Stand upright on the balls of your feet with your knees slightly bent and your arms bent in front of your body or supported on your hips. Bounce steadily in place (fast frequency) without putting your heels down (bounce on your toes).
Attention:
Keep your upper body upright (keep your core tensed).
Lighten:
Smaller/less intense jumps.
Harden:
Larger/intensive jumps; additional weight (on the chest/shoulders, hold in the hands, hold in front).
Variation:
Pull the tips of your feet towards your knees (bend your feet) with each jump.