People seek a greater quality of life and healthy aging that culminates in improved self-esteem and vitality in the performance of daily activities; this is generating a growing number of people enrolled in gyms in search of quick results. However, this training can result in physical and metabolic damage. During physical exercise, under conditions of oxidative stress, changes take place that lead to the onset of fatigue. The Agaricus brasiliensis mushroom is native to Brazil and has therapeutic potential, with widely studied antioxidant and immunomodulatory capabilities. However, little is known about its potential benefits regarding muscular strength. Therefore, this study evaluated the possible effects of supplementation with this mushroom with respect to strength performance before and after a resistance training session. A blinded randomized trial was performed with male volunteers (n = 5) randomly divided into 2 groups (placebo and treatment with A. brasiliensis). Perceptions of muscle soreness and performance were assessed before and after high-intensity resistance training sessions. The study was executed over a 24-day period. Promising results were found related to intrasession rapid strength, most likely a result of antioxidant action and redox balance. The bioactive compounds in A. brasiliensis revealed the potential to improve conditions of muscle fatigue without altering other parameters. Thus, this mushroom has become a target of great expectations in the fields of fitness and athletics.