Crunches certainly can make you feel like you're working hard, but compared to cardiovascular exercises and compound strength moves, they don't burn a bunch of calories.
Crunches strengthen your abdominal muscles — specifically the superficial rectus abdominis according to ExRx.net — which forms the front "six-pack," and the obliques, located at the sides of your waist. Exactly how many calories you burn during a set of crunches depends on your size, time spent crunching and intensity.
Crunches don't burn a lot of calories. And the number of calories they burn depends on your height and weight, the time you spend doing crunches and the intensity with which you do them.
Factors Affecting Caloric Burn
1. Body Size
A larger person naturally burns more calories than a smaller one. This makes sense when it comes to activities that require you to move your body through space, such as running, but it's true for crunches as well. For example, a 200-pound man standing 6 feet tall burns 34 calories in five minutes of crunching. If that man weighed 250 pounds, he'd burn 42 calories in the same amount of time.
2. Time Working Out
Realistically, you don't perform crunches for long periods of time. Even five minutes of straight crunching is a long time. Likely, you do one to five sets of crunches, with each set lasting one minute for, at most, five minutes of work. Three minutes of crunching for a 5-foot-8-inch woman who weighs 170 pounds burns 17 calories; if she goes for five minutes, she burns 29 calories.
How intensely you crunch also affects calorie burn. For example, a 5-foot-5-inch woman who weighs 150 pounds who crunches at a moderate intensity for five minutes burns 26 calories. If she crunches at a vigorous pace, she'll burn 46 calories. Vigorous crunches are usually done at a higher speed to complete a greater number of repetitions in a set period of time.
Crunch for Quality of Movement
Attention to your quality of movement and a moderate tempo makes crunches most effective for muscle building. Quickly lifting and lowering your torso to burn more calories misses the point of the movement, which is to strengthen the rectus abdominis and obliques.
When you move methodically, you're able to visualize the muscles contracting as you curl up. The contraction is really the key to the exercise. Quick, rigorous movement also makes it more likely that you'll strain your neck by pulling too hard on the back of your head and drawing your chin in toward your chest.
Better Ways to Burn Calories
If you're crunching in an attempt to slim your middle, alter your strategy. Crunches, and other abdomen-specific moves, don't burn much fat according to an article by exercise scientist Len Kravitz, PhD, of the University of New Mexico. They build muscle in your midsection, but you'll never see that washboard as long as it's covered with a layer of pudge.
Cardio exercise helps you burn calories and mobilize fat stores to slim down. Running, hiking, cycling and dance fitness are better ways to burn fat than crunching. To build the strongest abs, do more than just crunches. Build strength in your entire core, which encompasses your hips and back, as well as in the rest of your body to burn calories more efficiently every day.
Regular total-body strength workouts change your body composition to have more muscle and less fat so your metabolism increases. Do at least two total-body strength sessions per week. These sessions might include crunches, but also involve training the other major muscle groups of the back, chest, arms, shoulders, hips and legs.
Augment your crunch routine with other core strengtheners, such as bird dogs, planks and v-ups too. In 30 minutes of lifting weights at a moderate pace, a 155-pound woman burns 112 calories, according to Harvard Health Publishing.