Exploration of Gait Biomechanics and Muscle Pain of the Lower Extremity

The proposed study will be a randomized, crossover design in which experimental pain will be induced in healthy subjects using hypertonic saline injections to three muscles of the lower extremities: The gastrocnemius muscle, the vastus medialis muscle, and the semitendinosus muscle. Participants will be block-randomized to receive an injection in each of the three muscles and will receive either the painful or control condition first for each muscle. The participant will always be blinded to the type of injection received.

Following the injection, there will typically be a 15-minute window of pain (45). Within this timeframe, motion capture will be carried out for both the control and painful conditions. During motion capture, the participants will perform multiple walking trials of approximately 10 meters. The participants will be equipped with electromyography (EMG) sensors on key muscles of the lower extremities. The participants will be asked for NRS ratings every 30 seconds throughout the 15 minutes with expected pain. There will be a 15-minute washout between the muscle injections.

Inclusion criteria

• Healthy men and women aged 18-45 years

Exclusion criteria

• Pregnancy
• Drug addiction, defined as the use of cannabis, opioids, or other drugs
• Previous or current neurologic or musculoskeletal illnesses
• Current pain
• Lack of ability to cooperate