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Start to get into a pushup position, but bend your elbows and rest your weight on your forearms instead of your hands. Your body should form a straight line from your shoulders to your ankles.

Pull your abdominals in; imagine you're trying to move your belly button back to your spine.

Hold this for 20 to 30 seconds, breathing steadily.

Release, then repeat for another 20 to 30 seconds. That equals two complete sets. As you build endurance, you can do one 60-second set instead of two shorter ones.