GLP-1 Receptor Agonists and Physical Activity: What ENDO 2026 Data Shows

What did the ENDO 2026 observational study find?

An observational study presented at the Endocrine Society’s annual conference, ENDO 2026 (Chicago, June 2026), found that adults with obesity who initiated GLP-1 receptor agonist medications showed a measurable decline in daily physical activity, measured by consumer fitness wearables.[1]

The study used data from the NIH’s All of Us Research Program, a large US biomedical database that links participants’ electronic health records with data from connected devices, including Fitbit fitness trackers. From an initial cohort of 1,950 adults with obesity who started a GLP-1 medication, researchers identified 753 individuals with sufficient pre- and post-initiation wearable data for analysis. It is the first large study to use wearable fitness tracker data to examine physical activity among GLP-1 receptor agonist users.[1]

Researchers noted that this was the first large study to apply wearable fitness tracker data to the question of physical activity change following GLP-1 receptor agonist initiation — previous analyses had relied on self-reported activity measures, which are subject to recall bias.

Which GLP-1 receptor agonists were studied?

The study included participants who had been prescribed any of four licensed GLP-1 receptor agonist medications: semaglutide (known commercially as Ozempic and Wegovy), liraglutide, dulaglutide, and tirzepatide (Mounjaro/Zepbound). These are all approved pharmaceutical medicines regulated and prescribed for metabolic conditions. The study did not stratify outcomes by individual drug, so the finding reflects the class as a whole rather than any single compound.

For researchers, tirzepatide is of particular interest here: as a dual GLP-1/GIP agonist, its inclusion alongside mono-GLP-1 agonists means the ENDO 2026 dataset cannot disentangle the relative contributions of GLP-1 versus GIP receptor activation to the observed activity change. This remains an open experimental question. Velox Peptides supplies tirzepatide as an HPLC-verified research reagent (≥99% purity) for in vitro use only.

The GLP-1 compounds studied here are licensed pharmaceutical medicines dispensed via prescription, and the findings describe changes observed in human clinical populations. This is distinct from the in vitro research context in which Velox Peptides research reagents are used.

Why might GLP-1 receptor activation be associated with reduced spontaneous activity?

The ENDO 2026 study is observational: it identifies an association between GLP-1 medication initiation and reduced step counts, but does not establish mechanism. Researchers have proposed several hypotheses, each with some basis in existing literature.

Central GLP-1 receptor signalling

GLP-1 receptors are expressed not only in the pancreas and gut but also in the hypothalamus, brainstem nucleus tractus solitarius (NTS) and ventral tegmental area of the brain. In rodent models, GLP-1 receptor activation in these regions has been studied in connection with appetite suppression, reduced food reward motivation, and changes in spontaneous locomotor activity.[2] Some preclinical data suggest that central GLP-1 receptor agonism can reduce non-exercise activity thermogenesis (NEAT) — the energy expended through fidgeting, standing, and incidental movement — though this has not been confirmed in humans.

Caloric restriction and substrate availability

GLP-1 receptor agonists markedly reduce caloric intake through delayed gastric emptying and hypothalamic appetite suppression. Reduced caloric substrate may lower the energetic “drive” available to support spontaneous movement, particularly in individuals who were already sedentary. This is consistent with well-documented reductions in NEAT seen during caloric restriction in general, independent of drug mechanisms.[3]

Mechanical hypothesis: joint and muscle pain

The subgroup finding is notable: the largest step-count declines occurred in men and in individuals with joint or muscle pain. A plausible explanation is mechanical rather than pharmacological: individuals whose activity was previously constrained by musculoskeletal pain may not re-engage with movement during the early phase of weight reduction — even if their pain subsequently improves. The study’s observation that age, heart failure, and prior stroke did not modify the result suggests the mechanism may be more specific to musculoskeletal factors than to general frailty.

What does this mean for lean muscle mass research?

A well-documented finding across the GLP-1 receptor agonist literature is that these medications reduce not only adipose tissue but also lean muscle mass. In a 2022 analysis of tirzepatide trial data, approximately 39% of weight lost was lean mass, a proportion broadly consistent with findings from semaglutide studies.[4] Preservation of lean mass during weight reduction is an active area of research across the incretin field.

The ENDO 2026 physical activity finding adds a new dimension to this problem: physical activity — particularly resistance-type loading — is the primary physiological stimulus for lean muscle retention during caloric deficit. If GLP-1 medication initiation is associated with reduced spontaneous activity, this could compound, rather than counteract, the lean mass loss observed in trials. Researchers studying GLP-1 receptor pathways in vitro may wish to consider this dynamic when designing experimental protocols examining metabolic or anabolic markers.

Tissue repair and recovery research context

The lean mass question opens a parallel line of inquiry into peptides studied in the context of skeletal muscle and connective tissue repair. BPC-157 (pentadecapeptide BPC) is studied in preclinical models for its effects on tendon, ligament, and muscle tissue repair pathways. TB-500 (thymosin beta-4 fragment Ac-SDKP) has been investigated in recovery research across multiple tissue types. Whether GLP-1-associated reductions in physical activity interact with the tissue-level mechanisms studied for these compounds is not yet known; this is a potential experimental question for in vitro and animal model researchers.

BPC-157 and TB-500 are supplied by Velox Peptides as research reagents for in vitro use only. No claim is made that these compounds compensate for lean mass loss in any population. Research reference only.

How does this relate to retatrutide and next-generation triple agonists?

The ENDO 2026 study examined GLP-1 mono-agonists (semaglutide, liraglutide, dulaglutide) and the GLP-1/GIP dual agonist tirzepatide. It did not include retatrutide (LY3437943), Eli Lilly’s GLP-1/GIP/glucagon triple agonist, which remains investigational and is not yet approved for human use.

The addition of glucagon receptor agonism in retatrutide’s mechanism is relevant here. In rodent models, glucagon receptor activation has been associated with increased energy expenditure and thermogenesis — effects that could, in principle, interact differently with spontaneous physical activity than GLP-1 alone.[5] Whether glucagon co-agonism modifies the activity-reduction pattern observed with GLP-1 mono- and dual agonists is an open experimental question that the TRIUMPH Phase 3 programme — which enrolled over 2,300 participants and included sub-study endpoints — may eventually address in sub-analyses.

The TRIUMPH-1 trial results (announced 21 May 2026, reported 28.3% body-weight reduction at 80 weeks with retatrutide 12 mg) focused on weight and cardiometabolic endpoints; physical activity data from the trial, if collected via wearable sub-study, has not yet been reported.[6] Researchers interested in the receptor-level comparison can explore our retatrutide research overview and is retatrutide a GLP-1? guide for more on the mechanistic distinctions between receptor classes.

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