Tensor Fasciae Latae
Know it: This muscle (also known as the TFL) starts along the outer edge of your hip and can affect lateral movement (abduction), which is movement away from your body. A tight TFL can mean you're at increased risk for lateral knee pain, because it attaches directly to your ilio-tibial band--tissue that runs vertically along the outsides of your thighs to help stabilize your knees. Weak or tight abductors means you're constantly getting beat off the dribble, or you're late getting to the ball on the tennis court.
Test it: Try old-fashioned leg lifts. Lie on your side with your legs straight, and raise your top leg to about a 40-degree angle. Then lower it. You should be able to lift your leg in a straight line, without your hip or thigh moving forward, says Jeff Plasschaert, C.S.C.S., a strength coach based in Gainesville, Florida. Make sure you're using hip strength, though; many people substitute motion from their core and lower back to finish the movement.
Improve it: Stretching the TFL is the secret to improving your performance, say Robertson. To stretch your left TFL, stand with your left hip adjacent to a wall. Cross your right foot in front of your left foot. From this position, contract your core and left glute, and then push directly into your left hip. Don't let your hips move backward, and instead make sure your left hip pushes to the side. Hold for 20 to 30 seconds, and then switch legs so your other side faces the wall. Perform 2 or 3 reps on each leg every day.
Supraspinatus and Subscapularis
Know them: The supraspinatus is one of the small muscles at the top of your shoulder that makes up the rotator cuff; the subscapularis is a large muscle on the front of your shoulder blade. Blame your desk job for weak shoulders: If your upper body is rounded, it's most likely because your chest is tight, which means the opposing muscles in your shoulders are weak. Strengthen the stabilizing muscles, and you'll see improvement on your bench press and in overhead sports like swimming or tennis, as well as in your overall upper-body power.
Test them: Bring your arms straight out in front of you at about a 45-degree angle, your thumbs pointed up—like you're about to hug someone. Have a friend stand in front of you and push your arms downward with moderate pressure. (The friend's hands should be positioned above your wrists on your forearms.) If you feel soreness in your shoulders or can't resist the pressure, you probably need to strengthen your supraspinatus, Plasschaert says.
Improve them: "A lot of people think they need to work the rotator muscles like crazy," says Scott. But a simple move is all you need, says Robertson. Stand holding a light pair of dumbbells in front of your thighs, palms facing each other. Keeping your thumbs pointed up, raise your arms up at a 30-degree angle to your torso until just above shoulder height. Hold for 1 second, and lower to the starting position. Do 2 sets of 8 to 10 repetitions. The exercise will help you add pounds to your bench by improving the stability of your shoulders.