If your body were a bicycle, your abs and back muscles—your core—would be the frame. You need a strong core to keep you steady and upright on the bike, which allows your legs to turn the wheels and power your pedal stroke.

When it comes to building a stable core, people often turn to two traditional moves: crunches and sit-ups. Determining which one to add to your routine to get the most benefit can seem confusing. So we laid out the similarities and differences of crunches versus sit-ups, plus what you need to know about core strength in the first place—and whether these are really the key moves for strengthening your midsection muscles.

Why a Strong Core Is So Important for Cyclists

“It’s not an obvious observation because your legs, hips, and buttocks are generating most of the power when you’re on your bike, but the core is so active during a ride,” Peter Ronai, clinical professor of exercise science at Sacred Heart University in Fairfield, Connecticut tells Bicycling. “The core keeps the muscles in balance, plus it protects the spinal column, and helps to prevent fatigue.”

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Working together, the abs and back muscles do behind-the-scenes work to keep your spine long and strong so you can generate enough force to move forward with speed, Ronai continues.

While a strong core supports your power during a ride, it also reduces the amount of pain you might feel after a ride. “It is important to have a strong core to remain comfortable on the bike,” Kim Geist, M.S., C.S.C.S., certified exercise physiologist, strength and conditioning specialist, and level 2 USA Cycling coach explains to Bicycling. Back pain and other issues are often caused by not having a strong core. The muscles of the front of the body can often become tight from a regularly bent-over position, which can also contribute to aches.

Ronai agrees: “When someone is fatigued and not in good shape, they ride in an unsupported flexion of the spine and that can increase loading on the [spinal] discs. Over time, that can stress those discs.”

The core isn’t just your abs, though. It includes muscles in both the front, back, and sides of your body that allow you to bend forward, backward, side to side, and to rotate. That means your core also includes muscles of the entire back, as well as the glutes and hip flexors.

While it’s clear that a strong core is important for cyclists, what’s the best exercise to build those muscles? Should you go with the traditional crunches and sit-ups? This guide offers the answer.

All About Sit-Ups

Sit-ups are designed to strengthen your abs so that you can lift your body from a lying down position to sitting up, without using your hands and arms. But they actually aren’t the best ab exercise. “The sit-up has been around so long that not everyone realizes it’s not really an ab exercise,” says Ronai.

While the sit-up does work the rectus abdominis (those six-pack-looking muscles on the front of the body), internal and external obliques (sides of the torso), and transverse abdominis (deep core muscles that wrap around you like a corset), the sit-up mostly strengthens the hip flexors. “It’s not the best use of time for strengthening your core,” Ronai says.

Research backs this up. A small study of 18 participants published in the Journal of Strength and Conditioning Research in 2015 found that the traditional sit-up activated the hip flexors (namely, the quads) more than the abdominal muscles (or rectus abdominis). Researchers say this may result in more load on the lumbar (or low) spine—a spot in which many cyclists already experience pain.

As Pete McCall, C.S.C.S., personal trainer, explains to the American Council on Exercise, low back pain from sit-ups is a common complaint. He says it’s often due to overworked or tight hip flexors that put the low spine in a compromised position, resulting in discomfort. Performing the move on a hard surface can also cause aches.

While the sit-up exercise might not be the best move to target the abs—and you should definitely avoid it if it causes back pain or other discomfort or you find them difficult to execute with good form—cyclists do still need both strong and pliable hip flexors to push and pull the pedals. So, if strengthening the hip flexors is your goal and sit-ups don’t cause any aches, then it’s a fine exercise to add to your routine.

How to do a sit-up

To gain benefits from the sit-up, it’s important to perform it properly:

  1. Lie faceup with knees bent and feet flat on the floor. Cross hands to opposite shoulders over chest.
  2. On an exhale, curl the upper body up toward knees, coming up onto the tailbone, entire torso lifting off the floor. Maintain a tall posture at the top, shoulders down and back and chest tall. Avoid using momentum to sit up.
  3. On an inhale, slowly lower back down to the floor. Repeat.

All About Crunches

Crunches work your abdominal muscles by isolating the rectus abdominis, without rely on the hip flexors in the same way sit-ups do (though they still get in on the action a little). It also strengthens the internal and external obliques and transverse abdominis.

A research article published in the Strength and Conditioning Journal in 2011 questioned some studies that point to the negatives of spinal flexion (or rounding of the spine) via exercises like crunches. While some of these studies have suggested that too much spinal flexion can increase the risk of degenerative disc disease, researchers concluded that exercises like crunches are safe and do offer benefits, as long as you don’t have previous spinal issues or other contraindications like a herniated disc.

In fact, researchers say that exercises like crunches can actually improve the health of the spine and that spinal flexibility can lower risk of low back pain. Plus, these moves can lead to strength and muscle gains, particularly in the rectus abdominis. To reap the rewards, researchers suggest avoiding those 100 rep challenges, and instead, perform 6 to 15 reps of moves like crunches and sit-ups, taking about 48 hours of rest from spinal flexion after incorporating them into your strength routine.

How to do a crunch

To make the most of crunches, here’s how to perform them properly:

  1. Lie faceup with knees bent and feet flat on the floor. Place hands behind head, elbows wide.
  2. On an exhale, lift the head, neck, and shoulders off the floor, without pulling on the neck. Keep hands soft behind the head. Look up and forward as you crunch up, using your abs to lift.
  3. Inhale and lower head, neck, and shoulders back to the floor. Repeat.

Crunches vs Sit-Ups: Which One Is Better?

Both crunches and sit-ups are often referred to as ab exercises. While they both do work the abs, they aren’t the best exercises to target those muscles of the midsection. In fact, in 2016, the Marines and Navy phased out the use of sit-ups, as did the Army. All three branches include planks, but not sit-ups to test core strength. The Strength and Conditioning Journal article mentioned earlier also suggests that moves like squats, deadlifts, row, and push-ups will improve core strength and endurance, without the need for targeted core exercises.

However, both experts say that if you must choose between crunches versus sit-ups, the crunch is the better option for working the abs. It’s also often the safer of the two options, particularly for those with back issues, because it puts less strain on your low back.

The Best Core Exercises to Swap in for Crunches and Sit-Ups

For improved cycling performance, both Rodai and Geist suggest doing planks and other exercises in place of crunches and sit-ups, as these exercises are more effective at building core strength.

“There is a time and place for everything, but I prefer core exercises that are more global and/or more like what we do on the bike,” Geist says. “I select core exercises that engage more of the entire body more often than I select ones that target specific muscles of the core.” That’s why Geist has her clients practice plank variations.

Ronai’s favorite core exercise: roll-outs with elbows and forearms on a stability ball, as this movement mimics keeping the core steady while having to hold onto handlebars. “On a bike you’re tucking down for aerodynamics, and doing planks, bird dogs, and modified back extensions are more apt to address the muscles that help that pillar,” Ronai says.

Here’s how to do those moves:

How to do a plank

  1. Start in a position that mimics the top of a push-up, hands directly under shoulders, and forming a straight line from head to heels. Keep the neck relaxed, eyes focused on the floor a few inches in front of hands. Draw the navel toward the spine to keep the spine neutral.
  2. Hold the position for 10 seconds, working up to 60 seconds or more.

How to do a bird dog

  1. Start on all fours, abs engaged, shoulders right over wrists and knees right under hips.
  2. Extend the right arm forward, lifting it to shoulder height, and extend the left leg straight behind you, lifting it to hip height. Form a straight line from the extended hand to the extended foot.
  3. Hold for a few seconds, then return to all fours.
  4. Repeat on the other side and continue alternating.

How to do modified back extension

  1. Lie facedown, legs straight, toes on floor, and elbows bent, with hands next to shoulders in a goal-post like position.
  2. Slowly lift the head, chest, and arms off the floor, pressing the hips into the mat. Keep the head and neck neutral. Hold for 30 seconds.
  3. Lower back to floor. Repeat.

Geist points out that riders are moving their legs continuously in one plane while resisting the urge to tilt in another plane. She explains that a strong core allows the hips to more safely maintain control of the legs without rotating, maximizing your power and efficiency. To prepare for this, Geist also has her clients do planks with added movements, like lifting an arm or a leg, or both.

To add an anti-rotation element to a workout, Geist also typically suggests unilateral (or single-sided) exercises. This might include a single-arm overhead press or single-arm bent-over row. For the lower body, it might mean a single-leg deadlift. This forces the core to fire up while working the entire body, she says.

Research suggests this full-body approach may be more effective at building core strength than either crunches or sit-ups. In a systematic review published in International Journal of Environmental Research and Public Health in June 2020, free-weight exercises, such as the Bulgarian split squat showed greatest activation of the rectus abdominis and external obliques compared to more traditional core exercises. Squats, deadlifts, and hip thrusts also showed greatest activation of the erector spinae (muscles along the spine). Core stability moves, such as the plank, targeted the internal obliques the most, and the back extension showed the greatest lumbar multifidus activation (muscles of the low spine). More research is needed on the best exercises for the transverse abdominis, however.

While sit-ups and crunches have been the most common core exercises, the study noted, multi-joint free-weight exercises are more time efficient.

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Donna Raskin

Donna Raskin has had a long career as a health and fitness writer and editor of books and magazine articles. She bikes in a nearby county park, lifts weights, takes Zumba, and loves to walk/run with her dog, Dolly.