Skating

What makes hockey different from your average sport is the surface it is played on. Hockey is played on ice which offers minimal friction. The simplest mode of linear motion is moving with your feet straight forward in the direction of motion. Since ice has very low friction you can't speed up by running with your feet forward, that means hockey players have to move by a series of sideways pushes. During each stroke one skate makes contact with the ice for the push off while the other is raised and moved ahead before gliding on the ice. As a hockey player gains speed, the velocity of his pushing leg relative to the ice decreases. This reduces the amount of push force that he can exert on the ice.

In the Free Body diagram above it shows that leaning forward allows the leg to put a greater amount of force. When a player speeds up, his center of gravity moves ahead of the point of contact with the ice, where the normal force is applied.