When standing or seated, your muscles have to work to maintain that posture, says Adrianne Nina, Tier 3+ trainer at West Hollywood in California. Lying down, your body can completely relax, allowing you to access deeper ranges of motion during a stretch.
Grounded body rolls (which Nina demonstrates above) open your hips, chest, shoulders, and back while improving range of motion in the hips and thoracic spine. This will help you squat deeper during lifts, drive your arms more powerfully during sprints, and more.
Plus, when you roll from your back to your stomach, the contact between your body and the floor stimulates sensory nerve endings, including those in hard-to-reach places like the center of your back. As a result, even your tiniest muscles will become activated.
The bottom line:
Add grounded body rolls to any warm-up to increase range of motion. Complete 10 slow rolls per direction, pausing when you hit a tight spot.