Contradictory Tension: Lombard's Paradox in Human Biomechanics

How is it physically possible for a human being to stand up from a seated position, given that the two major muscle groups required to perform the action actually pull the bones in completely opposite directions? This bizarre mechanical contradiction in human anatomy is known in kinesiology as Lombard's Paradox. When you rise from a chair, you must extend both your hip and your knee. However, th...