Influence of Pain on Exercise-induced Hypoalgesia

Study Overview
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Brief Summary
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The purpose of this study is to investigate how acute pain induced by hypertonic saline prior to exercise influence the magnitude of exercise-induced hypoalgesia after a 3 min isometric wallsquat exercise in healthy subjects. The study is a single blinded (investigator) randomized cross-over trial The results from the study may be of great importance to the understanding of exercise-induced hypoalgesia, and whether the presence of pain affects the effects of exercise.

Detailed Description
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Exercise is recommended to promote and maintain health and as treatment for more than 25 chronic diseases and pain conditions. The mechanisms underlying pain relief of exercise are largely unknown but may be related to the modulation of central descending pain inhibitory pathways after acute exercise bouts. Exercise-induced hypoalgesia (EIH) is typically assessed as the temporary change in PPTs after a short acute exercise bout and EIH is seen as a proxy of descending pain inhibitory control. In general, EIH seems hypoalgesic (functional) in asymptomatic subjects. A hyperalgesic (impaired) EIH response has been reported in different chronic pain populations, although a functional EIH response also has been reported in subgroups of knee osteoarthritis patients. This implies differences in the acute response to exercise between healthy (pain-free) subjects and chronic pain patients, but it is still unknown whether the presence of pain itself affects the pain alleviating response (i.e. the EIH response) to acute exercise. It is hypothesized that acute pain will decrease the EIH response magnitude following hypertonic saline injection compared with the control injection. This study will increase the insight into the EIH mechanisms in healthy subjects in general, and how the presence of pain affects the body's own ability to modulate pain during exercise.

Official Title
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The Influence of Pain on Exercise-Induced Hypoalgesia in Healthy Subjects: A Randomized Controlled Trial

Conditions
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Pain

Intervention / Treatment
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* Behavioral: Pain (hypertonic saline)
* Behavioral: No pain (Hypotonic saline)


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: Pain-free Understands and writes Danish Exclusion Criteria: Pregnancy Previous addictive behavior defined as abuse of hash, opioids or other euphoric substances. Previous painful or mental illnesses, neurological or circulatory diseases in the form of heart or lung disease. Surgery within last 3 months Pain on the days of testing Pain for more than 2 weeks within the last 3 months

Ages Eligible for Study
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Minimum Age: 18 Years
Maximum Age: 50 Years

Sexes Eligible for Study
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All

Accepts Healthy Volunteers
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Accepts Healthy Volunteers

Study Plan
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How is the study designed?
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Design Details

Primary Purpose: Basic Science
Allocation: Randomized
Intervention Model: Crossover Assignment
Interventional Model Description: This study is a 2-arm randomized controlled cross-over trial with 1 week between arms
Masking: Single


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Experimental: Pain (hypertonic saline)<br>Injection (1 ml) of painful hypertonic saline (5.8%) prior to performance of the 3 min wall squat exercise | Behavioral: Pain (hypertonic saline)<br>* A bolus injection (1 ml) of hypertonic saline (5.8%) is injected into the right quadriceps femoris of the quadriceps femoris muscle 1 minute before performance of the 3 min wall squat exercise<br>|
| Placebo Comparator: No pain (Hypotonic saline)<br>Injection (1 ml) of non-painful isotonic saline (0.9%) prior to performance of the 3 min wall squat exercise | Behavioral: No pain (Hypotonic saline)<br>* A bolus injection (1 ml) of isotonic saline (0.9%) is injected into the right quadriceps femoris of the quadriceps femoris muscle 1 minute before performance of the 3 min wall squat exercise<br>|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Pressure pain threshold at the right quadriceps muscle where injection is performed. | Between group comparison of the primary outcome, which is change in pressure pain threshold at the right quadriceps muscle from before wall squat to after wall squat. Pressure pain threshold is measured with a hand held pressure algometer. | Before and after the 3 minutes wall squat | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Pressure pain threshold at the non-dominant trapezius muscle | Between group comparison of the secondary outcome, which is change in pressure pain threshold at the left trapezius muscle from before wall squat to after wall squat. Pressure pain threshold is measured with a hand held pressure algometer. | Before and after the 3 minutes wall squat | 
| Pressure pain threshold at the left quadriceps muscle where injection is not performed. | Between group comparison of the secondary outcome, which is change in pressure pain threshold at the left quadriceps muscle from before wall squat to after wall squat. Pressure pain threshold is measured with a hand held pressure algometer. | Before and after the 3 minutes wall squat | 
| Pain Intensity in thighs | Pain intensity in both thighs are assessed with numerical rating scales with 0 = no pain and 10 = maximal pain. | Assessed before and immediately after hypertonic and isotonic saline injection as well as after 1, 2 and 3 min of wall squat, and immediately after the end of wall squat | 

 Terms related to the study
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Keywords Provided by Centre Hospitalier Valida
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Exercise-induced hypoalgesia, Pressure pain threshold, hypertonic saline