Nails are turning blue which i hear is due to low oxygen in blood cells. can lack of physical activity & outside air cause this?

Probably not: Blue nails can be from poor perfusion due to vascular disease, low oxygen (hypoxia), or from toxins such as methemoglobenemia. Deconditioning (lack of activity) may be a symptom of low oxygen and not a cause. Outside versus inside air have the same oxygen content. I would advise you see an md to do a workup for anemia, oxygen levels, and vascular disease.