What does the leg carry trunk model describe?

• A. When you don’t have enough ground reaction force, your muscle will need to generate more force (jumping from hard surface vs. soft surface)
• B. Leg muscles stabilize the trunk independently of surface hardness
• C. Ground reaction force always reduces muscle demand
• D. Legs primarily absorb impact without altering trunk dynamics

Answer: (C)

The leg carry trunk model describes how the ground reaction force generated through the leg supports the trunk, reducing the active effort required from trunk muscles. When the foot contacts the ground, the reaction force travels up the leg and helps carry the trunk’s load and deceleration, so the trunk-stabilizing muscles don’t have to work as hard. This is why ground reaction force tends to reduce muscle demand for the trunk. The idea that stabilization is independent of surface hardness isn’t correct because the force transmitted through the leg changes with the surface, and the trunk’s load is shared with the leg-ground system rather than being managed solely by trunk muscles. It also isn’t accurate to say legs merely absorb impact without affecting trunk dynamics; the trunk’s movement and stabilization are influenced by how the leg and ground interact.