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Clenching leg muscles reduces pain sensitivity everywhere

PainSci » bibliography » Smith et al 2017
Tags: chronic pain, exercise, counter-intuitive, good news, pain problems, self-treatment, treatment

Two articles on PainSci cite Smith 2017: 1. Pain & Injury Survival Tips2. The Complete Guide to Neck Pain & Cricks

PainSci commentary on Smith 2017: ?This page is one of thousands in the bibliography. It is not a general article: it is focused on a single scientific paper, and it may provide only just enough context for the summary to make sense. Links to other papers and more general information are provided wherever possible.

Exercise is well-known to suppress pain sensitivity — exercise induced hypoalgesia, or EIH — but the effect is unpredictable. Exercise may have no effect on some kinds of pain, or even cause a setback. For instance, chronic pain after whiplash injuries is known for being EIH resistant.

So this study tested the effect of two kinds of exercise on 21 patients with chronic pain after whiplash, basically trying to find out if one of them is better. They measured pain sensitivity before and after with a simple pressure test, one in the neck and one in the shin. The two exercises were:

  1. 30 minutes of cycling had no effect at all. This is actually good news in this context, because it didn’t make sensitivity worse.
  2. 3 minutes wall squatting actually helped! Basically, these patients just clenched their leg muscles to hold themselves in a squat against a wall. Easy!

Clenching leg muscles didn’t just help the neck. After brief exercise of muscles far from the troubled area, pain sensitivity was reduced not only in the neck, but everywhere else as well — a systemic effect! Which is intriguing. This a surprisingly good result from an easy, safe exercise.

The authors suggest that chronic pain problems may be helped by an “exercise program directed at non-painful muscles performing isometric exercises.”

This trial failed to find any relationship between the results and psychological factors and conditioned pain modulation (a measure of pain sensitivity, often abnormal in people with chronic pain).

~ Paul Ingraham

original abstract Abstracts here may not perfectly match originals, for a variety of technical and practical reasons. Some abstacts are truncated for my purposes here, if they are particularly long-winded and unhelpful. I occasionally add clarifying notes. And I make some minor corrections.

BACKGROUND AND AIMS: Reduced pain sensitivity following exercise is termed exercise induced hypoalgesia (EIH). Preliminary evidence suggests that impairment of EIH is evident in individuals with whiplash associated disorders (WAD) following submaximal aerobic exercise. This study aimed to compare EIH responses to isometric and aerobic exercise in patients with chronic WAD and healthy controls and investigate relationships between EIH, conditioned pain modulation (CPM) and psychological factors in patients with chronic WAD.

METHODS: A cross sectional pre-post study investigated the effect of a single session of submaximal aerobic cycling exercise and a single session of isometric timed wall squat exercise on EIH in a group of participants with chronic WAD (n=21) and a group of asymptomatic control participants (n=19). Bivariate analyses between EIH and baseline measures of CPM and psychological features (fear of movement, pain catastrophization and posttraumatic stress symptoms) were also investigated.

RESULTS: The isometric wall squat exercise but not the aerobic cycling exercise resulted in EIH in both groups (P<.023) with no between-group differences (P>.55) demonstrated for either exercise. There were no significant associations measured between EIH (for either exercise performed), and CPM, or any of the psychological variables.

CONCLUSIONS: This study showed that individuals with chronic WAD and mild to moderate pain and disability, and no evidence of dysfunctional CPM, demonstrated reduced pain sensitivity, both in the cervical spine and over the tibialis anterior following an isometric, timed wall squat exercise. Cycling exercise did not increase pain sensitivity.

IMPLICATIONS: Individuals with chronic WAD and mild to moderate levels of neck pain and disability may experience less pain sensitivity both locally and remotely following an exercise program directed at non-painful muscles performing isometric exercises. Individuals cycling for 30min at 75% of age-predicted heart rate maximum do not experience increased pain sensitivity.

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