Pain‐evoked trunk muscle activity changes during fatigue and DOMS

Abstract

Background Muscle pain may reorganize trunk muscle activity but interactions with exercise‐related muscle fatigue and delayed onset muscle soreness (DOMS) is to be clarified. Methods In 19 healthy participants, the trunk muscle activity during 20 multi‐directional unpredictable surface perturbations were recorded after bilateral isotonic saline injections (control) and during unilateral and bilateral hypertonic saline‐induced low back pain (LBP) in conditions of back muscle fatigue (Day‐1) and DOMS (Day‐2). Pain intensity and distribution were assessed by visual analogue scale (VAS) scores and pain drawings. The degree of fatigue and DOMS were assessed by Likert scale scores. Root‐mean‐square electromyographic (RMS‐EMG) signals were recorded post‐perturbation from six bilateral trunk muscles and the difference from baseline conditions (Delta‐RMS‐EMG) was extracted and averaged across abdominal and back muscles. Results In DOMS, peak VAS scores were higher during bilateral control and bilateral saline‐induced pain than fatigue (p < 0.001) and during bilateral compared with unilateral pain (p < 0.001). The saline‐induced pain areas were larger during DOMS than fatigue (p < 0.01). In response to surface perturbations during fatigue and DOMS, the back muscle Delta‐RMS‐EMG increased during bilateral compared with unilateral pain and control injections (p < 0.001) and decreased during unilateral pain compared with control injections (p < 0.04). In DOMS compared with fatigue, the post‐perturbation Delta‐RMS‐EMG in back muscles was higher during bilateral pain and lower during unilateral pain (p < 0.001). The abdominal Delta‐RMS‐EMG was not significantly affected. Conclusion Facilitated and attenuated back muscle responses to surface perturbations in bilateral and unilateral LBP, respectively, was more expressed during exercise‐induced back muscle soreness compared with fatigue. Significance Back muscle activity decreased during unilateral and increased during bilateral pain after unpredictable surface perturbations during muscle fatigue and DOMS. Accumulation effects of DOMS on pain intensity and spreading and trunk muscle activity after pain‐induction.

Alterations in Temporal Summation of Pain and Conditioned Pain Modulation Across an Episode of Experimental Exercise-Induced Low Back Pain

“…The exercise-induced-LBP model produced pain intensities and disability levels consistent with, or even higher than, those reported in similar LBP models 6,31,36 , with participants completing nearly twice as many repetitions as that reported previously 31 . Such pain and disability levels correspond to those observed in mild nociceptive LBP 60 or recurrent LBP conditions 43 , but are generally lower than that seen in complex chronic pain populations 42,43,46 .…”

“…An eccentric trunk extension exercise, as developed previously 31,36 , was used to induce muscle fatigue and subsequent DOMS in the low back ( Fig. 1A).…”

“…following the last repetition to quantify perceived muscle fatigue 31 . Total exercise time and number of repetitions were recorded.…”

Experimental Low Back Pain Decreased Trunk Muscle Activity in Currently Asymptomatic Recurrent Low Back Pain Patients During Step Tasks

“…Furthermore, higher pain intensity in the controls during bilateral compared with unilateral pain is in line with previous observations. High pain intensity and increased referred pain areas have been observed in the trapezius 19 , masseter 64 and longissimus 41,42 muscles during bilateral experimental pain, probably caused by summation from converging inputs from nociceptors bilaterally 27 . The present study is, however, the first demonstration of spatial summation from bilateral hypertonic saline-induced pain in R-LBP patients during currently asymptomatic periods.…”

“…The sample size estimations were conducted a priori in GPower 3.1.9.2 based on results from previous studies of pain-evoked differences in trunk muscle EMG 41,42 The difference between baseline and pain conditions for the step phase duration (Deltatime) was analyzed with three-way ANOVA with group as between and phases and condition as within factors. Pearson's correlation coefficient (r) was used to correlate Delta-time between the two pain conditions and correlate Delta-time with pain NRS scores for each of the two pain conditions.…”