Sumo wrestlers are a group of athletes who have high levels of fat mass and fat-free mass, not often observed in most other forms of competitive sports. Research on Sumo wrestlers may provide insight into weight gain to enhance sports performance. Regarding the energy balance of Sumo wrestlers, energy intake exceeds energy expenditure over a considerable period, for gaining weight, since Sumo wrestlers that have greater body mass possess one of the most effective ways to win. In fact, Sumo wrestlers have body weights in excess of 100 kg, with fat mass in excess of 30 kg and fat-free mass greater than 80 kg. Additionally, percent fat of the upper-leagues wrestlers ("Sekitori") remained at about 25%, and fat-free mass and the force generation capability was larger in the upper-leagues wrestlers than in the lower-leagues wrestlers. Sumo wrestlers, especially Sekitori wrestlers, can be considered to be athletes.