Fragmented Sleep, Pain, and Biomechanics

The Impacts of Fragmented Sleep on Biomechanics and Pain of the Shoulder and Knee

This interventional study aims to test the effects of sleep disruption on pain sensitivity and biomechanics in healthy individuals during experimental knee and shoulder pain. The main question the study aims to answer is:

1) Does sleep fragmentation increase experimental knee and shoulder pain and what are the underlying mechanisms?

Participants will receive two injections a) Hypertonic saline (painful) in the knee and b) hypertonic saline (painful) in the upper arm.

This study will include healthy participants for one baseline session and one follow-up session separated by three nights of experimental sleep disruption.

The sleep fragmentation will involve three forced awakenings per night for three consecutive nights between sessions. These awakenings will be planned at 00:00, 02:30, and 05:00.

In each session, the participant will answer questionnaires and have their pain sensitivity assessed using cuff-pressure algometry. Following this, they will first receive a painful saline injection into the infrapatellar fat pad of the knee. After a washout period, they will receive another painful saline injection into the deltoid muscle of the shoulder. For both injections, the pain will be rated on an NRS scale (0 representing 'no pain' and 10 representing 'worst pain imaginable') every 30 seconds, and the distribution will be marked on a body chart.

Inclusion Criteria:

• Healthy men and women aged 18-45 years
• Must have a smartphone available during the experiment

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