Back in 2005, I was involved in an accident with a car pulling out of a driveway without looking. The road to rehab was long but straightforward, despite a shattered scapula in eight different places and a few broken ribs. At the time, many of my friends remarked at how quickly I recovered, and claimed that it must have been because of my fitness.
Thinking through the process afterwards, I felt that my quick recovery had more to do with my ability to distinguish between pain and physical discomfort. I was willing to push myself in rehab right to the point of actual pain instead of mistaking fatigue or discomfort as pain.
This past Sunday, my good pal Rob and I were out on a club ride. Rounding a graveled corner at walking pace, Rob slid out. He slammed his right side on the pavement and ended up with a femur fracture. Besides being sympathetic to what he was going through, I came across a newspaper that investigated the relationship between aerobic fitness and pain perception.
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Jones et al. 2014
Surprisingly, very little research has been done to explore the relationship between aerobic training and pain perception. What we do know from scientific studies is that acute exercise provides a hypoalgesic effect. The endorphins you produce during exercise reduce your pain perception in the short term.
Chronic exercise also decreases pain sensitivity in patient populations suffering from chronic pain. However, the presence of persistent pain as a confounding factor in these studies means that we cannot directly translate such findings to otherwise healthy populations.
A group from the University of New South Wales in Australia decided to tackle this topic, and their results were published this summer in the prestigious journal of Medicine and Science in Sports and Exercise.
In this study, they chose to train moderately fit individuals over a six-week period. They tested both pain tolerance and pain threshold (point at which pain is noticeable or significant).
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Some of the methodological details included in the study:
1. Twenty-four total participants with no history of chronic pain, disease or depression.
2. There was a control group (no exercise training) and exercise group, each consisting of 12 participants (11 females in exercise group and 10 females in control group).
3. The exercise group performed 18 training sessions over six weeks, consisting of 30 minutes of cycling at 75 percent of heart rate reserve. Starting peak aerobic capacity was 36.3 mL/kg/min—a "normal" to moderate fitness range.
4. The control group performed no systematic training during the six weeks, and were instructed not to alter their normal physical activity patterns. Starting peak aerobic capacity was 42.9 mL/kg/min—normal to moderate range of fitness.
5. Pain threshold was tested at four muscles: trapezius, biceps, rectus femoris (quadriceps muscles), and tibialis anterior (one of the shin muscles). A blunt force-measuring probe was systematically applied at these sites, and the participants responded when the pressure turned into pain.
6. Pain tolerance was measured by ischemia, the blockage of blood to a limb as might happen with a tourniquet. Participants had a blood pressure cuff placed around their arm at 200-mmHg pressure, and were asked to perform periodic gripping exercise to the point of tolerance.