Crunches: how Upfit checks your form

Upfit tracks the crunch as a half-crunch. Your shoulder blades peel off the mat, you squeeze, then you lower. It is not a full sit-up.

How do I do a crunch?

Lie on your back with your knees bent and your feet flat. Put your hands behind your head with your elbows wide. Lift your shoulder blades off the mat and squeeze your abs. Then lower with control. Keep a steady pace and stop if your neck or back hurts.

How do I set up my phone for crunches?

Crunches are tracked side-on. Lie with your body parallel to the phone: your head off to one side of the picture and your feet off to the other. The camera needs to see your shoulders, hips and legs. The app tells you which way to lie.

What does Upfit check on a crunch?

Lying flat, your shoulders and hips sit at about the same height in the picture. As you curl up, the line from hips to shoulders tilts. Upfit measures that tilt and checks:

• Knees bent. If your legs stay straight for a sustained stretch of the rep, it is rejected. The coach reads this as a set-up fault and mentions it before depth.
• Lift. Your shoulders have to curl up far enough. A tiny movement is rejected as shallow.
• Tempo. Under about three quarters of a second is fast. Over about three seconds is slow. Both still count.

When does a crunch count?

A rep counts when you curl up past the lift check with your knees bent, then return to flat on the mat. The coach says the number aloud.

What does the coach say?

These are real lines from the app's voice set:

• "Bend those knees — feet flat, knees pointing up to the ceiling!"
• "Peel those shoulder blades off the mat on the crunch — even a little higher!"

What can't Upfit check on a crunch?

Upfit does not check your hands or your neck, so it cannot tell if you pull on your head. It does not check that your lower back stays on the mat or where your feet are. It measures the tilt of your torso, so it is tuned to a small curl. A big sit-up is not what it is looking for.

Where can I read more?

• What Upfit can't check, including how the form score works
• How Upfit works
• All exercise pages

Upfit is an iPhone app, out now on the App Store. It is a fitness app, not medical advice. Stop if you feel pain or dizziness.