Few health topics have grown as quickly as GLP-1 medications. Originally developed for type 2 diabetes, GLP-1 receptor agonists such as semaglutide and tirzepatide are now widely used for weight management.

A few clients have mentioned that they’ve heard GLP-1 drugs might strengthen their knees, and they’re curious how much of that is true. The honest answer is that some of it is well supported, some of it is promising but unproven, and some of it is hype. Here is where the GLP-1 research stands, and what it means for how you train.

WHAT WE KNOW: GLP-1 TREATMENT, WEIGHT LOSS AND KNEE PAIN

The strongest evidence comes from the STEP 9 trial, a randomized, placebo-controlled study of 407 adults with obesity and painful knee osteoarthritis. Everyone received diet and activity counselling. Those taking semaglutide lost an average of 13.7% of their body weight, compared with 3.2% on placebo, and reported much larger drops in knee pain. The authors reported “greater reductions in body weight and pain related to knee osteoarthritis” (New England Journal of Medicine, 2024). Physical function improved as well. 

This part of the picture is reasonably solid. Carrying less weight means less stress on the knee with every step. Research on exercise and weight loss has long shown that each pound lost removes roughly four pounds of load from the knee during walking. Our earlier post on exercise, body weight and arthritis explains why stairs, squats, and single-leg movements load the joint so heavily. A GLP-1 can help people reach a lower body weight, and that can make the knee feel better.

WHAT IS STILL PRELIMINARY: CARTILAGE AND THE JOINT ITSELF

Here we need to be careful. In animal and laboratory studies, GLP-1 receptor agonists have reduced inflammation and cartilage breakdown. A few human studies hint at slower cartilage loss. Large medical-records analyses have also linked GLP-1 use to fewer knee replacements. A 2026 study in a pain medicine journal concluded that these drugs “may represent a complementary strategy within non-surgical knee osteoarthritis management” (Regional Anesthesia & Pain Medicine, 2026). Note the word may. Records-based studies cannot rule out other explanations, such as differences in activity level or overall health, and the authors say more rigorous studies are needed.

Not every study agrees, either. A 2026 diabetes cohort study found no lower risk of developing osteoarthritis among GLP-1 users compared with another diabetes drug. Another recent review noted that “direct cartilage-, synovium-, subchondral bone-, or structure-modifying effects remain unproven” (Frontiers in Pharmacology, 2026). So, to be clear: no one has shown that GLP-1 medications regrow cartilage. Anyone who says otherwise is getting ahead of the evidence.

WHY LESS PAIN IS NOT THE SAME AS A HEALTHIER JOINT

Less pain and a healthier joint are not the same thing. Much of the benefit seen so far may come from weight loss and reduced inflammation rather than from repaired tissue. Pain relief is valuable, since it can make it easier to move, but it can also tempt people to do more than the joint is ready for. A knee that hurts less is still a knee with osteoarthritis, and it still needs to be strengthened and respected.

THE MUSCLE PROBLEM THAT GLP-1 USERS RARELY HEAR ABOUT

This is where our work as trainers comes in. Weight lost on a GLP-1 is not all fat. Body-composition studies of semaglutide and tirzepatide suggest that roughly a quarter to as much as 40% of the weight lost can be lean mass. Lean mass is not purely muscle, and the proportion varies from person to person, but the concern is real. Your quadriceps, hamstrings and glutes are the knee’s shock absorbers. If they shrink while the scale drops, you may have a lighter body that is less capable of controlling the joint. That is especially important for adults over 50, who are already at risk of losing muscle with age.

HOW STRENGTH TRAINING PROTECTS YOUR KNEES ON A GLP-1

Resistance training is the best-supported tool for holding on to muscle during weight loss, and it works alongside a GLP-1, not against it. Strong thigh and hip muscles share the load with the joint and improve control when you stand up, climb stairs, or walk downhill. In our work with clients, we often build programs around compound movements like squats, bench squats, and deadlifts, adjusting depth, load, and tempo to suit each person’s knees. Done well, this approach builds muscle without aggravating sore joints. Our guide to strength training for seniors covers the fundamentals.

REDUCING UNNECESSARY JOINT LOADING AND IMPROVING MOVEMENT

A smart strength program does more than build muscle. It teaches your body to move better. We work on hip strength, so your knees do not collapse inward, on balanced single-leg control, on ankle mobility, and on sitting and standing patterns that spread the load across more muscles. We also manage volume and progression, because the goal is to lower unnecessary stress on the knee, not to avoid loading it altogether. Gradual, well-coached loading tends to leave joints more resilient, while too much too soon can set people back, especially when pain has recently improved.

WHAT WE TELL CLIENTS WHO ARE TAKING A GLP-1

We do not prescribe or advise on medication, and decisions about a GLP-1 belong with you and your physician. What we can do is help you get the most from your body. Start strength training early rather than waiting until you have lost a lot of weight. Aim for at least 2 sessions a week that challenge all the major muscle groups. Eat enough protein, as your doctor or dietitian recommends, and be patient if appetite is low. Report new or worsening knee pain to your healthcare provider. Whatever the research eventually shows about cartilage, a stronger body will serve your knees well.

THE BOTTOM LINE ON GLP-1 AND KNEE HEALTH

The GLP-1 story is encouraging but unfinished. Reduced knee pain, better function, and weight loss are supported by good trial evidence. Cartilage protection, slower disease progression, and fewer replacements are interesting early signals, not proven benefits. The one thing that is certain is that muscle matters. Whether or not you take a GLP-1, a well-designed strength program is one of the most reliable ways to protect your knees and your independence.

START THE CONVERSATION WITH A PERSONAL TRAINER

If you are using a GLP-1, thinking about one, or simply dealing with sore knees, our team would be glad to talk. We will listen to your goals, ask about your joints, and design a strength program that fits. Contact Nielsen Fitness today to start talking to a personal trainer.