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HR lower during the second half of the IM run
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I was going over my 2015 race data from IMAZ and I have noticed something interesting.

During the second half of my run leg my average HR dropped from 145bpm to 136bpm. My run average run pace over the same period only dropped by 20 seconds per mile. Does it make sense? Could it be attributable to a temperature differential that I did not spot? The run course is 2 loops, so things like the total elevation should be the same. It was raining quite a bit during the first half.

Does it mean that I left a lot on the table? This was my second IM, and I did not run with a HR monitor the first time, so I have nothing to compare this to. I looked at some of the flybys from IMAZ 2015 on Strava and the majority had the HR increasing during the 2nd lap unless they were walking.

Next races on the schedule: none at the moment
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Post deleted by gall1972 [ In reply to ]
Re: HR lower during the second half of the IM run [alex_korr] [ In reply to ]
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I have noticed the same on my previous IM. I am no expert but I believe it's due to a lack of leg strength/conditioning and onset of fatigue to be able to physically drive your body hard enough to raise your heart rate up aerobically in the late stages of the race.

I learned a long time ago that the only pertinent information you offer is found within the last sentence.
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Re: HR lower during the second half of the IM run [mopshiv] [ In reply to ]
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mopshiv wrote:
I have noticed the same on my previous IM. I am no expert but I believe it's due to a lack of leg strength/conditioning and onset of fatigue to be able to physically drive your body hard enough to raise your heart rate up aerobically in the late stages of the race.

^^^^ This. most amateurs if not all don't have strong enough Chassis' to push hard enough to keep your HR up. It's why I always question age groupers that focus on a lot of speed workouts for Ironman training. I have a friend who is a well known coach in the industry that says he always wants to grab all the age groupers who are walking at mile 18+ and say "hey! do you wish you could have got some more 400 repeats in on the track? another speed session?" haha. I'm not saying speed is wrong but fatigue sets in so much for 85% of the people doing the race that we should focus on endurance and strength as we go. building your maximum aerobic capacity not your threshold level

Kirk Noyes

Downtubes are for Dinosaurs

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Re: HR lower during the second half of the IM run [kman74] [ In reply to ]
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I am curious at what IM marathon pace folks think that speed workouts become necessary. Obviously individual, but outside of some fartlek on my medium runs I had very little quality running relative to overall volume prior to IMLOU this past year.
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Re: HR lower during the second half of the IM run [kman74] [ In reply to ]
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If i remove the 1st 30 minutes where I'm going too fast, excited, still adjusting after being mostly horizontal for 5 hours. Then factor in net elevation gain/loss, and I ran only 2 minute slow the 2nd 1/2 and HR was comparable with the difference being a drop in run economy causing a drop in pace at the same energy output. IF I had a running power meter, it would likely confirm that.

It's not a matter of power output, for most, it's a matter of fatigue. I challenge you to show me someone that doesn't have a drop in economy, even the best pro. They are still human and they are pushing their limits.


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