When I work at my desk, I use a variation of the Pomodoro Technique. I set the timer app in Windows for 25 minutes and work until it goes off. Then I take a five minute “break” and do something that involves standing for five minutes. This includes reading while standing.
Here is a study that suggests that standing may improve attention. The press release from the Association for Psychological Science explains:
Their new findings lend support to recent research suggesting that the attentional stress caused by maintaining an upright posture actually improves selective attention.
peakmemory 
I may (or may not) have mentioned here that Ernest Hemingway used to write standing up! When he was at Finca Vigia in Cuba (where he lived from 1939 to 1961), he would prop his typewriter up on some books atop a short bookcase.
Papa Hemingway wasn’t the only one:
http://www.openculture.com/2013/10/ernest-hemingway-standing-desk.html