Rather than shooting for 50 or 70 or whatever, just get to where you can do all 100 w/out stopping...
One good workout is to hold yourself at a 45 degree angle and tense your abs and just hold it as long as you can. If you feel it in your back or your legs, adjust your angle.
One good workout is to hold yourself at a 45 degree angle and tense your abs and just hold it as long as you can. If you feel it in your back or your legs, adjust your angle.