So let’s review a huge list of abdominal exercise substitutions:
1) Replace crunches with:
Planks, mountain climbers, and stability ball jackknives
2) Replace cross-crunches (i.e. twisting or oblique crunches) with:
Side planks and cross-body mountain climbers
3) Replace sit-ups with:
Stability ball jackknives, stability ball planks, stability ball pikes, stability ball rollouts, and hanging knee raises.