Female athletes are up to 10 times more likely to tear their ACL than men. Not exactly the kind of thing where you want the odds in your favor. But we can thank hormonal and anatomical differences for putting us out in front on this one. Stay strong by strengthening your knees. Tom Holland, the author of "Beat the Gym", recommends walking lunges. Try two-three sets of 15, three times per week, making sure your knee never reaches past your toes. Hold dumbbells to up the intensity.