2004 and I had to have a stress test. On the 220- age- I should have been 163 as my Max. At that time I was treating 165 as my max- but the stress test does take you near your limits. I hit just over 170 and fell off the bike. The Cardio nurse conducting the test mentioned something about swimmers and cyclists and suggested that I keep to the 165 as my max.
That 220 - your age is a good guide to what your max could be. Now comes the problem of working out what the 80%-90% of your max is. Two methods.
Max HR less resting HR- In my case- 165- 70=95
80% of 95=76
76+resting HR is 76+70= 146.
So to ride at 80% of my Max is to ride at 146. As I normally ride at 140 to 150 once I have warmed up- that is about right for me. 90% would be 155 and that is about the max I allow myself to ride at- but will get to the 165 on steep hills and even exceed this if I have to.
The other method is just to take your max and 80% of that so 80% of 165 is 133.
You have to decide on what your max is going to be- and I do not suggest that as a 50 year old- just coming back into cycling you try to see 170 on your first ride- Build up to it
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How long was I in the army? Five foot seven.
Spike Milligan