10 exercises that are a total waste of your time
Why it's a waste: They just aren't that effective. "Research has shown that the crunch is less effective at stimulating muscle fibre than exercises that require the spine to stabilize, like the plank."
What to do instead: Planks. "They activate more muscles in the core than crunches do," says Travis Barnes, a certified personal trainer at Journey Fitness Coaching in Elmira, New York. Plus, he adds, they don't strain your back as crunches can.
4. The broomstick side bend or rotation
Why it's a waste: While you may think you're strengthening your core or burning fat, you're not. "There's really no resistance when you put a bar weight behind the neck and start twisting or bending. It's much better to work against gravity," says Justice.
What to do instead: A side plank, with or without movement. "Planks work against against gravity, consequently working your muscles more efficiently and effectively."