High-Intensity vs. Moderate-Intensity Cardio for Flat Abdominals

Flat Abdominals

Who doesn’t want flatter abs, especially when summer rolls around and it’s time to pull lighter, more revealing clothing from the back of the closet? But getting flat abdominals is a challenge for many people, especially women. You need the right exercise and diet, healthy sleep habits, stress management, and good posture for your abs to look firm and tight. All of those factors play a role in how your ab muscles look and whether you develop strong, more defined abdominal muscles when you train.

For many women, the roadblock to getting flat abs is body fat percentage. To have abdominal definition show through, most women need a body fat percentage of 20% or less, although some women have visible abs at a slightly higher body fat percentage while other women may need to go below 20%. One lifestyle habit that helps reduce body fat is cardio, but what type is best for getting flat abs? In this article, we’ll look at whether high-intensity cardio or moderate-intensity cardio can best help you meet your objective.

Cardiovascular Exercise: Is High or Moderate Intensity Better for Abs?

Since a high body fat percentage keeps most women from having flat abs and muscle definition, losing body fat is helpful for some. Most people do moderate-intensity cardio in hopes of losing fat. Moderate-intensity cardio is exercising at an intensity you can sustain for 30 minutes or more, like brisk walking, jogging, cycling at a moderate pace. There are benefits to this since moderate-intensity cardio burns calories and improves cardiovascular fitness.

In contrast, high-intensity exercise is best epitomized by high-intensity interval training or HIIT, a workout structure where you exercise at 80 to 90% of your maximum ability for 30 seconds to a minute, followed by recovery exercise where you partially recover. Then you repeat this sequence until 10 to 20 minutes have elapsed. High-intensity interval training, because of the intense nature of the exercise, can be shorter and still offer cardiovascular benefits and other health and fitness benefits too.

Which of these two workout structures is better for getting flat abs? Although your body taps into fat as fuel during low to moderate-intensity exercise, HIIT training may still offer more fat-burning bang for the buck. Studies show that HIIT stimulates production of PGC-1 alpha 1, a protein that boosts the activity of the fat-burners inside cells called mitochondria, more than low to moderate-intensity cardio does. Plus, studies show that when PGF-1 alpha rises inside muscle cells, it activates another protein on the surface of fat cells called irisin that aids in fat loss.

Why is irisin beneficial?  When irisin binds to the surface of fat cells, it increases thermogenesis, the rate at which your body burns fat. So, irisin has a thermogenic effect, helping to burn excess fat, even after a workout is over. You may have heard that HIIT training produces more of an afterburn than moderate-intensity exercise, and the production of irisin in response to an intense workout is one reason why.

Does high-intensity exercise lead to greater fat loss, including abdominal fat loss, than low-to-moderate intensity cardio? According to a study published in the Journal of Obesity, it does. Participants that did vigorous exercise lost more abdominal fat than those who worked out at a low-to-moderate intensity. So, doing that HIIT workout is the best bet for getting your abs in shape. In addition, high-intensity interval training also improves insulin sensitivity, making it favorable for metabolic health and weight control.

Building Abdominal Definition

If you’re looking for six-pack abs, you need defined abdominal musculature too, and that comes from hypertrophying the muscles. Low to moderate-intensity cardio, although a calorie burner, could make hypertrophying your abdominal muscles harder. When you do long periods of low to moderate-intensity cardio, it activates an energy-sensing molecule called AMPK. However, when AMPK is turned on, it inhibits the activity of the mTOR pathway, the main pathway your muscles use to create new muscle proteins. So long periods of low-to-moderate intensity cardio can make it harder to build muscle. Some studies show this “interference” effect while others do not.

Of course, you also need strength training to build stronger, more defined abs. Don’t depend too much on abdominal crunches and other abdominal isolation exercises to accomplish your goal. Although they’ll modestly hypertrophy your ab muscles, they do little to burn fat. That’s why more fitness trainers recommend that clients do compound exercises, like squats, deadlifts, and push-ups to get flat abs. These exercises work your core and abdominal muscles indirectly by forcing them to stabilize your body. Plus, they burn more calories than abdominal isolation exercises that have little calorie-burning benefits.

Studies show that you’ll lose more body fat, including around the tummy, by doing both cardio exercise, preferably high intensity, and strength training large muscle groups through multi-joint exercises. It’s not a question of one of the other, but both.

It Takes a Holistic Approach

Exercise is important for getting flat abdominals, but so is the diet you eat and other lifestyle habits. Cut back or eliminate sugar and ultra-processed foods while boosting the fiber and protein content of your diet. Stop restricting calories and focus on the quality of what you eat. Also, avoid drinking sugar and calories by replacing those sugary beverages with unsweetened green tea or water. Sleep and stress management matters too. Too little sleep and unmanaged stress raises the stress hormone cortisol, and that causes fat redistribution so more of your body fat ends up around your tummy and waistline.

The Bottom Line

By increasing PGC-1 more, high-intensity cardio may give you an edge for losing belly fat and getting flat abs, but you still need strength training, especially compound exercises that work multiple muscle groups in the lower body. Don’t get into an endless crunch cycle; do them in moderation. Include planks in your routine as they work your entire core. Also, look at the bigger picture. What and how you eat, sleep, and stress management matter for flat abs too.



  • J Obes. 2011; 2011: 868305.Published online 2010 Nov 24. doi: 10.1155/2011/868305.
  • Effect of Exercise Type During Intentional Weight Loss on Body Composition in Older Adults with Obesity. Obesity, 2017; 25 (11): 1823 DOI: 10.1002/oby.21977.
  • Am J Physiol Regul Integr Comp Physiol. 2011 Jun;300(6):R1303-10. doi: 10.1152/ajpregu.00538.2010. Epub 2011 Mar 30.
  • J Obes. 2011; 2011: 868305. Published online 2010 Nov 24. doi: 10.1155/2011/868305.
  • Metab Syndr Relat Disord. 2009 Aug; 7(4): 363–368.doi: 10.1089/met.2008.0060.


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That Stubborn Abdominal Pooch! Surprising Reasons Your Abs Aren’t Flat

5 Ways to Get More Benefits from Abdominal Training

Are You Taking a Balanced Approach to Abdominal Training?

Are Planks Better Than Crunches for Abdominal Development?


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