Advance, advance, advance. Whenever you begin to master any exercise, ask yourself, “How can I make this movement harder?” Always keep advancing. Always take that next step in an exercise’s progression to keep your muscles guessing—and growing.
When it comes to the plank—the best basic stability exercise for your rectus abdominus and transverse abdominus muscles—an easy way to take things to the next level involves the use of a Swiss ball and a flat bench. Try the following learning progression
Conventional plank on the floor, with your weight on your forearms and your toes.
Plank with your forearms on a Swiss ball and your toes on the floor.
Plank with your forearms on a Swiss ball and your toes on a flat bench.
Do the advanced version, then reach out, using your abs to keep your body in one rigid line.