# VO2 Interval duration



## Srode (Aug 19, 2012)

I would like to improve my 2 to 4 minute power, and am starting to work on intervals for this power zone. Is it better to focus on 3 minute interval durations which I can do at a power right in the middle of VO2 Max power zone (10x3) for 60 minutes, then retest monthly and up the target power for the interval based on the results of the test, as opposed to starting at 2 minute interval (12x2)for 60 minutes training straddling vo2max and Anerobic zones, then extend the interval duration during the month as I am capable, or perhaps 4 minute intervals (8x4) straddling VO2 Max dipping into Threshold occasionally (hard to maintain 4 minutes all in VO2 consistently for me, particularly at the end of the intervals).


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## Alex_Simmons/RST (Jan 12, 2008)

Srode said:


> I would like to improve my 2 to 4 minute power, and am starting to work on intervals for this power zone. Is it better to focus on 3 minute interval durations which I can do at a power right in the middle of VO2 Max power zone (10x3) for 60 minutes, then retest monthly and up the target power for the interval based on the results of the test, as opposed to starting at 2 minute interval (12x2)for 60 minutes training straddling vo2max and Anerobic zones, then extend the interval duration during the month as I am capable, or perhaps 4 minute intervals (8x4) straddling VO2 Max dipping into Threshold occasionally (hard to maintain 4 minutes all in VO2 consistently for me, particularly at the end of the intervals).


it's not necessarily a straightforward questions to answer, as it would help to understand what element of your physiology needs the most work. 

2-4 minute power, while dominantly aerobic, still has a sizeable anaerobic component, and it may be that you need a little more focus on work at that end than on the aerobic (but aerobic is still primary).

What intervals you choose is more a matter of what you physiological development needs are.

In general, when targeting short range power (and assuming you have developed your threshold power as a fundamental element), then you either do work that's focussed on improving VO2max, or you do work focussed on improving anaerobic work capacity. There are spill over benefits from doing one on the other of course.

If focussed primarily on developing VO2max, then 2-3 minutes isn't long enough for intervals. Make them 4-6 minutes and do ~ 15-30 minutes of time at level in any one session and approx same recovery duration as the interval length.

If developing AWC is your need, then there are a multitude of hard efforts you can do to drain your AWC battery, but you'll need to allow for longer recoveries between sets. How long depends on a few things (these can be vomit inducing).


If you are not sure, then just do 2-3 minute efforts, make them hard enough so you can do 3-4 intervals at minimum and no more than 6-7 intervals maximum. If they are so hard you can't do enough, or too easy you can do more, then adjust the power next time. I sometimes prescribe 2-3 min hard efforts, usually as hill repeats with ~10-15-min in between, and these are a bit of a hybrid physiologically.


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## Srode (Aug 19, 2012)

thanks Alex, very helpful

I'd like to improve my FTP too of course however my shorter interval power is pretty flat relative to my FTP. My 1 minute power is about 200% of my FTP, and 5 minute power is about 12% higher than my FTP. Does that help with suggesting where to focus (Anerobic vs VO2 Max)? 

For workouts in the intervals you prescribe, is the approach one set per session typically with the total duration at level 20 to 60 minutes depending on duration of the interval with a couple sessions / week in the training plan?


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## Alex_Simmons/RST (Jan 12, 2008)

Srode said:


> thanks Alex, very helpful
> 
> I'd like to improve my FTP too of course however my shorter interval power is pretty flat relative to my FTP. My 1 minute power is about 200% of my FTP, and 5 minute power is about 12% higher than my FTP. Does that help with suggesting where to focus (Anerobic vs VO2 Max)?
> 
> For workouts in the intervals you prescribe, is the approach one set per session typically with the total duration at level 20 to 60 minutes depending on duration of the interval with a couple sessions / week in the training plan?


It's next to impossible to give specific advice on a forum, and IMO isn't sensible to do so. And I'd probably want more than a snapshot of power profile in order to make such assessments. If that represents your best FTP & 5-min power, then yes you might benefit from shorter harder work, but you might also be a poor responder to such work. Some like you are just better off bringing threshold up and then trying to squeeze out a little extra on the side.

If doing level 5 (Coggan) work, then I wouldn't do more than 1 hour total of dedicated structured L5 intervals of reasonable duration per week. I'd consider that a lot for most people. And that would be during a specific phase of training. Level 6+ work is trickier to dose out, very individual.

You have to be careful how you dose out such work, it has various effects, both physiologically and psychologically, and the time course for improvements (and decay) is much faster (in the order of days/weeks) and hence timing of such work also needs care.

There are many ways to incorporate this sort of work. It can be a few randomly placed efforts of ~ 5-min through another ride, right through to doing a couple of days / week dedicated to this type of work. The former is good for transitioning to such a dedicated phase, and/or just keeping you on your aerobic toes. A little of everything is fine.


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## Creakyknees (Sep 21, 2003)

Alex is right, it's not a simple thing.

But. 

Put a playlist together with a bunch of up-tempo 3-4-and-5 minute songs that inspire you to ride hard. Plug in, crank up, haul ass for the length of a song. 

Voila, vo2 intervals.


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## Srode (Aug 19, 2012)

Thanks Guys, I'm going to try incorporating some shorter intervals into my riding and trainer rides and see if I can progress with your advice. Much appreciated!


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## jsedlak (Jun 17, 2008)

Alex_Simmons/RST said:


> it's not necessarily a straightforward questions to answer, as it would help to understand what element of your physiology needs the most work.
> 
> 2-4 minute power, while dominantly aerobic, still has a sizeable anaerobic component, and it may be that you need a little more focus on work at that end than on the aerobic (but aerobic is still primary).
> 
> ...


If 2-4 minute power is "dominantly aerobic," then how will 2-3 minute efforts improve AWC?


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## Alex_Simmons/RST (Jan 12, 2008)

jsedlak said:


> If 2-4 minute power is "dominantly aerobic," then how will 2-3 minute efforts improve AWC?


While such efforts are dominantly aerobic, there is still a significant contribution from Anaerobic Work Capacity (AWC - measured in joules), how much contribution will depend on how hard you go. This will always be the case for any effort longer than about 60-seconds* since while energy available from aerobic metabolism is effectively unlimited, we only have a limited and fixed AWC at our disposal.

Substantially and rapidly depleting AWC stimulates physiological systems to adapt to that demand and respond by increasing our AWC.

So while an effort may be dominantly aerobic, it can still substantially deplete AWC and provide the body with a stimulus to respond and adapt to that demand. Such responses occur in a matter of hours, days and weeks. The adaptation time course for AWC is relatively short.

While you can pretty well "empty the AWC tank" in about 60-90 seconds if you go hard enough, it's also possible to deplete AWC over longer durations - what determines the rate AWC is used is how much of the power demand cannot be met by aerobic metabolism.

For hard efforts of 2-3 minutes, you will use both aerobic metabolism and a proportion of your AWC. How much of your AWC depends on how hard you go. A maximal effort for that duration will fully deplete AWC, slightly sub maximal efforts will leave a little in the tank.

_Recovery of AWC is however a wholly aerobic process_, and it takes a while to "recharge", hence why longer recoveries are required between efforts that substantially deplete AWC, but much less recovery between efforts that all aerobic. If AWC is not substantially recharged between hard efforts, then on subsequent efforts you'll either be forced to go slower/lower power, and/or reduce the duration of your effort.

That's part of the irony of improving AWC, if it's something you expect to tap into on a regular basis (e.g. think of any cycling event with multiple frequent high power demands like a crit or points race), what might dictate performance is not so much the size of the AWC but how much of it we need to tap, and our recharge rate. Each of those factors is dictated by our aerobic fitness (and how crafty a rider we are). 

It's why some people mistakenly think that when they get dropped after the third or fourth attack that they need to work on their ability to "surge", when it's far more likely they need to work on their aerobic capabilities (and possibly their race craft).


There are several ways to measure AWC, and it can be reasonably estimated with data gathered with a power meter. The best known is the use of the Monod & Scherrer Critical Power model. Another clever method is to estimate the Maximal Accumulated Oxygen Deficit.


* 60-seconds performed maximally is approximately the duration where contribution from aerobic and anaerobic metabolism to the energy/power demand is about equal.


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## jsedlak (Jun 17, 2008)

Alex_Simmons/RST said:


> Substantially and rapidly depleting AWC stimulates physiological systems to adapt to that demand and respond by increasing our AWC.


What is "substantially" and what is "rapidly" in this context? In what percentages of maximum effort should we be riding, and for what sort of interval?



Alex_Simmons/RST said:


> So while an effort may be dominantly aerobic, it can still substantially deplete AWC and provide the body with a stimulus to respond and adapt to that demand. Such responses occur in a matter of hours, days and weeks. The adaptation time course for AWC is relatively short.
> 
> While you can pretty well "empty the AWC tank" in about 60-90 seconds if you go hard enough, it's also possible to deplete AWC over longer durations - what determines the rate AWC is used is how much of the power demand cannot be met by aerobic metabolism.
> 
> For hard efforts of 2-3 minutes, you will use both aerobic metabolism and a proportion of your AWC. How much of your AWC depends on how hard you go. A maximal effort for that duration will fully deplete AWC, slightly sub maximal efforts will leave a little in the tank.


What is our goal when doing an interval workout? My understanding has been that we are loading up a specific system for the duration of the interval and then letting it recover. The goal of recovery is to be long enough to let the system just barely come back to normal before loading it up again. Is my understanding incorrect?

In the above, you are suggesting much the opposite. You are telling us that a 2-3 interval is good for anaerobic capacity _because_ it loads both anaerobic and aerobic systems. This seems entirely inefficient to me.



Alex_Simmons/RST said:


> _Recovery of AWC is however a wholly aerobic process_, and it takes a while to "recharge", hence why longer recoveries are required between efforts that substantially deplete AWC, but much less recovery between efforts that all aerobic. If AWC is not substantially recharged between hard efforts, then on subsequent efforts you'll either be forced to go slower/lower power, and/or reduce the duration of your effort.


But wait - if AWC is recovered during aerobic work, wouldn't a 2-3 minute interval where we are not anaerobic the entire time cause that system to recover (even slightly)?


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## Alex_Simmons/RST (Jan 12, 2008)

jsedlak said:


> What is "substantially" and what is "rapidly" in this context?


Substantially means a large portion of. If I had to put a number on it, say anywhere from 25-100% would be substantial. How hard you go, and how long you go hard for, determines how substantial.

Rapidly means quickly. In context of AWC, it's possible to deplete AWC within 60-90 seconds if you go hard enough. It's also possible to deplete AWC less rapidly over a few minutes or more gradually over 20 or 30-minutes. So in this context, I'd say quickly means over a few minutes.



jsedlak said:


> In what percentages of maximum effort should we be riding, and for what sort of interval?


That's a function of many things. 

I'm not saying what people should or should not be doing, only explaining what happens when they do what they do.



jsedlak said:


> What is our goal when doing an interval workout? My understanding has been that we are loading up a specific system for the duration of the interval and then letting it recover. The goal of recovery is to be long enough to let the system just barely come back to normal before loading it up again. Is my understanding incorrect?


The goal of training (interval or otherwise) is to induce specific physiological adaptations that enhance performance.

Once you understand that, then the nature of how one performs intervals becomes clearer (and will vary accordingly).



jsedlak said:


> In the above, you are suggesting much the opposite. You are telling us that a 2-3 interval is good for anaerobic capacity _because_ it loads both anaerobic and aerobic systems. This seems entirely inefficient to me.


I have not said that at all. 

Firstly, all I have said is that such efforts (done hard) tax both systems heavily (which they do).

Secondly I have not said whether one _should _do them, nor whether such efforts are optimal for achieving the particular training goal one is interested in. Hence my initial response in this thread.

Keep in mind however that all efforts greater than a handful of seconds, whether done maximally or not, involve aerobic metabolism. Even a kilometre time trial has approximately 50% of the energy demand supplied by aerobic metabolism.

And also keep in mind that hard (dominantly) aerobic efforts that are designed to primarily tax us at or near VO2max levels, by their very nature, will also tap our anaerobic metabolism / anaerobic work capacity.



jsedlak said:


> But wait - if AWC is recovered during aerobic work, wouldn't a 2-3 minute interval where we are not anaerobic the entire time cause that system to recover (even slightly)?


Well yes, but the efforts as discussed here are done at a power/effort that is above such a level that would enable recovery.

AWC can only recover when the energy demand falls below threshold power level (~FTP), and the further below threshold, the more rapidly it will recover. So while an effort above threshold will still be predominantly aerobic, you won't be recharging your AWC battery until your power output drops below threshold.

There is also a reasonably predictable time course for the recovery of AWC, and the primary variable in that function is how far below threshold power you are when recovering.

If you totally exhaust your AWC, then you'll require about 30-minutes of _doing nothing at all _to fully recharge your AWC. If you fully deplete AWC, but keep riding, then the time required to fully recharge will be much longer.

What tends to happen during such supra threshold intervals is we start out with 100% of AWC, then we deplete it substantially (e.g. 30%), then recover and top up, but we never really get all of it back (e.g. 5-10%), so the next effort depletes AWC further, then a bit of a top up, and so on until we simply run out, and no matter what we do, we simply do not have the ability to go harder than threshold any more (and usually we are too knackered to go even that hard).


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