1. Jog in one place for 3 minutes.

2. Do 25 jumping jacks.
When landing, bend your knees slightly to reduce the impact on knee joints. {relatedarticles}
3. Do 15 crunches.
Lie flat on your back with your knees bent. Place your hands behind your head with elbows pointing outwards. Support your neck with your hands. Keep your neck in a straight line with your spine. Flex your waist to raise the upper torso from the mat. Lower yourself until the back of your shoulders touch the mat.
Muscle worked: rectus abdominis