1.  Stand against mahcine with the low back pad placed above the belt line. 
2.  Grasp a strap in each hand and place over shoulders comfortably. 
3.  Keeping the arms close to the body, tighten abdomen. 
4.  Curl downward as far as controllable. 
5.  Return slowly to the start position and repeat movement.

Primary Muscles

External Oblique, Rectus Abdominis