Energy Expenditure and Neuromuscular Function in Young Adult Women With a Naturally Thin Build (LeanErgy)

Summary

People with a low BMI (\<17.5) are most often considered to have anorexia nervosa (AN). However, recent literature suggests that there is a category of individuals with the same low BMI who do not meet the diagnostic criteria for anorexia nervosa but who have specific differences that make them a separate entity: constitutional thinness (CM). Constitutional thinness differs from anorexia nervosa in several ways. First, unlike AN, CM individuals do not have eating disorders and express a strong desire to gain weight. Another difference concerns the menstrual cycle: without oral contraception, AN individuals experience amenorrhea, while CM individuals have regular menstrual cycles. Biological signs of malnutrition are also present in anorexia nervosa, whereas this is not the case in constitutional thinness. Indeed, concentrations of IGF1, free T3, and leptin are significantly reduced in AN compared to healthy subjects, whereas there is no significant difference between healthy subjects and CT. Finally, in terms of body composition, there is a significant difference in particular in the percentage of fat mass between MC and AM subjects, with the MC group having a significantly lower percentage of fat mass than the control subjects but significantly higher than the AM subjects. The clinical management of MC patients could involve nutritional management of patients but also management in the form of an Adapted Physical Activity intervention program. However, this type of program using physical activity and a nutritional approach must be based on a characterization of the energy profile and physical abilities of MC patients, which remains to be studied. Germain et al. proposed measuring the physical activity level of MC patients using Actiheart (a combination of heart rate and accelerometer) and compared it with that of normal-weight (NW) individuals, finding no difference between the groups. However, this analysis remains a secondary analysis of their study, as the statistical power and choice of tool are certainly not appropriate for this question. Our team recently conducted the Nutrilean project, which for the first time questioned the aerobic and muscular capacities of women with CM compared to their NP counterparts. While our results show lower force production capacity in CM patients, suggesting neuromuscular adaptations to the chronic mechanical unloading caused by CM rather than an impairment of contractile abilities themselves, this remains to be explored more specifically. Indeed, these differences disappeared after normalization to body weight or muscle mass, suggesting a reduced gross force production capacity, but probably reflecting a normal physiological adaptation to low body and muscle mass. It now appears necessary to carry out more specific neuromuscular analyses in order to better understand the mechanisms, adaptations, and/or potential neuromuscular dysfunctions in this population. Similarly, while the results do not appear to show any impairment in the aerobic capacity of CM, they do highlight a potential impairment in their energy efficiency during locomotion, which may also reflect an adaptation to chronic exposure to lower mechanical loads.

In this context and following on from the work carried out to date by our team, the main objective of this study is i) to compare the lipid oxidation capacity and energy cost of walking between MC and NP participants; ii) to explore the adaptations of this energy cost in MC women in response to mechanical overload.

Conditions

• Constitutional Thinness

Interventions

DIAGNOSTIC_TEST

Evaluation of the maximum oxidation point of lipids

The Lipoxmax measurement will take place in the morning, on an empty stomach. It will consist of a submaximal incremental exercise comprising five stages of six minutes each, with loads determined based on the power output obtained during the maximum oxygen consumption test and corresponding to 25%, 35%, 45%, 55%, and 65% of theoretical VO2 max. During the last minute of each stage, continuous measurement of VO2 and VCO2 will be used to calculate the average QR and then calculate the respective oxidation rates of carbohydrates and lipids, followed by the lipid oxidation rate at each stage. The oxidation rate curve is parabolic in shape, and modeling this curve will determine the lipoxmax point and the percentage of VO2max at which this lipoxmax point is obtained.

DIAGNOSTIC_TEST

Evaluation of the energy cost of walking

The energy cost of walking for participants will be assessed once for the NP group and twice and randomized for the MC group. All participants will have their energy cost assessed based on their body weight, and so will be in the MC group with a mechanical overload applied to simulate a BMI of 20 kg/m² (normal weight). This overload will be simulated with a weight corresponding to the weight required to achieve this BMI. Energy expenditure and energy substrates will be assessed during the walking exercise using portable indirect calorimetry (MetaMax, Inc.).This one is of the classic methods for measuring resting energy expenditure. For this exercise, participants will have to remain seated at rest for 10 minutes and then standing at rest for 5 minutes before performing an incremental submaximal walking exercise on a treadmill, consisting of 5 stages of 6 minutes each: i) 0.75 m.s-1; ii) 1 m.s-1; iii) 1.25 m.s-1; ii) 1.5 m.s-1; iv) 2.25 m.s-1. Each stage will be separated by 5 min.

DIAGNOSTIC_TEST

Neuro-muscular assessments

Neuromuscular function will be assessed using isokinetic dynamometry. Neuromuscular function of the lower limb (knee flexion/extension) Neuromuscular function of the upper limb (elbow flexion/extension)

Sponsors & Collaborators

• Centre Hospitalier Emile Roux

  lead OTHER

Study Design

Allocation

NON_RANDOMIZED

Purpose

OTHER

Masking

NONE

Model

PARALLEL

Eligibility

Min Age

18 Years

Max Age

35 Years

Sex

FEMALE

Healthy Volunteers

No

Timeline & Regulatory

Start

2025-12-15

Primary Completion

2027-10-15

Completion

2028-02-15

Countries

• France

Study Locations