Sit-Ups vs Crunches: What Actually Works for Your Core

Sit-ups and crunches are the first core exercises most of us learn — in school PE, in the army, in every beginner workout plan. They’re also two of the most argued-about. Is one better than the other? Are sit-ups bad for your back? And will either of them give you visible abs?

Here’s the straight answer.

The difference

A sit-up takes you all the way from lying flat to sitting upright. Your abs start the movement, but your hip flexors — the muscles at the front of your hips — do a lot of the work of pulling you the rest of the way up. That’s why anchoring your feet under something makes sit-ups so much easier.

A crunch is a shorter movement. You only lift your head and shoulder blades off the floor, curling your ribcage towards your hips, and your lower back stays down. That keeps the work focused on your rectus abdominis, the “six-pack” muscle, with much less help from the hip flexors.

Is one better?

For targeting your abs specifically, crunches are the more focused exercise. Sit-ups train your abs and hip flexors together, which is useful for some sports but means your abs aren’t doing all the work.

But there’s a bigger question than “which one”.

Are sit-ups bad for your back?

It’s debated, and the honest answer is: it depends on the person. Some spine researchers have raised concerns that doing lots of repeated, loaded spinal bending can aggravate back problems, especially in people who already have them. Others point out that the spine is built to bend and that, for healthy people, moderate volumes are fine.

What’s clear is that sit-ups have fallen out of favour as a fitness test. The US Army, for example, dropped them from its fitness test in favour of the plank.

A sensible approach: if your back is healthy, sit-ups and crunches in moderation are fine. If they cause back pain, swap them out — there’s no shortage of alternatives that train your core just as well.

Core exercises worth doing instead (or as well)

• Plank. Hold a straight line from head to heels on your forearms. It trains your core to resist movement, which is what it does most of the time in real life and in heavy lifts.
• Dead bug. Lie on your back, arms up, knees bent at 90 degrees, and slowly lower the opposite arm and leg while keeping your lower back pressed into the floor. Great for beginners and back-friendly.
• Hanging knee raise. Hang from a bar and bring your knees up towards your chest. Hard on your abs and grip.
• Cable crunch. Kneel at a cable machine with a rope attachment and crunch down. Unlike floor crunches, you can add weight as you get stronger.
• Ab wheel rollout. Kneel and roll a wheel forward as far as you can control, then pull back. Advanced — start with short rollouts.

A balanced core session might be a plank, one ab exercise like cable crunches or hanging knee raises, and something rotational like a cable woodchop.

The bit nobody wants to hear

No amount of sit-ups or crunches will give you visible abs on its own. You can’t burn fat from a specific spot by training the muscle underneath it. Abs show when your overall body fat is low enough, which comes down mostly to diet, total activity and consistency over time.

Core exercises still matter — a strong core makes you better at almost every other lift and helps protect your back. Just don’t expect them to do the job of your diet.

Many of these exercises need a cable machine or a pull-up bar. If your current gym is short on those, find a better-equipped gym near you.