The same ACE study hooked participants up to electrodes to measure rectus abdominus activation during two types of crunches: arms folded across the chest and fingers interlocked behind the head. The researchers suspected that hands-under-the-head crunches would be less effective because people seem to pry their head up with their hands instead of engaging the abs. But to their surprise, both methods were equally as effective. Just make sure your crunches are slow and controlled.
Credit: Natalie Young / Getty Images
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