In a recent study published in Sports Medicine, researchers examined how structured exercise and glucagon-like peptide-1 receptor agonist (GLP-1 RA) therapy—used alone or in combination—affect physical fitness during long-term weight maintenance following diet-induced weight loss.
Obesity and Physical Fitness: Why Weight Loss Alone May Not Be Enough
Globally, more than 650 million adults live with obesity, a condition strongly associated with reduced mobility, poor cardiorespiratory fitness, and lower quality of life. Although weight-loss interventions can reduce body weight, many individuals continue to struggle with everyday activities such as brisk walking or climbing stairs.
This gap raises a critical question: does weight loss alone translate into meaningful improvements in physical fitness?
While medications such as GLP-1 receptor agonists have proven effective for weight reduction, earlier studies suggest that a substantial portion of pharmacotherapy-induced weight loss may involve fat-free mass. Consequently, concerns remain about long-term physical function, muscle quality, and independence, highlighting the need to evaluate the role of structured exercise alongside medication.
Study Design and Participant Eligibility
As reported by news-medical.net, the researchers conducted an exploratory secondary analysis within a randomized, placebo-controlled clinical trial involving adults aged 18 to 65 years with obesity and without diabetes mellitus. Participants had a body mass index between 32 and 43 kg/m².
Initially, all participants completed an eight-week low-calorie diet of approximately 800 kilocalories per day. Only those who achieved at least a 5% reduction in body weight qualified for randomization into the intervention phase.
Intervention Groups and Treatment Approach
Over a 52-week period, the trial assigned participants to one of four groups. One group received placebo with usual physical activity, while a second group combined placebo with structured exercise. A third group received the GLP-1 RA liraglutide alongside usual physical activity, and a fourth group received liraglutide combined with structured exercise.
Researchers administered liraglutide at a daily dose of 3.0 mg, using stepwise dose escalation to improve tolerability.
Structured Exercise Program and Fitness Measurements
The structured exercise intervention aimed to meet World Health Organization physical activity guidelines. It included supervised group-based interval cycling and circuit training, complemented by individually performed moderate-to-vigorous physical activity. Participants wore heart-rate monitors to objectively track exercise intensity.
Researchers assessed physical fitness at baseline, after the low-calorie diet, and at the end of the 52-week intervention. Key outcomes included stair-climb performance, cardiorespiratory fitness measured as peak oxygen consumption (VO₂peak), and muscle strength assessed by maximal isometric knee extensor torque.
Participant Adherence and Exercise Exposure
Of the 193 participants randomized, approximately 85% completed the full 52-week intervention. Participants assigned to exercise completed a median of 2.65 exercise sessions per week, equating to roughly 108 minutes of moderate-to-vigorous activity weekly.
Importantly, exercise adherence did not differ between participants receiving liraglutide and those receiving placebo, indicating that GLP-1 RA therapy did not reduce engagement in physical activity.
Exercise Drives Improvements in Physical Function
Participants who engaged in structured exercise demonstrated the most consistent improvements in physical function. Notably, those in the combined exercise and liraglutide group completed the stair-climb test significantly faster than participants receiving liraglutide alone or placebo.
Exercise alone produced comparable functional gains, whereas liraglutide alone did not improve stair-climb performance, despite sustained weight loss. These findings underscore the importance of exercise for enhancing mobility and lower-limb function.
Cardiorespiratory Fitness Improves With Exercise, Not Medication Alone
Cardiorespiratory fitness, expressed as VO₂peak relative to fat-free mass, increased by approximately 10% in both the exercise-only and combined treatment groups. In contrast, liraglutide alone did not result in a statistically significant improvement compared with placebo.
Furthermore, exercise increased absolute VO₂peak and maximal cycling power, reinforcing its central role in improving cardiovascular capacity.
Muscle Strength and Quality Remain Preserved
Across all groups, absolute muscle strength remained stable, indicating that neither structured exercise nor liraglutide led to declines in maximal knee extensor strength.
However, strength relative to body weight improved in all active treatment groups, reflecting weight loss with preserved muscle function. Muscle quality declined in the placebo group but remained stable in participants who exercised or received liraglutide.
Greater Exercise Volume Yields Better Fitness Outcomes
Dose–response analyses revealed that higher volumes of moderate-to-vigorous exercise produced superior functional outcomes. Each additional 10 minutes of weekly exercise correlated with faster stair-climb times and higher VO₂peak relative to fat-free mass.
These results demonstrate that even modest increases in physical activity deliver measurable benefits beyond those achieved through diet-induced weight loss alone.
Key Implications for Long-Term Obesity Management
Overall, the study shows that structured moderate-to-vigorous exercise serves as the primary driver of improvements in physical fitness during long-term weight maintenance, even when GLP-1 RA therapy supports weight loss.
While GLP-1 receptor agonists effectively sustain weight reduction, they do not substantially enhance physical fitness in the absence of exercise. In contrast, structured exercise—either alone or combined with pharmacotherapy—produces clinically meaningful improvements in mobility, cardiorespiratory fitness, and functional independence.
Conclusion: Exercise Remains Central to Functional Health
These findings highlight the importance of integrating structured exercise programs into obesity treatment strategies. Rather than focusing solely on weight loss, clinicians and policymakers should prioritize exercise alongside pharmacotherapy to optimize long-term functional health outcomes in adults with obesity.