This article was published in the Aesthetics Journal. We would like to thank the authors and the Aesthetics Journal for sharing it with the IMCAS community.

Dr Nestor Demosthenous and aesthetic nurse Amanda Demosthenous explore the impact of GLP-1 receptor agonists on muscle composition

Skeletal muscle is a dynamic, metabolically active organ essential for maintaining health throughout the lifespan. Beyond providing strength and locomotion, muscle regulates glucose metabolism, supports immune signalling and contributes to endocrine communication through the secretion of myokines.¹ A decline in muscle mass and function, known as sarcopenia, represents one of the most clinically significant hallmarks of ageing and is associated with frailty, metabolic dysfunction, reduced mobility and diminished quality of life.²

In modern clinical practice, muscle health must be reframed as a therapeutic priority rather than an incidental outcome of exercise. The rapid adoption of pharmacological weight-loss therapies, particularly glucagon-like peptide-1 (GLP-1) receptor agonists, has intensified the importance of preserving lean tissue.² While these medications provide unprecedented metabolic benefits, emerging evidence demonstrates that a substantial proportion of total weight loss may derive from non-fat mass, including skeletal muscle.^3,4

Muscle preservation influences glucose homeostasis, insulin sensitivity, inflammatory burden and functional independence.^5,6 Protecting skeletal muscle during ageing and therapeutic weight loss represents a critical frontier in preventative and metabolic medicine.

The physiology of muscle loss

The physiology of muscle loss through ageing is multifactorial and reflects a convergence of hormonal, neurological and cellular changes. Sarcopenia and dynapenia typically emerge from the fifth decade of life, progressing at approximately 1% annual loss of muscle mass and 2-3% annual reduction in strength.⁷ These rates accelerate in sedentary individuals, those experiencing chronic disease and patients exposed to prolonged caloric restriction.

A central feature of ageing muscle is anabolic resistance: a diminished ability of skeletal muscle to respond to dietary amino acids and mechanical loading.8 Even when protein intake appears adequate, older muscle demonstrates blunted activation of muscle protein synthesis pathways.⁸ This reduced responsiveness shifts the balance toward net protein breakdown and gradual tissue attrition. The phenomenon is compounded by reduced physical activity, which further suppresses anabolic signalling and accelerates fibre atrophy.⁹

Type II muscle fibres, responsible for explosive strength and rapid force production, are preferentially lost with age.¹⁰Their degeneration compromises balance, gait stability and protective reflexes, contributing to increased fall risk and injury.² At a cellular level, ageing muscle exhibits mitochondrial dysfunction, impaired satellite cell activity and elevated inflammatory signalling. These changes collectively impair regenerative capacity and energy efficiency, making recovery from illness or injury slower and less complete.²

Importantly, sarcopenia is not an unavoidable consequence of ageing but a modifiable condition. Resistance exercise and targeted nutritional strategies consistently demonstrate the ability to slow or reverse muscle decline.^11,12 However, these interventions are rarely embedded systematically into clinical care. Muscle loss is often recognised only after functional impairment becomes visible, at which point reversal is more difficult. A preventative framework that treats muscle preservation as a primary therapeutic objective is therefore essential.^8,11,12

What GLP-1 receptor agonists are and how they work

GLP-1 receptor agonists are pharmacological analogues of GLP-1, an incretin hormone that enhances glucose-dependent insulin secretion and suppresses appetite. Agents such as semaglutide and tirzepatide act centrally on hypothalamic appetite pathways while delaying gastric emptying and improving glycaemic regulation.¹³ These mechanisms create sustained caloric deficit and facilitate significant weight reduction.

Different GLP-1 variations differ in receptor affinity, duration of action and dual hormonal activity.¹⁴They differ across five clinically meaningful axes, molecular design (exendin vs. human analogue); half-life and dosing frequency; relative gastric vs. central appetite effects; presence or absence of dual incretin activity (tirzepatide); and finally, magnitude of weight reduction.¹⁴

Tirzepatide additionally activates glucose-dependent insulinotropic polypeptide pathways, potentially amplifying metabolic effects.¹⁵ While these agents were originally developed for diabetes management,¹⁶ their weight-loss efficacy has expanded their use into broader obesity and lifestyle medicine.

The emergence of GLP-1 receptor agonists introduces a new dimension to the clinical management of muscle. Rapid calorie deficit creates a physiological environment in which muscle protein breakdown may exceed synthesis. Research indicates that 25-39% of total weight lost during GLP-1 therapy may originate from lean tissue rather than adipose stores.¹⁷

Loss of skeletal muscle reduces resting energy expenditure and impairs glucose disposal, paradoxically undermining some of the metabolic benefits achieved through weight reduction. Patients may appear healthier by scale weight while experiencing silent deterioration in tissue quality. Furthermore, weight regain following discontinuation of GLP-1 therapy disproportionately restores fat mass rather than muscle,¹⁸ worsening body composition relative to baseline and increasing the risk of sarcopenic obesity.¹⁹

GLP-1 therapy must therefore be conceptualised not as isolated pharmacology but as part of a broader metabolic intervention. Protecting skeletal muscle is essential for ensuring that weight loss translates into functional improvement rather than physiological compromise. Clinics that ignore lean tissue dynamics risk achieving cosmetic weight reduction at the expense of long-term resilience. The challenge for clinicians is to develop structured protocols that integrate pharmacological therapy with muscle-preservation strategies. These protocols must be practical, measurable and adaptable across diverse patient populations. Muscle health cannot remain an abstract concept discussed in theoretical terms; it must become an operational target embedded into everyday clinical decision-making.

Patient suitability

Not all patients respond to GLP-1 therapy in the same way. Individuals with low baseline muscle mass, sedentary lifestyles or age-related anabolic resistance are particularly vulnerable to disproportionate lean tissue loss.² Aesthetic patients seeking rapid body transformation may prioritise weight reduction without appreciating functional consequences.

Clinicians should consider baseline strength, nutritional habits and activity levels when advising patients. Those with pre-existing sarcopenia or mobility limitations require intensified preservation protocols from the outset. Muscle monitoring should be presented as a safety measure rather than an optional enhancement.

Gastrointestinal intolerance, nausea and early satiety may impair nutritional adequacy, particularly protein intake.²⁰Rapid weight reduction may also exacerbate fatigue, orthostatic symptoms and functional weakness. In patients with insufficient resistance training, these effects can compound lean tissue loss.¹³

Contraindications include a history of medullary thyroid carcinoma, multiple endocrine neoplasia syndromes and certain gastrointestinal disorders.²¹ Clinicians must evaluate medical suitability alongside aesthetic goals. Muscle-preservation strategies cannot compensate for inappropriate pharmacological use.

Relevance in medical aesthetic practice

In medical aesthetic practice, clinicians are uniquely positioned to identify early signs of sarcopenic change. Patients frequently seek treatment for volume loss, fatigue or diminished physical tone without recognising the underlying muscular component. Integrating muscle assessment into aesthetic consultations reframes treatment from purely cosmetic correction toward physiological preservation. Protecting skeletal muscle aligns aesthetic goals with long-term metabolic health and positions clinics as leaders in responsible body-composition management.

A practical muscle-preservation framework begins with recognising skeletal muscle as a measurable clinical variable rather than an invisible background tissue. In the context of GLP-1 therapy and ageing populations, clinicians must treat lean mass in the same way they monitor blood pressure or glycaemic markers: as a core determinant of patient outcomes. This shift requires systematic assessment protocols that move beyond simple scale weight. Clinical evaluation of muscle health should encompass three domains: tissue quantity, strength and functional performance.¹¹ Each domain provides distinct but complementary information. Body composition analysis using dual-energy X-ray absorptiometry or high-quality multi-frequency bioelectrical impedance enables estimation of total lean mass and appendicular skeletal muscle.²² While DEXA remains the gold standard, repeatable in-clinic impedance systems provide a practical alternative for longitudinal monitoring. Two reputable brands are InBody and Hume. Baseline measurement prior to initiating GLP-1 therapy is essential, with reassessment every eight to 12 weeks during active weight reduction. Trend analysis is more clinically meaningful than single measurements; progressive lean mass decline relative to total weight loss signals disproportionate muscle catabolism.²³

Strength testing offers an additional layer of insight into neuromuscular integrity. Handgrip dynamometry is inexpensive, reproducible and strongly associated with frailty risk, hospitalisation and long-term mortality.¹¹ A reduction of approximately 5% or greater over a monitoring interval should prompt intervention. Functional assessments such as sit-to-stand performance, gait speed and timed mobility testing add ecological validity by measuring real-world muscular competence.^2,24 These tests correlate closely with independence and fall risk, particularly in older adults.

When interpreted together, these metrics allow clinicians to distinguish healthy body recomposition from sarcopenic weight loss. A patient who loses total mass while maintaining strength and functional capacity is likely preserving muscle. Conversely, declining performance despite scale improvement indicates physiologically unfavourable tissue loss.²³

Monitoring protocols during GLP-1 therapy must be explicit and structured. Patients should receive early counselling that muscle preservation is an integral therapeutic objective. Appetite suppression frequently reduces protein intake unintentionally, while rapid caloric restriction accelerates muscle protein breakdown. Without targeted intervention, the physiological environment strongly favours lean tissue depletion.

Clinicians should track lean mass trends, strength markers, dietary protein adequacy and resistance exercise adherence at every follow-up. Lean mass exceeding approximately one quarter of total weight loss signals clinically significant muscle depletion and warrants escalation of intervention.²² This threshold represents a practical trigger point rather than an absolute rule, but it highlights patients who are drifting toward sarcopenic obesity.

Resistance exercise remains the cornerstone of muscle preservation. Mechanical loading is the most potent stimulus for muscle protein synthesis and cannot be replaced by pharmacology alone.^8,9 Even modest training volumes provide protective benefit when applied consistently. Clinicians should prescribe structured programmes involving two to four resistance sessions per week, progressive overload targeting major muscle groups and performance to moderate fatigue. Referral to a local personal trainer experienced in resistance training is best. Exercise prescriptions should be written with the same clarity as medication instructions. Vague recommendations to “be more active” fail to produce measurable outcomes.

Nutritional optimisation acts synergistically with mechanical loading. Older adults and individuals in caloric deficit require elevated protein intake to overcome anabolic resistance.^8,9 Current evidence supports daily protein intake of approximately 1.2–1.6 g/kg body weight, distributed evenly across meals to maximise muscle protein synthesis.²⁵ High-leucine protein sources stimulate mTOR signalling and enhance anabolic responsiveness.²⁵ In patients struggling to meet targets through whole foods, supplementation may be clinically appropriate.

Adjunctive nutrients such as omega-3 fatty acids and vitamin D support neuromuscular function, mitochondrial health and inflammatory regulation.^26,27 While not substitutes for resistance training or adequate protein, these interventions contribute to an anabolic environment that favours tissue preservation. The most effective nutritional strategies are those translated into practical behavioural anchors: protein-first meals, structured meal timing and post-exercise amino acid intake. Referral to a local nutritionist can help patients design a nutritional programme where they ‘eat with intent’.

Aesthetic treatments

Muscle stimulation technologies provide an additional therapeutic pathway, particularly for patients unable to perform sufficient voluntary resistance training. Neuromuscular electrical stimulation (NMES) and high-intensity focused electromagnetic modalities generate supramaximal contractions capable of recruiting deep motor units and inducing hypertrophic signalling.^28-30 These technologies are not replacements for exercise but valuable adjuncts in mobility-limited populations, post-surgical recovery or severe deconditioning.

NMES has been evaluated across immobilisation, critical illness and orthopaedic rehabilitation contexts. In mechanically ventilated ICU patients, early NMES attenuated quadriceps atrophy compared with standard care, demonstrating preservation of muscle cross-sectional area during disuse.³¹ Similarly, in older adults and mobility-limited populations, it has been shown that NMES improves muscle strength and functional performance, particularly when voluntary contraction is insufficient.³² It has been shown that NMES improves quadriceps strength recovery and functional outcomes compared with exercise alone.³³ Mechanistically, electrically evoked contractions recruit high-threshold motor units non-selectively, bypassing central inhibition and generating sufficient mechanical tension to stimulate hypertrophic pathways.

Early integration of stimulation protocols in high-risk GLP-1 patients may mitigate rapid lean tissue loss. Beyond physiological benefits, visible improvements in strength and tone can reinforce behavioural adherence, creating a feedback loop between measurable progress and patient motivation.³⁴ Clinics that combine resistance training, nutritional guidance and device-assisted stimulation create a multimodal environment that supports muscle preservation from multiple angles.

A structured clinical implementation framework is required to translate muscle-preservation theory into daily practice. Without operational systems, even well-informed clinicians struggle to apply evidence consistently. The rise of GLP-1 therapy has created a patient population in which lean tissue monitoring is no longer optional but essential. Clinics must therefore adopt a repeatable model that integrates pharmacology, exercise physiology and nutritional science. This would involve baseline risk stratification as discussed above, scheduled lean tissue monitoring and a standardised muscle prevention protocol (resistant training prescription, protein strategy, adjunctive neuromuscular stimulation).

Special considerations

Age-related anabolic resistance amplifies the risk of muscle loss during caloric restriction.^8,9 Older adults require stronger mechanical stimuli and higher protein intake to achieve equivalent anabolic responses. Ageing muscle demonstrates anabolic resistance – a diminished stimulation of muscle protein synthesis in response to amino acids and resistance exercise – due to impaired mTORC1 signalling, reduced amino acid sensitivity and neuromuscular alterations. Consequently, older adults require higher per-meal protein doses and stronger mechanical stimuli to achieve hypertrophic responses equivalent to younger individuals.³⁵ Clinicians managing ageing patients on GLP-1 therapy must therefore apply more aggressive preservation strategies.

Resistance training intensity is a key determinant of adaptation.¹² Older adults are capable of significant strength gains when appropriately supervised. Muscle stimulation technologies provide additional value in this demographic by delivering high-intensity contraction without excessive joint loading.^28,29

Behavioural adherence and patient engagement represent the final and often most underestimated pillar of muscle preservation. Physiological strategies fail without sustained behavioural execution. Patients frequently equate treatment success with scale weight alone; clinicians must actively reorient expectations toward body composition, strength and functional capacity.^7,8 This reframing is not cosmetic language but a clinical necessity.

Educational discussions should emphasise skeletal muscle as a protective metabolic organ rather than an aesthetic feature. Muscle influences longevity, glucose regulation and resilience to illness. When patients understand that muscle loss carries measurable long-term risk, adherence to resistance training and protein intake improves substantially.8 Behavioural change becomes easier when the rationale is physiological rather than purely visual.

Lack of long-term data and prevention strategies

Despite widespread enthusiasm for GLP-1 therapy, long-term studies examining muscle outcomes remain limited. Most trials focus on weight reduction and glycaemic control rather than body composition quality.³⁶ The absence of extended follow-up data raises important questions regarding sustained muscle health and functional ageing.

Prevention strategies must therefore operate ahead of definitive evidence. Resistance training, protein optimisation and muscle stimulation represent low-risk interventions with established benefits independent of pharmacology.^11,12

Muscle health is a determinant of longevity, independence and metabolic stability. Ageing and pharmacological weight loss both threaten skeletal muscle integrity through mechanisms that accelerate protein breakdown and impair anabolic signalling.³⁷

Clinicians must reframe muscle as a core therapeutic endpoint. Preservation of lean tissue is not secondary to weight loss; it is central to sustainable metabolic health.³⁸