Rectus abdominis activity increases when which muscles are actively flexing the hip?

Rectus abdominis activity increases when which muscles are actively flexing the hip?

• A. Ankle plantar flexors
• B. Hip flexors
• C. Knee flexors
• D. Hip abductors

Answer: (B)

When the hip is actively flexed, the body needs the trunk to stay stable so the leg can lift smoothly. The rectus abdominis increases its contraction to brace the abdominal wall, support the spine, and maintain proper posture as the hip flexors pull the leg upward. This stabilization (and the slight rise in intra-abdominal pressure that comes with it) gives the hip flexors a solid base to work against and helps prevent unwanted movement of the trunk. The other muscle groups listed don’t create that same stabilization demand during hip flexion. Ankle plantar flexors act far from the hip, knee flexors mainly influence knee motion, and hip abductors move the leg sideways rather than assist with the sagittal-plane hip flexion that requires abdominal stabilization.

When the hip is actively flexed, the body needs the trunk to stay stable so the leg can lift smoothly. The rectus abdominis increases its contraction to brace the abdominal wall, support the spine, and maintain proper posture as the hip flexors pull the leg upward. This stabilization (and the slight rise in intra-abdominal pressure that comes with it) gives the hip flexors a solid base to work against and helps prevent unwanted movement of the trunk.

The other muscle groups listed don’t create that same stabilization demand during hip flexion. Ankle plantar flexors act far from the hip, knee flexors mainly influence knee motion, and hip abductors move the leg sideways rather than assist with the sagittal-plane hip flexion that requires abdominal stabilization.