Back in May 2021, I did a Metabolic Lactate Testing to identify in what areas of my physiological parameters I needed more work for my cycling fitness. My results shown below told me that my FatMax which is the point my body is utilizing a bit more calories from fat than carbs as a source of fuel was around 169 watts/ 127 heart rate occurring at a lactate blood accumulation of 1.5 mmol/L. The max fat burning rate then was ~ 4kcal per min. For reference, Top Agers in Ironman can burn around 6-7kcal/min and Pros >7Kcal/min from fat. Mine, even for AGers was rather low. More so, my Lactate Threshold (LT1), the point at which your body burns around the same number of calories from fat and carbs, and, the point your body can clear lactate a bit more efficiently, was “only” around 185w/133 heart rate.
All this despite me hitting some of my best Functional Threshold Power (FTP) in years at ~275w or 4.18 W/kg pre-test by doing what I refer to as a more “traditional” training approach:
1. Increase FTP by doing 1-2 sweet spot rides
2. Improve aerobic capacity (VO2max) with short intense intervals (1 ride)
3. Improve “fatigue resistance” by doing some mid/long rides at lower intensities (i.e. ~70-75% FTP). (1-2 rides)
You can see my FTP and training distribution from January 2021 to May 2021 pre testing below and how for those months, less than 57% of the time I trained at Zone 1-2 (green), 40-45% was spent in the "pink" Zone 3-4 riding tempo, sweet spot or FTP type of rides and 5% of the time I spent it near VO2max
How come two important parameters like FatMax and LT1 were so low? Easy, first of all, FTP is just a way of using power in a field test to “guesstimate” the point at which our body achieve what’s known as the Lactate Threshold 2 (LT2) – This LT2 is the point at which our bodies are already accumulating great amounts of lactate, yet we can still achieve steady-state clearing lactate as fast as it accumulates.
Think of it like this, anything under LT1 which is our 1st physiological border, you can exercise for hours without experiencing “significant” amounts of fatigue. Anything under LT2 is more physiologically taxing, but you can still sustain this for up to 1 hour if riding at/near LT2 or say complete a marathon, or a 70.3 when exercising between LT1 and LT2. And anything over LT2 which is like our 2nd physiological border, well you are on the clock and you’ll only be able to handle said effort for a shorter period (like a 20 min test, or a 5 min VO2 max test).
In my case, you can see during my test that my lactate blood concentration changed a little from FatMax at 1.5 mmol/L to LT1 at 1.9 mmol/L yet, it then accumulated quicker from LT1 1.9mmo/L to LT2 3.6 mmol/L, and above LT2, it just built rather rapidly hitting 11.3 mmol/L at VO2max!
Also, FTP tends to get overestimated for most athletes while LT2 tends to occur at lower watts/HR. Remember FTP should be “the power/intensity you can sustain for 1 hour”, we never test it that way! Instead, we may use the critical power model doing shorter effort (i.e. 5 min, 10 min, and 20 min) which is what I normally do and this method tends to place you in a closer range to your true LT2. Or the most popular yet more inaccurate version which is doing a 20 min maximal effort and taking 95% of that (which is what I did pre-test) or worst, assuming your 20 min max effort is your FTP! Well, since I was lazy and just took FTP from a Zwift ride (which uses the inaccurate 95% of 20 min power), it was in a rather inaccurate estimate (~275w) while my actual LT2 was more like 255w. (If I would have done my usual Critical Power model test, it would have been closer at 265w)
With my overestimated FTP it’s easy to see how riding at say 70% of FTP (192w) vs FatMax (169w) are 2 different things. Based on that traditional FTP training approach, my “easy rides” weren’t targeting FatMax or even LT1 for that matter. And by targeting sweet spot/FTP consistently when I already had a "solid" level in that area, I wasn't addressing areas I needed to become a better mid/long course triathlete.
Why is FatMax/LT1 so important anyway? Lactate is the byproduct of converting carbs into fuel by fast-twitch fibers which release it into the blood and, it’s shuttled to the slow-twitch fibers to get reused as fuel getting it cleared out of the blood. But for that, you need lots of healthy/efficient mitochondria in those slow-twitch fibers, and in absence of that, when intensity increases, lactate accumulates faster than it clears therefore your body just gets used to having more lactate concentration and will tend to prioritize burning more carbs over fat, pretty much anytime you exercise above LT1 (i.e. training at tempo/Sweet spot/FTP/VO2max).
By doing training between Zone1/2 (FatMax and LT1) it builds more powerful, healthy, and efficient mitochondria which will allow you to burn more fat vs carbs at those intensities, clear more lactate, reuse lactate as fuel, and sparing more of your carbs reserves which in turn can make your LT2 better!
This can be great if your physiology already has a strong FatMax but not so much LT2 or if you have a low aerobic capacity (VO2max). But if it’s like mine was in May known as a "carb-burning machine" with a solid FTP/Vo2Max, well, despite that you will still struggle with long stuff because you burn through your carbs reserves quicker. For instance, at 145 pounds and 15% body fat, I can store about 21 pounds of fat (that’s 76,000 calories!). While for carbs, in general, we can store ~2500-3500 calories (depending on weight, height, gender, fitness level, etc.) Let’s be generous and say I can store 2750 calories of carbs. Well, you can see how carbs are a big “fuel tank” limitation.
With the test information, I spent the last 4 months focusing on improving my FatMax and LT1 and you can see my training distribution since May below. In that time, I averaged 4 rides per week. 2 of those were 1hr doing Zone1/2 only while one was 2+ hrs. And the 4th ride was between LT1/LT2 in the form of Tempo or Sweet spot swapping it for a VO2max session every 3 weeks. All sessions were either based on power or heart rate depending on how my body felt on that given day due to sleep, nutrition, stress, recovery, weather (heat in TX summers means higher HR), etc. If feeling good, I went by power, if feeling fatigued I went by Heart Rate.
With this approach, I spent training at zone 1-2 (green section) as follows: May 70%, June 68%, July 88%, August 98% and so far 90% in September.
Below is my power distribution using Training peaks iLevel zones; for reference, their endurance = my Zone 1-2, Tempo & sweet spot = my Zone 3, FTP = my Zone 4, and FRC/FTP = my Zone 5. Again, when I was riding by power, you can still see since May, about 80% of my training was Zone 2 or lower (endurance), only 14% was Zone 3 (tempo/sweet spot) like 4% was at FTP (zone 4) and even less doing zone 5.
Here is another distribution based on HR. This shows how guiding your training by HR can be a great tool sometimes and others it may not. In super-hot/humid days in TX, just guiding everything by HR could result in undertraining riding lower than FatMax/LT1. But you can use HR earlier in the summer while your body heat adapts to prevent you from overdoing it, and later on, you can train more by power at a slightly higher HR and be ok. On the flip side, guiding some sessions HR only can be a fantastic tool when you are fatigued, maybe getting sick, when stressed (if you use Heart Rate Variability), etc. will prevent you from pushing “too hard” on that given day.
So, with my super simple training approach, what were the fitness gains and subsequent testing results? Well, as shown below, my FatMax improved by ~21 watts and LT1 by ~26 watts. Better yet, my LT2 (“real” FTP) also improved a little despite me not caring nor focusing on it at all, and my VO2max stayed about the same. Better yet, all markers improved while Lactate concentration stayed the same though HR was slightly higher but understandable as now I’m producing a bit more power. What’s best my fat utilization improved to 5.4 kcal/min. If I keep this rate of gains for Ironman next year, I may get my fat burning into the 6-7 kcal/min range top AGers tend to have!
So, what’s the message I want to convey?
We shouldn’t just follow the traditional “a higher FTP is better” approach as having a strong FTP may not be what you need for a strong 70.3 or Ironman.
Your FTP is guesstimated using a 20 min test will be overestimated. It's good for the ego but not for your training.
FTP or Critical Power or LT2 for that matter is just ONE of various physiological markers that are very important for your training development. By only focusing on one, you may be missing a great opportunity to improve your real "weaknesses".
Don’t be afraid to target your specific needs thinking you’ll “lose” your top-end power/speed. You won’t! It will most likely stay the same or it may improve it without even focusing on it.
Finally, get some metabolic testing done. It's among the simplest yet more powerful ways to get a deeper insight into your physiological training needs. This will allow you to look at your fitness “engine” in detail, allow you to make better inform training decisions and achieve greater fitness gains. You can do so at a local university in the sports physiology department, with a good coach, or at the FreeSpeed Lab.
Cheers.