Obesity-associated poor muscle quality: prevalence and association with age, sex, and body mass index

Valenzuela et al. BMC Musculoskeletal Disorders https://doi.org/10.1186/s12891-020-03228-y (2020) 21:200 RESEARCH ARTICLE Open Access Obesity-associated poor muscle quality: prevalence and association with age, sex, and body mass index Pedro L. Valenzuela1*, Nicola A. Maffiuletti2, Gabriella Tringali3, Alessandra De Col3 and Alessandro Sartorio3,4 Abstract Background: Muscle quality (i.e., the expression of muscle function per unit of muscle mass) has been proposed as a clinically-relevant measure to detect individuals at risk of functional incapacity. Individuals with obesity might be at an increased risk of having poor muscle quality. Thus, we aimed to analyze the prevalence of poor muscle quality in obese individuals, to determine associated variables, and to provide normative values for this population. Methods: 203 individuals with obesity (103 women, age: 18–75 years, body mass index (BMI): 35–64 kg·m− 2) participated in this cross-sectional study. Their muscle strength (handgrip dynamometry), muscle power (sit-to-stand test) and muscle mass (bioelectrical impedance analysis) were measured, and muscle quality (strength/power to muscle mass ratio) was compared with reference values obtained in young healthy individuals. Muscle quality was individually categorized as normal, low or poor based on specific muscle strength and power (i.e., strength and power per unit of muscle mass, respectively). Sex and age-specific normative values of specific muscle strength and power were computed for the whole cohort. Results: Age and being a woman were inversely associated with specific muscle strength, with age being also inversely associated with specific muscle power. A small proportion of participants (6%) presented with an impaired (i.e., low/poor) specific muscle power while most of them (96%) had impaired specific muscle strength. Eventually, 84% of the participants were deemed to have poor muscle quality. Being a woman (odds ratio [OR]: 18.09, 95% confidence intervals [CI]: 4.07–80.38), age (OR: 1.06, 95%CI: 1.03–1.10) and BMI (OR: 1.22, 95%CI: 1.07–1.38) were independently associated with a higher risk of poor muscle quality in adjusted analyses. Conclusions: These findings show a high prevalence of poor muscle quality among individuals with obesity, with age, sex and BMI being independent predictors. Keywords: Obesity, Muscle function, Skeletal muscle, Disability, Aging * Correspondence: 1 Department of Systems Biology, School of Medicine, University of Alcalá, Ctra Barcelona, Km, 33 600 28871 Alcalá de Henares, Spain Full list of author information is available at the end of the article © The Author(s). 2020 Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated in a credit line to the data. Valenzuela et al. BMC Musculoskeletal Disorders (2020) 21:200 Background Aging is related to a number of structural and functional changes at the neuromuscular level (e.g., muscle mass loss, impaired neuromuscular activation, intramuscular infiltration of non-contractile tissue, fiber type shift) that result in worsened muscle function [1]. This results in impaired muscle quality, that is, worsened strength/ power per unit of muscle mass [2]. Research has shown that impaired muscle function is a better predictor of functional limitations and mortality than muscle mass [3, 4]. For instance, individuals with good muscle quality have been reported to be at a lower risk of functional impairment than those with poor muscle quality, whereas an increased risk of functional impairment has been observed in subjects with greater muscle mass but poor muscle quality [5]. These results confirm therefore the importance of muscle quality as a prognostic factor of functional inability and mortality. Apart from aging, other factors – particularly in relation with lifestyle – can influence muscle quality. Obesity is reaching epidemic proportions, with its prevalence increasing worldwide and having doubled since 1980 [6]. Among several other complications (e.g., cardiovascular diseases), obesity seems to impair skeletal muscle function. Some studies have shown that a higher body mass index (BMI) was associated with greater muscle mass and even with an increased absolute force and power production capacity [7, 8]. However, when normalized to body mass or muscle mass, obese individuals showed impaired muscle function (i.e., decreased muscle quality) [7, 8]. Although obesity and impaired muscle function are considered independent risk factors of morbidity and mortality, the combination of these two conditions has recently been reported to markedly increase the risk of disability [9–11] and mortality [12] compared to the presence of any of these individuals risk factors alone. However, despite the clinical relevance of muscle quality, particularly in individuals with obesity, the prevalence of poor muscle quality in these individuals compared to the general population remains largely unknown. The main aims of this study were therefore to analyze the prevalence of poor muscle quality and to determine the variables associated with an increased prevalence of poor muscle quality in a heterogeneous group of obese individuals. We also aimed to provide normative values of muscle quality for individuals with obesity of different age ranges, that could potentially be used as a standard for future studies. Material and methods Experimental design and participants The present study followed a cross-sectional, observational design, and complies with the STROBE checklist for observational studies. The study took place between Page 2 of 8 April 2014 and February 2015. Participants were recruited through personal interview before a 3-week inhospital multidisciplinary weight-management program. Inclusion criteria were having obesity of grade II or more (BMI > 35 kg·m− 2) and being older than 18 years. There were no particular exclusion criteria, apart from not being able to perform the physical tests. Participants were additionally categorized a (...truncated)