VO₂max testing and metabolic games

I’m in another research study, this one is testing the acute effects of L-arginine ingestion on exercise. They’re looking at the growth hormone levels in the blood during submaximal exertion in endurance trained athletes and so need to have a good idea where anaerobic threshold is. This means that they need to know quite a bit about my physiology to determine what normal is before they can do the double-blind test on what L-arganine will do to my two one hour riding sessions, which are to be done at 80% of my anaerobic threshold power. All that just to say that I could get a free VO₂-max test out of the deal which, if you ask me, is always a good trade!

This also required body composition testing done by underwater weighing and I scored 7.2 % body fat which I think was probably reasonably accurate and also pretty acceptable for the base-season of my year. 7.2% fat means I’ve got about 14 lbs of fat on me which either sounds like a lot, or it doesn’t sound like much, depending on who you are. I take this to mean the following: If I think I can lean up to about 6% fat by race-day I have to loose a whole kilogram of fat. That also means I only have a kilogram of fat to loose. If you’re a calorie counter that’s a matter of coming up short on average 100 calories per day from here until race day, which is silly-easy if you adopt that method of body-composition control. I’ll reference you to a recent pair of blog posts written by my coach Steven Lord entitled “Calorie Counting Futility” and “More on Calorie Counting Futility” which very specifically address the issue of leaning-up as an athlete. I think you can probably tell by their titles what his opinion is! I never have been a long term calorie counter and I don’t intend on being one.

I have previously had both great success and negligible success adopting a simple strategy of shifting towards “lean protein and more salad vegetables” during lead-ups to a couple races in the previous few seasons. The philosophical strategy behind that was to phrase the choices positively so that I am trying to get satiated on those fuel sources and then will naturally reduce the component that processed carbohydrates plays in my diet. I’m currently modifying the method to incorporate a bit of a negative statement which I’m not totally certain about, as I don’t like the idea of not eating things, I think it’s more mentally healthy to phrase this stuff in the positive. For now the strategy is again a shift towards incorporating “lean protein and more salad vegetables” as well as “minimizing consumption of processed carbohydrates outside a window of 2 hours before and 2 hours after exercise”. Interestingly, that means if I’m doing a double workout in the day it doesn’t really apply. I am not monitoring my weight too closely these days and I am certainly not monitoring my body composition frequently even though I have access to a four-point electrical impedance tool which has proven reliable in the past. As I’ve written before in this blog, I found that doing so had me miss the forest for the trees.

Now that I sound like I’ve got an eating disorder I’ll get back to the VO₂-max test.

This first figure shows my oxygen consumption with increasing wattage. It shows that I maxed out with one minute at 540 Watts (on an average of 60kms, and strictly less than 100kms, per week on the bike since October – not bad!) and had a peak oxygen uptake of 5.4 L/min which is a pretty good absolute score. I have scored as high as 5.7 L/min previously but that was following the Sea-to-Sea bike tour where I absolutely loaded my body with aerobic work and rode 6 days a week for 9 weeks, a far cry from the point in my season where I’m at right now. My relative score is good but not great. It definitely qualifies me for the study, but it also shows I’m not yet race-ready.

This second chart shows the results of gas-analysis. I crossed over to anaerobic work at 4 L/min with an estimated power output of between 320 and 360 Watts. The corresponding HR to this crossover occurred in the range of 165-170 bpm. Previously, I had been treating my threshold HR on the bike to be around 176 bpm which is a slight overestimate. The results of the test give me an indication that in future I need to down-estimate my cycling threshold HR by a few bpm to the high 160’s rather than the mid 170’s. A more accurate measure is unnecessary (as HR will vary day to day) and unavailable because the step-test protocol goes in 40 Watt increments and lets your HR settle intermittently rather than gradually ramping through all of the different power-outputs. Interestingly I only reached a max-HR of 196 bpm during the test. I have always cracked 200 bpm during previous tests. It’s possible that I am dealing with a tiny bit of residual fatigue from the race this past weekend which could have made a bit of difference.

This figure is the one that I find the most interesting but it’s also the most inaccurate as it’s based on a hack calculation I did of substrate consumption during exercise. I used the table of “Thermal Equivalents of Oxygen for the non-protein respiratory quotient” from “Essentials of exercise physiology, Volume 1 By William D. McArdle, Frank I. Katch, Victor L. Katch” and directly substituted my respiratory exchange ratio (RER) during the test for the respiratory quotient (RQ) quoted from the table. This is a poor assumption and I know it. The testing protocol recording this data was also rather rapid and so it means that I didn’t have the opportunity to settle in to a nice and calm fat burning metabolic state during the early part of the test. This is seen by a low fat consumption in the early stages which is almost certainly false. Then as the test progresses towards anaerobic threshold my fat consumption trails off and so when I hit anaerobic threshold I am by definition exhibiting an exchange ratio of one. This is where the assumption that RER=RQ is obviously problematic. It’s almost guaranteed that I am still metabolizing some fat at this workload but the assumption implies that I cannot be.

RER – the Respiratory Exchange Ratio is the ratio of expired CO₂ to the inspired O₂ during exercise and it is measured at the mouth by the gas analysis machine.

RQ – the Respiratory Quotient is the ratio of CO₂ produced by cellular respiration to the quantity of O₂ consumed during cellular respiration. Burning carbohydrates produced 6x CO₂ molecules for each 6x O₂ molecules consumed giving an RQ of 1.0 Burning lipids which are a more energy dense molecule requires more O₂ to metabolize the fuel for the same amount of CO₂ produced.

Over a long period of time when the body functions at a constant exertion (or rest) the time average of RER is equal to the time average of RQ.

One other thing that’s interesting to do is calculate my efficiency in converting chemical energy to mechanical energy. If we look at threshold power and say that I was at 340 Watts (estimate) and I was metabolizing 20 calories per minute that means I was consuming 1394 Watts of chemical energy and exhibiting a conversion ratio of 24.4%. OK, for those of you in the know you’re very aware that 24% conversion efficiency is pretty much the gold standard in cycling so I’ll admit I cherry picked my estimate to put me there. If you look at the results over the sub-threshold exertions (below) you’ll see that there is a trend that shows me displaying a false peak in efficiency while the metabolic process RQ is translated through my blood and lungs to display itself as an RER measured at my mouth. Where the gross efficiency settles before the next incremental increase would be the true measure of my conversion ratio. As shown in the little table I do exhibit excellent conversion factors but I’m not a world record breaker.

OK, one final calculation for the nerds who read all the way to the end:

I know that the result is going to turn out poorly because as I already discussed there’s lots of evidence to believe that fat burning has been underestimated by the testing protocol and my lack of comprehensive skills in doing the calculations. But, I figure I should run the calculation anyways. I finished at 240 Watts with a HR that was settled right around my Ironman HR last year when all prepped up for the race in Penticton. I was significantly more aerobically fit at that point than I am now so I should have tested with a higher fat burning capacity at that HR than I did during the test, but let’s presume I’m the same. Over all of the records at 240 Watts I averaged a caloric expenditure of 14.3 calories per minute. The average percentage of that that came from fat was 21% or 3.0 calories per minute. That means I burned 858 calories per hour while riding the bike at Ironman, which totals a caloric burn of 4476 calories (5:13 bike split) and I will have been able to process 939 calories of my fat reserves on the bike. I have already well documented my nutrition strategy for Ironman on the blog so I won’t reiterate all the points here except to say that I ingested 2500 calories while on the bike. This calculation means I could have had a bike-leg caloric deficit of 1037 calories. Considering that I can EASILY burn 1000 calories per hour swimming (I’ll tell you right now I swam way harder than I biked) then I should have reached T2 having burned through more than 2000 calories of stored glycogen… (average adult’s stored glycogen is 2000 calories) and while I may be able to load myself up on a bit more than that because I’m a big person and because I employed some caloric storage training and because I did pre-race carbo fueling and the pre-race banana that entered my bloodstream during the swim for ~100 calories) these estimates show that I would have been starting the marathon with nothing in the tank, or at least with less than ~20% of my glycogen reserves.

Like I said, the calculation wasn’t going to work. I was burning more fat than this estimate leaves us to believe. I’m pretty sure that I did the bike glycogen neutral or perhaps even glycogen positive to restore some reserves lost on the swim. The deficit by these estimates would have required me to have burned 6.3 calories per minute of fat on the bike. That estimate is probably a lot closer to the truth and it’s not unreasonable to believe that I could have done that, it only amounts to 44% of my calories from fat at that workload. Considering I was riding a mix of easy and steady, that’s not an unreasonable thing to expect of my body. I’ve seen metabolic testing profiles elsewhere online with ironman exertion fat consumption ratios both at and above this 45% range.

I’ll conclude this post with one final thought. Going faster at Ironman doesn’t require that you burn as much fat as you can on the bike. Going faster at Ironman requires you doing the bike split as quickly as you can and still deliver yourself to the beginning of the run capable of running your best marathon. That probably doesn’t mean that you need to have your glycogen stores full if you’re reasonably capable of consuming calories while running and run with any sort of reasonable efficiency. If we look at how much professional ironman athletes eat (or Kona qualifying AG athletes in the M25-39 AGs) during the run portion of the event compared to athletes who are running standalone marathons in comparable times (2:40-3:00) we see a big discrepancy. Clearly the professional ironman athletes are not arriving in T2 with full glycogen stores or they wouldn’t have to eat like that. I know it’s dangerous to compare yourself to the pros to learn how to go faster (Scott Molina on IMTalk last week had excellent stuff to say on this topic – listen if you’re interested) but I think it is indicative of the fastest strategy on the bike leg NOT being anywhere close to 100% conservative.