As sport coaches, I think we can unanimously agree that not many sport movement patterns involve a strict forward flexion (shoulders moving toward the waist). The only time I can think of at this moment is when athletes are tying their shoes, skates, etc. With this knowledge, it would seem that this motion is not something that needs to be trained repetitively. If we can all agree this is not an important action, why do we still see athletes train with their backs on the ground doing sit ups, crunches, etc? I'm not sure we can come up with a good answer as quickly. The truth is there are better ways to train the core musculature (involving a complex set of muscles not just the rectus abdominis). One of these ways is in the vertical, or standing, position. Here are three exercises that will load the "core" in a vertical positon rather than on the ground, not to mention save your lower back from excessive and unnecessary shearing force.
1.) Belly Press (Pallof Press)- Stand Perpendicular to a Cable Column and grip both hands around a conventional cable column handle at belly button height. Press the handle in a straight line away from your body and do not rotate through your hips or shoulders. Repeat for repetitions or hold for time.
2.) Landmines- There are a lot of variations to this exercise, but basically all you need to do is stand away from the bar holding the bar and allow the bar to move to one side while maintaining the same position with your shoulders and hips, so again not moving. When you feel your core working return to the middle and repeat on the other side. Complete repetitions.
3.) Stability Bar Press- In the same position as the Belly Press, but with a straight bar, pull the bar across your body and push straight out with the hand closest to the cable column, maintain proper posture throughout the exercise and repeat for repetitions.
Sorry there are not any videos for these exercises, I am still experimenting with the format, when I find out how I will post videos to go along with the explanations, all of these are on youtube.com if you want to see them being performed. Thanks for reading today.