Although poor cardiorespiratory function is a powerful predictor of mortality in patients with obesity, functional evaluation has been given little attention after laparoscopic sleeve gastrectomy (LSG). The aim of this study was thus to investigate the impact of LSG on functional capacity analysing a shorter and longer post-surgical follow-up. In this observational study, 24 patients with severe obesity (BMI 44.04 ± 5.84 kg/m, age 47.0 ± 9.0 years) performed cardiopulmonary exercise testing 7 months pre-, 6 and 16 months post-LSG. Exercise capacity, oxygen uptake and VO kinetics were analysed during treadmill exercise testing. Although patients showed an improved peak work capacity after LSG, parameters of maximal absolute aerobic capacity demonstrated a significant decrease, which was confirmed also in the follow-up analysis. Furthermore, the time constant Tau (τ) of the fundamental component of VO kinetics was altered by LSG, however, within the 16 months of follow-up it returned towards baseline values. It can thus be concluded that LSG improved peak work capacity along with a lower maximal absolute aerobic capacity, which might be due to a loss of muscle mass and potentially impaired peripheral oxidative muscle metabolism. However, VO kinetics might suggest an initial restoration of peripheral oxidative muscle capacity after a longer follow-up.