Muscle Synergies in Pain and Pain Anticipation

Universite de Picardie Jules Verne

Status: Not yet enrolling

Conditions: Pain Anticipation; Nocebo Effect; Pain

Treatments: Other: Gait assesment; Other: Pain expectation conditioning

Study type: Interventional

Funder types: Other; Industry

Identifiers

NCT07251387

2025-5551-1H

Details and patient eligibility

About

This study investigates how the anticipation of pain affects muscle synergies. Two groups will be compared: an experimental group, who first experience actual pain from capsaicin cream and are then presented with a harmless cream deceptively labeled as capsaicin, against a control group, who are presented with a harmless cream labeled as potentially painful, without any prior painful experience. The changes in muscle synergies will be measured during walking tasks.

Full description

Participants will be recruited through university announcements. Eligibility will be determined by a screening process that assesses prior experience with capsaicin cream. Healthy adults aged 18-35 who meet the inclusion criteria will be enrolled and assigned to one of two groups based on their screening responses:

1. Experimental Group ("Prior Experience"): Individuals who report a prior painful experience with capsaicin cream.
2. Control Group ("No Prior Experience"): Individuals who report no prior experience with capsaicin cream.

All participants will take part in a single experimental session. Both groups will receive identical negative verbal suggestions indicating that a neutral, harmless cream is a potent capsaicin formulation likely to cause pain.

Participants will complete a walking assessment on a treadmill. The speed will be incrementally increased from 0.8 m/s to 1.1 m/s. Throughout this task, muscle activity will be recorded via electromyography (EMG), and ground reaction forces will be captured by force platforms embedded in the treadmill.

Following the initial walk, participants will complete a set of standardized questionnaires to establish baseline scores for pain perception (Visual Analog Scale, VAS), fear of movement (Tampa Scale of Kinesiophobia, TSK), and pain catastrophizing (Pain Catastrophizing Scale, PCS).

The neutral cream will be applied to the knee, specifically in the area between the lateral epicondyles of the femur, in a 4 cm wide band. Participants will immediately fill out the VAS to report any pain sensations. The walking assessment is repeated, measuring the same physiological signals (EMG and ground reaction forces).

The primary objective is to determine whether a prior painful experience with capsaicin causes individuals to generalize that pain memory to a neutral sensation, leading to different outcomes than in those who only have a negative expectation. We will specifically investigate the magnitude of this effect on muscle synergies and ground reaction forces.

Enrollment: 34 estimated patients

Sex: All

Ages: 18 to 35 years old

Volunteers: Accepts Healthy Volunteers

Inclusion criteria

• Aged 18-35 years old
• Healthy participant with no self-reported diagnosed neurological, musculoskeletal, or cardiovascular disorders
• Body Mass Index (BMI) < 30
• Ability to walk unaided for at least 10 minutes without major physical limitations

Exclusion criteria

• Presence of pain at the time of testing
• Self-reported diagnosed condition affecting mobility
• Known allergy to any component of the study cream
• Allergy to EMG electrode adhesives
• Inability to stand unassisted for more than 1 minute
• Inability to walk/run at the required speed and distance
• Weight exceeding 150 kg (due to treadmill limitations)
• Recent intake (prior intervention) of:
• Analgesics (within 6 hours)
• Cigarettes (within 6 hours)
• Caffeine (within 2 hours)
• Skin lesions at the cream application site
• Pregnancy
• Failure to understand instructions
• Daytime pain reported by participant on day of experimentation

Trial design

Primary purpose: Basic Science

Allocation: Non-Randomized

Interventional model: Parallel Assignment

Masking: Single Blind

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34 participants in 2 patient groups

Prior Experience Group

Experimental group

Description:

Participants in this arm have experienced capsaicin cream before and will be given a neutral cream. They will be told that the cream contains capsaicin and will cause pain.

Treatment:

Other: Pain expectation conditioning

Other: Gait assesment

Control Group

Sham Comparator group

Description:

Pariticpants in this arm have never experienced capsaicin cream before and will be given a neutral cream. They will be told that the cream contains capsaicin and will cause pain.

Treatment:

Other: Pain expectation conditioning

Other: Gait assesment