The more massive and heavy an athlete, the more the athlete's body mass resist change. So a giant 300 Ib athlete has to produce great muscular force to get his body mass moving. Once moving in particular direction, the athlete must produce an immense amount of muscular force to stop or to change direction. This means that athletes with less body mass have less inertia and need to apply less force to get themselves going. Likewise, they need less force than a more massive athlete to maneuver or stop themselves, once they're on the move.