A new study published in Sports Medicine reveals that structured exercise, rather than weight-loss medications alone, drives improvements in physical fitness during long-term weight maintenance following diet-induced weight loss. The research highlights the critical role of physical activity in promoting mobility, cardiovascular health, and functional independence for adults with obesity.
Obesity and the Limits of Weight Loss Alone
Obesity affects over 650 million adults globally and is linked to reduced mobility, lower cardiorespiratory fitness, and diminished quality of life. While diet or pharmacotherapy can reduce body weight, these interventions may not always translate to meaningful improvements in everyday physical function. Many individuals who achieve weight loss still struggle with activities like brisk walking or climbing stairs, raising questions about the effectiveness of weight reduction alone in restoring physical fitness.
Pharmacological treatments for obesity, including glucagon-like peptide-1 receptor agonists (GLP-1 RAs), have proven effective in reducing weight. However, previous research suggests that a significant portion of weight loss from medications may include fat-free mass, potentially impacting long-term strength and functional independence. This underscores the need to understand how exercise interacts with medications to improve overall functional health.
Study Design and Participants
This exploratory secondary analysis was conducted within a randomized, placebo-controlled clinical trial involving adults aged 18 to 65 with obesity, defined as a body mass index (BMI) of 32–43 kg/m², and without diabetes. Participants first completed an eight-week low-calorie diet of approximately 800 kilocalories per day. Only those achieving at least a 5% reduction in body weight were eligible for the subsequent 52-week intervention.
Participants were randomly assigned to one of four groups:
- Placebo with usual physical activity
- Placebo plus structured exercise
- Liraglutide (a GLP-1 RA) with usual physical activity
- Liraglutide combined with structured exercise
Liraglutide was administered at 3.0 mg per day with gradual dose escalation to ensure tolerability.
Structured Exercise Program
The exercise regimen aimed to meet World Health Organization physical activity guidelines and included supervised interval cycling, circuit training, and individual moderate-to-vigorous activity. Heart rate monitors ensured participants maintained the target intensity.
Physical fitness assessments were conducted at baseline, after the low-calorie diet, and at 52 weeks. Measures included stair-climb performance, cardiorespiratory fitness (VO₂peak), and muscle strength (maximal isometric knee extensor torque). Linear mixed-effects models were used to analyze differences between groups.
Key Findings: Exercise Drives Functional Gains
Of the 193 participants randomized, 85% completed the study. Those assigned to exercise averaged 2.65 sessions per week, totaling about 108 minutes of moderate-to-vigorous activity weekly. Exercise adherence was similar regardless of whether participants received liraglutide or placebo.
Mobility and Physical Function
Participants in the exercise groups, particularly those combining exercise with liraglutide, showed significant improvements in stair-climb performance, reflecting enhanced lower-limb function and mobility. Liraglutide alone, despite promoting weight loss, did not improve stair-climb outcomes.
Cardiorespiratory Fitness
VO₂peak relative to fat-free mass increased by roughly 10% in the exercise and combined treatment groups, while liraglutide alone showed no significant change. Exercise also improved absolute VO₂peak and maximal cycling power, demonstrating enhanced cardiovascular capacity.
Muscle Strength and Quality
Muscle strength remained stable across all groups, indicating that neither exercise nor liraglutide reduced absolute strength. Strength relative to body weight improved in all active treatment groups, and muscle quality was preserved with exercise or liraglutide, but declined in the placebo group.
Dose-Response Relationship
Higher volumes of moderate-to-vigorous exercise were linked to superior functional outcomes. Each additional 10 minutes of weekly activity was associated with faster stair-climb times and higher VO₂peak, emphasizing that even modest increases in exercise yield measurable benefits beyond those achieved during the initial low-calorie diet.
Implications for Obesity Management
The study concludes that structured moderate-to-vigorous exercise is the main driver of improved physical fitness during long-term weight maintenance, even when weight loss is supported by GLP-1 RA therapy. While weight-loss medications are effective for reducing body weight, they do not significantly enhance physical fitness without concurrent exercise.
These findings highlight the importance of combining pharmacotherapy with structured exercise programs to maximize mobility, cardiovascular health, and functional independence in adults with obesity, rather than focusing solely on weight reduction.
