During work: maintain good posture (sitting or standing), but otherwise, accept that the job is sedentary. Do not allow this issue to distract you from the work. I do not understand the concept of "downtime between daily tasks"; there is always more R, or D, or both. Otherwise, I only have what is essentially (to me) "bleeding obvious" advice. Drink water; not, say, sugar-laden fizzy drinks from a vending machine. Steer clear of any free cookies in the lab kitchen; eat fruit instead... but now I'm just regurgitating general dietary advice.
After work: as already recommended in other comments, if possible, use your commuting time to counteract your sedentary time at work. Swap sedentary commuting time for active commuting time. For example, run or cycle to work. (Hopefully, your lab has a shower, although I have worked in offices in the UK that were built as recently as the 1990s that had no showers.) If you live too far from work to run or cycle, then run or cycle partway; if you live very close to work, deliberately extend your commute. Active commuting - "bookending" your working day with physical exercise - has mental benefits: it clears your head, to and from work. On the days I cycle, I also do push-ups when I arrive at work and just before I leave. Pull-ups, too (on a metal frame under an external staircase), but now I'm sounding like a geek even to myself...
Slashdot Mirror
During work: maintain good posture (sitting or standing), but otherwise, accept that the job is sedentary. Do not allow this issue to distract you from the work. I do not understand the concept of "downtime between daily tasks"; there is always more R, or D, or both. Otherwise, I only have what is essentially (to me) "bleeding obvious" advice. Drink water; not, say, sugar-laden fizzy drinks from a vending machine. Steer clear of any free cookies in the lab kitchen; eat fruit instead... but now I'm just regurgitating general dietary advice.
After work: as already recommended in other comments, if possible, use your commuting time to counteract your sedentary time at work. Swap sedentary commuting time for active commuting time. For example, run or cycle to work. (Hopefully, your lab has a shower, although I have worked in offices in the UK that were built as recently as the 1990s that had no showers.) If you live too far from work to run or cycle, then run or cycle partway; if you live very close to work, deliberately extend your commute. Active commuting - "bookending" your working day with physical exercise - has mental benefits: it clears your head, to and from work. On the days I cycle, I also do push-ups when I arrive at work and just before I leave. Pull-ups, too (on a metal frame under an external staircase), but now I'm sounding like a geek even to myself...
Good luck with the job!