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

Purpose: 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.

Methods: Anthropometric measures, body composition (Dual-X-ray absorptiometry), physical activity and sedentary time (GT3x actigraphs), and maximal aerobic capacities (cycling test) were assessed in 18 constitutionally thin (CT-body mass index < 17.5 kg m) and 17 normal-weight (NW-body mass index between 20 and 25 kg m) women. Energy efficiency was assessed during a submaximal cycling test and a walking exercise.

Results: 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). 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.

Conclusion: 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.