Caffeine is worldwide used for its power to increase cognitive and physical performance. The ergogenic effects of caffeine, however, do not depend on a direct action on muscles. Actually, the actions of caffeine on skeletal muscles, take place at millimolar concentrations which are far above the micromolar level reached after a regular consumption of coffee or similar drinks, and close to a lethal concentration. At millimolar concentrations caffeine exerts a powerful effect on sarcoplasmic reticulum (SR) activating the release of calcium via ryanodine receptors and, possibly, inhibiting calcium reuptake. For this reason caffeine has become a valuable tool for studying SR function and for diagnostics of SR related muscle disorders. This review aims to briefly describe the effects and the mechanism of action of caffeine on sarcoplasmic reticulum and to focus on its use to study intracellular calcium dynamics in human muscle fibers in physiological and pathological conditions.

中文翻译：

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咖啡因作为研究人体骨骼肌肌质网和细胞内钙动力学的工具。

咖啡因因其增强认知和身体机能的能力而在全球范围内使用。然而，咖啡因的增效作用并不依赖于对肌肉的直接作用。实际上，咖啡因对骨骼肌的作用是在毫摩尔浓度下发生的，该浓度远高于经常饮用咖啡或类似饮料后达到的微摩尔浓度，并且接近致死浓度。在毫摩尔浓度下，咖啡因对肌质网 (SR) 具有强大的作用，通过兰尼碱受体激活钙的释放，并可能抑制钙的再摄取。出于这个原因，咖啡因已成为研究 SR 功能和诊断 SR 相关肌肉疾病的宝贵工具。