The muscles at the front, sides and back of your neck. They nod, tilt and turn your head and hold it steady, and strengthening them can ease the aches that come with long days at a desk.

The front of your shoulder cap. It lifts your arm forward and overhead, so it works in push-ups, presses and every time you lift something onto a high shelf.

The back of your shoulder cap. It pulls your arm backward, balancing out all the pushing and pressing you do; rows, face pulls and reverse flyes train it.

Four small muscles running from your shoulder blade to the top of your upper arm. They rotate your arm and keep the ball of your shoulder centered in its socket, helping protect it when you lift, throw or reach.

The outer side of your shoulder cap. It raises your arm out to the side and adds width to your shoulders; lateral raises and overhead presses train it.

The saw-toothed muscle along the side of your ribs, under your armpit. It pulls your shoulder blade forward around your ribcage, like when you throw a punch, and rotates it upward so you can reach overhead.

The large, fan-shaped muscle across the front of your chest. It pushes your arms forward and pulls them across your body, powering push-ups, presses and hugs.

The broad, wing-shaped muscles running down the sides of your back. They pull your arms down and back toward your body, powering pull-ups, rows and climbing out of a pool.

The sloping muscles between your neck and the tops of your shoulders. They shrug your shoulders up, help steady your neck and keep your shoulders from sagging when you carry heavy bags or weights.

The muscles between your shoulder blades. They squeeze your shoulder blades together, steadying them in every row and pull and helping you keep your shoulders back instead of rounding forward.

The muscle on the front of your upper arm. It bends your elbow and turns your palm up, helping you lift, carry and pull everything from groceries to kids.

The muscles between your elbow and wrist. They power your grip, move your wrist and help bend your elbow, which is why carries, hangs and hammer curls work them hard.

The horseshoe-shaped muscle on the back of your upper arm. It straightens your elbow, so it works in every push and press and whenever you push yourself up out of a chair.

The long muscle down the front of your stomach (your six-pack). It curls your ribcage toward your hips and, with the deeper core muscles beneath it, braces your trunk to keep your spine steady.

The columns of muscle running alongside your spine, thickest in your lower back. They straighten and support your spine, helping you stand tall and lift safely from the floor.

The layered muscles along the sides of your waist. They twist and bend your torso and keep it from twisting when it shouldn't, which matters for sports, carrying and lifting.

Your largest muscle, forming most of your buttocks. It drives your hips forward to stand up, climb stairs, run and jump, and it takes strain off your lower back when you lift.

The deep muscles linking your lower spine and pelvis to the top of your thigh bone. They lift your knee toward your chest as you walk, run or climb, and can feel tight after long hours of sitting.

Your smaller glute muscles, high on the outer side of each hip. They lift your leg out to the side and keep your pelvis level and knees in line whenever you stand on one leg, walk or run.

The muscles on the back of your lower leg. They point your foot and lift your heels, pushing you off the ground every time you step, jump or climb stairs.

The three muscles on the back of your thigh. They bend your knee and swing your leg back, teaming up with your glutes when you sprint, jump or lift something off the floor.

The group of muscles on the inside of your thigh. They pull your legs together and steady your hips during squats, lunges and side-to-side movements.

The four muscles on the front of your thigh. They straighten your knee and power squats, stairs, getting out of a chair and every step you take.

The muscle along the front of your shin. It lifts the front of your foot so your toes clear the ground and curbs as you walk or run, then lowers it gently after your heel lands.