Eurycoma longifolia, commonly known as Tongkat Ali, has garnered attention for its potential to support muscle health, particularly in the context of exercise and physical performance. The scientific basis for its use in supporting the muscles body system centers around its reported effects on testosterone levels and body composition. Several small-scale human studies and animal research suggest that supplementation with Eurycoma longifolia extract may increase serum testosterone, which in turn supports muscle mass and strength, especially in individuals experiencing age-related testosterone decline or those engaged in resistance training. For example, a randomized, double-blind, placebo-controlled study published in the Journal of the International Society of Sports Nutrition (2013) found that subjects taking Eurycoma longifolia extract experienced increased muscle strength compared to placebo after five weeks of supplementation. Other studies have noted reductions in body fat and improvements in lean body mass, although findings are not universally consistent and more robust, large-scale trials are warranted. The proposed mechanisms include stimulation of endogenous testosterone production and reduction of cortisol, both of which may influence muscle growth and recovery. While traditional use has focused on general vitality and sexual health, current scientific evidence provides moderate support (rating 3/5) for Eurycoma longifolia as a supplement to aid muscle strength and body composition in specific populations.