Relationships Between Muscle Activity, Soft Tissue Changes, and Movement Strategies in Individuals With Chronic Low Back Pain (E-LBP)

- Inclusion criteria for CNSLBP participants

Adult aged 18 to 65 years (inclusive) Have freely given written informed consent Present with pain located between the thoracolumbar junction and the inferior gluteal fold, with or without pain in one or both legs This pain must have been present for more than 12 weeks, on a daily or near-daily basis (at least 4 days out of 7) Participants must not be undergoing any treatment, or must have been on a stable analgesic treatment for at least 2 weeks prior to inclusion in the study Must not have performed, in the 72 hours preceding participation in the study, any unusual intense physical activity (e.g., carrying a heavy load (> 25 kg), sporting activity) likely to transiently alter muscle activity or the mechanical properties of the tissues studied

- Non-inclusion criteria for CNSLBP participants

Known contraindications or limitations to walking Cardiovascular risk factors (uncontrolled high blood pressure, poorly controlled diabetes or diabetes with complications, severe untreated dyslipidemia), or heart disease contraindicating physical activity Ongoing litigation following a workplace accident

Any form of specific low back pain, with an identified cause or secondary to an underlying condition, including in particular:

Pain related to a cancer diagnosis Spinal cord or cauda equina symptoms (pyramidal signs, coordination disorders, motor or sensory deficits, sphincter disorders, etc.) Pain following an infection (night sweats, fever, chills, intravenous drug abuse, immunodeficiency, recent surgery, urinary or skin infection, etc.) Recent or pathological fractures (road traffic accidents, history of osteoporosis, chronic corticosteroid use, advanced age, unexplained weight loss, fatigue, history of cancer, etc.) Inflammatory rheumatism (ankylosing spondylitis, rheumatoid arthritis, or other rheumatic diseases) Vascular problems (cold feet, diminished peripheral arterial pulse, etc.) Disabling radicular irradiation, at the investigator's discretion Participants must not have undergone an intensive rehabilitation program within the last 3 months, nor received physiotherapy, manual therapy, acupuncture, or any other type of manual medicine or bodywork treatment outside their usual care, within the 4 weeks preceding inclusion Severe, unstabilized psychiatric condition Person presenting with a pathology or orthopedic disorder affecting locomotion Recent spinal surgery (< 3 months before the inclusion visit) Systemic corticosteroid use, or corticosteroid injection at the lumbar spine, within the last 3 months Muscle relaxant use in the week preceding the experiment

- Inclusion criteria for asymptomatic participants

Adult aged 18 to 65 years (inclusive) Have freely given written informed consent Person presenting no form of low back pain and matching the age and male-to-female ratio characteristics of the CNSLBP group*

In accordance with Article L1121-8-1 of the French Public Health Code, participants must be affiliated to, or beneficiaries of, a social security scheme

To ensure correspondence in terms of age and sex ratio between the CNSLBP group and the healthy group, the frequency of age and gender categories among CNSLBP participants will be used to build, by matching, the group of healthy participants.

- Non-inclusion criteria for asymptomatic participants

Person reporting an ongoing chronic pain complaint or a history of significant chronic pain (≥ 4/10 for at least 6 months) (HAS, 2019) Person unable to perform the walking tasks studied without excessive discomfort or fatigue

- Non-inclusion criteria common to CNSLBP and asymptomatic participants

Known contraindications or limitations to walking Cardiovascular risk factors (uncontrolled high blood pressure, poorly controlled diabetes or diabetes with complications, severe untreated dyslipidemia), or heart disease contraindicating physical activity Severe, unstabilized psychiatric condition Person presenting with a pathology or orthopedic disorder affecting locomotion

(*) Persons referred to in Articles L. 1121-5 to L. 1121-8 and L. 1121-12 of the French Public Health Code:

Pregnant, parturient, or breastfeeding woman Person deprived of liberty by judicial or administrative decision Person hospitalized without consent and not subject to a legal protection measure, and person admitted to a healthcare or social institution for purposes other than research Person subject to an exclusion period for another study Adult subject to a legal protection measure (guardianship, conservatorship, or court protection), or adult unable to express consent and not subject to a protection measure