Odds are that if you exercise—even if you don’t—you’re familiar with the concept of core training. What you might not know is that it’s not just about doing crunches. Core strength is about much more than achieving a flat stomach; it’s also about healthy posture, reducing pain, and performing everyday movements with ease. Below is a quick primer on the muscles you’ll be working, why you need to work them, and what are among the best exercises for strengthening your body’s “power center.”

The Muscles of the Core

While many of us associate the core with the abdominal muscles alone, it’s actually a complex system of muscles located in the trunk and hips that assist us in practically all movement, from lifting a heavy object to jogging in a straight line on the treadmill. These include muscles in the hip and pelvis like the pubococcygeus (PC or pelvic-floor) muscle, which contracts to control urine flow, as well as the glute medius and minimus, which stabilize the pelvis while walking or jogging and while standing on one foot.

The muscles of the low back are also included in the core musculature; the erector spinae is the best known and is responsible for extending the back, and though it can become very tight is often a weak muscle group. Another back muscle involved in core movement is the multifidus, a deep vertical muscle which stabilizes the vertebrae and helps absorb impact, reducing joint degeneration in the spine. Also of importance is the quadratus lumborum (QL), which is found on either side of the low back and flexes the spine laterally (side-bending); it’s often forced to pick up the slack from weak erector spinae muscles during back extension.

The remaining muscles of the core include the four abdominal muscle groups: the rectus abdominus (or “six-pack”), the external obliques, the internal obliques, and the transverse abdominus. The rectus abdominus flexes the spine forward and is the primary muscle group used to perform crunches. The external obliques, the diagonal muscles to either side of the six-pack, rotate the spine and are used during twisting movements.

Beneath the external obliques lie the internal obliques, which assist in spinal rotation as well as stabilize the core during abdominal exercises; they also function antagonistically to the diaphragm to help us breathe properly. (The diaphragm, while not technically an abdominal muscle, is also considered a core muscle; it contracts to enlarge the thoracic cavity, allowing us to take deep breaths.) Finally, the deepest layer of abdominal muscle is the transverse abdominus. The transverse abdominus draws in the abdominal wall to compress the ribs and stabilize the thoracic spine and pelvis. This muscle helps prevent injury during heavy lifting movements.

Why We Need Core Strength

As we age, the core muscles along with the rest of our muscle groups begin to decrease in mass. Subsequently we lose strength, gain body fat, and develop muscular and postural imbalances. While most of these changes happen over years, postural imbalances can appear relatively quickly and become quite pronounced, especially among women who are sedentary, such as those who sit hunched over a desk all day.  The combination of gravitational forces compressing the spine coupled with weakened postural muscles can result in noticeable changes in alignment, such as a forward head position, rounded shoulders, and a curved upper back.

Training the muscles of the core that are involved in maintaining proper alignment can help resolve these postural issues. Strengthening the muscles of the low back is a good start—exercises like back extensions can help address weak erector spinae muscles, and sitting atop a stability ball can help train the multifidus and transverse abdominus, both of which are heavily involved in maintaining upright posture. Similarly, exercises like the plank hold (see below) recruit the abdominal, back, and hip muscles and teaches them to work together to support the spine in a straight line.

A related issue stemming from core muscle weakness is pain, particularly back, neck, and hip pain (all commonly reported among sedentary populations in the U.S.). In the absence of an injury, most pain in this region is caused by muscle imbalances, imbalances that pull the body out of alignment and force stronger muscle groups to compensate for weaker ones. The good news is that these imbalances are easily (and inexpensively) fixed with core exercise.

By stretching tight muscles and strengthening weak ones, like the abdominals, upper back, low back, and glutes, the muscles will return to their proper lengths. When this happens, regular alignment can resume and pain generally disappears. For example, weak glutes paired with tight hip flexors can cause the pelvis to tilt anteriorly (imagine the back arching slightly and butt sticking out). This places upward pressure on low back muscles, making them tight and painful. Strengthening the glutes and stretching the hip flexors, therefore, can help resolve this imbalance.

A final benefit of core training is that having a strong core makes all demands on the body—whether from exercise or everyday activities like lugging groceries or gardening—easier to handle. When we lift heavy objects, brace ourselves to absorb impact, or are forced to keep our balance, it’s our core muscles that carry the load, draw in to protect us from injury, and prevent us from tipping over. So it only makes sense to keep these muscles working at full strength.

By following the exercises below (which can easily be paired off and distributed among three separate workouts) you’ll be better prepared for all the jobs the core muscles perform: drawing in for good posture and heavy lifting, stabilizing for balance and coordination, and strengthening and stretching for improved alignment. Perform two sets each of these core moves (choose a minimum of two exercises per workout session) three times a week in addition to full-body strength training, cardio, and stretching for optimum results.

Recommended Core Exercises

Opposite-Arm-and-Leg Reach: Get down on all fours with knees directly under hips and hands directly under shoulders. Draw in transverse abdominus muscle (pull belly button toward spine) to keep torso stationary. Slowly reach left arm straight in front of you while simultaneously extending right leg straight behind you (limbs should be parallel to floor). Do not rock side to side or allow low back to dip. Pause at the top, then return to starting position and repeat on other side. Do 8-10 reps each side.

Plank hold/Side plank: Lie face-down on the floor with legs straight and elbows propped directly under shoulders. Lift your weight onto elbows and toes so that your body forms a straight line and is held off the floor. Making sure to keep abs and glutes pulled in, hold this position as long as you can (ideally 30+ seconds). For the side plank, roll onto your side with one elbow propped under shoulder and lift hips off floor so that body forms a straight line; hold as long as you can and repeat on other side.

Stability Ball Crunches: Lie on your back on a stability ball with hips slightly lower than shoulders. Your tailbone should be in contact with the ball and knees bent 90 degrees with feet planted on floor. Place hands behind your head with elbows wide, look straight up at ceiling, and slowly curl shoulder blades off the ball without pulling forward on head or neck. Ball should not move. Exhale as you lift; then inhale and lower until your abs stretch slightly. Perform 15 reps.

Stability Ball Low Back Extensions: Lie face down on a stability ball so that torso is parallel to the floor, chest is just past the front of the ball, and knees are slightly bent (you may want to place feet against a wall). Place hands lightly behind your head just as you would for a crunch. Keeping knees bent and ball stationary, slowly extend the spine so that chest lifts a few inches off the ball (draw abs in to avoid hyperextending). Lower back down and repeat for 10-15 reps.

Supine Knee Twists: Lie on your back on the floor with knees positioned directly above hips so that hips and knees are bent 90 degrees, and spread your arms straight out to either side. Keeping both shoulder blades on the floor, inhale and slowly rotate hips to the right, dropping your knees as far as you can toward the ground. Exhale and slowly bring knees back up; repeat on the left side. Do 8-10 reps each direction.

Heel Touchdowns: Lie on your back with your arms at your sides and your legs lifted above your hips, knees bent 90 degrees. Keep your abs drawn in to maintain contact between your low back and the floor at all times. One at a time, lower your leg from the hip joint, keeping your knee bent, until your heel touches the floor, then exhale and lift your leg back up using your abdominal muscles. Repeat on the other leg, alternating for 10 reps each side.