I am training to become more competitive in getting into law enforcement. For over a year now, I’ve been working out about nine times a week (run six, lift three). My weak point is my lungs in the two-mile run, where I do about 14:00 (down from over 16:30 a year ago). My weak point is my lungs. I “stumbled” upon cycling and found that after a month of cycling, I can go four to six hours averaging about a 80 – 90% estimated maximum heart rate (not including a ten minute break every hour).
My question is how long (time wise per workout) and estimated maxumum heart-rate is too much? At what point in the workout do I reach diminishing return and should stop? I heard that the body will start to burn muscle at some point.
Also, how often should I go on a four hour and six hour ride? is once a week too long? (I will probably ride once or twice per week in replacement for some of the running.)