Out of Breath

I have had this problem on and off. Sometimes when I ride and 99% of the time it is when I am getting started from a stop or it is the first few miles of a ride. I find myself out of breath and it feels like it is coming from my legs. So what is this? I also have a bad habit of breathing thru my mouth instead of inhaling thru the nose and then exhaling out of the mouth. (which I was told was the best way). What do you all think?

Start slower. Your body needs time to warm up. I could go into the physiological aspects, but it doesn't matter. It is not unusual for your heart rate to initially be faster. After a few miles, it will even out.

I can't do the breathing through the nose routine. I have been trying to breath deeper into my lungs. Hard to break old habits.