Safety of abdominal exercises

Abdominal exercises also put some degree of compressive force on the lumbar spine, putting unwanted stress on the lower back. In addition, exaggerated abdominal exercise can cause respiratory problems. A study of twelve exercises concluded that no single exercise covered all abdominal muscles with high intensity and low compression.

High challenge-to-compression ratio Crunch with feet anchored Crunch with feet free Bicycle crunch Hanging straight leg raise	Low compression, lower challenge Crunch with feet anchored Crunch with feet free
High challenge, higher compression Straight-leg sit-up Bent-leg sit-up	Low challenge-to-compression ratio (not recommended!) Supine straight-leg raise Supine bent-leg raise Hanging bent-leg raise Static cross-knee crunch

The benefit of focused training on the "deep core" muscles such as the transversus abdominis has been disputed, with some experts advocating a more comprehensive training regimen.