KNEE SLEEVE · REAL-TIME FORM FEEDBACK
Feel the fix, mid-squat.
Preflex notices when your knee drifts or you sink too deep, and nudges you with a gentle buzz while you can still correct it.
Being developed with physical therapists. A training aid, not a medical device.
Eyes-free
Keep your head up. The cue is a buzz on your thigh, not something to watch on a screen.
Any room
No camera to prop up and no lighting to get right. Everything runs on the sleeve.
Set by your therapist
Your PT chooses your depth and alignment limits, so the feedback matches your plan.
Most rehab happens when nobody is watching.
We spoke with 10 physical therapists. They told us patients do most of their exercises alone, and that good form tends to slip as soon as they do.
Preflex is there for those reps, with the correction your therapist would give at the moment you need it.
HOW IT WORKS
Four steps. The first two take seconds.
Pull it on
Slide the sleeve over your knee while seated. Printed marks show where it should sit.
Stand still for three seconds
Preflex learns your straight-leg position, then checks it with one easy bend.
Squat
If your knee caves inward or you pass your depth limit, you feel a buzz on your outer thigh. Move toward the buzz.
See how it went
Your reps and cues save to the app and reach your therapist before your next visit.
THE SLEEVE
Made to be worn, washed and forgotten about
A stretch sleeve from mid-thigh to mid-calf, with two small pods on the outside of your leg, clear of the kneecap.
Works with single-leg, two-leg and chair squats. Weight and battery life are design targets for the current prototype.
THE APP
Your progress, without the homework
The sleeve does the coaching on its own, so your phone can stay in your pocket. Afterwards, the app shows you what happened.
- Reps completed and cues felt, for every session
- Your week at a glance, so missed days are easy to spot
- Shared with your therapist automatically
FOR PHYSICAL THERAPISTS
Assign squats for home, and know they were done well
Your limits, per patient
Set depth and knee-alignment thresholds for each patient. Preflex has no built-in idea of "correct".
Every session, every rep
See who is on track, who has gone quiet, and how often each patient needed a cue.
Records built for RTM
Sessions upload with timestamps, the kind of record Remote Therapeutic Monitoring is based on.
QUESTIONS
Good to know
Is Preflex a medical device?
No. Preflex is a training aid for exercise form. It does not diagnose or treat any condition, and it does not replace your physical therapist.
Do I need my phone while I exercise?
No. Sensing and feedback run on the sleeve itself. The app is for set-up and for looking back at your sessions.
What does the cue feel like?
A short vibration on the outside of your thigh. Moving your knee toward the buzz brings it back into line.
Which exercises does it work with?
Squats: single-leg, two-leg and chair squats.
When can I get one?
Preflex is still a prototype, with volunteer testing planned for early 2027. Join the list and we will tell you when a pilot opens.
Who is behind Preflex?
Preflex Technologies is a team of six engineers at the University of Colorado Boulder, working with Design Center Colorado.
Be first to try Preflex
Leave your email and we will let you know when the pilot opens, whether you are doing the exercises or prescribing them.