An emphasis is always placed on core exercises (anterior abdominals) over any type of exercise when it comes to training runners. Unfortunately little attention is paid to the low back (specifically low back pain exercises) , glutes, or hip flexors. Without strong glutes and a low back that can support ones self properly. The hamstrings will not be able to generate enough force / power even though you might place particular attention to strengthen these three muscles.
A key when training or working out in any sport is that any one muscle is only as strong as the weakest link in the entire kinetic chain. The kinetic chain being a term used by most sports medicine and exercise science professionals to describe a sequence or a chain of events. In this case multiple muscles engaging to complete motion of the skeletal system.
The curl-up done on an exercise ball dramatically increases the number of muscles that have to engage and stabilize you during the exercise. This exercise will activate your COMPLETE core -> back muscles (posterior abdominals) and all the abdominal muscles.
The key point to performing low back pain exercises, such as this one is to only curl-up as far as the contraction / activation / tightening of your abdominal muscles and flex forward no further. Note no pressure should be placed on your neck by your arms. Perform 3 sets of 20 for a total core workout.
If you wish to make things more difficult push out abs while trying to curl-up or let a little more air out of the ball to force more contraction of low back muscles, glutes, and other leg muscles for stabelizing your body while performing the exercise.
If you have any questions please email me at drshepard@bnchiro.com