What is the cause of a 'bouncing' with marked vertical swaying at maximum velocity?

• A. Push-off force directed too vertically.
• B. Inadequate knee drive.
• C. Slow arm swing.
• D. Foot strike too far in front of center of mass.

Answer: (A)

At max-sprint speed you want the ground reaction force to push you forward rather than lift you up. When the push-off is directed too vertically, most of that force goes into raising the body's center of mass rather than driving it forward. The result is a pronounced vertical bounce and a swaying of the body with each step, which wastes energy and reduces forward velocity. That’s why a vertical push-off best explains the described pattern.

Inadequate knee drive would limit forward propulsion but doesn’t inherently cause the repeated vertical bouncing. Slow arm swing can affect tempo and coordination but isn’t the primary driver of vertical oscillation. Foot strike too far in front of the center of mass tends to create braking, hindering forward progress rather than producing the vertical bounce seen at maximum velocity.