What is torque? (Credit BASI Pilates)
For most synovial joints, when a muscle contracts it produces rotation of a body segment about the axis going through a joint, resulting in flexion, abduction external rotation, dorsiflexion, or other joint movements. This is termed rotary motion and the effectiveness of a force to produce rotation is termed torque. Torque can be defined as the amount of force multiplied by the moment of force, defined as the perpendicular distance from the line of force to the axis of rotation.
In Pilates mat work, this principle is very important for both exercise effectiveness and safety. In essence, the weight of the limbs is the same, but moving them closer or farther away from the trunk markedly affects the torque they exert and the amount of muscle force that must be generated.
The issue of torque is even more important with the legs because the weight of the legs is so much greater than the arms. So when you perform Hundred, the farther the legs move away. the greater their movement of force and the greater the torque they will generate. This requires the hip flexors to work harder to counterbalance this greater torque.
The required increase in the force of muscle contraction can be quite large because a muscle’s line of force tends to run quite close to joints, resulting in a small moment of force. If the abdominals are not working adequately, this forceful contraction of the hip flexors, particularly the iliopsoas, can anteriorly tilt the pelvis and pull the lumbar spine into hyperextension, a potentially injurious situation for the lower back.
When performing any exercise in which the legs are held off the mat, it is essential that you select a leg height at which you can consistently maintain the stability of the pelvis and lumbar spine to both protect your body from injury and get the most benefit from the exercise.