Why exercise is essential for restoring fitness after GLP-1-based weight loss

In a recent study published in the journal Sports Medicine, researchers evaluated how structured exercise and glucagon-like peptide-1 receptor agonist (GLP-1 RA) therapy - alone or combined - influences physical fitness during long-term weight maintenance following diet-induced weight loss.

Obesity, fitness, and the limits of weight loss 

More than 650 million adults worldwide live with obesity, a condition strongly linked to reduced mobility, lower cardiorespiratory fitness, and poorer quality of life. Even after losing excess weight through medication or diet, many people still struggle with everyday activities such as brisk walking or climbing stairs. This raises an important question: Does weight loss alone lead to meaningful improvements in physical fitness?

Several medications, including GLP-1 RAs, are currently used to treat obesity. Previous research suggests that a significant portion of weight lost during pharmacotherapy may be fat-free mass, raising concerns about long-term physical function and independence. Understanding how structured exercise interacts with weight-loss medication is therefore critical—not just for reducing body weight, but for improving functional health.

Study design and participant selection

This exploratory secondary analysis was conducted within a randomised, placebo-controlled clinical trial involving adults aged 18 to 65 years with obesity, defined as a body mass index between 32 and 43 kg/m², and without diabetes. All participants first 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 were eligible for randomisation.

Intervention groups and treatment allocation

The 52-week intervention allocated participants to four groups: placebo with usual physical activity; placebo plus structured exercise; liraglutide (a GLP-1 RA) with usual physical activity; and liraglutide combined with structured exercise. Liraglutide was administered at 3.0 mg per day, with stepwise dose escalation based on tolerability.

Exercise programme and fitness assessment

The structured exercise programme met World Health Organization physical activity guidelines and included supervised group-based interval cycling and circuit training, alongside individually performed moderate-to-vigorous activity. Exercise intensity was objectively monitored using heart-rate devices.

Physical fitness was assessed at baseline, after the low-calorie diet, and after 52 weeks. Outcomes included stair-climb performance, cardiorespiratory fitness measured as peak oxygen consumption (VO₂peak), and muscle strength assessed via maximal isometric knee-extensor torque.

Key findings

Of the 193 participants randomised, about 85% completed the intervention. Exercise adherence averaged 2.65 sessions per week, or roughly 108 minutes of moderate-to-vigorous activity. Importantly, GLP-1 RA treatment did not reduce exercise participation.

Improvements in physical function were most pronounced in groups that exercised. Stair-climb performance improved significantly in the exercise and combined exercise-liraglutide groups, while liraglutide alone showed no such benefit despite sustained weight loss.

Cardiorespiratory fitness (VO₂peak relative to fat-free mass) increased by about 10% in groups that exercised. Muscle strength remained stable across all groups, while muscle quality declined only in the placebo group.

Further analysis showed that even modest increases in weekly exercise time led to measurable gains in fitness.

Implications

The study shows that structured exercise, not medication alone, is the primary driver of improved physical fitness during long-term weight maintenance. While GLP-1 therapies support weight loss, meaningful gains in mobility, fitness, and independence depend on regular, structured physical activity. - Source: news-medical.net

Did you know?
A landmark real-world study suggests the shingles vaccine may significantly reduce the risk of Alzheimer’s disease and other forms of dementia.