AB FAB
Crunches can help build core strength, improve flexibility and more
Workout regimens often flame out as quickly as it takes them to start trending. But others can stand the test of time. Exercises like tai chi, running, swimming, hiking and yoga have been around for centuries and are as good for you today as they were in ancient times.
The same can be said of long-standing resistance training exercises and bodyweight movements like pull-ups, squats, push-ups and sit-ups.
Crunches are another enduring bodyweight exercise, and here's everything you need to know about them.
How to do crunches
Crunches are a popular abdominal exercise that is similar to a sit-up but with a shorter range of motion. They are considered a form of resistance training because the movement causes your abdominal muscles to work against the resistance of gravity and your own body weight, explains Dr. DJ McDonough, a cardiovascular disease researcher at the University of Minnesota's School of Public Health.
The exercise is performed laying on your back (preferably on a yoga mat or other soft surface), with your knees bent and your feet on the ground in front of you about as wide apart as your hips. Arms are either crossed to opposite shoulders over your chest or hands are placed on either side of or behind your head. Then, lift your head and shoulder blades off the ground before releasing the position and resting your head back on the ground.
"Focus on curling the spine rather than simply lifting your upper back off the ground," McDonough says. "And try to imagine your chest touching your belly button as this will ensure proper spinal flexion is taking place and the target abdominal muscles are being hit."
"So long as you are creating tension in your abs, you are exercising them," says Melanie Adams, an American College of Sports Medicine certified exercise physiologist and a professor of exercise science at Keene State College in New Hampshire.
She says variable movements also can be introduced, such as lifting your head and shoulders toward one side or the other or lifting your feet into the air as you slowly bicycle kick to perform an exercise known as bicycle crunches.
Advantages over sit-ups
No matter which variations you follow, crunches have the advantage over sit-ups of being able to better target abdominal muscles.
"Because the movement is smaller, you can control momentum more," Adams says. "This creates a longer contraction — demanding more endurance and more stability from your core."
Crunches also put less strain on lower back muscles and joints. This can be helpful for anyone, but is especially beneficial "for those with previous back problems as crunches can be far less taxing than sit-ups," says Quinn Hess, a Salt Lake City-based personal trainer and fitness coach.
When done properly, the exercise has also been shown to strengthen the lower back — reducing risk of injury and lower back pain. Crunches can improve flexibility and posture as well.
Targeting abdominal muscles
The most sought-after benefit of doing crunches is muscle building. Traditional crunches, where you only lift your head and shoulder blades straight up and down, "primarily targets the rectus abdominis or upper abdominal muscles," Hess says.
The movement also strengthens the transverse abdominis — a deep muscle that stabilizes the core — and a group of muscles that runs along the spine known as the erector spinae.
Modified crunches can work additional muscle groups.
"Laying on your side as you do crunches will also target your oblique muscles," Hess says.
Lifting your head and shoulders to one side or the other or engaging in bicycle crunches by involving your legs will, too. These and other variations like ones involving free weights or resistance bands also can engage hip flexor, leg and butt muscles.
How much to crunch
When it comes to choosing how many crunches to do, it's best to first consider your experience level.
"A beginner would benefit by starting with fewer sets and reps such as three to four sets of 10 to 15 reps a day," Hess says. "Someone with a lot more experience may work up to as many as 100 a day — but the focus should always be on quality over quantity."
Adams agrees, noting that rather than teaching number of reps, she teaches duration.
"Do the exercise slowly and controlled for 20 to 30 seconds and then build up," she recommends. "The key is to hold your position often enough that you fatigue your muscles. Your ab muscles should feel shaky and like you're unable to do another rep when you end the set."
How to do crunches
1 Lay on your back, preferably on a yoga mat or other soft surface.
2 Bend your knees, and place your feet as wide apart as your hips.
3 Cross your arms over your chest, or place your hands behind your head.
4 Lift your head and shoulder blades off the ground.
5 Release, and rest your head back on the ground.
