Age Alters Muscle Activation but Not Energy Expenditure During Sedentary Behavior Alternatives: 783 Board #99 June 1, 2: 00 PM - 3: 30 PM.

Abstract

PURPOSE: The mechanisms to explain the protective metabolic effects of breaking up sitting time remain unexplained. Meanwhile, there is limited evidence to suggest both older and younger adults respond similarly to sedentary behavior (SB) alternatives. The purpose of this study is compare physiological responses SB alternatives in young and old adults. METHODS: Eleven younger adults (21-35 yr) and eleven older adults (62-76 yr) performed five randomly ordered 20-minute tasks: 1) continuous chair sitting, 2) continuous stability ball sitting, 3) continuous desk standing, 4) sitting interrupted by 2-minutes walking, and 5) sitting interrupted by 2-minutes standing. Muscle activation was determined by percent normalized electromyography amplitude (%NEA) of upper (trapezius and erector spinae) and lower (rectus femoris and medial gastrocnemius) body muscles and total body energy expenditure (EE) was collected via indirect calorimetry. Linear mixed effects models controlling for gender with a Tukey post-hoc analysis were used to determine significant differences between age groups and across tasks. RESULTS: For both age groups, lower body muscle activation and EE were significantly influenced by the SB alternatives (p<0.01) with no differences present between age groups. Upper body muscle activation in response to the SB alternatives were not consistent between younger and older adults (p<0.05). Specifically, younger adults did not show a significant difference in upper body muscle activation between tasks, while older adults showed a significantly higher upper body muscle activation during the sitting interrupted by walking task compared to all other tasks (p<0.05). The upper body muscle activation during the sitting interrupted by walking task in older adults (10.8 ± 1.5% max) was over twice the activation level of younger adults (4.8 ± 0.6% max, p<0.05). CONCLUSIONS: SB alternatives had little effect on upper body musculature of young adults, while older adults required twice the muscle activation of younger adults to perform an interrupted walking task. Whether age-related divergences in muscle activation differentially affect metabolic health markers needs to be determined.