Total-body fitness requires a lot more than endurance and brute strength. If you don't have good flexibility (and many people don't), you're limiting your exercise horizons. "Nine out of ten people I work with—either new clients or people just starting a fitness program—don't understand the benefits of stretching and don't do it, partly because they don't know how to do it correctly," says Dixie Stanforth, a lecturer in the department of kinesiology at the University of Texas. Flexibility—the ability to move muscles and joints through their full range of motion…