COPD may weaken your ability to control leg muscles

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

Inclusion Criteria: COPD patients : * GOLD II - III or IV * FEV1 \<80% of predicted values * Men and women aged 40 years and over * French-speaking participant * BMI \<30 kg / m² * Stable condition (i.e. without exacerbation) for more than 15 days * Able to express their consent in writing prior to any participation in the study * Affiliates or beneficiaries of a social security * Minimum score of 26 on the MMSE questionnaire of 3 months or less Healthy volunteers : * Men and women aged 40 years and over * French-speaking participant * BMI \<30 kg / m² * No known chronic respiratory, cardiovascular, metabolic, renal or neuromuscular pathologies * Able to express their consent in writing prior to any participation in the study * Affiliates or beneficiaries of a social security * Minimum score of 26 on the MMSE questionnaire of 3 months or less For all participants : -Subject who has not objected to the reuse of data collected Exclusion Criteria: COPD patients : * Alcoholism, i.e. \> 21 glasses a week for men and \>14 glasses a week for women * Psychiatric pathologies or antecedent of behavioral disorders * Patients treated with oral or systemic corticosteroids (\> 0.5 mg / kg / day for \> 7 days) * Contraindication to the application of a magnetic field (i.e. right hip arthroplasty, pelvic / abdominal surgeries) * Severe vision or hearing problems not corrected * Patient oxygen dependent * Patients in exclusion period from another research protocol * Pregnant women (known pregnancy) or lactating women * Patient deprived of liberty by a judicial or administrative decision * Patient subject to a legal protection measure or unable to express their consent * Patient who is not sufficiently fluent in reading and understanding the French language to be able to consent to participate in the study * Patient unable to follow study procedures and to respect visits throughout the study period * Person with a medical history that, in the opinion of the investigator, could interfere with the results of the study * Any condition that, in the opinion of the investigator, could increase and compromise the safety of the person in the event that he / she participates in the study * Any other reason that, in the opinion of the investigator, could interfere with the evaluation of the aims of the study Healthy volunteers: * Alcoholism, i.e. \> 21 glasses a week for men and \>14 glasses a week for women * Psychiatric pathologies or antecedent of behavioral disorders * Patients treated with oral or systemic corticosteroids (\> 0.5 mg / kg / day for \> 7 days) * Contraindication to the application of a magnetic field (i.e. right hip arthroplasty, pelvic / abdominal surgeries) * Severe vision or hearing problems not corrected * Subjects in exclusion period from another research protocol * Pregnant women (known pregnancy) or lactating women * Regular physical activity with a frequency greater than 3 sessions per week * Participant deprived of liberty by a judicial or administrative decision * Participant subject to a legal protection measure or unable to express their consent * Participant who is not sufficiently fluent in reading and understanding the French language to be able to consent to participate in the study * Participant unable to follow study procedures and to respect visits throughout the study period * Person with a medical history that, in the opinion of the investigator, could interfere with the results of the study * Any condition that, in the opinion of the investigator, could increase and compromise the safety of the person in the event that he / she participates in the study * Any other reason that, in the opinion of the investigator, could interfere with the evaluation of the aims of the study