Written by: Joe Siegel
A Lot of athletes are starting some work on improving their Vo2max this time of year (Vo2max is the maximal rate of O2 uptake during exercise). It is the limiter in maintaining a primarily aerobic (using O2) energy pathway during intense, above threshold exercise. If one needs more energy than the aerobic energy system can provide, they will start pulling from primarily anaerobic pathways (which don't use O2). Anaerobic energy is very powerful but very short lasting - you cannot maintain it for very long. Therefore, it stands to reason that improving your aerobic capacity and the rate at which you can deliver O2 to your body is very important.
Why do we train above threshold though? For cyclists it is obvious - racing requires a lot of effort above threshold and quite simply, you don't do well in mass start races without the ability to go over threshold (utilizing both aerobic and anaerobic energy pathways). For TTers and Triathletes, the need is still there however. Another determiner for athletic performance is FTP - functional threshold power - i.e. the power one can maintain "for a long duration" without fatiguing. Go over FTP and you will fatigue much quicker. Go under FTP and you can maintain for very long times. Please note that FTP is NOT defined as one hour power, this is a common misconception though. The Time to Exhaustion (TTE) at threshold usually ranges from 30 min to an hour or more and it will depend on the athlete's specific training to that point.
Now, before getting too off track - why Vo2 for triathletes, TTers and other athletes who won't go over threshold for racing? Well, there's a limiter in raising FTP, namely VO2max. A typical cyclist can maintain about 80% of Vo2max at threshold. As we peak and really push threshold training, that number can grow to about 90%. At that point we hit a wall, and FTP does not improve as we are limited by the amount of O2 we can deliver. So, raise the Vo2 and you can keep raising FTP! When we do this work and the order is not a rule though. This is part of the "art" of coaching to optimize a training plan for each individual athlete and their specific constraints and goals (That is not the focus of this post).
Ok, Vo2max is important, now how do we make it better? More specific to our needs - how do we improve the power (watts) we can hold at Vo2max? Well, quite simply, we do intervals over threshold, but under the transition to too much anaerobic work. Classically, that means you train 105% to 120% of your FTP, your Zone 5 or Vo2 zone. The classic zones are great when dealing with power at or under threshold. However, athletes will vary greatly at over threshold efforts (and as you go more and more over threshold, that variance increases more and more) - see the picture for a good visual of this phenomena. It's become more obvious that we need an individualized approach! For me, that meant spending a lot of time to look at past efforts, using RPE and HR to gauge efforts and choosing interval targets by a bit of "feel" and guesswork (along with feedback from the athlete). That's the old school way (either just assuming 105%-120% or trying to hone in with a lot of leg work and some guessing/feel) but we're new school now. New modeling and software has given coaches and athletes alike the ability to very precisely target Vo2 intervals.
If we can feed the model good data, the model can very precisely and accurately pinpoint Vo2max and power at Vo2max. Also using the model, it can suggest the optimal power and duration for each interval. Keep in mind (and before you fire your coach because the software does all the work for them) that this is a model and these are still estimates. There needs to be an educated human in the loop to validate all intervals and targets before sending them off for completion. I know my athletes data is good in about 60% of cases and the model would be very misleading at least 40% of the time for example. "All models are wrong, but some are useful" (a quote/idea commonly attributed to George Box) - this one is very useful, but it is still not reality and we must keep that in mind. We need to know what the model is telling us - and what it isn't. We also need to know the model's strengths and weaknesses, and use cases which create known weaknesses and error.
Now, the workouts. Let's say we have good data and the model passes our litmus test for reasonability and feasibility - let's bang out some intervals!! Case one below is me. I was doing 4 min intervals targeting 100% power at Vo2max. The blue line shows Vo2 tracking upwards and then leveling at right around 100%. The data was pretty good, the effort felt very maximal, breathing was pegged and we see a trend of HR rising progressively for each set - a good indication that I was at or very close to 100% of Vo2max.
Sometimes though, the model isn't right - we need to move the model. That's why in over threshold work, it's important to realize that if you can do more, you should do more. That's what I told this athlete for this set (note, he is an experienced cyclist and familiar with the feeling and intensity of maximal aerobic work). Watch - he's exceeding 100% of Vo2max for each interval. Through all but the last interval, he's progressing just like my workout in holding steady power for each and holding similar %Vo2max for each. His model was just under reporting capability a smidgen. Well, this workout just fed the model new data for future workouts - he moved his model. Models are representative of what you've DONE, not necessarily what you CAN DO. As we train and improve, we constantly are setting new goalposts and moving the model. Quick note on the last interval though - he screwed it up. Being the last interval, he decided to go for "hero watts", which turned out to be unsustainable. He went so far over Vo2max that he recruited much more anaerobic energy which does not provide for the sustained energy he needed to complete the interval. As such, his power dipped way off, Vo2 dipped way down and he needed to recover, before surging for the tail end of the interval. What's interesting is that overall, his power average for the interval was in line with the rest - he hit the power number. However, by being able to track VO2, we know he didn't hit the INTENT of the interval, he did not do the best work to improve his Vo2max. That's ok - it was one of six - he still did great work. However, it's an important note that going "off script" too much in our intervals, even if the end result seems good, it may be sabotaging the specifics of the work we are trying to address. Note that exact preciseness in wattage is fairly impossible and not expected, especially with riding outside on the road. There is no magic switch where a watt over is the wrong work and a watt under is the right work. It's a range and a transition between zones of adaptation. Variation is OK, within reason.
For a summary - Vo2max is the maximal rate of O2 uptake during intense physical exertion. It represents a power over threshold and it is unique to each individual athlete. We train our Vo2max and power at Vo2max in order to perform better in aerobic supra-threshold efforts AND to provide additional "room" for subsequent growth in threshold. Using a classic metaphor if VO2max is the roof of a house and the ceiling is FTP - you will reach a limit to ceiling height if one does not also raise the roof.
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