Friendly tip to the woman we've all seen slogging away hours half bent-over on a cardio machine: Exercise only leads to results if you use good form. For walkers, that means keeping hands relaxed and arms bent 90 degrees while driving elbows back and then fists forward to shoulder height, Dixon says. "Form is even more important for runners," she adds, "because too much upper-body movement, such as crossing your arms over your midline, can tire your body out more quickly." Which means you can't last the half hour you planned to be on your feet. Consider this permission to check yourself out in the mirror from time to time, and try these 10 ways to improve your running technique.