Summary: Researchers identified a crucial behavioral paradox in contemporary weight management: adults taking glucagon-like peptide-1 (GLP-1) receptor agonists show a measurable decline in daily physical activity, despite losing weight.
Using passive wearable sensor data from the National Institutes of Health (NIH) All of Us Research Program, investigators combined Fitbit activity records with linked electronic health records to study real-world movement patterns in adults treated for obesity with GLP-1 receptor agonists.
Contrary to the common assumption that weight loss leads to increased physical activity, the study found a consistent drop in both daily step counts and minutes of moderate-to-vigorous physical activity (MVPA) after starting GLP-1 therapy. This decline raises important concerns because preserving lean muscle requires ongoing physical activity, particularly resistance training, during periods of rapid weight loss.
Key Facts
- Challenging a long-held assumption: Clinical practice often presumes that substantial weight loss will naturally prompt patients to move more. Large-scale, continuous monitoring through wearables in this study demonstrates the opposite: metabolic weight loss while on GLP-1 drugs was associated with reduced daily movement.
- Risk to lean muscle mass: GLP-1 receptor agonists—including semaglutide, liraglutide, dulaglutide and tirzepatide—reduce both fat and lean muscle tissue. Because muscle is central to strength, resting metabolism and glucose regulation, maintaining activity—especially resistance exercise—is essential to protect long-term function and metabolic health.
- Real-world wearable data: This is the first major study to leverage continuous, real-world data from wearable fitness trackers at scale in adults taking GLP-1 medications, avoiding the limitations of self-reported exercise logs.
- Measured exercise decline: On average, daily steps fell from 5,047 to 4,487, and MVPA decreased from 28 to 22 minutes per day after initiating therapy—changes that are significant at the population level and clinically relevant for muscle preservation.
- Groups at higher risk: The steepest declines in activity were observed among male participants and individuals with pre-existing joint or muscle pain. Age, chronic heart failure and prior stroke did not significantly alter the downward trend.
- Robust cohort and design: From 1,950 adults who began GLP-1 therapy in the NIH database, researchers analyzed a subset of 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.
- Clinical implications: Study lead Sajana Maharjan, M.D., stresses that these findings require a shift in prescribing practices: GLP-1 medications should not be used in isolation. Structured, enforced exercise programs—particularly those emphasizing resistance training—should accompany pharmacotherapy to protect muscle and functional capacity.
Source: Endocrine Society
Adults with obesity who lose weight while taking GLP-1 receptor agonist medications significantly decreased their physical activity, which is essential to protect muscle, 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 are effective at reducing body weight but also reduce lean muscle mass. That dual effect makes preserving physical activity a clinical priority so patients maintain strength and metabolic health, says study lead Sajana Maharjan, M.D., of HSHS St. John’s Hospital in Springfield, Illinois.
The retrospective pre–post cohort study used All of Us data, which links participants’ electronic health records with Fitbit activity records. From 1,950 adults with obesity who started a GLP-1 medication, investigators selected 753 individuals with adequate wearable-device data for analysis. The cohort was predominantly female (78.6%) with an average age of 52.7 years.
Each participant’s activity was compared before and after treatment initiation, focusing on daily steps and MVPA minutes. On average, steps decreased from 5,047 to 4,487 per day, and MVPA declined from 28 to 22 minutes per day. The pattern held across most demographic and clinical subgroups, with the largest declines found in men and in people with joint or muscle pain. The study found no evidence that weight loss while taking these medications led to spontaneous increases in activity.
“Many assume that losing weight will naturally lead to more physical activity, but our data show that is not the case for people taking these drugs,” Maharjan said. “Exercise cannot be optional—clinical programs must actively integrate behavioral supports and structured physical activity into treatment plans.”
Key Questions Answered:
A: Although a lighter body might be expected to facilitate movement, the study shows weight loss from these medications does not automatically increase activity. Potential explanations include drug effects on systemic energy balance, appetite signaling and central nervous system pathways, as well as reduced spontaneous daily energy expenditure when caloric intake falls rapidly.
A: Rapid weight loss from GLP-1 receptor agonists reduces both fat and lean muscle. Muscle is essential for resting metabolism, strength and glucose regulation. If activity falls during treatment, patients risk losing substantial muscle mass, which can weaken physical function, impair joint stability and create longer-term metabolic challenges after discontinuing medication.
A: The findings argue against prescribing GLP-1 medications as standalone therapy. Clinicians should incorporate structured exercise prescriptions, behavioral interventions, remote monitoring with wearables, and mandatory resistance training programs from the outset to actively protect muscle and preserve function during weight loss.
Editorial Notes:
- This article was edited by a Neuroscience News editor.
- The original journal paper was reviewed in full by the editorial team.
- Additional context was added by staff to clarify clinical implications.
About this exercise and GLP-1 research news
Author: Jenni Gingery
Source: Endocrine Society
Contact: Jenni Gingery, Endocrine Society
Image credit: Neuroscience News
Original Research: Findings presented at ENDO 2026.