Get in the half-sit-up position with your feet anchored. Maintaining this half sit-up position while doing any movement with the arms will challenge the abs, and this one hits the delts as well.
Try to keep your spine and neck as neutral as possible. Go light and do the exercise for one continuous minute, or go a bit heavier and aim for 10-15 reps.
It's a very common problem; almost an epidemic, you could say. This may not be comforting, and it may be something you've heard before, but, "it happens to a lot of guys."
Matt Phelps is hugely pissed about the term "failure" and what it really means. He thinks exercise physiologists have one idea while the guys in the trenches, i.e., the guys in the gym, have a different, more realistic idea.