4. The muscle: tibialis anterior
Have you ever suffered from shin splints? If so, listen up: failing to strengthen this vital muscle—which runs along the bottom part of your leg, next to your shin bone, and plays a huge role in forming a healthy gait—can increase your risk of getting those nagging lower-leg pains. "The tibialis anterior plays a vital role in walking, running and sprinting," says Andrews.
Strengthen it: Do this 2-3 times a week: Sit on a chair with your feet flat on the floor, then—keeping your heels on the floor—raise your toes off of it for 8-10 reps. To increase the challenge, you can balance a small dumbbell (5 lbs) on your foot for added resistance. Or you can also sit on a high chair or bench, with enough room for your feet to dangle, and do the same exercise with a dumbbell between them.
5. The muscle: obliques
All the crunches in the world won't get you six-pack abs without working these puppies. The obliques include the external and internal obliques, which cross diagonally from the bottom of your rib cage to your pubic area. "Functionally, they keep you stable in an upright position," says Andrews. "Cosmetically, the obliques form a 'frame' around the mid-section of your abs. Problem is, most people believe they're strengthening them by doing side bends— but they won't work."
Strengthen it: Do Bicyle Crunches. Lie on your back with your legs extended, feet about 10 inches off the ground, and your hands behind your head. Rotate your right elbow toward your left knee, keeping your opposite elbow on the ground and your opposite leg straight. Exhale as you rotate, thinking about your ribs squeezing toward your hips, then straighten your leg back to the start position. Pause, then repeat the motion to the opposite side. Do 8-10 reps 2-3 times a week.