Similar effects of fatigue induced by a repetitive pointing task on local and remote light touch and pain perception in men and women

Abstract

Background Women involved in repetitive, fatiguing, jobs develop more neck and/or shoulder musculoskeletal disorders than men. Sex differences in the pain response to exercise could contribute to the higher prevalence of neck/shoulder musculoskeletal disorders in women. The objective of this study was to assess sex differences in pain sensitivity following a fatiguing upper limb task. Relationships between measures of fatigue and of the sensitivity to nociceptive and to non-nociceptive stimulations were also explored. Methods Thirty healthy adults (15 women) performed a fatiguing repetitive pointing task with their dominant arm. Upper limb electromyography was recorded from the dominant upper trapezius, anterior deltoid and bicep brachii and from the contralateral tibialis anterior. Before and immediately after the repetitive pointing task, pressure pain and light touch sensitivity thresholds were measured over the same muscles. Results Electromyographic signs of fatigue were observed only in the anterior deltoid and biceps brachii muscles. Pressure pain thresholds over both muscles increased slightly (effect size ≤ 0.34), but no changes occurred over the upper trapezius and the tibialis anterior. Light touch thresholds increased moderately to importantly after the repetitive pointing task over all four muscles (effect sizes = 0.58 to 0.87). No sex differences were observed in any sensory variable. Moreover, no or weak correlations (r = -0.27 to 0.39) were observed between electromyographical signs of fatigue, light touch threshold and pressure pain threshold variables. Conclusions We observed sex-independent effects of a repetitive upper limb task on the sensitivity to painful and to nonpainful stimuli. Moreover, the hypoalgesia induced by the repetitive pointing task was weak and localized, and did not directly correlate with the induced muscle fatigue. Results suggest that fatigue-related changes in the sensitivity to noxious and innocuous stimuli could not explain women’s greater prevalence of neck/shoulder musculoskeletal disorders.

What are the best indicators of myoelectric manifestation of fatigue?

“…The VIP value of the activity of the median and anterior deltoids ranged between 0.73-1.61, which is qualitatively smaller than the VIP value of median frequency, mobility, Higuchi fractal dimension, spectral entropy, and fuzzy entropy (1.26-2.28) for these muscles. Similarly to activation level, there were changes in activity for a large proportion of the participants in the upper trapezius (90%), although this muscle is not supposed to fatigue [72,73]. Thus, our results further confirm that amplitude related MMF indicators are not relevant f or assessing muscle fatigue.…”

“…Considering that median frequency is sensitive to both muscle fiber conduction velocity and motor unit synchronization [17,114], mobility is sensitive to conduction velocity [56], spectral entropy is sensitive to muscle fiber conduction velocity and motor units firing rate [56], and fuzzy entropy and Higuchi fractal dimension are sensitive to the increase of motor unit synchronization [90,104] occurring with muscle fatigue, our results emphasize the need to consider and combine a variety of MMF indicators that are sensitive to all parameters of motor unit behavior affected by fatigue in order to improve its assessment. Noteworthy, median frequency, mobility, spectral entropy, fuzzy entropy, and Higuchi fractal dimension were the only indicators that both showed low VIP values and changed for a moderate proportion of the participants (14%-38%) during RPT initiation and termination for the trapezius muscles, which did not show signs of fatigue during the RPT used in the present study [72][73][74]. These five indicators may therefore have good specificity to assess muscle fatigue, and future investigations should focus on their combination into a single MMF indicator to maximize the sensitivity and specificity of muscle fatigue assessment.…”

“…This task has been shown to fatigue the anterior and medial deltoid [72][73][74]. Every 30 seconds, participants reported their RPE using the CR-10 Borg scale (RPE) [62] without interrupting the RPT movement.…”

“…In a recent study, Ni et al, [68] showed that time, frequency, and time- Consequently, the aim of the present study was to determine the best MMF indicators, f rom 15 MMF indicators identified in the literature as potentially relevant to assess muscle fatigue during a repetitive pointing task (RPT) performed with the upper limb. We hypothesized that for the anterior and medial deltoids, which are the muscles showing the largest signs of fatigue during the upper limb repetitive task used in the present studies [72][73][74], the mobility, median frequency, spectral entropy, fuzzy entropy, multiscale entropy [24,28,41,75,76], and degree of multifractality [40,47,49,53] will have greater importance to predict the evolution of the RPE. In addition, these MMF indicators will significantly change for a large proportion of the participants in the anterior and medial deltoid in comparison to approximate and sample entropy, recurrence quantification analysis, correlation dimension, and the largest Lyapunov exponent [28,40,46,55].…”

Neuron-Glia-Immune Triad and Cortico-Limbic System in Pathology of Pain

“…Sex differences are reported in the incidence and prevalence of musculoskeletal pain. Studies from healthy adult volunteers who underwent experimental pain to identify pressure pain threshold did not find any sex differences in muscle fatigue times between men and women, although the attitude towards pain differed between the sexes [ 68 , 69 ]. Anatomical differences may explain sex differences in risk towards certain injuries and associated pain [ 70 ], although the mechanisms behind these sex differences are not known.…”