New research presented at ENDO 2026 links the growing use of GLP-1 drugs for weight loss to a drop in everyday movement, and experts are urging that exercise be built into treatment rather than treated as optional. The study tracked fitness device data and found participants walked fewer steps and spent less time in moderate-to-vigorous activity after starting medications like semaglutide or tirzepatide. Clinicians disagree on whether this pattern is an inevitable side effect or a fixable gap in how these drugs are prescribed and followed.
Researchers examined records from a National Institutes of Health program that matched participant files to fitness tracker activity, focusing on 753 adults with obesity who began a GLP-1 medication. The cohort skewed female and had a mean age in the early 50s. Investigators compared movement before and after treatment started to measure behavioral change tied to medication use.
On average, daily steps fell from 5,047 to 4,487, and moderate-to-vigorous physical activity dropped from 28 minutes to 22 minutes per day after beginning therapy. The biggest declines showed up among men and among participants who already had joint or muscle pain, while age, heart failure and prior stroke did not appear to alter the trend. These objective activity shifts were the headline finding the team shared at the meeting.
Sajana Maharjan, MD, emphasized the physiologic issue behind the numbers, noting that GLP-1 drugs can reduce both fat and lean muscle mass. The study team warned that physical activity is “essential for preserving strength and long-term health,” she said. They also concluded that medication alone did not reliably boost movement or motivation in this group.
Investigators were clear about limits: the work was retrospective and observational, which shows association but not direct causation. The participants were mostly middle-aged women, a factor that could narrow how broadly the results apply. The dataset also lacked measures such as prior exercise habits, patient motivation and the level of physician guidance provided during therapy.
Dr. Peter Balazs noted some expected physiology behind the behavioral drop. “In fact, being in a calorie deficit can cause the body to conserve energy, resulting in a lower metabolic rate,” he said. “Additionally, side effects of weight-loss medications, such as nausea, fatigue or gastrointestinal discomfort, may further reduce a person’s ability or desire to be physically active,” the expert added.
Balazs pressed the clinical point bluntly: exercise “is not optional.” He told colleagues that patients need resistance training and consistent daily movement like walking to preserve lean muscle mass, metabolic health and long-term weight control. “Exercise plays a critical role during weight loss,” Balazs said.
Not every clinician sees the findings the same way, and some say results reflect how care is delivered rather than an unavoidable drug effect. “Weight loss often serves as the impetus that motivates patients to become more physically active and more engaged in their overall health,” one provider said, arguing successful outcomes depend on more than the prescription alone. “The success of GLP-1 therapy is directly tied to the expertise of the provider,” she went on.
That provider described a hands-on approach in practice: “In my practice, if a patient is unable to exercise, is not meeting protein goals or shows concerning muscle loss on body composition analysis, I will often hold or adjust the medication – because preserving strength, function and metabolic health is just as important as weight loss,” she said. If a GLP-1 patient becomes too fatigued to exercise, develops nutritional deficiencies or loses excessive muscle mass, Kahn warned that this reflects a “monitoring problem” rather than a medication problem, as these medications “require close clinical oversight.”
