Your core is tired. Let it rest on the ball.

Planks and crunches aren't the only way. Sometimes the best core workout is sitting down.

Your core stabilizes you all day. Sitting at a desk. Carrying groceries. Holding your phone. By the time you get to yoga, your core is already fatigued.

What the ball does

Sitting on an unstable surface forces your core to engage — without you flexing. It's passive core training. You're not crunching. You're balancing.

Try this

Sit on the ball. Feet flat on the floor. Hands on your hips. Close your eyes. See how long you can stay balanced without opening them. That's your core working.

Size guide

Your knees should be at 90 degrees when you sit on the ball. If your knees are higher than your hips, the ball is too small. If your knees are lower, it's too big.