Sitting for extended periods of time can be hazardous to your health, research shows, sparking a fast-growing trend of standing — or walking — while you work. Standing desks and treadmill desks are expensive, but those who have used them say they’re great for feeling energized and productive, rather than fatigued and drowsy, during the workday. We evaluate dozens of expert and user reviews to identify the best treadmill desks, standing desks and standing desk mats.