I am on heart medication and attempting to get back into karate after 3 years off. What I am finding is that I have no stamina, after 3 or 4 sparring matches I need to take a break and reoxegenate my body. I know my heart rate will not get above 140 no matter what I do so how does this affect my ability to train? Is anyone else dealing with this and what do yu recommend. Thanks STeve