EXAMINING THE ASSOCIATIONS BETWEEN LEAN MASS, MUSCULAR STRENGTH, MUSCLE QUALITY AND PHYSICAL FUNCTION

Sydney Reigle

doi:10.23860/thesis-reigle-sydney-2020

Abstract

Objective: The determinants of physical function are not well characterized among middle-aged women. The primary aim of this cross-sectional study was to determine the strength of the associations between lean mass, muscular strength, muscle quality, and physical functional ability in a cohort of middle-aged women. The secondary aim was to determine the measure of muscle quality most highly associated with measures of physical function. Methods: Middle-aged women (N=111, age, 53.14 ±6.15 years) had body composition (via dual energy x-ray absorptiometry), physical activity (via accelerometer), and physical function (via Transfer Task (TRANSFER), 30-Second Chair Stand (30-CS), 6-Minute Walk Test (6MWT), 8-Foot-Up-And-Go (UP-GO)) assessed objectively. A lower body physical function composite score was also calculated. Lower body strength was measured using isokinetic dynamometry for isometric knee flexion and extension at 60 degrees, isokinetic flexion and extension at 60 degrees per second, and isokinetic flexion and extension at 180 degrees per second. Muscle quality was defined as muscular strength normalized for upper leg lean mass and calculated using: 1) isometric knee flexion and extension at 60 degrees (MQ-ISO), 2) isokinetic knee flexion and extension at 60 degrees per second (MQ-KN60), 3) isokinetic knee flexion and extension at 180 degrees per second (MQ-KN180). Results: The lower body physical function composite score was significantly associated with percent lean mass, MQ-ISO, MQ-KN60, and MQ-KN180. Partial correlations, controlled for age and average steps per day, found that MQ-KN60 was the variable most highly associated with the physical function composite score. Results from a hierarchical linear regression showed that 1) age, average steps per day, and MQ-KN60 are independently associated with physical function composite score, explaining 3%, 18.1% and 14.3% respectively, and 2) age, average steps per day, MQ-KN60 were significantly associated with, TRANSFER, 30-CS, and 6MWT. Conclusion: In middle-aged women, percent lean mass, muscular strength, and muscle quality were all significantly associated with physical functional ability. The association between MQ-KN60 and the physical function composite score was stronger than all other measured variables. This data provides insight into the most relevant measures to consider when examining the independent contributors to physical functional ability in middle-aged women.

Highlights

In 2014, 83 million Americans were between the age of 45 and 64 years, and it is projected by 2060 the number of Americans who are middle-aged will increase to 100 million [1]
In order to fully understand physical function and its determinants in middle-aged adults, muscle mass, muscular strength, and muscle quality should all be assessed, as all have been found to be independently associated with physical functional ability [13,49,66,68] and each have been separately associated with adverse health outcomes [8,50,51,64,69]
The physical function composite score was significantly associated with body mass index (BMI) (r=0.39,), percent body fat (r=-0.50), percent lean mass (r=0.50), average moderate to vigorous physical activity (r=0.38), average steps per day (r=0.39), KN-180 (r=0.33), KN60 (r=0.31), MQ-ISO (r=0.25), MQ-KN60 (r=0.45), MQ-KN180 (r=0.44)

Summary

Introduction

In 2014, 83 million Americans were between the age of 45 and 64 years, and it is projected by 2060 the number of Americans who are middle-aged will increase to 100 million [1]. Recent studies report that middle-aged adults, middle-aged women, self-report difficulties performing daily activities and have poor physical function [2–4], where up to 25% of women between the age of 42 and 52 years old [2]. Extensive research assessing physical function in older adults demonstrates that physical function performance is associated with physical activity level [6], lean mass, and muscular strength [5,7–10], significantly less is known about physical function in middleaged adults. One way to examine the association between lean mass and muscular capacity is by calculating muscle quality. Muscle quality assesses the association between muscular strength and lean mass, it may be an optimal independent variable to examine when evaluating determinants of the changes in physical function, compared to lean mass and muscular strength alone [12]

Methods

Results

Conclusion