Why Certain Exercises Can Make Your Stomach Bigger Instead of Smaller

Crunches, situps and all of your favorite ab exercises provide the deep burn that feels like you're scorching body fat and getting closer to a lean, toned stomach. But after the weeks and months of effort, it's discouraging to find your stomach actually growing from training.

What gives?

All hope isn't lost and you're still taking positive action toward better health and your best body. But, if you're noticing your abs growing rather than your waistline shrinking, it may be time to change your training.

Whether your goal is a tight, toned stomach or bigger biceps, the process of building muscle is the same. According to the National Academy of Sports Medicine, there are three primary factors that influence muscle growth: mechanical tension, metabolic stress and muscular damage.

Mechanical Tension: Tension is the result of lifting heavy weights through a full range of motion. Basically, if you lift heavy weight at a relatively slow speed, you'll promote muscle growth.

Metabolic Stress: If you've felt your legs "pumped" after a hard leg workout, you've felt metabolic stress. This burn or pump is the result of muscular byproducts like lactate and the inability of blood to escape a working muscle. That means this metabolic stress, or "burn" during a high-rep set of crunches signals your muscles to grow.

Muscular Damage: The soreness you feel after a workout, whether it's your legs from squats or abs from crunches, is an indication of muscular damage. This damage tells your muscle fibers they must grow bigger and stronger to become more resilient to the same workout next time. As a result of muscular damage, your muscles are triggered to grow.

Building muscle is the same whether it's your quads or your abs. If you train any muscle frequently by promoting tension, stress and damage, it will grow — your stomach included.

And while muscle growth and strength are generally a good thing, too much growth on your abs can leave you with the "blocky" or square-ab look rather than tight and toned.

Instead of classic flexion-based exercises, such as situps and crunches, focus on isometrics like planks. This minimizes the metabolic and muscular damage of resistance training to build a stronger, but not necessarily bigger, stomach. Pick one exercise from each category and train twice per week for stronger abs.

Read more: The Science of Building Muscle

Extension exercises can help with a stomach that sticks out. These exercises resist flexion of the spine, like arching your lower back. This can help prevent back pain and injury while focusing on your rectus abdominus, or six-pack muscles.

HOW TO DO IT: Assume a plank position on a stability ball, with elbows underneath your shoulders and palms supinated.

Keep the spine neutral and glutes squeezed while holding the position for time. Perform two or three sets of 30- to 60-second holds twice per week.

HOW TO DO IT: Starting on your hands and knees, bring the left foot forward directly under the chest while straightening the right leg.

Keeping the hands on the ground and core tight, drive the right leg back, switching legs. The left leg should now be extended behind the body with the right knee forward. Perform two or three timed sets of 30 to 60 seconds twice per week.

True anti-rotation exercises are done to resist rotation at the lumbar spine and focus primarily on strengthening your obliques and quadratus lumborum.

HOW TO DO IT: Begin on your side with your bottom elbow directly underneath your shoulder.

Prop your body up on your elbow looking straight ahead and forming a straight line from ankle to ear. Hold your body in place for 30 seconds per side. Repeat on each side for two sets.

HOW TO DO IT: Assume a half-kneeling position with hips perpendicular to a cable machine, with the inside knee down. Hold a cable handle with both hands in front of your body, directly in front of your chest from a cable set at midchest height.

Squeeze your glute on the down leg, keeping the arms fully extended, actively resisting the movement from the pulley. Perform two sets of 30 seconds, holding steady for the entire duration. Switch positions, repeat on the opposite side and repeat twice.

Read more: How to Strengthen Your Core with Planks

If you want abs that are strong and toned but not blocky, focus on a fat-loss diet and improving total body strength.

When you strength train other muscles, use compound exercises that stimulate your entire body like squats, deadlifts, rows and overhead presses to build balanced strength, promote lean muscle growth and fat loss.

Then, focus your abs training on isometric exercises to build strength, but not the size of your abs.