[SkyPuncher]

I think you’re incorrectly jumping to correlations/causations.

Your references are due to sedentary, not laying down. You can have a sedentary life standing in place most of the day. Likewise, the problem is being sedentary, not what position your sedentary in.

[consumer451]

Look at the logic in my comment link, does this not make sense? This seems like basic physics and cardio to me.

The less time that your heart has to fight against pressure/gravity, the weaker that muscle will become. This is pure causation.

https://news.ycombinator.com/item?id=40549893

[hyko]

It’s a reasonable hypothesis, but you’d need to experiment to validate it. It’s easy to imagine how prolonged exposure to bed rest or microgravity may trigger heart muscle remodelling in a way that intermittent bouts of lying down would not.