Hello dear
Warm welcome to Healthcaremagic.com
I have evaluated your query thoroughly .
* Difficulty in breathing is due to lungs capacity level of oxygenation drive
at certain point of exertion , beyond which there are issues to bother
you .
* Running properly on flat ground do not arise knee joint problems .
*
Sudden cardiac death comes in picture when you go on running beyond
and beyond the limits of your body`s capacity .
* Your stamina can increase progressively provided you do it rhythmically
along with other deep breathing exercises ,
YOGA , managing vitals with
balanced nutritious diet , hydration levels , weight , blood sugar and
other parameters for the same .
Welcome for further assistance .
Regards .