I am a fit 52yo female that exercises 4-5 x per week and also do weight training and yoga. Running is my primary form of CV fitness but I also bike. I have been exercising regularly since my 30's. I have always had trouble breathing during strenuous exercise. It keeps my from running faster and longer distances. I just rode my bike only 5 miles and my heart rate was 195 when biking up hill. I was almost gasping for air. I have been tested for allergies but all were negative. I don't have any wheezing and do not have asthma. My resting heart rate is 56. The shortness of breath/increased heart rate has not improved despite continued exercise. I push myself by sprinting and doing interval training without improvement.