Abstract Background Metabolic syndrome (MetS) is a health disorder characterized by metabolic abnormalities that predict an increased risk to develop cardiovascular disease (CVD) and type 2 diabetes (T2DM). It can be resolved, and its complications reduced, by lifestyle interventions offered in primary care. The objectives of this study were to evaluate the impact of the exercise program of the CHANGE feasibility study on physical fitness and physical activity habits, and assess associations between changes in MetS components and cardiorespiratory fitness (CRF). Methods In this analysis of 192 of the 293 adults with MetS in the overall study, the impact on physical fitness [aerobic capacity, muscular fitness and flexibility], and non-supervised physical activities was investigated over 12 months. In the CHANGE program, aerobic capacity, muscular fitness and flexibility were assessed at baseline, after 3 months of weekly supervised exercise, and following 9 additional months during which participants had one monthly session of supervised exercise. Additionally, CRF response was also examined in relation to changes in MetS components [fasting glucose, high-density lipoprotein (HDL) cholesterol, triglycerides, blood pressure, waist circumference (WC)]. Results Fitness variables were significantly increased at 12 months with most of the improvements reached by 3 months (estimated VO₂ max: 6 and 12%; partial curl-ups: 55 and 80%; push-ups: 50 and 100%; flexibility: 22 and 10% in men and women, respectively, p < 0.001). As expected, the duration and intensity of supervised aerobic physical activity increased during the first 3 months of supervision in both men and women, and remained unchanged for the duration of the program. The duration of non-supervised physical activities did not change during the program in men whereas an increase in manual work of moderate intensity was recorded in women between 3 and 12 months. In women, mean changes in WC were significantly greater among high VO₂ max responders than low responders, between 0 and 12 months, as well as between 3 and 12 months (− 3.42 cm and − 4.32 cm, respectively, p < 0.05). No associations were seen with MetS components in men. Higher intensity activities were maintained by both sexes at one year. Conclusion Patients with MetS participating in the CHANGE lifestyle program improved physical fitness and physical activity habits by three months and maintained these gains over one year. Women who achieved a greater VO₂ max increase had greater reductions in WC compared to low VO₂max responders.