We are not doctors on here, but like you, we are or have quit smoking.
I think you should post your questions to the doctor or even better, go and see your doctor. You need to be assessed according to age, weight and health. Only a physician can answer your questions.
If you need support on your quit, then we are here for you.
I know of no mechanism by which cardiovascular exercise can repair lung tissue damaged by smoking. Only time will address the tar already deposited in your lungs.
Exercise is beneficial as a preventive measure for many cancers and heart disease, but whether it is dangerous for you would depend on the results of an assessment by your physician.
The situation is not gloomy, however, and one immediately begins to benefit from improved health in many ways after quitting.
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