Similar maximal aerobic capacity but lower energy efficiency during low-to-moderate exercise in women with constitutional thinness: new results from the NUTRILEAN study

Individuals with constitutional thinness have been presented with a lower muscular energy metabolism at the cellular level but their effective aerobic capacities and exercise-related energy efficiency remains unexplored. The present study compares maximal and sub-maximal aerobic capacities between subjects with constitutional thinness and age-matched normal-weight ones.

Anthropometric measures, body composition (Dual-X-ray absorptiometry), physical activity and sedentary time (GT3x actigraphs), and maximal aerobic capacities (cycling \(\dot{\text{V}}\text{O}\) $\dot{\text{V}}\text{O}$ _2peak test) were assessed in 18 constitutionally thin (CT—body mass index < 17.5 kg m⁻²) and 17 normal-weight (NW—body mass index between 20 and 25 kg m⁻²) women. Energy efficiency was assessed during a submaximal cycling test and a walking exercise.

CT had a lower body mass and body mass index compared to NW. Absolute peak oxygen uptake and maximal aerobic power were lower in CT subjects compared to NW (ES: − 1.63 [− 2.40; − 0.86] and − 1.32 [− 2.05; − 0.58], p < 0.001). \(\dot{\text{V}}\text{O}\) $\dot{\text{V}}\text{O}$ _2peak related to body mass was not different between groups. Gross and net efficiency (ES: − 0.78 [− 1.48; − 0.06], p = 0.03 and ES: − 0.73 [− 1.43; − 0.01], p = 0.05) were lower in CT compared to NW during the submaximal cycling exercise. The gross energy cost of walking related to body mass was lower in subjects with CT (ES: − 1.80 [− 2.60; − 0.97, p = 0.05), with no difference for the net one. Perceived exertion was similar between groups in responses to both submaximal exercises.

Constitutionally thin women do not show impaired aerobic capacities at moderate to maximal intensities despite lower energy efficiency while cycling and walking at low-to-moderate intensities.