Explain how base of support and line of gravity influence balance in a dynamic movement, and give an example.

• A. Balance is unaffected by base of support; only strength matters.
• B. A wide base of support and maintaining a vertical line of gravity over it improve balance; example: landing from a jump with slightly bent knees to maintain COM over the base.
• C. Maintaining the line of gravity outside the base improves balance.
• D. A narrow base with deliberate leaning always improves balance.

Answer: (B)

Balance in dynamic movement hinges on where the center of mass sits relative to the base of support. The base of support is the area covered by the parts of the body in contact with the ground, usually the feet, and the line of gravity is the vertical line straight down from the center of mass. When this vertical line passes through the base of support, the body remains stable because gravitational torque keeps you upright and easily allows small adjustments to stay balanced during movement.

A wider base of support expands the area within which the line of gravity can fall while still maintaining balance. This makes it easier to control your body during actions like landing or changing direction, because you have more room to keep the COM above the feet and absorb forces without tipping.

For example, landing from a jump with the knees slightly bent helps keep the center of mass over the base of support. The knee bend lowers and cushions the body, allowing quick adjustments to keep the vertical line of gravity within the contact area of the feet. This absorbs impact and maintains balance, whereas a stiff, extended-knee landing can shift the line of gravity outside the base and make balance harder to regain.

So the correct idea is that a wider base of support, with the line of gravity staying over it, supports balance in dynamic movement; moving away from this—such as narrowing the base or leaning with the line outside the base—reduces stability.