Stupid Question Alert!

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Jan 2016
1:20pm, 24 Jan 2016
105 posts
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stilldreaming
Whenever I add some training onto Fetch, it seems to predict my finish time for different distances but I don't understand where these figures are coming from?!? Today's run of just under 8 miles at 9.22 pace seems to predict a half marathon time of 2:28:47 and a marathon time of 6:24:58 :-( Am I missing something obvious here?
Jan 2016
1:30pm, 24 Jan 2016
3704 posts
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Jono.
its just a calculator SD - there's a formula (which I cant remember the name off) for predicting marathon times
Jan 2016
1:33pm, 24 Jan 2016
34 posts
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thing
I think it's based on the Riegel formula - see run-down.com - or something similar.

The half and marathon times look long as it assumes that 8 miles at 9:22 was your race pace, not a training pace, so extrapolated out to long distances means you'd be running much slower than 9:22.
Jan 2016
1:34pm, 24 Jan 2016
11248 posts
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Dvorak
Based on your Riegel number, found here http://www.fetcheveryone.com/training-calculators-riegel.php

The basic principle is that your pace will drop as distances extend, though how much varies from person to person.
Jan 2016
2:58pm, 24 Jan 2016
157 posts
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soozie
Didn't sound right to me so I checked 1 of my old training logs where I ran 8 miles. Pace was just over 11 mjn/miles and predicted half time of just over 2.30 and am sure the predicted marathon time started with a 5.
Jan 2016
5:20pm, 24 Jan 2016
3331 posts
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minardi
Stilldreaming - are you sure you put in 8 miles and not kilometres? That prediction seems way off
Jan 2016
5:27pm, 24 Jan 2016
106 posts
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stilldreaming
Minardi - just checked and it's all in miles (I don't do those new-fangled km thingies!!).

Thanks for the links - it does say on the link page to contact Lord Fetch if numbers look dodgy, so think that's what I'll do! I'm not the fastest of runners, but my predictions seem wildly off the mark :-)
Jan 2016
5:31pm, 24 Jan 2016
107 posts
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stilldreaming
And now I'm even more confused, because those numbers have changed since I updated my training earlier and now it's predicting a marathon time of 4:35:45 ... which is much more around what I'd expect! Very weird ...... ;-)
Jan 2016
5:55pm, 24 Jan 2016
11250 posts
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Dvorak
Your Riegel number does adjust over time. The "standard" value I think is 1.06, though mine was generally 1.09 and is now currently 1.11 (I've been logging quite a bit of slow stuff recently.). So that suggests that your last training resulted in the value adjusting.
Jan 2016
8:23pm, 24 Jan 2016
1665 posts
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MudMeanderer
Stilldreaming: The algorithm on here uses a curve fit to estimate the exponent bit in the expression. So if you convert well to distance (or can't race short fast), it may be less than 1.06, but if you collapse as things get longer it could be over, possibly by a considerable margin.

However (unless it has changed since I last logged a decent number of races), it struggles a bit if you do a mix of very flat (think track race) and very lumpy/technical (e.g. lakeland fell race), where the correlation between distance and pace becomes very weak, and some of the estimates can be quite far out. It may however have been changed relatively recently though.

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Whenever I add some training onto Fetch, it seems to predict my finish time for different distances ...

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