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

Brandon J. Shad, Janice L. Thompson, Andrew M. Holwerda, Ben Stocks, Yasir S. Elhassan, Andrew Philp, Luc J. C. Van Loon, Gareth A. Wallis*

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

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Abstract

Purpose 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. Methods 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 ((H2O)-H-2) 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). Results 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%center dot d(-1) during HPA to 1.01 +/- 0.38%center dot 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). Conclusions One week of reduced physical activity and increased sedentary time substantially lowers daily myofibrillar protein synthesis rates in healthy young men.

Original languageEnglish
Pages (from-to)2125-2134
Number of pages10
JournalMedicine and Science in Sports and Exercise
Volume51
Issue number10
DOIs
Publication statusPublished - Oct 2019

Keywords

  • SKELETAL MUSCLE
  • PHYSICAL ACTIVITY
  • INACTIVITY
  • SEDENTARY
  • MUSCLE DISUSE ATROPHY
  • SKELETAL-MUSCLE
  • ANABOLIC RESISTANCE
  • AMBULATORY ACTIVITY
  • SEDENTARY BEHAVIOR
  • LEAN MASS
  • INGESTION
  • EXERCISE
  • REST
  • TIME

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