Prolonged standing at work has been shown to be associated with a number of potentially serious health outcomes, such as lower back and leg pain, cardiovascular problems, fatigue, discomfort, and pregnancy related health outcomes. Recent studies have ...

Basically the short of the long of it is that you should not sit or stand for longer than an hour without doing a few minutes of the opposite.

Otherwise you will start experiencing accelerating fatigue.

Places of work that require standing should prioritize letting workers sit for a couple of minutes once an hour at minimum. It retains 95% of productivity (if not boosts it when fatigue goes down), and reduces fatigue by at least half when compared to perpetual standing.