Sit-ups and yoga practice abdominal movements (sit-ups are about half, then stop there to breathe for 5 times, and then lie down slowly)

If you are a girl, you can use a plastic belt.

Skipping rope reduces the whole body! Hula hoop every day 15 minutes!

You can relax after taking a hot spring or something.

Or sign up for a hip-hop class, which is super lightening. . .