2 handed overhead 20 lb dumbbell swing(modified)to make good cardiovascular exercise to meet my physical/spiritual trai

Modified 2-handed overhead dumbbell swings - 2-handed overhead& behind neck 20 lb dumbbells swings lifted with bent elbows. I do 13 minutes of these non-stop while breathing in and out 6 to 8 times per dumbbell swing. Very difficult cardiovascular exercise to do and took me 2&1/2 years to work up to them. Modified to work well for my very intense physical/spiritual training purposes.