Hi, inadequate oxygenation can produce symptoms of breathlessness, as the body tries in an effort to compensate for the decreased oxygen supply. The breathlessness could be due to cardiac or lung disorders. Breathlessness on exertion could be due to the decreased lung function. Again in cardiac disorders the heart is unable to pump the blood adequately, more so when subjected to stress like exercise. The calf pain and altered sensation in the feet could also be due to decreased oxygenation. Certain systemic disorders like anemia, diabetes, vitamin deficiencies and thyroid disorders can cause these symptoms. So, if your symptoms are troublesome consult your doctor for an evaluation. Regards.