Oxygenation and Activation of the Vastus Lateralis during Dynamic Constant External Resistance Leg Extension Muscle Actions in Older Women with and without Sarcopenia

Authors

Brianna D. McKay, University of Nebraska-LincolnFollow

First Advisor

Joel Cramer

Date of this Version

Summer 8-2019

Comments

A Thesis Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Master of Science, Major: Nutrition and Health Sciences, Under the Supervision of Professor Joel T. Cramer. Lincoln, Nebraska : August 2019

Copyright 2019 Brianna D. McKay

Abstract

The purpose of the present study was to compare muscle strength, size, activation, and oxygenation between older women with and without sarcopenia during dynamic fatiguing leg extension bouts with high (5-repetition maximum[5-RM]) and low (30% of estimated 1-RM[30%1-RM]) loads. Eleven women (n = 6 non-sarcopenic [mean ± SE; age = 75.8 ± 2.6y] and n = 5 sarcopenic [age = 74.5 ± 3.1y]) were screened for eligibility and sarcopenic status. Descriptive assessments including demographics (age, height, and weight), body composition by dual-energy x-ray absorptiometry (fat mass[FM], fat-free mass[FFM] and percent body fat[BF%]), muscle size by ultrasonography (leg extensor muscle cross-sectional area[mCSA], vastus lateralis [VL] thickness, subcutaneous fat thickness, and echo intensity[EI]), muscle strength (leg extensor[5-RM], handgrip[HG]), muscular endurance (30%1-RM to exhaustion), and functionality (gait speed) were measured. During the 5-RM and 30%1-RM tasks, muscle activation was measured by surface electromyography (EMG), while muscle oxygenation was measured by near-infrared spectroscopy (NIRS). FM, BF%, subcutaneous fat, and EI indicated the presence of sarcopenic obesity (p ≤ 0.05). Relative skeletal mass index and HG were lower (p ≤ 0.05) in the sarcopenic group, but no other descriptive measures were different between groups (p > 0.05). Despite no differences (p > 0.05) in leg extensor muscle size or strength between sarcopenic and non-sarcopenic older women, the sarcopenic women exhibited 13 – 21% lower (p ≤ 0.05) muscle oxygenation across all repetitions of the high- and low-load tasks. EMG amplitude (EMG_RMS)increased, while EMG mean power frequency (EMG_MPF) decreased (p ≤ 0.05) across repetitions during both tasks, but there were no differences between groups. These findings suggest the presence of a clinical sarcopenic classification may not uniformly impact the size or strength of all muscles. If greater variability is expected among muscle activation strategies of older adults, using EMG to distinguish between sarcopenic and non-sarcopenic women without differences in leg extensor muscle size, strength, or endurance may be difficult. However, lower muscle oxygenation, which may reflect skeletal muscle blood flow, in clinically sarcopenic older women may be important to consider when recommending exercise or nutrition interventions for either oxygen or dietary nutrient delivery.

Advisor: Joel Cramer