If your clients take tirzepatide and you coach them through strength work, the newest trial is one study worth knowing: 120 sedentary adults aged 50 to 70 without diabetes, trained under supervision. Adults who lifted weights three times a week under supervision lost less lean mass than those on the medicine alone, and their strength went up while strength fell in the medicine-only group. The study, the Tirzepatide and Resistance Exercise (T-REx) trial, was published in Nature Medicine on 2026-11-09. Weight loss and fat loss were similar in both groups, so the training did not change how much weight came off. Medication questions still belong with each client’s prescriber.
What did the T-REx trial find about lean mass and strength?
The Nature Medicine paper, published online on 2026-11-09, reports that both groups lost about the same weight and fat over 40 weeks. The difference was in lean tissue and strength. The authors say training “did not completely prevent” lean mass loss, but it reduced that loss: total lean soft tissue fell 4.67 kg on tirzepatide alone and 3.57 kg with training.
Quick facts as of 2026-11-11
| Measure (40 weeks) | Tirzepatide alone (T) | Tirzepatide plus training (T+REx) | Between-group result |
|---|---|---|---|
| Total weight change | -22.61 kg | -22.28 kg | P=0.694 |
| Total fat mass change | -17.19 kg | -17.98 kg | Difference -0.77 kg (95% CI -2.14 to 0.60), P=0.700 |
| Total lean soft tissue change | -4.67 kg | -3.57 kg | Difference 1.09 kg (95% CI 0.43 to 1.75), P<0.001 |
| Appendicular lean soft tissue change | -3.55 kg | -2.92 kg | Difference 0.63 kg (95% CI 0.30 to 0.96), P<0.001 |
Strength was measured as one-rep max lifts. The paper reports that all three lifts fell on tirzepatide alone and rose with training, with every between-group difference at P<0.001.
| Lift (one-rep max) | Tirzepatide alone | Tirzepatide plus training |
|---|---|---|
| Bench press | Fell 4.09 kg (8.4%) | Rose 4.68 kg (10.7%) |
| Lat pulldown | Fell 4.42 kg (6.5%) | Rose 8.58 kg (15.7%) |
| Knee extension | Fell 4.42 kg (9.0%) | Rose 5.88 kg (17.5%) |
The authors describe the net strength gain from training as about 20%. Blood pressure, glucose, insulin, HbA1c and lipids changed in the same way in both groups, so training did not materially change tirzepatide’s benefits on those markers.
What training did the trial use?
Participants did three one-hour supervised group sessions a week for 40 weeks, in a gymnasium, led by accredited exercise physiologists. The program moved through five 8-week phases, from light and moderate technique work to moderate and vigorous strength and hypertrophy training. Adherence was 91%.
Everyone was told to keep their protein intake up, and no specific diet was given. A food-diary subset found similar energy and protein intake in both groups. The tirzepatide dose was raised over the trial, and most participants tolerated 15 mg weekly.
For a trainer, this is the blueprint the paper describes: how often the sessions ran, who supervised them, how the work progressed and how long the program lasted.
Who was in the trial, and what does that mean for your clients?
The trial enrolled 120 adults with overweight or obesity: 60 men and 60 postmenopausal women, with a mean age of 57.7 years (range 50.1 to 70.3). They had no diabetes or cardiovascular disease and were initially sedentary. Each person was randomized to tirzepatide alone or tirzepatide plus resistance exercise.
Population matters when you read any trial, so check who was enrolled before you apply a result to your own clients.
The trial tested one medicine, tirzepatide. It does not describe semaglutide, younger adults or people with diabetes, because those groups were not in it.
Is lean mass the same as muscle?
No. In this paper, lean mass means DXA lean soft tissue. That includes skeletal muscle but is not only muscle. The paper’s discussion estimates skeletal muscle loss at about 2.5 kg on tirzepatide alone and about 2 kg with training.
Does the study show that any strength training works?
The results describe one program: three supervised one-hour sessions a week, run by accredited exercise physiologists, with the phased progression described above. Any change to a client’s training should be set with that client’s prescriber and within your own scope of practice.
Where does training end and medical advice begin?
MedlinePlus personal trainer guide says a trainer can give professional exercise advice and general healthy-living tips, but should not tell you how to treat a medical condition. It also says a trainer should stay within the limits your provider sets on exercise, and should not prescribe or sell nutritional supplements.
For recovery from an illness or injury, MedlinePlus says to work with the health care provider or other health care professionals to create the exercise program.
Medication questions go to the prescriber: which dose, when to take it, side effects, or whether a medicine should change. A pharmacist can help with how a medicine is taken. When a client asks you one of these, the answer comes from the prescriber, and your job is to find out what exercise limits they have set.
What did the trial report about side effects?
| Item | Reported in the trial |
|---|---|
| Nausea | About half of participants, similar in both groups |
| Vomiting, constipation, diarrhea, indigestion | Each about one-third of participants, similar in both groups |
| Serious adverse events | Six in total (five on tirzepatide alone, one with training), all judged unrelated to tirzepatide or exercise by the authors |
| Completion | 111 of 120 (93%) finished; 6 withdrew for adverse events, 2 after a breast cancer diagnosis, 1 for personal reasons |
How do I read the news coverage without getting it wrong?
- The Yahoo Health article, republished from Men’s Fitness on 2026-11-10, summarizes one trial of 120 adults. The exact figures and design in this guide come from the Nature Medicine paper.
- newsGP, the news service of the Royal Australian College of General Practitioners, reported that training reduced lean muscle and tissue loss by “up to 25%” and improved strength by 10%. The newsGP report on the study gives those figures. The paper’s own numbers are in the tables above, and they are the ones to use.
- newsGP also described tirzepatide as “sold as Wegovy”. That is an error: Wegovy is semaglutide, and tirzepatide is sold as Mounjaro and Zepbound.
- Lean mass is not the same as muscle, as explained above.
What did the lead researcher say?
Winthrop Professor Danny Green, the lead investigator at the University of Western Australia, said in the University of Western Australia release: “We now know that muscle loss can be reduced and strength increased when regular resistance training is used alongside tirzepatide treatment.” The university says the trial is the first to show the effects of combining a GLP-1 medicine and resistance training on body composition, muscle mass, strength and cardiovascular health measures.
Speaking to newsGP, Green said some loss remained, “but the strength increased in the resistance training group.” He called GLP-1 medicines “blockbuster drugs” but “not the full toolkit”, and said GPs play a crucial role. He said what makes the study a world first is that body composition was tracked every eight weeks with DEXA scans.
How do I get qualified to coach clients on these medicines?
Working with these clients is a scope question as much as a training one. A 2017 review of trainer nutrition standards, indexed by PubMed, compared nutrition standards for personal trainers across ten countries and found they varied widely. It notes that trainers are well placed to provide nutrition care within their recommended scope of practice, and that going beyond that scope has been identified as an industry risk.
MedlinePlus advises looking for certification from an agency accredited by the National Commission for Certifying Agencies (NCCA). If you are still building your credentials, see how to become a personal trainer for the steps and costs, and most respected personal trainer certifications for the options.
Before you act: questions to settle your next step
- Ask each client’s prescriber what exercise limits they have set.
- Ask the prescriber or a pharmacist any question about dose, timing or side effects.
- Read the full Nature Medicine trial paper before you adapt any program, especially the protocol and phase details.
- Check your certifying body’s scope of practice for nutrition and client health questions.
Your next step is small: read the protocol section of the paper, then bring any medication question back to the prescriber.
By the Fitness Career Guide Editorial Team
This article is for general information purposes only and does not constitute medical advice. Consult your doctor or qualified healthcare provider before making changes to your health routine.