Human Functions Test 1 Practice Exam 2026 – Complete Study Resource

The primary muscle group responsible for knee extension during sit-to-stand is the quadriceps. When you push to stand, the quadriceps contract concentrically to straighten the knee, lifting your body up by extending the lower leg at the knee joint. They attach through the patellar tendon to the tibia, creating the extension torque needed to rise. The gluteus maximus mainly powers hip extension and pelvic stability, helping the overall rise but not driving knee extension. The hamstrings cross the knee and tend to flex the knee, so they don’t provide the main force to straighten the leg; they may help control movement or assist at times, but the quadriceps are the primary knee extensor. The core stabilizes the trunk, ensuring efficient transfer of force but not contributing directly to knee extension.