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One Week of Step Reduction Lowers Myofibrillar Protein Synthesis Rates in Young Men

Shad, Brandon J.1; Thompson, Janice L.1; Holwerda, Andrew M.2; Stocks, Ben1; Elhassan, Yasir S.3,4; Philp, Andrew5; van Loon, Luc J.C.2; Wallis, Gareth A.1

Medicine & Science in Sports & Exercise: May 7, 2019 - Volume Publish Ahead of Print - Issue - p
doi: 10.1249/MSS.0000000000002034
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PURPOSE Across the lifespan, physical activity levels decrease and time spent sedentary typically increases. However, little is known about the impact that these behavioural 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.

METHODS Eleven men (22±2 y) completed 7 days of habitual physical activity (HPA) followed by 7 days 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 RT-qPCR.

RESULTS Daily step count was reduced by approximately 91% during SR (from 13054±2763 to 1192±330 steps·d-1; 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). MAFbx and myostatin mRNA expression were up-regulated whereas mTOR, p53 and PDK4 mRNA expression were down-regulated following SR (P<0.05).

CONCLUSION 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 & Metabolism Division, Garvan Institute of Medical Research, Sydney, New South Wales, Australia

Corresponding author: Dr Gareth A. Wallis, School of Sport, Exercise and Rehabilitation Sciences, University of Birmingham, Edgbaston, B15 2TT, UK. Phone: +44(0) 121 414 4129. Email: g.a.wallis@bham.ac.uk

B.J.S is funded by a University of Birmingham ‘Exercise as Medicine’ PhD studentship. None of the authors have any conflicts of interest or financial disclosures to declare. The results of the present study are presented clearly, honestly, and without fabrication, falsification, or inappropriate data manipulation and do not constitute endorsement by the American College of Sports Medicine.

Accepted for publication: 2 May 2019.

© 2019 American College of Sports Medicine