Phytoecdysteroids, especially 20-hydroxyecdysone found in plants like Spinacia oleracea (spinach) and Rhaponticum carthamoides, have attracted interest for their potential to support muscle health and growth. Scientific studies, mainly in animal models and in vitro experiments, suggest that phytoecdysteroids may enhance protein synthesis in skeletal muscle and reduce protein breakdown, which could theoretically promote muscle growth and improve physical performance. For example, a 2008 study published in Phytomedicine demonstrated increased grip strength and muscle mass in rats supplemented with ecdysterone compared to controls. In vitro studies (e.g., Gorelick-Feldman et al., 2008) have shown increased protein synthesis in muscle cells exposed to phytoecdysteroids.

Human data, however, is limited and generally of low quality. A randomized controlled trial by Isenmann et al. (2019, Archives of Toxicology) found that ecdysterone supplementation during resistance training increased muscle mass and strength in young men compared to placebo, but the sample size was small and further research is needed. Overall, while there is some early scientific evidence suggesting a positive effect of phytoecdysteroids on muscle mass, the evidence is not robust or consistent enough to warrant a high rating. The use is therefore based on preliminary scientific findings rather than established tradition or strong clinical validation.