I woke at 4:30AM and drove across the desert to the University of New Mexico Exercise Physiology Lab. The lab techs put me on a scale for a weight check and then fit me with a mask that will measure all of my oxygen consumption and carbon dioxide discarded. The mask pulls on my neck and the nose clip forces me to breath exclusively through my mouth. I’ll be doing two tests on a treadmill. The first is a VO2MAX an all out 12 minute effort for me to run as fast and steep as I can. My heart rate, O2, CO2 are being carefully monitored to determine my best fat burning and associate them with heart rate values. Two weeks later I return and run a much slower test called VO2SubMax which takes an hour. The VO2SubMax is about running at the most efficient paces in order to find the ideal heart rate range for optimal fat burning.
The FASTER study was released by Metabolism Journal in March of 2016. This study inspired the above testing. What I learned from FASTER was confirmed with my own anecdotal test results.
- The elite low carb runners burn between 1.15 – 1.74 g/min of fat. I’m middle of the elites at 1.36 g/min. This numbers were only apply to the full on VO2MAX test.
- Optimal fat burning occurs near 64% of VO2MAX. This is a heart rate used to test the FASTER participants for three hours on the treadmill with the masks on. My testing revealed that my best sustained fat burning was exactly at 64% of my full effort (117 BPM [64%] out of 183 BPM [MAX]).
I can rely on fueling from 80% of my own fat if I keep my heart rate between 115-145 BPM.
- Phil Maffetone’s 180 formula also appears to be quite accurate. According to Phil based on my age (40) I’m able to run at 180 – AGE and I get a +5 for being fit so 145BPM as a maximum for ideal fat burning. My VO2SubMax test confirmed that I was still burning fat at almost the same levels at heart rates between 125 BPM up to 145 BPM.
Warmup and reasonable pace seem crucial to maintaining a high percentage of fat burning.
- I’m able to go for 5-10 minutes on just ketones (fat burning being over 100%).
- Garmin’s Heart Rate Zones appear to be dead on (warm-up | easy | aerobic | threshold | maximum) completely line up with the data gathered.
- My peak was 1.36 g/min and only on the VO2MAX as that is what the professional ultra runners seem to average.
While my findings agree with the FASTER study please keep in mind I am not a professional ultrarunner. I also happen to be older, slower, shorter and even slightly fatter than most of the studies participants.