Apparently, exercise is not enough toward off risks of sitting still for long periods.

Researchers who tracked people over 45 found that those inactive for more than 12.4 minutes at a time had almost twice the risk of dying during the study period as those inactive for less than 7.7 minutes at a time.

This effect held even when people did vigorous exercise.

References

Diaz, K.M., Howard, V.J., Hutto, B., Colabianchi, N., Vena, J.E., Safford, M.M., Blair, S.N. & Hooker, S.P. (2017) Annals of Internal Medicine. 167(7), pp.465-475. DOI: 10.7326/M17-0212.

New Scientist (2017) Get Up, Stand Up. New Scientist. 16 September 2017, pp.5.