When we stop training (known as detraining) the body beings very rapidly to feel “safe and secure” so it then begins to “preserve energy”. Understand all the biological factors that increased baseline VO2 Max in the first place, are closely connected, and will fall together like dominos. When you stop training almost immediately your requirement for blood volume decreases, and so does your stroke volume (the amount of blood pumped per heart beat) this increases your heart rate at both rest and during increased intensity demand…this leads to a loss of fitness and the bad news?  Expect within only three weeks of detraining to lose fitness VO2 max levels of near 20%  #Alterations in anaerobic threshold as the result of endurance training and detraining. Ready AE,Quinney HA.