Effects And ERP Study Of Exercise On Pain Threshold And Pain Severity In Chronic Pain Patients

Background: Exercise-Induced Hypoalgesia(EIH)refers to the phenomenon of decreased sensitivity to pain after exercise.Exercise is an important approach to pain management,including laboratory acute exercise and generalized daily exercise exercises.Physical inactivity is a well-recognized pandemic health problem,especially among people with chronic low back pain.Many patients with chronic pain experience increased pain sensitivity,and increased pain sensitivity in turn increases the risk of developing chronic pain.EIH is composed of multiple mechanisms and influenced by multiple factors,complicating its application in pain management and research,and potentially confounding clinical trials.Objectives: Study 1: To explore the differences in pain and function among chronic pain patients at different exercise levels.Study 2: To explore the effect of isometric exercise on pain threshold and ERP research.Methods: Study 1: Subjects were divided into exercise group and inactivity group according to whether they participated in more than 150 minutes of moderate-intensity aerobic exercise per week,and each group included 31 patients with chronic non-specific low back pain,respectively.The primary outcome measure was Numeric Rating Scales to assess the degree of low back pain,and the secondary outcome measures were to assess the patients’ function(including lumbar flexion and extension range of motion,standing on one foot with closed eyes and lower limb Y balance test).Independent-samples T test or nonparametric test was used for comparison between groups.Study 2: 74 healthy subjects were included and divided into a high pain sensitivity group(n=37)and a low pain sensitivity group(n=37)according to the average heat pain threshold(HPT)of the upper and lower limbs.The acute exercise intervention program adopted 25% of the maximal voluntary contraction of the dominant hand and sustained continuous grip strength exercise for 3 minutes.Baseline and post-intervention outcome measures were measured,including measurement of pressure pain threshold(PPT),HPT,repetitive pulse heat stimuli(RPHS)at the exercising side wrist flexor and contralateral tibialis anterior muscle.During RPHS,electroencephalo-graph(EEG)signals,pain intensity score and pain unpleasantness score were recorded.And Trail Making Test(TMT)was completed.Time domain analysis and spectral analysis were performed on EEG data.Differences in outcome indicators(post-intervention minus baseline)were compared between groups by covariance analysis,and Pearson or Spearman correlation analysis were used to study the correlations between behavioral results and EEG results.Results: Study 1: Compared with the patients in the lack of exercise group,the patients in the exercise group had significantly lower most severe pain scores in the past week(p<0.01),significantly lower average pain scores in the past week(p<0.01),significantly greater range of motion in waist flexion and extension(p<0.05),significantly longer standing on one foot with eyes closed(p<0.05),and significantly better results on the lower limb Y balance test in most directions.Study 2: Isometric exercise significantly improved the exercising side wrist flexor and contralateral tibialis anterior muscle HPT in both groups;isometric exercise significantly improved the PPT of exercising side wrist flexor in both groups and the PPT of contralateral tibialis anterior muscle in the low pain sensitivity group;compared with the subjects in the high pain sensitivity group,subjects with low pain sensitivity had significantly greater HPT difference(F=4.079,p=0.047)and PPT difference(F=6.297,p=0.014)in the exercising side wrist flexor,and had significantly larger PPT difference of the contralateral tibialis anterior muscle(F=4.728,p=0.033).In the high pain sensitivity group,the RPHS pain intensity score after exercise was significantly higher than the baseline(t=-2.143,p=0.039)and the difference was significant between groups(F=4.899,p=0.030).In terms of EEG results,the high pain sensitivity group significantly reduced N2 amplitude(t=-2.269,p=0.029);P2 amplitude was significantly decreased after exercise in the low pain sensitivity group(t=2.286,p=0.028).In terms of correlation,N2 amplitude difference was significantly correlated with RPHS target temperature(r=0.266,p=0.011);P2 amplitude difference was significantly correlated with body mass index(r=0.244,p=0.018).Conclusions: Study 1: Physically active patients with chronic non-specific low back pain have lighter pain intensity and better function than physically inactive patients,including low back range of motion,static and dynamic balance.Study 2: Acute isometric exercise has a pain-inhibiting effect and is influenced by pain sensitivity and type of pain stimuli.With the increase of pain sensitivity,the pain inhibition effect of exercise is weakened or even manifested as a pain facilitation effect.In addition,EIH was also associated with exogenous pain stimulus intensity and body mass index.