopause and menopause lose 1–2% of muscle mass annually, and supplementation can slow muscle and bone decline; due to lower baseline muscle, women may respond more strongly.

Emerging research links creatine to cognitive and mood benefits, including reduced mental fatigue, improved performance under stress or sleep deprivation, and enhanced memory in low-creatine groups such as vegetarians or the elderly. It may also mitigate depressive symptoms via improved brain energy and neurotransmitter balance, especially during estrogen fluctuations. Though generally safe, it is not recommended for those under 18 or with kidney disease. Since the FDA does not regulate supplement purity, third-party-tested products are advised, notably Thorne (5 g/serving, quadruple-tested), Nutricost (100 servings, 5 g/scoop), and Peach Perfect (5 g creatine plus 1 g collagen and 1 g BCAA per serving).