What makes rowing popular with elite athletes and CrossFitters is exactly what many in the general fitness population dislike about it: your weaknesses cannot be hidden on the rowing machine. It is a human polygraph of physical and mental performance. Stroke for stroke, you are provided with feedback that both reveals any weak spots and very visibly demonstrates the relationship between performance and proper technique.  —Angela Hart, "Rowing Technique," CFJ

The goal is to create positions that maximize efficiency and prevent heel striking, which translates into hitting the brakes.

Though the hip flexors are the primary movers in the GHD sit-up, the abs play a strong role in stabilizing the torso to prevent hyperextension of the spine. This is, in our opinion, a more functional role for the abs than trunk flexion. Carefully introduced and practiced, the GHD sit-up is a potent tool for reeducating the athlete to use the hip flexors more efficaciously and safely.