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GLP-1 and GLP-1/GIP medications can produce reductions in lean mass during substantial weight loss, but this does not automatically mean clinically significant muscle wasting or loss of strength.
A 2026 meta-analysis of 20 randomised trials involving more than 15,000 participants found that lean mass represented approximately 25–39% of total weight lost with incretin-based medications. However, lifestyle programmes that included resistance training had a more favourable lean-mass profile, with lean mass accounting for about 17.5% of weight lost.
The practical message is simple: weight loss should be accompanied by resistance exercise, adequate nutrition and monitoring of physical function.
Semaglutide and tirzepatide have changed expectations around non-surgical weight management because they can produce substantial reductions in body weight while also improving several metabolic outcomes.
The expansion is reflected in prescribing and regulatory activity. In March 2026, the FDA approved a higher-dose formulation of Wegovy, Wegovy HD, for chronic weight management in eligible adults. The FDA has also continued to expand and review the role of incretin-based therapies in obesity and metabolic disease.
This growing use creates a new rehabilitation question: What happens to physical capacity while body weight is falling quickly?
A lower number on the weighing scale does not necessarily mean better muscle health.
When calorie intake decreases substantially, the body loses both fat and non-fat tissue. Rapid weight reduction can therefore reduce lean soft tissue alongside adipose tissue.
However, lean mass is not identical to skeletal muscle. DXA- or BIA-derived lean mass can include water and other non-fat tissues, so describing every kilogram of lean-mass reduction as “muscle loss” is scientifically inaccurate. Current reviews emphasise the need to assess muscle quantity together with strength and physical performance.
For physiotherapists, this distinction matters. Instead of focusing only on body weight, monitor whether the patient is maintaining:
● Strength
● Functional capacity
● Walking tolerance
● Balance
● Stair-climbing ability
● Resistance-training performance
● Daily physical activity
This is one of the most interesting findings emerging in 2026.
A July 2026 systematic review examined objectively measured physical activity across seven studies and six trials involving 924 participants. Most studies did not find a statistically significant overall reduction in physical activity. However, five of seven studies showed numerically lower free-living activity, and one reported approximately 1,144 fewer steps per day in the GLP-1 group. Structured exercise participation was generally similar between groups.
This suggests an important distinction:
Patients may still be capable of exercising, while unconsciously moving less during the rest of the day.
Less walking, fewer standing breaks and reduced spontaneous movement can gradually lower total activity.
Resistance training should become a central part of rehabilitation for suitable patients using GLP-1-based weight-loss therapy.
A practical starting programme can include 2–3 resistance-training sessions per week, covering the major movement patterns:
● Squat or sit-to-stand
● Hip hinge
● Push
● Pull
● Step-up or lunge
● Calf strengthening
● Core and trunk exercises
For many beginners, 1–3 sets of approximately 8–12 controlled repetitions can provide a useful starting point. The load should be challenging while maintaining good technique, then progressively increased as tolerance improves.
The objective is not to make every session exhausting. It is to provide the mechanical stimulus required to tell the body: this muscle is still needed.
Research and expert recommendations consistently support progressive resistance exercise alongside GLP-1 therapy to help preserve lean mass and physical function.
This may become one of the most valuable roles for physiotherapists in GLP-1-supported weight management.
Instead of prescribing only a 45-minute workout, the physiotherapist should look at the patient’s entire day.
For example:
Morning:
Add a short walk or mobility routine rather than remaining sedentary after waking.
Workday:
Use brief movement breaks, standing periods and walking between tasks.
After meals:
Introduce short, comfortable walks when medically appropriate.
Home:
Encourage stairs, household movement and other safe opportunities to break up prolonged sitting.
Exercise:
Maintain structured resistance training even as body weight decreases.
This is particularly important because the 2026 physical-activity evidence suggests the possible reduction may occur more in non-obligatory spontaneous activity than in the ability to complete prescribed exercise.
A GLP-1 rehabilitation assessment should go beyond BMI and weight.
Useful measures include:
● Sit-to-stand performance
● Grip strength when relevant
● Functional lower-limb strength
● Gait and walking tolerance
● Balance
● Exercise capacity
● Resistance-training performance
● Step count or activity data when available
● Falls risk in older or vulnerable patients.
Body-composition measurements can also be useful, but they should be interpreted alongside functional measures rather than in isolation.
A patient who loses 15 kg but maintains strength and function presents a different clinical picture from someone who loses the same amount while becoming weaker, less active and increasingly fatigued.
Physiotherapists should not independently prescribe medical nutrition therapy outside their scope, but they should recognise the importance of adequate protein and nutrition during weight loss.
Current expert recommendations support adequate protein intake alongside resistance exercise, with some consensus recommendations suggesting more than 1.2 g/kg/day in appropriate patients, while recognising that individual needs vary with age, body composition, kidney health and clinical circumstances.
Patients with poor appetite, significant gastrointestinal symptoms or difficulty meeting nutritional needs should be referred to an appropriate medical or nutrition professional.
The evidence does not yet establish that every person prescribed a GLP-1 medication must receive physiotherapy. However, the emerging model strongly supports integrating structured physical activity and resistance training into weight-management care, particularly for people at higher risk of functional decline or lean-tissue loss.
This positions physiotherapists as more than exercise instructors.
They can assess movement, identify strength deficits, prescribe progressive loading, monitor function and help patients maintain everyday activity while their body weight changes.
The 2026 evidence increasingly supports treating the quality of weight loss—not just the quantity—as a clinical outcome.
Current evidence does not establish that GLP-1 medications directly destroy skeletal muscle. Lean mass can decline during substantial weight loss, but this is not equivalent to proven muscle wasting or functional deterioration.
Cardiovascular exercise is valuable for health and fitness, but resistance training provides a more direct stimulus for maintaining muscle strength and lean tissue during weight reduction.
For many adults, two to three resistance sessions per week provide a practical starting point. The programme should be individualised according to age, baseline fitness, medical conditions, symptoms and training experience.
No. A preventive approach is more logical. Strength, activity levels and functional capacity can be assessed early so that exercise becomes part of the weight-loss strategy rather than a response to weakness after it develops.
Some lean mass loss may occur during substantial weight reduction, but evidence suggests it can be reduced through resistance exercise, adequate nutrition and appropriate monitoring.
GLP-1 medications can produce remarkable weight loss, but successful treatment should not be measured by the scale alone. Preserving strength, movement and physical function should be part of the same plan. In 2026, physiotherapy has an increasingly relevant role in helping patients lose excess weight while protecting the muscle and function they need for everyday life.