The crunch strengthens the trunk flexor muscles.
Strengthening the trunk and hip muscles helps to improve gait, which in turn improves the muscle balance around the knee.
In case you cannot see the video, here is a still sequence -
The crunch strengthens the trunk flexor muscles and hip muscles, and helps improve your gait, which in turn improves the muscle balance around your knee.
Lie on your back with your knees bent to support you. Hold a football between your hands high above your head with your arms straight.
Keeping the ball as high as you can, bend the trunk forwards, lifting your head off the pillow, and hold the position for a few seconds.
|Slowly relax, and repeat 5 times.|