Sit up. Just like your mother told you to. Sit up straight. Stand up straight—and feel healthy and powerful. Improving your posture does a world of good for you and for others.

CrossFit became one of the world’s largest sports gym chains by motivating people to compete with themselves and with others in a variety of fitness tests. While initially focused on Olympic weight lifting and gymnastics, the CrossFit world morphed into a dizzying variety of athletic performance drills—along the way, becoming a sport unto itself. Now what?

For decades there have been unsuccessful efforts to repair the anterior cruciate ligament (ACL) after rupture. Why? Because the forces required to tear the complex weave of the ACL’s collagen fibers involve both tearing and pulling apart. Think of a climbing rope: When overstretched the rope fails within its sheath, not just at a single clean edge. Here is why the ruptured anterior cruciate ligament is most often replaced (reconstructed) rather than repaired.