Planks are God's gift to people with low back pain, which is the third most expensive medical condition in the United States. More than $57 billion a year is spent on low back pain, behind only diabetes and heart conditions.
The key to planks is they strengthen the core muscles — the muscles in the front, the six-pack that everyone wants — and the back at the same time.
If you don't do them right, planks can actually hurt. Here's how to do planks better:
Stay firm. The idea of a plank is like a plank of wood. You don't want to be a wilting flower.
Don't sag. You should feel some lift in your butt as you contract your core muscles.
But don't pike, either! Keep your hips in line with your shoulders.
Relax your shoulders. People tend to be too tense in the shoulders and scrunch up. Be sure your shoulder blades are wide on your back.
Keep your hands and forearms aligned with your shoulders.
Relax your hands. Don't grip your fingers.
Put your forearms on the ground for a somewhat easier plank. Do a full push-up position to increase difficulty.
I recommend 3 minutes of planks a day to give yourself a better life: One minute center, one minute on each side. But you can start with 30 seconds, and you can try it with bent knees like an assisted push-up.