[proponentia]

Explanationless science always gets into difficulties.

That said, I suspect that watching TV all day everyday would kill a person, eventually, because thinking without a break depletes the CNS of resources which would otherwise be used to regulate the body.

(Note: TV watching is a kind of externally driven thinking. More draining than thinking about the show would be the guilt thoughts caused by watching TV all day given that our culture believes (a) that watching too much TV is bad, and (b) that productive work is good.)

However, it's misleading to claim that sitting around all day is unhealthy. For instance, you won't get a heart attack if you are a Buddhist Monk sitting in meditation.

Also, moving around all day would kill people, eventually, by similar means and for similar reasons to TV watching. For example:

http://en.wikipedia.org/wiki/Dancing_Plague_of_1518

[minsight]

"For instance, you won't get a heart attack if you are a Buddhist Monk sitting in meditation."

There's a claim that I won't buy without some sort of a citation.

[hugh3]

I googled "died while meditating" and found this dude:

http://en.wikipedia.org/wiki/Luang_Pho_Daeng

who not only died while meditating in a lotus position, but supposedly failed to decompose afterwards. (I don't know whether it was a heart attack though...)

[samtp]

You should know that Dr. Blair is basically the world expert in healthy habits and physical activity. He is cited in medical journals over 2000 times every year. This is not explanationless science, but science backed by 20 years of rigorous research.