Last month a woman I'll call Dana noticed something small. She was down a lot of weight on her GLP-1, and people kept telling her how light she looked. But she'd started using her hands to push off her thighs when she got up from the couch. She hadn't done that in years. She didn't mention it to anyone, because everyone was saying she looked great.

Nothing else in her life was measuring that moment. The scale was cheerful and the mirror was kind. Only the couch registered that her legs had changed.

This article is about giving that moment a number.

The metric nobody hands you

When you start a GLP-1, you get a weight, and maybe a waist measurement. Both describe size. Neither describes capacity, meaning what your body can do with what it has left.

That gap matters because weight lost on these medications is not all fat. Clinical trials of semaglutide and tirzepatide that included body-composition scans found that a meaningful share of the weight lost was lean mass. The exact share varies by study and by person. Lean mass includes muscle, but also water and other tissue, so the scans don't map one-to-one onto muscle. Still, the direction is well established: when you eat much less, your body draws on muscle as well as fat unless you give it a reason to keep the muscle.

The usual reasons are enough protein and mechanical load, which means lifting. The difficulty is knowing whether those are working. A DEXA scan can tell you, but it costs money, requires an appointment, and most people get one rarely if ever.

So you need something you can repeat in your living room.

Why the legs, and why a chair

Your lower body holds the largest muscles you own. The quadriceps, glutes, and hamstrings do the work whenever you stand, climb, or walk. They are also where age-related and diet-related muscle loss tends to show up as lost function: getting out of cars, handling stairs, getting up off the floor.

Researchers who study sarcopenia, the loss of muscle strength and mass, have used the sit-to-stand movement for a long time because it is a decent stand-in for leg strength. The European consensus definition of sarcopenia (EWGSOP2) includes the five-times sit-to-stand test as one way to assess low strength, with taking longer than 15 seconds flagged as a concern. The CDC's STEADI fall-prevention toolkit uses a 30-second chair stand test, with below-average scores varying by age and sex.

These tests were built mainly for older adults. A person in their thirties or forties on a GLP-1 isn't the intended population, so don't treat any cutoff as a diagnosis. The real value is in comparing yourself with yourself. Your own baseline, repeated under identical conditions, is a far more useful signal than anyone else's norm.

How to run the test properly

A test only means something if you can repeat it exactly, so the details matter.

Pick one chair and keep it. Use a sturdy, armless chair of ordinary height, about 17 inches (43 cm) to the seat. Put its back against a wall so it can't slide. Write down which chair you used.

Set your posture. Sit toward the front of the seat. Place your feet flat, about shoulder-width apart. Cross your arms over your chest, with hands on opposite shoulders. This matters, because the moment you use your hands you're no longer testing your legs.

Run the 30-second version. Start a timer. Stand fully upright, then sit all the way back down, repeating as many times as you can for 30 seconds. Count only complete stands. If you're mid-rise when time ends, it counts as a stand if you're more than halfway up.

Or the five-rep version. If 30 seconds feels like too much, time how long it takes to complete five full stands, arms crossed. Lower is better.

Add a note on how you feel. Next to the number, write a few words: rested or tired, fed or not, how long since your last shot. Your results will wobble with these things, and the note helps you read the wobble later.

How to read the number without fooling yourself

One score is just a starting point. What counts is how it moves over weeks.

Here is the logic. You're losing weight, so every rep requires you to lift less mass than before. If your leg strength simply stayed the same, your score should go up, because you're moving a lighter body with the same engine. A score that holds flat while you lose weight can therefore mean you've lost some strength. A score that drops is a clearer signal, and a reason to look at your protein and your training.

There are two honest caveats.

First, the test is noisy. Sleep, soreness, nausea, and a skipped breakfast can each cost you a rep or two. That's why you retest on a consistent schedule, say every two to four weeks, at a similar time of day. Look for a trend across several readings, and ignore any single bad day.

Second, a bad number doesn't prove muscle loss. Low fuel, dehydration, and poor sleep can all reduce performance without any change in tissue. This is the same ambiguity that makes strength drops on a GLP-1 hard to read. The test tells you something is off. It doesn't tell you what. Either way, it's information you didn't have before.

What to do when the number slips

A slipping score has few causes, and the fixes are boring. That's good news, because boring fixes are doable.

Start with whether you're hitting your protein target across the week, not on your best day. Then check whether you're doing any resistance training that loads the legs: squats to a chair, step-ups, split squats, leg press, or loaded carries. Muscle responds to being asked to work, and sit-to-stand improves most reliably when you train the movement itself, since the test measures the thing you've been practicing.

If the number is low, or you've noticed real changes like pushing off with your hands, bring it to your prescriber or a physical therapist. A concrete observation ("my 30-second count went from 14 to 11 over two months") is far easier to act on than a vague worry about feeling weaker.

Your next moves

  • Test today, before you decide anything. Pick your chair, cross your arms, and do the 30-second test once. Write the date, the count, and one line about how you felt.
  • Fix the conditions. Tape a note to the chair or put a reminder in your phone: same chair, same wall, arms crossed, same time of day.
  • Schedule the retest. Put it on your calendar every three weeks, ideally the same day of your injection cycle so you compare like with like.
  • Add one leg movement to your week. If you don't lift yet, do three sets of sit-to-stands with a slow lowering phase, two or three days a week. Stop each set a couple of reps before you'd have to use your hands.
  • Take the numbers to your next appointment. Bring your log. If the trend is down, ask your doctor or a physical therapist whether your protein and training plan needs to change.

The measure that matches the goal

Most people on a GLP-1 are not trying to be lighter for its own sake. They want to feel capable in their own bodies, to climb stairs, play with their kids, travel, and stop negotiating with their knees. The scale can't tell you whether that's happening. A chair can.

That is the idea behind Lean, which tracks protein targets and strength alongside the weight so a number like your chair-stand count sits next to the scale and tells you whether the weight you're losing is the weight you meant to lose. If you'd like a place to keep that log, you can find it at lean.lumenlabs.works. But the test works with a chair and a pen, so start there.