New research is helping medical experts devise formulas for how long a typical office worker should spend sitting and standing.

Studies have found that sedentary behavior, including sitting for extended periods, increases the risk for developing dozens of chronic conditions, from cancer and diabetes to cardiovascular disease and nonalcoholic fatty liver disease. Some ergonomics experts warn that too much standing also can have negative effects on health, including a greater risk for varicose veins, back and foot problems,...