Antrodia camphorata (AC) is a rare and unique mushroom that is difficult to cultivate. Previous studies have demonstrated the bioactivity of the compound Ergosta-7,9(11),22-trien-3β-ol (EK100) from AC in submerged culture. The purpose of this study is to evaluate the potential beneficial effects of EK100 on fatigue and ergogenic functions following physiological challenge. Male ICR (Institute of Cancer Research) mice were randomly divided into three groups (n = 8 per group) and orally administered EK100 for six weeks at 0 (Vehicle), 10 (EK100-1X), and 20 (EK100-2X) mg/kg/day. The six-week Ek100 supplementation significantly increased grip strength (p = 0.0051) in trend analysis. Anti-fatigue activity was evaluated using 15-min. acute exercise testing and measuring the levels of serum lactate, ammonia, glucose, blood urea nitrogen (BUN), and creatine kinase (CK) after a 15-min. swimming exercise. Our results indicate that AC supplementation leads to a dose-dependent decrease in serum lactate, ammonia, BUN, and CK activity after exercise and significantly increases serum glucose and glycogen content in liver tissues. Biochemical and histopathological data demonstrated that long term daily administration of EK100 for over six weeks (subacute toxicity) was safe. EK100’s anti-fatigue properties appear to be through the preservation of energy storage, increasing blood glucose and liver glycogen content, and decreasing the serum levels of lactate, ammonia, BUN, and CK. EK100 could potentially be used to improve exercise physiological adaptation, promote health, and as a potential ergogenic aid in combination with different nutrient strategies.