correction factor for indoor vs outdoor FTP?

Chris M. · November 5, 2010 12:21PM

I am new to power, and rode outside today for the first time since performing my indoor FTP test. While riding outdoors at a touch over 100% of my FTP for the 2x6 intervals, my HR was 19 beats lower than it was during the test. I know that HR can vary, but there is a huge difference in effort for me between riding at 165 and 146. Should I determine a wattage that more closely estimates my indoor FTP HR and go with that? Say, add 10%?

Jeff Braaten · November 5, 2010 3:25PM

I know there will be a lot of smarter folks than me chime in on this but I have had similar questions in the past. First about the HR, we all know there are multiple variables accounting for it. Mine is almost always higher indoors since I can't get the same cooling as outdoors even with a fan. Time of day, caffeine, how much sleep, the stock market, it all affects HR. If you are training with power HR should only be a minor variable to consider. What I would suggest doing is adding about 10% to you indoor FTP ( not your HR ) and use that value for outdoor riding. If it seems to difficult back it off some. Eventually you will want to do an outdoor test when the weather permits you to ride mainly outdoors again.

Keith Wick · November 5, 2010 3:38PM

i've found that I'm about 10-20 watts lower inside than outside. when i do my power intervals i try to keep them within a 10 watt zone anyway, so having this range suits my riding style anyway. For example if I'm at 200 FTP, then when i go outside when i look at my PT i'll want to see a number between 210 and 220.