Summary: Researchers have revealed an important behavioral paradox in contemporary weight-management: adults taking glucagon-like peptide-1 (GLP-1) receptor agonist medications exhibit a measurable, clinically meaningful decline in daily physical activity despite weight loss.
Using un-coerced, real-world wearable sensor data from the National Institutes of Health (NIH) All of Us Research Program, investigators combined Fitbit activity records with electronic health records to study adults treated for obesity with GLP-1 receptor agonists.
Instead of increasing movement as they lost weight, patients experienced a significant reduction in both daily step counts and minutes of moderate-to-vigorous physical activity (MVPA). This decline creates a tangible risk to lean muscle preservation, since sustained physical activity—particularly resistance training—is essential to protect muscle mass and long-term metabolic health during rapid weight loss.
Key Facts
- Dismantling the activity assumption: For years, clinicians have often assumed that meaningful weight loss naturally leads to increased spontaneous movement. This large-scale, objective tracking study challenges that assumption by showing that metabolic weight loss associated with GLP-1 therapy actually coincides with reduced daily movement.
- Risk to lean muscle mass: GLP-1 receptor agonists—such as semaglutide, liraglutide, dulaglutide and tirzepatide—reduce both fat and lean tissue. Because lean muscle is central to strength, mobility and metabolic regulation, preserving muscle requires deliberate, consistent resistance training and daily activity during treatment.
- Real-world wearable data: This is the first major medical study to analyze continuous, real-world data from wearable fitness trackers among a large cohort of adults using GLP-1 receptor agonists, avoiding the inaccuracies of self-reported exercise logs.
- Quantifying the exercise deficit: Across the cohort, average daily step counts fell from 5,047 to 4,487 steps per day, and average MVPA dropped from 28 to 22 minutes per day after starting GLP-1 therapy—changes that are clinically meaningful for muscle preservation and cardiovascular fitness.
- High-risk subgroups: The steepest declines in physical activity were observed among male participants and people with pre-existing joint or muscle pain. Factors such as chronological age, chronic heart failure or prior stroke did not significantly alter the downward trend.
- Robust cohort metrics: From 1,950 adults with obesity who initiated GLP-1 medications in the NIH database, the study analyzed 753 participants who had sufficient long-term wearable-device data. The analytic cohort was 78.6% female with a mean age of 52.7 years.
- Call for integrated interventions: The investigators emphasize that prescribing GLP-1 medications without structured, muscle-preserving behavioral support is insufficient. Future weight-loss protocols should incorporate mandatory physical-activity programs—especially resistance training—and wearable monitoring to protect lean mass and sustain metabolic benefits.
Source: Endocrine Society
Adults with obesity who lost weight while taking GLP-1 receptor agonist medications significantly decreased their physical activity, putting muscle preservation at risk, according to a study being presented at ENDO 2026, the Endocrine Society’s annual meeting.
GLP-1 receptor agonists such as semaglutide, liraglutide, dulaglutide and tirzepatide reduce both fat and lean muscle mass. Study lead Sajana Maharjan, M.D., of HSHS St. John’s Hospital in Springfield, Ill., highlights that preserving strength and long-term metabolic health requires intentional physical activity while patients are on these medications.
The retrospective pre–post cohort study used All of Us Research Program data, which links participants’ electronic health records with Fitbit activity records. Among the 1,950 adults with obesity who began a GLP-1 medication, 753 had sufficient wearable-device data for analysis. The analytic sample was predominantly female (78.6%) with a mean age of 52.7 years.
Investigators compared each participant’s activity before and after initiating GLP-1 therapy, focusing on daily step counts and minutes of moderate-to-vigorous physical activity. On average, steps declined from 5,047 to 4,487 per day, and MVPA decreased from 28 to 22 minutes per day after starting medication. The pattern was consistent across most demographic and clinical subgroups, with the largest reductions in men and in people with baseline joint or muscle pain. The analysis found no evidence that weight loss from these medications led to spontaneous increases in physical activity.
“Although many assume weight loss will naturally encourage more movement, our findings indicate the opposite in this context,” Dr. Maharjan said. “Exercise should not be treated as optional for people taking these medications. Clinicians and weight-loss programs must pair GLP-1 therapy with structured interventions that preserve muscle and promote sustained activity.”
This represents the first large-scale study to evaluate continuous fitness-tracker data in adults using GLP-1 receptor agonists, offering objective insight into real-world behavioral changes during pharmacologic weight loss.
Key Questions Answered:
A: Although a lighter body might be expected to make movement easier, the data show that weight loss on GLP-1 drugs does not automatically increase activity. Potential explanations include drug-induced changes to systemic energy balance, appetite and central nervous system signaling, and reductions in spontaneous daily energy expenditure once caloric intake falls. These mechanisms likely reduce the drive for incidental movement even as body weight declines.
A: Rapid weight loss from GLP-1 receptor agonists can include loss of lean muscle mass as well as fat. Muscle is essential for resting metabolic rate, strength, mobility and glucose regulation. When activity falls during drug-induced weight loss, muscle loss can accelerate, leaving people weaker, increasing fall and injury risk, and contributing to adverse metabolic consequences when the medication is stopped.
A: The study supports abandoning the practice of offering GLP-1 medications as standalone therapy. Clinicians should pair prescriptions with mandatory, structured exercise programs—especially resistance training—use remote wearable monitoring to track activity, and deliver behavioral coaching from treatment initiation to actively protect muscle and maximize long-term health benefits.
Editorial Notes:
- This article was edited by a Neuroscience News editor.
- The journal paper was reviewed in full by the editorial team.
- Additional context was added by staff to clarify clinical implications and practical recommendations.
About this exercise and GLP-1 research news
Author: Jenni Gingery
Source: Endocrine Society
Contact: Jenni Gingery – Endocrine Society
Image: The image is credited to Neuroscience News
Original Research: The findings described here will be presented at ENDO 2026.