Begin with a thorough warm-up, including dynamic stretching and mobility exercises for the shoulders, hips, and ankles. For push-ups, focus on maintaining a straight line from head to heels and engaging the core. Modify with knee push-ups if needed. In squat cleans, focus on keeping the barbell close to the body and using the legs to generate power. Use a weight that allows for good form throughout the set. During box jumps, focus on landing softly and fully extending the hips at the top of the jump. Use a box height that challenges you but allows for good form. This circuit is designed to challenge your strength and endurance. Pace yourself throughout the 21 minutes and focus on maintaining proper technique. Finish with a cooldown involving stretching, particularly focusing on the shoulders, hips, and legs.