Analgesic Effects Of Aerobic Exercise Based On Contact Heat Evoked Potentials(CHEPs)

Objective:As one kind of non-invasive and non-pharmaceutical therapies,physical exercise has been widely used in chronic pain management.Exercise has the effect of reducing the individual sensitivity to nociceptive stimuli.This phenomenon is termed exercise induced hypoalgesia(EIH)or exercise induced analgesia.It is a form of endogenous pain modulation characterized by increased pain perception threshold and pain tolerance during and after exercise as well as decreased pain rating to painful stimuli.EIH has important clinical implications both in treatment and evaluation.The effect of aerobic exercise with different intensities on pain sensitivity remains controversial.Thus,we applied electroencephalography(EEG)to determine the electrophysiological mechanism of aerobic EIH,and provides theoretical basis for the application of aerobic exercise in pain assessment and treatment.Methods:Forty-five healthy subjects were recruited,including 23 males and 22 females.Subjects were randomly divided into three groups: moderate intensity exercise group(15,24.73 ± 3.17),low intensity exercise group(15,24.40 ± 2.16)and control group(15,24.27 ± 3.01).The moderate intensity exercise group and low intensity exercise group took a bout of cycling for 25 min(5 min warm-up and 20 min training).The interventions in control group included 2 min warm-up and 23 min quiet sitting on cycle ergometer?The exercise intensity of the three groups was 70% heart rate reserve(HRR),50% HRR and quiet sitting(control),respectively.Pressure pain threshold(PPT)test,heat pain threshold(HPT)test,pain rating to repetitive pulse heat stimuli(RPHS)and the EEG recording during RPHS were performed before and after the interventions.Finally,one way ANOVA was used to evaluate between-group differences of PPT,HPT,and EEG results,and repeated measure of ANOVA was used to analyze the impact of test time(pre-test,post-test)× block(block1,block2,block3,block4,block5,block6)× intervention conditions(medium intensity exercise,low intensity exercise,control)on pain rating of RPHS(including pain intensity and unpleasantness),LSD method was used for post hoc test,paired t test was used for comparison within groups,and Spearman method was used for correlation analysis.Results:1.In terms of behavioral index.There was a significant between-group difference in PPT after exercise(thenar muscle: F=5.032,p=0.011),and the post hoc test indicated that PPT in moderate intensity exercise group was significantly higher than the control group(p=0.004).The PPT increased significantly following moderate aerobic exercise(rectus femoris: t=-0.271,p=0.017;tibialis anterior muscle: t=-2.36,p=0.033).Moderate aerobic exercise increased HPT within-group(tibialis anterior muscle: t=-2.219,p=0.044),and decreased both pain intensity ratings(Block 2: t=2.403,p=0.031;Block 3: t=4.796,p<0.001;Block 4: t=2.794,p=0.014;Block 5: t=3.566,p=0.003;Block 6: t=4.605,p<0.001)and pain unpleasantness ratings(Block 3: t=5.137,p<0.001;Block 4: t=3.367,p=0.005;Block 5: t=3.629,p=0.003;Block 6: t=2.992,p=0.010)to heat stimulations.Low intensity exercises made pain unpleasantness ratings lower(Block 1: t=2.415,p=0.030;Block 2: t=3.287,p=0.005;Block 4: t=2.646,p=0.019;Block 5: t=2.567,p=0.022).There was a significant negative correlation between the change of heat pain intensity ratings and %HRR(p=0.007,r=0.438).There was a significant positive correlation between the change of PPT in thenar muscle and heart rate during exercise(p=0.012,r=0.403),and between the change of PPT in tibialis anterior muscle and %HRR(p=0.016,r=0.386).2.In terms of EEG index.As a component of contact heat evoked potentials(CHEPs),the amplitude of P2 reflecting pain perception was significantly lower after moderate intensity exercise(t=2.355,p(27)0.05).In terms of brain oscillation,the power density of alpha oscillation significantly increased than pre-exercise(t=-2.31,p(27)0.05).The source location of the P2 component showed that the dorsal anterior cingulate gyrus(dACC)is responsible regions for aerobic EIH.The change of alpha power density was positively correlated with RPE score and exercising heart rate(RPE score: p=0.020,r=0.372;heart rate: p=0.019,r=0.374).Conclusion:Aerobic exercise has the effect of systematic analgesic and which is highly dependent on the exercise intensity and which is related to the exercise intensity.Medium-intensity aerobic exercise reduces the sensitivity of proximal and distal exercising sites,and low-intensity aerobic exercise can selectively inhibit the emotional response to painful stimuli.The analgesic mechanism of aerobic exercise involves the enhancement of the central descending inhibitory function.