Why is it recommended that you flex your knees and hips when lifting a heavy object rather than just flexing your hips and back?
1. Flexing at the knees and hips increases the overall vertical force.
2. Flexing at the knees and hips decreases the overall vertical force.
3. Flexing at the knees and hips decreases the resistance arm and torque at the lumbar spine.
4. Flexing at the knees and hips increases the resistance arm and torque at the lumbar spine.