what is limiting the time you can ride at FTP?

[dominikk85]

FTP is defined as the critical power for 60 minutes. but what is limiting a well trained rider to 60 minutes? I understand what limits you at higher intensities (like cp 10 minutes or so which is highly anaerbic which means constant pace will cause an increasing lactate level) but isn't FTP very close to lactate steady state? theoretically after an initial raise your lactate should stay pretty constant at FTP. so why can you not go 2 hours at that pace when you are well trained? what is happening in the body?

 

[daveryanwyoming]

A few thoughts:

- FTP represents a power a bit above lab tested OBLA or MLSS so your blood lactate should be rising throughout an hour ridden at FTP.

- Even if you ride below OBLA or MLSS you'll eventually fatigue even if you continue to fuel as you ride. IOW we don't understand all the reasons athletes fatigue or why their power falls off even when they ride at apparently sustainable levels.

- Power for shorter durations such as 5, 10, 15 or even 45 to 60 minute MMP are predicted fairly well using Monod and Scherrer's two part model based on AWC and CP but their model doesn't account for any fatigue and their CP term (which BTW is very close to field tested FTP) should by their definition be sustainable for a very long time. In practice it is not and actual rider's MMP curves fall off quite a bit from what their model suggests for very long durations such as efforts longer than 90 minutes or so.

So basically FTP is max sustainable power for roughly an hour on an ideal day (not day in, day out reliable hour power) but that power is above an athlete's OBLA/MLSS so it's not surprising that we struggle to complete a full hour at FTP as we're playing a deficit spending game in blood lactate terms when we ride that hard. But even if we did ride a bit easier we couldn't sustain it indefinitely. There's also the question of overall conditioning and fatigue resistance. IOW, a rider might be able to punch out some strong 20 to 30 minute efforts but find their power drops off quite a bit by an hour just because they lack the base and basic conditioning to sustain their efforts. Longer efforts, more base and increased fatigue resistance not to mention plain old riding focus to sustain hard efforts for a full hour can help a lot there.

-Dave

 

[gudujarlson]

Originally Posted by dominikk85 .

FTP is defined as the critical power for 60 minutes. but what is limiting a well trained rider to 60 minutes? I understand what limits you at higher intensities (like cp 10 minutes or so which is highly anaerbic which means constant pace will cause an increasing lactate level) but isn't FTP very close to lactate steady state? theoretically after an initial raise your lactate should stay pretty constant at FTP. so why can you not go 2 hours at that pace when you are well trained? what is happening in the body?

Models to Explain Fatigue during Prolonged Endurance Cycling
http://www.google.fi/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&ved=0CDEQFjAB&url=http%3A%2F%2Fwww.cfa.harvard.edu%2F~jfliu%2F18573378.pdf&ei=XC-cUNa7JNPZ4QTugIGwAg&usg=AFQjCNHrz-0xU513ng0EWDsM5SM_lUw-KQ&sig2=N1eCqG-w7bVwVcK8iMNqmw

 

[SolarEnergy]

Originally Posted by dominikk85 .

FTP is defined as the critical power for 60 minutes. but what is limiting a well trained rider to 60 minutes? I understand what limits you at higher intensities (like cp 10 minutes or so which is highly anaerbic which means constant pace will cause an increasing lactate level) but isn't FTP very close to lactate steady state? theoretically after an initial raise your lactate should stay pretty constant at FTP. so why can you not go 2 hours at that pace when you are well trained? what is happening in the body?

If I understand your question correctly, I'd answer that the causes of fatigue aren't clear yet, as surprising as this might sound.

But for sure, glycogen depletion along with accumulated o2 deficit probably play a big role. As lactate level increases (and it does increase quite significantly during a 60m TT), your system tries to use it. For that it needs oxygen. So part of the o2 uptake is used to metabolize sugar and fat, but as the lactate level increase, part of it tries to metabolize it too.

As Dave mentioned, your FTP should normally be (if well trained) quite close to your CP (not talking CP60 here, but the actual CP).

So the reason why you're struggling holding this intensity level for 60min are probably the same as why you can't maintain power (or speed) at MLSS for more than this period of time, since CP tries to correlate with performances (speed or power) at MLSS. So the implications here for you, is that if you want to research for up-to-date info on speculation as to what may cause fatigue, look for fatigue at MLSS or CP, you're likely going to find much more data than if you look for causes of fatigue at FTP.