Back in February 2021, Katie Solbo came to the FreeSpeed lab to do metabolic testing as she was preparing for her triathlon racing season focusing on 70.3 and Ironman although due to Covid, the Ironman ended up canceled. Before the test, below is her training distribution by Time in Zone (TiZ) from January to December 2020. She follows a 6 zone scheme as Zone 1 FatMax, Zone 2 LT1, Zone 3 Tempo, Zone 4 LT2 (aka FTP), Zone 5 VO2max and Zone 6 Anaerobic.
Katie spent around 50% of her training at Zone 1/2, 43% at Zone 3/4, and 7% at/above zone 5/6. All this while riding on average ~5hrs per week, with some weeks riding as much as 7:30-8:30 hrs.
Her metabolic test results are shown below and they told a common story that we see with many Triathletes; even though she had a rather strong VO2max of 52.1 ml/min/kg at 300 watts and FTP 227 watts, her power/heart rate at her first lactate threshold (LT1) was below average.
This was noticeable on her lactate curve as she kept accumulating lactate as the intensity increased and it raised quickly at the LT1 which is the first significant inflection point above her baseline. This meant that her LT1 took place at ~175 watts or 58% of her power at VO2max while her LT2 (what most know as FTP and it tends to be overestimated for many) took place at ~227 watts or 75% of her VO2max power.
This meant that while she could meet the energy demands to produce ~227 watts for 1 hour of 15 kcal per min (kcal/m), 98% of the energy was supplied from carbohydrates. And even at lower intensities, her body would supply energy from carbs at a faster rate than fat.
This is clear on the following graph; at LT1 ~175 watts with an energy expenditure of 12.7 kcal/m, 45% came from fat storage, and the rest from Carbs (~7 kcal/min). By 210 watts she needed 13.7 kcal/min, yet she was only supplying around 15% of the energy from fat and by LT2 it was almost zero percent.
This is a big issue for endurance athletes as we can only store a limited amount of carbs in our bodies (~1 pound) and not all can be used, while we can store a lot more fat (i.e. a 150 lbs athlete with 12% body fat can store 18 pounds!). Given Katie's Ironman goals, her LT1 which is the intensity an athlete could race it (plus/minus) and her energy expenditure of ~7 kcal/min from carbs. It meant she would need to supply quite a bit of carb (80-100 grams per hour) and still she most likely would run low on energy for the run.
So come one can an athlete have a strong VO2max and/or FTP, yet, have an underdeveloped LT1? Because spending time improving VO2max is primary a central adaptation (related to the cardiorespiratory system) while LT1 is primarily a peripheral adaptation (at the muscle level) and it relates to metabolic capacity or how efficient an athlete is at supplying fuel for energy aerobically. FTP is a combination of both central and peripheral adaptations, however, if the training is not properly supported with enough LT1 training, the body will gravitate to supply the energy demands from carbs primarily which hinders metabolic capacity at lower intensities.
On the other hand, improving your LT1 can improve all intensities above. Although, it is not just about doing one type of training or another. It’s about targeting primarily your main limitations based on your 1) needs (metabolic) and 2) goals (racing distance). At times, this may mean spending far less time at LT2 or VO2max and more at LT1 or lower but not completely abandoning LT2/VO2max. And that’s exactly what Katie did under her coach’s advice and based on the metabolic test results. In other words, she focused on targeting the right training intensities.
Fast forward to March 2022 and below is the TiZ distribution for her training, particularly over the last 5 months. As you can see she spent 78% at Zone 1/2, 21% at Zone 3/4, and 1% at Zone 5/6
Also, because she, unfortunately, had to deal with a foot injury, she was able to do a bit more riding and she average ~ 6:48h of riding per week.
Below are her latest metabolic test results; as you can see her LT1 improved by 25 watts to 200 watts. Better yet, her lactate curve “flattens” a bit from baseline to LT1 meaning, she has improved the rate at which he supplies fat for energy demands. Also, her LT2 improved to 240 watts despite spending less than half of the time focusing on it as the previous year, Finally, her V02max improved to ~315 watts at 55.1 ml/min/kg; hence also a higher Vo2max even with a little training emphasis on it!
This meant that her LT1 took place at 63% of her power at VO2max (5% improvement) while her LT2 (FTP) took place at ~240 watts or 76% of her VO2max power
Finally, the way her body meets energy demands at a given power changed rather successfully as shown below as now she supplies a greater % of fat for fuel at higher power. At LT1, now ~49% of the total energy expenditure comes from fat, a 4% improvement. At 220 watts, she now supplies 26% of fuel from fat and even at LT2 she now supplies 5% of fuel from fat. Katie not only improved the height of the fueling utilization curve (more kcal from fat per minute) but also, the breadth of her curve (burns fat at higher intensities).
In summary, by performing a metabolic test, Katie was able to pinpoint the areas of her physiological profile that needed more attention given her needs & goals and by spending time targeting the right intensities under her coach’s guidance, she was able to improve various physiological markers like FatMax/LT1 as well as other markers like LT2 (FTP) and VO2max despite not specifically targeting those like many programs tend to mostly do. More importantly, she improved the areas that were a bit of a weaknesses for her but are vital for her Ironman/70.3 goals.
Now with her latest testing, she and her coach have reassessed what areas need further development and attention to plan accordingly. We can’t wait how much she gets to improve when we test again in 6 months!
If you want to learn more about our metabolic test or schedule an appointment, follow this link.