Heart rate zones

[bluesbird]

I paddle a kayak and use a garmin forerunner 301 heart rate monitor during training sessions.
I seem to have 2 max heart rates, depending on the day and I dont know why. I can go to the river one day and for no apparent reason only get my heart rate up to 145 or 150, beyond that I get an upset stomach and feel awful. I will try several days later and be able to go to 165 and hold it there and feel good. I dont eat within 3 hours of paddling and use 2 endurolytes within 15 min of start.
How do I make sure I am getting a heart rate of 165 on race day?
What am I missing?
Thanks,
Larry C.

[mandohack]

Dredging up an old post here ...

Could it be that your HRM strap is losing contact with your chest during paddling, thereby causing BPM rate errors? What is your body telling you on those days that you hit 165? Are you exhausted? Can you hold a conversation? What about those days where your max is only 150? Remember, too, that heat will quickly elevate HR. Are the higher max days hotter?

Lose the HRM strap for a few weeks and listen to what your body is saying, see if you get that same variance.

On the other hand, if your HR is hitting 165 and never higher, I'd go with that for the max since less than that isn't.

[ssrknordic]

Bluesbird-It could be a few things, as previously mentioned strap adjustment can be one, if it gets very wet you will get inaccurate data/lost beats. Other potential factors: There could be many reasons for this (fatigue, hydration level, biochemical). The heart is a muscle hence is subject to fatigue like all of your other muscles, and is subject to normal variations in performance. If you are well rested then it will be able to hit a true max, if fatigued then there will be a decrease in performance 10% in this instance, there can even be daily variations of 10%, due to a host of factors. Cardic drift is also another factor in the heat, for the same work output level the heart rate will be increased. Hydration: if you are dehydrated, blood is more viscious, heart has to work harder to pump, it will not reach the same max or work output level.

Hope this helps!