Exercise does not produce hypoalgesia when performed immediately after a painful stimulus

Abstract

<jats:title>Abstract</jats:title> <jats:sec id="j_sjpain-2018-0024_s_999"> <jats:title id="d1724619e61371">Background and aims:</jats:title> <jats:p>Exercise-induced hypoalgesia (EIH) and conditioned pain modulation (CPM) are assumed to reflect descending pain inhibition. Potential interactions between EIH and CPM may be important in the therapy of chronic pain, as reduced CPM and increased pain after exercise are frequently observed. This study compared the EIH response after CPM was activated using a cold pressor task with the EIH response after a control condition.</jats:p></jats:sec> <jats:sec id="j_sjpain-2018-0024_s_998"> <jats:title id="d1724619e61379">Methods:</jats:title> <jats:p>Thirty-one participants (age: 27.7±9.8; 15 female) completed two sessions: a cold pressor task (CPT) session, i.e. testing EIH with preceding CPM activation induced using a 2 min CPT at approximately 2°C, and a control session, i.e. testing EIH after a control condition (2 min of quiet rest). EIH was induced using a 15 min bicycling exercise at a target heart rate corresponding to 75% VO2 max. Repeated measures ANOVAs on pressure pain thresholds (PPTs) at the hand, back and leg were used to determine the effects of exercise after the cold pressor test and control condition. Furthermore, correlations between CPM and EIH, in the CPT session as well as control session, were calculated at each assessment site.</jats:p></jats:sec> <jats:sec id="j_sjpain-2018-0024_s_997"> <jats:title id="d1724619e61387">Results:</jats:title> <jats:p>A significant time x condition interaction (F(1, 30)=43.61, <jats:italic>p</jats:italic>&lt;0.001, partial η<jats:sup>2</jats:sup>=0.59), with Bonferroni-corrected <jats:italic>post-hoc t</jats:italic>-tests showed that PPTs increased after exercise in the control session (<jats:italic>p</jats:italic>&lt;0.001), but not in the CPT session (<jats:italic>p</jats:italic>=0.125). Furthermore, there was a small positive correlation of EIH in the control session and CPM at the hand (r=0.37, <jats:italic>p</jats:italic>=0.043). There was a moderate negative correlation of EIH in the CPT session and CPM at the hand (r=−0.50, <jats:italic>p</jats:italic>=0.004), and smaller negative correlations at the back (r=−0.37, <jats:italic>p</jats:italic>=0.036) and at the leg (r=−0.35, <jats:italic>p</jats:italic>=0.054).</jats:p></jats:sec> <jats:sec id="j_sjpain-2018-0024_s_996"> <jats:title id="d1724619e61423">Conclusions:</jats:title> <jats:p>Attenuated EIH after the CPM activation in comparison to a control condition suggests that EIH and CPM may share underlying pain inhibitory mechanisms on a systemic level. This assumption is further supported by the finding of small to moderate significant correlations between EIH and CPM at the hand. The attenuated EIH response furthermore suggests that these mechanisms are exhaustible, i.e. that its effects decline after a certain amount of inhibition.</jats:p></jats:sec> <jats:sec id="j_sjpain-2018-0024_s_995"> <jats:title id="d1724619e61432">Implications:</jats:title> <jats:p>In patients with chronic pain, assessing the current capacity of the descending pain inhibitory system – as indicated by the CPM response – may aid to make better predictions about how patients will respond to exercise with respect to acute pain reduction.</jats:p></jats:sec>

Walking increases pain tolerance in humans: an experimental cross-over study

“…The relative test-retest reliability of the hypoalgesic response after walking in this current study shows comparable ICCs to what has been demonstrated previously in studies investigating the test-retest reliability of the EIH responses after high intensity aerobic exercise [13], moderate aerobic exercise [37] and isometric wall squat [14]. Moreover, the relative reliability of EIH across different sessions is comparable to the reliability of the CPM response [38] that may be partly responsible for the EIH response [2,16,17]. It has been suggested that a high focus on standardizations of test protocols and action to prevent assessor bias would increase reliability in test-retest investigations [39].…”

“…The painful CPM paradigm show similar widespead hypoalgesic manifestations as seen for exercise [2], and exercises that consistently produce hypoalgesia is often percieved as moderately painful [13,14]. Moreover, studies have shown larger hypoalgesic responses after painful exercise compared with non-painful exercise [15], and several studies have shown a positive association between the CPM response and the EIH response [2,16,17] suggesting that subjects with reduced CPM have less effect from exercise.…”

Exercise‐induced hypoalgesia in young adult females with long‐standing patellofemoral pain – A randomized crossover study

“…The current findings of a decreased CPM effect after exercise corresponds with a recent study demonstrating that CPM is decreased subsequent to exercise (Alsouhibani et al., ). Gajsar et al., suggested that if CPM and EIH share similar descending pain inhibitory mechanisms, further subsequent CPM effect may not be possible due to a ceiling effect (Gajsar et al., ). As the effect of CPM is thought to be short‐lived (Kennedy, Kemp, Ridout, Yarnitsky, & Rice, ), it is unclear if this could have had an influence the current study design.…”

“…Additionally, in the current study the EIH effect detected was small and not consistent across outcomes. The magnitude of the EIH effect has recently been shown to be diminished when evaluated after a CPM paradigm (Gajsar et al, 2018) which may have influenced the possibility to detect EIH in the current study. Furthermore, it is unknown if patients have a similar EIH response, as the majority of research has been on healthy individuals (Koltyn.F, 2000).…”

“…It has previously been proposed that the EIH response as an anti-nociceptive mechanism is related to descending pain inhibition which is psychophysically assessed by the conditioning pain modulation (CPM) paradigm (Lemley, Hunter, & Bement, 2015). Recently, CPM was shown to be attenuated following EIH (Gajsar, Nahrwold, Titze, Hasenbring, & Vaegter, 2018). Moreover, temporal summation of pain (TSP), a pro-nociceptive pain mechanism which is evaluated as the relative increase in pain to sequential stimuli with equal intensity, has also been shown to be attenuated by exercise (Alsouhibani, Vaegter, & Hoeger Bement, 2018;Vaegter, Handberg, & Graven-Nielsen, 2015a).…”