Define center of mass and explain its relevance to running gait mechanics.

• A. The center of pressure on the foot
• B. The point of highest velocity in running
• C. The seat location of energy supply
• D. The center of mass is the point where mass is evenly distributed and influences balance

Answer: (D)

Center of mass is the point where the body's mass can be considered to be concentrated, acting as the balance point around which gravity and movement occur. In running, where this point moves relative to the foot and the base of support governs stability and how efficiently you move forward. When the COM stays appropriately over the stance foot during the contact phase, the body can transfer energy smoothly, keeping braking forces low and allowing the leg and trunk to work like a spring, storing and releasing energy with less effort. The vertical and forward motion of the COM also shapes posture: a controlled, slight forward lean from the ankles and a cadence that matches leg stiffness help keep the COM on a favorable path. If the COM drifts too far from the base of support, corrective muscular effort is needed, increasing energy cost and the risk of losing balance. Remember, the center of pressure on the foot is a different concept related to where ground reaction forces act, not the mass balance point of the body.