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645 race prediction times way too optimistic

Hi there!

I was checking out my race prediction times after a month of 645 use now and it is way too optimistic! It says 18min for 5k, 38min for 10k and 1:24 for half marathon, where my times for now are 23:45, 49min and 1h55 respectively. I know I've been training and pushing harder on interval, sprints, and long runs over the last two months and probably I could beat those 3 personal records by a few minutes now (it's just been a while since I run to beat the clock instead of a training session with intervals of rest, recover, etc). Once I run the half marathon tomorrow that I've been training for the last months I'll go back to eventually try and beat those times.

Nevertheless, there is a huge gap between what I think I could beat and the prediction the garmin makes.

One think I observe during my training is that my hear rate does not change significantly between a easy pace, such as 5:20/km, for instance, to a harder pace, as 4:40/km. It does change, but from something around 150 to 160. Even when I got for shorter sprints that I max out at 3:50/km, my HR tops out at 169-170 BPM. I even thought it could be a measurement error and used a hrm-run to double check it, and the strap confirms the watch readings. I believe this "phenomenon" could be responsible for garmin 645 thinking I can run a half marathon in 1h26min, while I can't just yet maintain a 5min/km pace in such a long distance for now. He thinks that since I go 4/km at shorter distances with a "calm" HR, I can run those races on those times. But, basically, I'm always dead before I can go at faster paces that could put me in a Zone 5 HR. I just never get to zone 5. I think even the lactate threshold guided test I would fail because of that...

What do you guys think?

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Top Replies

Former Member over 5 years ago +2

Even if your maxHR is off, there's a huge inaccuracy in the predictions by 645.

By my personal observations, the race predictions in 235, 935 and 645 are way too optimistic. In 245 and 945 they are…
DrGabrielSilva over 5 years ago in reply to mikew_nt +2

I really like Runalyse cause it get all your workouts and history for a better prediction

https://runalyze.com

All Replies

0 whlightnin over 6 years ago

How did you determine your maximum heart rate you entered into the settings? It sounds like that's off somehow.

0 CaduPrado over 6 years ago in reply to whlightnin

Actually, I didn't. The system automatically set it, I guess that based on my age, maybe?

0 CaduPrado over 6 years ago in reply to CaduPrado

Which is 30, btw

0 Hammarsal over 6 years ago in reply to CaduPrado

There's your problem probably. Your maximum heart rate value is a guesstimation, which determines all other values petty much. Try to do a max heart rate test e.g.like hill repeats, to get a more accurate value. Having said that I find the race predictions rather optimistic too, even after having done max heart rate testing.

0 CaduPrado over 6 years ago in reply to Hammarsal

Thanks, I'll look into that.

BTW, I've finished the half marathon today at 1:43, way better than I expected but still far from the obviously optimistic prediction

0 CaduPrado over 6 years ago in reply to CaduPrado

Would the lactate threshold test a way to set the max hr?

0 WillNorthYork over 6 years ago in reply to CaduPrado

No, the LT test requires max HR to be set properly.

Try hill repeats as suggested above. Some details here (scroll to the part which describes the field test):

www.polar.com/.../

0 caferey over 6 years ago

This was a common problem when the 620 came out. Reduce your max HR by about 5 beats. That’ll bring down your VO2 max by a few points which in turn will bring down your race predictions. The marathon time will probably be unrealistic unless you train like a Kenyan, but your shorter distances should be more like what you could do.

Keep in my mind they’re just predictions, watch gives you the same times if you run 40 or a 140km a week.

0 pcraenme over 6 years ago

I experience the same and my max HR setting is correct and my heartrate zones are setup using my lactate treshold value. Best is to just ignore these values, since they are purely based on vo2max values. Just use your vo2max value trend as an indication of your physical condition (going up or down). Works quite well in my case.

0 Roedema over 6 years ago in reply to WillNorthYork

Does the LTHR guided test really depend (much) on max HR? I did happen to first set my max HR based on some hill repeats before trying the guided test, and I reckon it used that to set the "zones" for the test. But I assumed the result was based purely on HRV. I also thought I could estimate a range for my max HR based on LTHR commonly being between 85% and 90%, higher for better conditioned athletes. (Divide LTHR by .9 and .85 to come up with a ballpark.) Perhaps this is a recipe for adjusting both numbers over time.

https://www.garmin.com/en-US/performance-data/running/#lactate-threshold