Many elite athletes are submitted to frequent rapid weight loss periods to meet their competition weight category and then experience weight cycling (lowing and gaining weight regularly). This weight cycling induce severe temporary energetic and metabolic changes and when repeated over time can lead to permanent metabolic adaptations that might favor metabolic disorders, body weight gain and body composition changes (favoring fat mass). The exact effects of this weight cycling are not clear yet, especially in terms of metabolic, energetics, nutritional functional and psychological impacts. Better understand these adaptations and their variations during weight loss and weight gain in regular weight cycler is of main importance to prevent these athletes for future health issues.

The aim of the present project if to assess these metabolic, functional, energetic and nutritional adaptations during weight loss, weight stable and weight gain periods in athletes experiencing regular weight cycling.

After an inclusion visit to ensure the eligibility of athletes to complete the entire study, each subject will perform 3 experimental sessions of 2 visits each : i) two visits during a period of maintenance of body weight (CON); ii) two visits during weight loss (WL); iii) two visits during a weight regain (WG). The order of the periods (maintenance, loss or weight gain) will depend on the dynamics of the weight variations of each athlete (endurance sport and weight class) during the season and will therefore be individualized.

All experiments will be conducted in the same way for the CON, WL or WG session.

Upon arrival, each subject will perform a resting metabolism with continuous measurement of heart rate variability (≈ 30 min). Then, from 8:30, blood and saliva samples will be taken (≈ 10 min). Then (≈ 8:45), they will perform anthropometric and body composition measurements (waist circumference, hip circumference, bioimpedance, DXA) (≈ 30 min). Following these measurements (≈ 9:15), the subjects will eat a standardized breakfast and the report to food will be evaluated thanks to the Leeds Foods Preference Questionnaire before and after the meal. They will then be asked (≈ 10h) to complete the Profile of Mood State Questionnaire to measure the athlete's psychological state. Participants will then perform a measurement of muscle function (≈ 10:30).

During the second visit, carried out between 1 and 5 days after the first visit, the maximum aerobic capacity of the athletes will be evaluated by mid-morning stress test.

Inclusion Criteria:

• Subjects aged 18 to 35 (inclusive),
• exercising at least 4 sessions of endurance or weight-based sporting activities per week for a performance objective,
• having variations of at least 5% of their weight body during the last 3 sporting seasons (a sporting season corresponds to a year during which alternates the periods of training, recovery and participation in official competitions).
• Subject capable of providing informed consent to participate
• Subject with a social security insurance.

Exclusion Criteria:

• Medical or surgical history deemed by the investigator to be incompatible with the study.
• Presence of chronic pathology.
• Disorders of eating behavior.
• Subjects born very prematurely defined as a pregnancy inferior to 28 weeks.
• Subjects having used a treatment for a small stature (eg growth hormone).
• For women: irregular menstruation (changes in menstrual cycles ≥ 6 days).
• Sports subjects with a stable weight during the last three sporting seasons (weight variation <5%).
• Take medication that can change body temperature.
• Pregnant or lactating women.
• Subjects with gastrointestinal complications and / or contraindications to ingestion of the capsule (eg diverticulosis, inflammatory bowel disease, gastrointestinal surgery ...).
• Subjects needing MRI during ingestion of the capsule or having a pacemaker or other implanted electro-medical device.
• Person under guardianship or not subject to a social security scheme.
• Refusal to sign the information and consent leaflet.
• Refusal of participation