Just because you exercise, it doesn’t mean you can sit all day. In fact, despite recreational exercise, prolonged sitting is associated with inflammation. Science is showing that low “non-exercise physical activity,” such as little activity at work, is linked to a higher incidence of death from cardiovascular disease. Let’s look at an extreme form of sustained inactivity—bed rest—and just how badly 10 days of bed rest can affect your epigenetics.
Bed Rest Rapidly Changes Gene Expression Patterns Inside Muscle
Use it or lose it, right? Well, just how much muscle do you lose when you’re not using muscle? One study reported up to a three percent loss in muscle mass (in quadriceps) and a five percent loss in strength for every week of bed rest. But that’s not all. The biochemistry inside the healthy muscle changed for the worse: protein synthesis decreased and protein degradation simultaneously increased!
This finding spurred scientists to dive deeper: what genes are being turned on or turned off during bed rest, and would a small, 10-day stint in bed be enough to alter the expression of these genes? It turns out, the answer is yes.
The results of several studies have shown that seven or more days of bed rest resulted in global changes in gene expression patterns (differentially impacting some 4,000 genes) even before appreciable muscle atrophy was observed. The main pathways altered by bed rest were related to inflammatory signaling and cellular structure.
Bed Rest Alters Gene Whisperers: miRNAs (Micro RNAs)
The expression of genes is highly regulated by environmental signals through a process called epigenetics. The addition or subtraction of methyl groups can turn genes off or on; the single-stranded miRNAs (aka micro RNAs) also similarly affect expression of genes. Each one is thought to impact not just one, but hundreds of genes.
Scientists in Europe recently reported for the first time that 10 days of bed rest downregulated 15 key human miRNAs that epigenetically control pathways important to cellular health and metabolism. The results of muscle biopsy before bed rest and after bed rest showed a large downregulation of miRNA signaling in many pathways involved in fat cell signaling; glutathione, glutamine, and fatty acid metabolism; mTOR and insulin signaling; and even muscle cell growth (myogenic).
The authors noted that not just bed rest, but inactivity in general, is enough to downregulate these critical miRNA pathways.
Tips and Key Takeaways
Loss of lean muscle mass from sedentary activity is just the tip of the iceberg. Short-term bed rest shows global shifts in key mediators regulating the expression of genes involved in favorable metabolic targets.
If you have to sit (due to travel, work, or even injury), try breaking up prolonged sitting time with a walk every 90 minutes or so to offset this danger. Some studies suggest that getting up for five minutes or so every half hour may offer similar benefits. (Scientists reported that five minutes of exercise at intervals throughout the day for forty minutes total were more effective at burning fat than forty-five consecutive minutes of exercise.)
The bottom line is that you should move every 45–90 minutes for a brisk walk, or run up a flight of stairs, or do push-ups or sit-ups or something to get your blood pumping. This will lead to beneficial changes in your skeletal muscle physiology and the genetic expression of key metabolic regulatory hubs inside your coveted fat-burning organ: muscle.
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2) Režen, T., Kovanda, A., Eiken, O., Mekjavic, I. B., & Rogelj, B. (2014). Expression changes in human skeletal muscle miRNAs following 10 days of bed rest in young healthy males. Acta Physiologica, 210(3), 655–666. doi:10.1111/apha.12228