There seem to be two schools of thought on health related to those knowledge workers with desk jobs. One is based on science, and one isn’t. The first suggests you should do something physically active while sitting (Zwift “working desk” and bouncy balls come to mind). The second encourages the most relaxation possible while “seated” in order for encourage mental focus and recover from other, planned strenuous activities daily. The second is far better both for the work you are doing and your health.
It sounds obvious, but one should focus on the exact activity one is doing at any moment and avoid distractions from that activity when possible. Knowledge work—especially coding—demands intense focus. Bouncing around on a bouncy ball, or spinning your legs, is just going to distract you. Even walking on a treadmill is usually too distracting. I am a fan of standing desks for some things, but even that suffers from one critical flaw: any physical activity while working prevents your body from entering a state of physical recovery.
When I work in a reclined position with a laptop I barely push 64bpm and my back takes no strain whatsoever. My circulation is better, fewer clot possibilities in lower legs. My legs are warmer because circulation is easier. This is the reason a partially seated, reclined position in a hospital bed is what it is. It is the optimal position to remain alert while still in the best state for physical recovery. That’s right, coding from a hospital bed (or something like it) is absolutely the best thing you can do to recover. When I sit upright in a well-supported tech chair, I average 80bpm. When I stand, slightly more, about 85bpm. I find myself sweating after longer coding or writing sessions, not so in a reclined position. Plus, I’m just happier all around. There is something really stressful about feeling physical discomfort of any kind while coding and writing.
This physically recovery and diminished stress from working in a reclined position allows the body to fully recover from daily medium to hard workout sessions, which are far better for your health than any quirky idea while you are trying to work. When it comes to endurance training, you want to either be training, or recovering, never in between. This is why so many pro athletes have a planned nap during the day, to recover the body for the next training session. All of these considerations increase dramatically with age as recovery becomes more and more difficult.
The suggestion to workout while sitting at your desk is absolutely ridiculous, the worst thing you can do for endurance training. The only people who should consider it are those who never, ever want to do any actual training. But it is scientifically better for the human body to have daily, medium to hard physical training efforts mixed with full recovery.
I will say that going for a walk or hike and taking a notepad is wonderful for thinking through ideas, but those are forms of recovery activities, not workouts. A good workout will make it impossible to think of anything else but the workout.