Intensity factor

A light bike doesn't replace good fitness.

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the jackel
Posts: 73
Joined: Wed Aug 22, 2007 7:44 pm
Location: London

by the jackel

This may be a dumb question, sorry if it is.

I understand the principle of IF but was wondering how to apply it beyond the 1hr mark. For example, I rode for 1.5 hrs the other day at an IF of 0.97. I appreciate this means I rode quite hard but what is the max that is realistic for that time frame, or for 2 hours or 3hours? Is there a simple guide that you shouldn't be able to achieve an IF greater than 0.xx for a given time period ( unless your FTP is incorrect obviously)?

by Weenie


TobinHatesYou
Posts: 6023
Joined: Mon Jul 24, 2017 12:02 pm

by TobinHatesYou

the jackel wrote:
Fri Jul 31, 2020 9:57 pm
This may be a dumb question, sorry if it is.

I understand the principle of IF but was wondering how to apply it beyond the 1hr mark. For example, I rode for 1.5 hrs the other day at an IF of 0.97. I appreciate this means I rode quite hard but what is the max that is realistic for that time frame, or for 2 hours or 3hours? Is there a simple guide that you shouldn't be able to achieve an IF greater than 0.xx for a given time period ( unless your FTP is incorrect obviously)?

It depends entirely on the type of efforts you are doing. Like, you can certainly achieve greater than 1.00 IF for 60min or longer if you do a lot of short bursty/sprint efforts. For a steady effort where normalized power ~ average power, then .97 seems about the practical max for a 90min stretch.

the jackel
Posts: 73
Joined: Wed Aug 22, 2007 7:44 pm
Location: London

by the jackel

Thanks for taking the time to reply

I appreciate this is subjective to an individual but is there a benchmark or guide for a 2 and or 3hr ride? What might the maximum achievable IF be, on the assumption its a hard effort target than loads of sprints?

petromyzon
Posts: 523
Joined: Mon Apr 05, 2010 4:14 pm

by petromyzon

Here is a good summary of Critical Power models that have been used to address this for evenly-paced efforts.

https://www.gssiweb.org/sports-science- ... erformance

Clearly it's a model, it is not perfect and there will be individual variability. A criticism of this strategy is that it is very sensitive to the quality of the data over the short intervals used to fit the model. E.g. if there are even small inaccuracies in measurement of power over the shorter intervals this can result in 10's of Watts of error at the asymptote.

Further, individual motivation and practical issues such as terrain and interruptions can add so much variability that there is almost no point predicting the results. You just need to get out there and do what you can do.

You would also expect the answer to be very different depending upon the type of athlete - I bet Ironman athletes would be up in the high 90's like your number but a road racer with very developed anaerobic/glycolytic capacity like Sagan or Gilbert might not be able to get anywhere near 0.97.

Finally, as Tobin alludes to, there are issues with the Normalized Power calculation. In an ideal world your NP allows the assessment of the physiological stress of a variable effort >30mins by giving you a consistent average power to which it is equivalent. If you can generate a 60 minute NP greater than your FTP on a consistent basis then either your FTP needs increasing (good) or the calculation doesn't work for your physiology (annoying). This is a so-called "NP-buster". I've never been able to do it but plenty of people can.

Why do you want to know a guide for IF out to several hours? If it is because you are worried about having your FTP set too low then I would suggest you concentrate on getting a more robust FTP estimate. If it is to guide performance in longer events then you've just got to get out there, do the events and let experience be the best guide.

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