Are crunches and sit-ups effective?

They build abdominal muscle but don't reveal it — visibility depends on body fat. Planks, dead bugs, and carries train the core more functionally and are gentler on the lumbar spine.

Visible abs are mostly a body fat matter. Training abs increases thickness but does not remove the layer covering them.

Planks, dead bugs, bird dogs, hanging leg raises and loaded carries train the core against real-world demands and are gentler on the lower back than high-rep crunches.