President Obama addressed the attacks in San Bernardino, Calif., and overseas from the Oval Office. (Associated Press)

President Obama spoke on live TV from the Oval Office on Sunday night to tell the world that the United States will not take the threat of terrorism sitting down. So he didn't sit down.

Maybe it's as simple as that. Or maybe he strained his back playing basketball on Saturday and needed to stand for medical reasons. Whatever the impetus, let's get one thing straight: Obama's choice to stand at a podium in his office rather than sit behind the Resolute Desk, as is customary in an Oval Office address, was very deliberate — as all decisions about presidential imagery are.

It's not as though he keeps a dais parked in front of the desk all the time. The mere fact that he and his staff said, "Hey, let's bring one in," means they believed there was something to gain by getting the president on his feet.

What were they going for? And did it work?

Dismissing the hoops hypothesis as pretty far-fetched, I'm betting Obama's upright posture was the result of two considerations: the way he would be perceived and the way he would feel.

We've long been told — and know intuitively — that standing up makes you look more powerful and confident. This is why phrases such as "stand up for yourself" and the aforementioned "not going to take this sitting down" exist in our culture. Obama's critics consistently call him weak on terrorism, which was part of the reason he spoke Sunday night. Standing up is a simple, unstated way for him to project strength.

More important to the president, however, might be what standing up does for his own comfort level. As we at The Fix noted before the speech (and before we knew Obama would be at the lectern), he seemed stiff and uncomfortable in his two previous Oval Office addresses, when he took the more traditional seated posture.

Obama went five years between "Ovals," which tells us how much he likes doing them. He clearly prefers standing in the East Room or the Rose Garden to deliver important messages, but apparently he felt the magnitude of this moment — confronting terrorism on the heels of last month's Islamic State attacks on Paris and last week's mass shooting in San Bernardino, Calif. — called for the backdrop of his office. So he combined the two formats.

There's a bit of science to the whole standing thing, too.

A 2011 article in Scientific American, "How You Can Become More Powerful by Literally Standing Tall," summarized the findings of an Ivy League study that measured the hormonal effects of posture.

More impressively, expansive postures also altered the participants’ hormone levels. Using salivary samples, Carney and colleagues found that expansive postures led individuals to experience elevated testosterone (T) and decreased cortisol (C). This neuroendocrine profile of High T and Low C has been consistently linked to such outcomes as disease resistance and leadership abilities.

Who couldn't use an extra jolt of testosterone to take on the terrorists?

Still, I think Obama lost some of the Oval Office impact by using the podium. If you didn't know in advance that he was in the Oval Office (or if you tuned in a few seconds late and missed the slow zoom from the original wide angle), would you have picked up on the setting? There were flags, drapes and some family portraits in the background, but, for most of the 13-minute telecast, there was no desk.

It's the desk that really signals to the viewing public that this is where the president works; this is where he makes key decisions. The desk is the most important prop on the Oval Office set, and Obama didn't use it.

In many situations, there are benefits to standing. But in the Oval Office, Obama was trying to have it both ways.