I am 6'1 185 pounds and I've worked out by lifting weights and running for many many years.
3 years ago I did smoke 1 pack of cigs per WEEK for 1 year. There were a few random nights where I would smoke a whole pack of cigs in just one night while drinking.
Anyways, I'm not sure why, all things considered, my sp02 is consistently only 95%. I work on an ambulance and have used a couple different monitors that we have available and use on our patients. Mainly always 95% and sometimes 96%.