Fast heartbeat
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Otherwise,
Maximum heart rate = [220 - age] = 220 - 52 = 168
This is theoretical and only approximates max heart rates. I have seen many peope go higher than there max. predicted.
When you start to hit 80% of your max heart rate, you start to use anaerobic metabolism (you start to build up lactate). If you are trying to exercise for long periods, you are not going to be able to do this unless you are very fit. I would recommend working out in the 60-70% max predicted heart rate area. ALWAYS start slowly. In fact, I recommend starting so slowly that you are running uncomfortably slow. Most people just straight into full work out, go anaerobic early and feel exhausted for the rest of their work out. Build into your work out -- start slow and pick it up toward the end. You will work out longer, burn more calories and feel better about your workout.
I would advise you to keep you heart rate in the 110 range very early in the workout and if you neet to slow down to keep their, walk if you have to.
If it hurts, you are probably working out too hard.
I hope this clarifies your question. Good luck.
Should I be concerned? Can a virus cause this?