2. The muscle: erector spinae
You probably work your upper back and traps for that wide expanse, but you're likely neglecting the very muscles that keep you upright. The erector spinae is actually a bundle of muscles and tendons that extend throughout the lower, mid and upper back. "They're more about posture than anything," says Holland. "Weak spinal erectors and poor posture may lead to back pain and sports injuries."
Strengthen it: Lie face down over a back extension machine with heels anchored. (You can also use a fitness ball if you have a partner to hold down your ankles). Place your hands behind your head with elbows out to the sides. Slowly raise your torso (don’t swing) just until your body forms a straight line, with ears, shoulders, hips, knees and ankles in line. Slowly return back to start. Do three sets of 10-12 reps.
3. The muscles: gluteus medius and minimus
Few muscles get as much attention as the gluteus maximus, yet it could not reach its full potential without these two lesser-known helpers, which serve to stabilize the pelvis— especially when standing on one leg, says Guy Andrews, MA, CSCS, executive director of ExerciseEtc.com. "They're vital for any athletic performance and crucial for walking and climbing stairs. Plus, when they're toned they lift up the glutes."
Strengthen it: Using a heavy resistance tubing circle, step inside the tubing with both feet and fasten around each ankle. Stand in a wide sports stance, knees slightly bent, toes pointed straight ahead and hands on hips or out in front. Step out to the side and continue walking sideways for 8-10 steps, then repeat in the opposite direction. Perform 2-3 sets, 2-3 times a week.