Arginine creatine, typically referring to either a combination of the amino acid L-arginine and creatine, or to creatine bound to arginine, is most often used in sports nutrition to support muscle performance and potentially muscle tone. The scientific evidence supporting its use for improving muscle tone (defined clinically as the resting tension in muscle) is moderate but not definitive.

Creatine supplementation is well-established in scientific literature for its role in increasing muscle phosphocreatine stores, leading to improved strength, power output, and muscle mass with resistance training. These adaptations can indirectly improve muscle tone, especially in individuals with low baseline muscle mass or tone, such as older adults or those in rehabilitation. Multiple high-quality studies and meta-analyses confirm creatine's efficacy for increasing lean body mass and strength, though direct evidence on passive muscle tone per se is less robust.

L-arginine is a precursor to nitric oxide, which can enhance blood flow, but evidence for its direct impact on muscle mass or tone is weaker. Combinations of creatine with arginine have not shown clear superiority over creatine alone in clinical trials.

In summary, scientific evidence moderately supports the use of creatine (and by extension, arginine creatine) for improving muscle characteristics that may relate to tone, although direct research on muscle tone (as opposed to mass or strength) is limited.