Today’s CrossFit.com Workout of the Day features GHD sit-ups. The primary benefit of the GHD sit-up is to develop the core musculature strength to prevent movement of the spine in a high-force/high-velocity setting. The static contraction of the abdominals is more potent than the dynamic one seen in crunches. However, the spine does not remain completely static throughout the movement; there is some flexion and extension: The athlete extends slightly past neutral at the bottom to take the trunk

Breakdown of the GHD Sit-up "The lesson we’ve drawn from the GHD sit-up is that in spite of the primacy of hip flexors over trunk flexors, or the abs, in this sit-up it recruits the abs powerfully in two ways. First, the movement takes the trunk from hyperextension to full flexion, albeit with negligible load. (No crunch can match this range of motion.) Second, the role of the abs in this sit-up is powerful and largely isometric—i.e., they stabilize the torso from undue extension." Read more abo