Across the lifespan, physical activity levels decrease and time spent sedentary typically increases. However, little is known about the impact that these behavioral changes have on skeletal muscle mass regulation. The primary aim of this study was to use a step reduction model to determine the impact of reduced physical activity and increased sedentary time on daily myofibrillar protein synthesis rates in healthy young men.
Eleven men (22 ± 2 yr) completed 7 d of habitual physical activity (HPA) followed by 7 d of step reduction (SR). Myofibrillar protein synthesis rates were determined during HPA and SR using the deuterated water (2H2O) method combined with the collection of skeletal muscle biopsies and daily saliva samples. Gene expression of selected proteins related to muscle mass regulation and oxidative metabolism were determined via real time reverse transcription-quantitative polymerase chain reaction (RT-qPCR).
Daily step count was reduced by approximately 91% during SR (from 13,054 ± 2763 steps per day to 1192 ± 330 steps per day; P < 0.001) and this led to an increased contribution of sedentary time to daily activity (73% ± 6% to 90% ± 3%; P < 0.001). Daily myofibrillar protein synthesis decreased by approximately 27% from 1.39 ± 0.32%·d−1 during HPA to 1.01 ± 0.38%·d−1 during SR (P < 0.05). Muscle atrophy F-box and myostatin mRNA expression were upregulated, whereas mechanistic target of rapamycin, p53, and PDK4 mRNA expression were downregulated after SR (P < 0.05).
One week of reduced physical activity and increased sedentary time substantially lowers daily myofibrillar protein synthesis rates in healthy young men.
1School of Sport, Exercise and Rehabilitation Sciences, University of Birmingham, Birmingham, UNITED KINGDOM
2Department of Human Biology, NUTRIM School of Nutrition and Translational Research in Metabolism, Maastricht University Medical Centre, Maastricht, THE NETHERLANDS
3Institute of Metabolism and Systems Research, University of Birmingham, Birmingham, UNITED KINGDOM
4Centre for Endocrinology, Diabetes and Metabolism, Birmingham Health Partners, Birmingham, UNITED KINGDOM
5Diabetes and Metabolism Division, Garvan Institute of Medical Research, Sydney, New South Wales, AUSTRALIA
Address for correspondence: Gareth A. Wallis, Ph.D., School of Sport, Exercise and Rehabilitation Sciences, University of Birmingham Edgbaston, B15 2TT, United Kingdom; E-mail: email@example.com.
Submitted for publication December 2018.
Accepted for publication May 2019.
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Online date: May 10, 2019