Jumping jacks: how Upfit checks your form

Jumping jacks are a fast bodyweight move. Upfit counts each full out-and-in cycle from your front camera and speaks a cue when a part of it is missing.

How do I do a jumping jack?

Start with your feet together and your arms by your sides. Hop your feet out wide and swing your arms up overhead. Then hop back to the start. Land softly on the balls of your feet. Slow down or step the move out if hopping is not right for you today.

How do I set up my phone for jumping jacks?

Jumping jacks are tracked facing the camera, because the checks read how wide your arms and feet go sideways. Prop the phone upright and step back until your whole body fits, with room for your arms to reach overhead and your feet to spread. Two to three metres (six to ten feet) is a good start.

What does Upfit check on jumping jacks?

Upfit watches one full cycle, from the closed position (feet together, hands down) out to the open position and back. At the end of the cycle it checks:

• Arm reach. Your arms have to come up at least partway, roughly chest to shoulder height. This check is lenient.
• Foot width. Your feet have to spread to at least about one shoulder width, and each foot has to move out from the middle of your hips.
• The hop. Your hips have to show a small up-and-down bounce, so stepping out slowly does not count.

Pace is judged differently. Every ten seconds or so the coach looks at your average time per rep and may ask you to speed up or slow down.

When does a jumping jack count?

A jack counts when you complete a full open-and-close cycle and pass all three checks above. A cycle with no hop, narrow feet or low arms is not counted.

What does the coach say?

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

• "Jack those feet off the floor — actually hop them out!"
• "Wider jack — pop those feet outside the shoulders!"
• "Arms clap overhead at the top of every jack!"

Watch: how Upfit checks jumping jacks

A short walkthrough of how to do it, the phone set-up, what the camera checks and what the coach says.

What can't Upfit check on jumping jacks?

The arm check is lenient. The coach asks for hands overhead, but the detector accepts arms that come up to about chest or shoulder height, so it will not insist on a full overhead reach. It also does not check that your arms and legs move together, how you land, or how hard your feet hit the floor.

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.