Extended leg and trunk form which type of position along the body's long axis?

• A. Power line
• B. Bent line
• C. Straight line
• D. Rounded line

Answer: (A)

When the leg is extended and the trunk stays aligned with the body's long axis, the body forms a straight line from foot to head, often called the power line. This alignment lets the ground reaction force be directed almost straight backward through the body, maximizing forward propulsion and minimizing energy wasted in bending or collapsing the torso. Keeping the leg extended creates a longer push and the stacked trunk keeps the hips, knees, and ankles in sync, so force is transferred efficiently into forward movement. A bent line means joints create angles that disrupt smooth force transfer, and a rounded line shows undue curvature of the spine or pelvis, which also reduces propulsion. So the straight-line, power line position best supports powerful sprinting.