Most people are doing bicycle crunches wrong — slow the exercise down to build a strong core, a personal trainer says

• Bicycle crunches are a bodyweight exercise that works the whole core, from top abs to obliques.
• However, many people are missing out on the benefits by doing it wrong, according to a trainer.

Bicycle crunches are a popular bodyweight ab exercise for working all your core muscles without a gym.

However, common mistakes like moving too quickly or losing tension in your core can defeat the purpose of the exercise, according to Miriam Fried, NYC-based personal trainer and founder of MF Strong.

"Bicycle crunches can be effective, but most people do them incorrectly, with a flailing movement," she told Insider.

To build a stronger core with bicycles, focus on holding the basic position correctly, move precisely, and practice scaled versions of the exercise to perfect your form.

Keep your lower back against the floor

Done correctly, bicycle crunches can work every part of the abs, from the obliques on the sides of the core to the rectus abdominis ("top abs") and transverse abdominis (deep core muscle that helps stabilize the spine).

The foundation of the exercise is to engage your core by pressing your lower back tightly into the floor throughout the movement.

• Start by lying on the floor on your back with hands behind your head.
• Bend your knees until your thighs are perpendicular to the floor, pressing your lower back into the ground.
• Extend one leg out straight without touching it to the floor, while driving the other knee up towards the opposite elbow.
• Lift and rotate that elbow towards the knee, bringing your shoulder blade away from the floor.
• Switch sides and repeat.

If your lower back is arching or leaving the floor, that's a cue to adjust the exercise to make sure it's working your core instead of stressing your back.

Use slow, controlled movement

It's very common to see people performing bicycle crunches ineffectively by rushing them, according to Fried.

Speeding through the movement generates momentum, taking tension off the abs, which is the opposite of what you want from bicycle crunches, she said.

Instead, keep a steady, deliberate pace as you bring your opposite knee and elbow together and then extend back out to switch sides.

The American Council on Exercise recommends holding the top position (knee to elbow) for a second or two before lowering back to the start position.

Try similar exercises like dead bugs or hollow holds

If twisting prevents you from maintaining good form by causing your lower back to arch, consider working up to bicycle crunches with other exercise variations.

The hollow hold position is a simple way to practice stabilizing your core without movement, whether you're a beginner or a seasoned athlete.

• Start by lying on your back on the ground.
• Press your lower back into the ground and raise your legs. Keep your legs together and engaged, tensing your leg muscles.
• Lift your head and shoulders off the ground.
• Raise your arms overhead and behind you, creating a banana shape with your body.

The lower you hold your arms and legs, the more tension your abs will face, increasing the difficulty.

Hollow holds can be challenging even for a short duration, Fried said.

For an easier, scaled variation, try the dead bug exercise.

• Start by lying on your back on the ground.
• Bend your knees to 90 degrees, shins parallel to the floor.
• Raise your arms straight up in front of your chest.
• Slowly straighten and lower one leg towards the ground, bringing the opposite arm down over your head.
• Switch sides and repeat.

Both the hollow hold and dead bug can be effective, according to Fried, so chose the one you can do with good form.

"Hollow holds are a favorite for me, but I'll often have clients regress to a dead bug," she said.