Are you a man or a woman?

If it is a male, the base is not large, and self-esteem training is carried out after school every night. Might as well use it to buy some small equipment.

If you are a woman, do some core strength training for your waist, legs and abdomen after school every night, especially your hips.

Then run around the playground and run a few laps according to your own situation, regardless of the distance of 40 minutes.