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.