Nutrition and Skeletal Muscle

Stéphane Walrand, Stéphane Walrand

• Editore: Academic Press
• Anno: 2018
• ISBN:
  9780128104101
• Argomento: Médecine
• Categoria: Physiologie

Nutrition and Skeletal Muscle provides coverage of the evidence of dietary components that have proven beneficial for bettering adverse changes in skeletal muscle from disuse and aging. Skeletal muscle is the largest tissue in the body, providing elements of contraction and locomotion and acting as an important contributor to whole body protein and amino metabolism, glucose disposal and lipid metabolism. However, muscle loss, atrophy or weakness can occur when there are metabolic imbalances, disuse or aging. This book addresses the topic by providing insight and research from international leaders, making it the go-to reference for those in skeletal muscle physiology.

• Provides an understanding of the crucial role of skeletal muscle in global metabolic homeostasis regulation
• Delivers the information needed to understand the utilization of crucial supplements for the preservation of skeletal muscle
• Presents insights on research from international leaders in the field

Part I

General Aspects: Skeletal Muscle Physiology and Nutrition

Outline

• Chapter 1 Skeletal Muscle Mass Indices in Healthy Adults
• Chapter 2 Reduced Skeletal Muscle Mass and Lifestyle
• Chapter 3 Molecular Mechanisms of Postmeal Regulation of Muscle Anabolism
• Chapter 4 Adaptation of Skeletal Muscle Mass and Metabolism to Physical Exercise

Chapter 1

Skeletal Muscle Mass Indices in Healthy Adults

Heliodoro Alemán-Mateo¹ and Roxana E. Ruiz Valenzuela², ¹Departamento de Nutrición y Metabolismo, Coordinación de Nutrición, Centro de Investigación en Alimentación y Desarrollo (CIAD), A.C. Hermosillo, Sonora, México, ²Departamento de Salud, Universidad Iberoamericana, Ciudad de México-Tijuana, Tijuana, Baja California, México

Abstract

Skeletal muscle (SM) is a key component of nutritional status and functionality. The adjustment of SM by height or other anthropometric parameters in young adults has generated several indices that serve as indicators of muscularity. These SM indices have been generated in distinct young adult populations around the world and are now the basis for diagnoses of sarcopenia. To our knowledge, 21 cutoff points based on SM exist for younger adult populations worldwide; specifically, 17 dual-energy X-ray absorptiometry (DXA)-derived appendicular skeletal muscle mass indices, 3 DXA-derived total SM indices (TSMI), and one DXA-derived total lean body mass index. In addition, there are seven indices derived from bioelectrical impedance analysis, one magnetic resonance imaging-derived TSMI, and one that uses an ultrasound technique. In conclusion, SM indices should be applied to specific gender and ethnic populations to avoid variations in estimates of the prevalence of sarcopenia in older people.

Keywords

Body composition; total and appendicular skeletal muscle mass; skeletal muscle indices; sarcopenia; older people; young adult populations; dual-energy X-ray absorptiometry; bioelectrical impedance analysis

Introduction

Skeletal muscle (SM) increases during postnatal development through a process of hypertrophy of the individual muscle fibers; a similar process may be induced in adult SM in response to contractile activity like strength exercises, and to androgens and β-adrenergic agonists [1]. SM remains relatively constant during the third and fourth decades of life but begins to decline at ~45 years of age in both genders [2]. In other words, age exerts a strong influence on SM, but gender does as well [3–8]. Several studies have demonstrated the effects of age and gender on SM, and some have examined the effects on its distribution [2,5–6]. Perhaps the most relevant study on this issue was published by Janssen et al. [2], who used an in vivo method to study body composition using, particularly, magnetic resonance imaging (MRI) to provide precise and reliable measurements of SM and its distribution in a broad sample of Caucasian men and women. The results of this study reported new findings on the behavior of SM mass during the lifecycle in both men and women subjects.

Due to the growing awareness of the importance of SM on functionality and other clinical entities in older age groups [9–16], there is a need to establish reference values for relative SM in young adult populations using the most precise and accurate methods available, and considering the factors of age, gender, and ethnicity. It is important to stress that few countries have been able to conduct national-level studies of this kind [10,17–19]. Some published works based on small samples of healthy young adult subjects reported data on SM [2,6,20–21] and proposed cutoff points for diagnosing sarcopenia—i.e., low SM mass—and sarcopenia syndrome [9,10,17,22–42]. To our knowledge, 21 cutoff points based on SM exist; specifically, 17 dual-energy X-ray absorptiometry (DXA)-derived appendicular skeletal muscle mass (ASM) indices, 3 DXA-derived total SM (TSM) indices, and one DXA-derived total lean body mass (LBM) index for younger adult populations around the world [9,17,22–36], together with seven indices derived from bioelectrical impedance analysis (BIA) [10,37–42], one that used an ultrasound technique [43], and one MRI-derived TSM index (TSMI) [19]. Before presenting the main results of the published ASM, TSM, and LBM indices, we will first review the biological bases that underlie them.

The Biological Bases That Underlie the Indices

Indices are association measurements that can be very useful in classifying nutritional status or, as in the present case, the stadia of SM, evaluating the chronicity of the skeletal muscle loss and assessing the efficacy of nutrition on loss of SM during the intervention therapy. They may also serve to quantify various components of body mass. Indices of this kind are usually divided into (1) those relative to weight and height and (2) those relative to body composition. SM indices are the ones most closely related to body composition that are used to diagnose presarcopenia and sarcopenia syndrome in geriatric populations. As mentioned above, SM tissue is dependent on age, gender, body weight, height, and ethnicity [2,5–6]. It is important to note that much of our current understanding of SM is based on studies that used DXA and MRI, two in vivo methods for analyzing body composition [2,5–6] that can accurately measure total or regional SM. DXA- derived lean tissue in arms and legs or ASM account for >75% of total SM [44], which constitutes the primary portion of SM involved in ambulation, physical activities, and functionality across the lifespan.

To clarify the origin of an index, particularly ASM, we examined the main findings reported by Gallagher et al. [6], who assessed SM components by DXA in 148 healthy adult women (80 African-Americans, 68 Caucasians) and 136 healthy adult men (72 African-Americans, 64 Caucasians) with an age range of 21.1–67.5 years. First, they noted a significant negative correlation between ASM and age in all four groups. After adjusting for age, they determined that ASM was significantly and positively correlated with body weight and height in both ethnic groups, and in both men and women. Using multiple regression models, they then explored the independent effects of height, weight, age, gender, and ethnicity on ASM. In their predicted ASM model, height and weight explained 64% and 67%, respectively, of ASM variance in the African-American and Caucasian women, and 63% and 39%, respectively, in the African-American and Caucasian men. Smaller contributions were found for age. Interestingly, after adjusting for height, body weight, and age, an effect of gender was also found, as the men were found to have greater ASM than the women in both groups of subjects across the entire age range. Finally, a significant effect of ethnicity on ASM was found, as the African-American men and women had greater adjusted ASM than the Caucasian subjects [6].

Three years later, Janssen et al. [2] examined the influence of age, gender, body weight, and height on TSM assessed by whole body MRI in a large, heterogeneous sample of 468 men and women aged 18–88 years. It is important to mention that this study included two additional ethnic groups—Asians and Hispanics—in assessing TSM and its distribution [2]. As in the case of Gallagher et al. [6], these researchers also reported a significant effect of height, body weight, age, and gender on total and regional or appendicular SM. In another significant finding related to this chapter, Janssen et al. [2], demonstrated that the substantial increase in body weight observed between 18 and 40 years of age was not associated with a corresponding increase in TSM. Instead, the absolute quantity of TSM was maintained into the fifth decade of life, but with noticeable losses thereafter. This finding is important so as not to limit the cutoff points for SM mass indices for people aged 18–40 years, as was originally proposed in Rosseta’s study [6], and the body composition reference values from National Health and Nutrition Examination Survey [17] or Korean studies [29,33–34].

Numerous body composition indices have been generated by considering the biological and statistical associations among certain aspects of body composition with age, and specific anthropometric variables; especially, the strong correlation between absolute SM and height. Originally, in order to define low SM mass or sarcopenia, it was necessary to have a measure related to the amount of existing SM [9], and as previously mentioned, the absolute values of SM correlates strongly with height. Therefore, ASM (kg) divided by height squared (ht²) produces an index of relative appendicular SM mass that serves as an indicator of muscularity. In fact, Baumgartner et al. [9] established that placing ht² in...