Age- and sex-specific effects in paravertebral surface electromyographic back extensor muscle fatigue in chronic low back pain

Gerold Ebenbichler,Josef Kollmitzer,Thomas Kienbacher,Richard Habenicht,Sara Ziegelbecker,Patrick Mair

doi:10.1007/s11357-019-00134-7

Abstract

The impact of aging on the back muscles is not well understood, yet may hold clues to both normal aging and chronic low back pain (cLBP). This study sought to investigate whether the median frequency (MF) surface electromyographic (SEMG) back muscle fatigue method—a proxy for glycolytic muscle metabolism—would be able to detect age- and sex-specific differences in neuromuscular and muscle metabolic functions in individuals with cLBP in a reliable way, and whether it would be as sensitive as when used on healthy individuals. With participants seated on a dynamometer (20° trunk anteflexion), paraspinal SEMG activity was recorded bilaterally from the multifidus (L5), longissimus (L2), and iliolumbalis (L1) muscles during isometric, sustained back extensions loaded at 80% of maximum from 117 younger (58 females) and 112 older (56 female) cLBP individuals. Tests were repeated after 1–2 days and 6 weeks. Median frequency, the SEMG variable indicating neuromuscular fatigue, was analyzed. Maximum back extensor strength was comparable between younger and older participants. Significantly less MF-SEMG back muscle fatigue was observed in older as compared to younger, and in older female as compared to older male cLBP individuals. Relative reliability was excellent, but absolute reliability appeared large for this SEMG-fatigue measure. Findings suggest that cLBP likely does not mask the age-specific diagnostic potential of the MF-SEMG back extensor fatigue method. Thus, this method possesses a great potential to be further developed into a valuable biomarker capable of detecting back muscle function at risk of sarcopenia at very early stages.

Highlights

It is widely accepted that muscle weakness is a major risk factor for low back pain (LBP)
Muscle function-based biomarkers that can identify chronic LBP (cLBP) patients at risk of early aging and sarcopenia—the latter is defined as a muscle disease rooted in adverse muscle changes that occur across a lifetime (Cruz-Jentoft et al 2019)—would be of utmost interest in the context of reducing the health burden of sarcopenia through early intervention (Calvani et al 2017; Ciolac and Rodrigues-da-Silva 2016)
The relative SEM values expressed as a percentage of the median frequency (MF)-surface electromyographic (SEMG) onsets were clearly lower than 10% in all of the different recording sites

Summary

Introduction

It is widely accepted that muscle weakness is a major risk factor for low back pain (LBP) This is true in older individuals who commonly experience both back extensor muscle weakness and chronic LBP (cLBP) (GBD Disease and Injury Incidence Prevalence Collaborators 2018; Hoy et al 2014). It may be hypothesized that back pain facilitates an age-related weakening process within the back extensors, thereby contributing to higher levels of painrelated disablement, early dependency, and the need for institutionalization or even early death (Beauchamp et al 2016; Suri et al 2009; Suri et al 2011) This process may be prevalent in older cLBP individuals. The sparse research conducted to date does not unequivocally support the idea that muscle function relates to chronic low back pain in aging persons

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