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 1x3 min seated isometric knee extension exercise in healthy women. The study is a blinded 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 pressure pain thresholds (PPT) 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 Women

Conditions
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Pain, Healthy

Intervention / Treatment
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* Behavioral: Pain (hypertonic saline)
* Behavioral: No pain (Isotonic 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 behaviour 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 in the lower extremities within the last 12 months Chronic or actual pain on the days of testing Under the influence on the days of testing Inability to cooperate

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

Sexes Eligible for Study
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Female

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 1-7 days between arms
Masking: Double


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 1x3 min Seated Isometric Knee Extension | Behavioral: Pain (hypertonic saline)<br>* A bolus injection (1 ml) of hypertonic saline (5.8%) is injected into the dominant vastus medialis muscle 20 cm proximal from the basis of patella before performance of the 1x3 min Seated Isometric Knee Extension.<br>|
| Placebo Comparator: No pain (isotonic saline)<br>Injection (1 ml) of non-painful isotonic saline (0.9%) prior to performance of the 1x3 min Seated Isometric Knee Extension | Behavioral: No pain (Isotonic saline)<br>* A bolus injection (1 ml) of isotonic saline (0.9%) is injected into the dominant vastus medialis muscle 20 cm proximal from the basis of patella before performance of the 1x3 min Seated Isometric Knee Extension<br>|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Change in pressure pain threshold will be assessed over the dominant quadriceps muscle | Between group comparison of the primary outcome, which is change in pressure pain threshold over the dominant quadriceps muscle before and after performing seated isometric knee extension. Pressure pain threshold is measured with a handheld pressure algometer. | Baseline, Day 2 (within 1 week of baseline), Day 3 (within 1 week of Day 2) | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Pressure pain threshold at the non-dominant quadriceps muscle and non-dominant trapezius muscle | Between group comparison of the secondary outcome, which is change in pressure pain threshold at the non-dominant quadriceps muscle and non-dominant trapezius muscle from before Seated Isometric Knee Extension to after Seated Isometric Knee Extension. Pressure pain threshold is measured with a handheld pressure algometer. | Baseline, Day 2 (within 1 week of baseline), Day 3 (within 1 week of Day 2) | 
| Pain Intensity in dominant thigh | Pain intensity is 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 1, 2 and 3 minutes into the Seated Isometric Knee Extension, and immediately after the end of the seated isometric knee extension |