Neural mechanisms of pain processing differ between endurance athletes and nonathletes: A functional connectivity magnetic resonance imaging study

Pain perception and the ability to modulate arising pain vary tremendously between individuals. It has been shown that endurance athletes possess higher pain tolerance thresholds and a greater effect of conditioned pain modulation than nonathletes, both indicating a more efficient system of endogenous pain inhibition. The aim of the present study was to focus on the neural mechanisms of pain processing in endurance athletes that have not been investigated yet.

Therefore, we analyzed the pain processing of 18 male athletes and 19 healthy male nonathletes using functional magnetic resonance imaging.

We conducted an fMRI study to physically identical stimuli in athletes versus nonathletes and analyzed the functional connectivity between predefined brain regions that are typically activated by nociceptive stimulation (Wager et al., 2013) during painful heat stimulation using a region of interest (ROI)-to-ROI connectivity analysis.

Fig. 1: Pain intensity ratings to heat pain and warmth perception in athletes versus nonathletes. There was no significant group difference in the rating of the 38°C warm stimulus (W = 151, p = .518), but a significant group difference in the rating of the heat stimuli. Athletes rated the painful thermal stimulation (45, 47, and 48.9°C) less intense than nonathletes (F(1) = 4.651, p = .033, d = 0.729).

Fig. 2: The bottom row shows the results of the conducted t-contrast. Comparing brain activation of nonathletes > athletes during painful heat stimulation. This contrast revealed stronger activation in nonathletes in several brain regions that are typically activated by nociceptive stimulation including bilateral thalamus, bilateral SI and MI, bilateral anterior and posterior Insula, right ACC, bilateral MCC, right PFC, and bilateral brain stem (BS).

To conclude, the investigation of the neural mechanisms of pain processing in endurance athletes is important to understand their exceptional abilities to modulate pain. Comparing the pain processing of heat pain stimuli between endurance athletes and nonathletes, our study revealed (a) lower pain intensity ratings in athletes to applied heat stimuli; (b) a reduction of the activation in several brain regions that are typically activated by nociceptive stimulation in athletes to applied painful heat stimuli; (c) stronger functional connectivity between brain regions that are typically activated by nociceptive stimulation to applied painful heat stimuli. However, no such differences were observed for warm stimuli. Lastly, post hoc correlation analyses revealed associations of the subject's fitness level and the brain activation strengths, subject's fitness level and functional connectivity, and brain activation strengths and functional connectivity. Our results suggest that endurance athletes differ in the neural processing of pain elicited by noxious heat.

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