Cardiorespiratory fitness and submaximal exercise dynamics in normal-weight obesity and metabolically healthy obesity

Cardiorespiratory fitness (CRF) is critical for cardiovascular health. Normal-weight obesity (NWO) and metabolically healthy obesity (MHO) may be at increased risk for cardiovascular disease, but a comparison of CRF and submaximal exercise dynamics against rigorously defined low- and high-risk groups is lacking.

Four groups (N = 40; 10/group) based on body mass index (BMI), body fat %, and metabolic syndrome (MetS) risk factors were recruited: healthy controls (CON; BMI 18.5-24.9 kg/m², body fat < 25% [M] or < 35% [F], 0-1 risk factors), NWO (BMI 18.5-24.9 kg/m², body fat ≥ 25% [M] or ≥ 35% [F]), MHO (BMI > 30 kg/m², body fat ≥ 25% [M] or ≥ 35% [F], 0-1 risk factors), or metabolically unhealthy obesity (MUO; BMI > 30 kg/m², body fat ≥ 25% [M] or ≥ 35% [F], 2 + risk factors). All participants completed a $\dot{\text{V}}$ O_2peak test on a cycle ergometer.

$\dot{\text{V}}$ O_2peak was similarly low in NWO (27.0 ± 4.8 mL/kg/min), MHO (25.4 ± 6.7 mL/kg/min) and MUO (24.6 ± 10.0 mL/kg/min) relative to CON (44.2 ± 11.0 mL/kg/min) when normalized to total body mass (p's < 0.01), and adjusting for fat mass or lean mass did not alter these results. This same differential $\dot{\text{V}}$ O₂ pattern was apparent beginning at 25% of the exercise test (P_Group*Time < 0.01).

NWO and MHO had similar peak and submaximal CRF to MUO, despite some favorable health traits. Our work adds clarity to the notion that excess adiposity hinders CRF across BMI categories.

gov registration: NCT05008952.