I love data. I'm fascinated by how our bodies adapt to exercise and nutrition, and with the technology that allows us to see objective data that confirm fitness progressions. In my years as a Personal Trainer and Metabolic Tech, I operated hundreds of resting and treadmill assessments (formally called Resting and Active Metabolic Assessments, respectively). I gained a lot of insight into how nutrition impacts our metabolism during exercise, and how chronic high-intensity exercise also blunts fat-burning. While I loved #allthedata, I also had to be able to explain the results to members who don't share my passion for science, in a way that's easy to digest, so to speak. I'll do my best to share some insights about metabolism with you, based on my own results.
Back in my personal trainer days, I'd often test 3-4 times a year or more. I fell off the routine a bit when I wasn't training regularly, but as my training is ramping back up, I wanted to establish a new baseline to compare future tests to. I also wanted to make sure I was progressing well with the workouts MK was giving me, and that my nutritional choices were keeping up good metabolic efficiency. I scheduled a test with Heather Kick, the Metabolic Specialist at our Chanhassen Life Time Fitness location. Heather is an avid runner and triathlete, so I knew she would be able to share some specific applications based on my results.
The Active Metabolic Assessment (AMA) includes two parts - a warm-up protocol and the main assessment. The warm-up primes the body's fat-burning engine, and also allowed my stiff muscles time to warm-up before we really got cranking. During each protocol, I wore a mask that is connected to the New Leaf metabolic cart. The cart collects a sample of each breath, measuring the ratio of carbon dioxide & oxygen exhaled. This is displayed in an RQ (Respiratory Quotient) value. At the beginning of the assessment, I had an RQ value of 0.71, which indicated that I was burning nearly 100% fat, with very little energy coming from carbohydrates. As the test progressed, my fat-burning stayed very strong until I reached 10.1 mph (under 6:00/mile pace). My legs were dying at that point, as we've been focused on rebuilding my aerobic base, and haven't done much speed-endurance work yet. I'll do a retest in 1-2 months to see if I can reach some faster paces, but for now my test ended at 10.1mph because I simply couldn't continue any longer.
Here is some of the information I received from doing the AMA test:
Heart Rate Zones:
Two key points here are (Aerobic) Base at 151HR (heart rate in beats per minute), which is where I'm burning 50% fat and 50% carbs. AT (Anaerobic Threshold) is effectively the end of fat-burning, at 167HR. When I did my very first metabolic test about 10 years ago, my Aerobic Base was much lower, as I was eating a high-carb diet and had recently changed from being a 5K track athlete to a marathon runner. I was burning almost all carbs, and I would feel exhausted and hungry after long runs as my blood sugar crashed and donut cravings hit hard. I was not at all efficient at burning fat, and it showed on race day. During my first two marathons, I hit the wall HARD by mile 20. Once I turned around my nutrition and improved my fat-burning, I was able to run more consistent paces in the 2nd half, and my marathon times dropped from around 3:15 down to 2:59 on a good day.
This time around, looking at my metabolism alone, I expected to be able to ramp up my pace on Active Recovery & Easy Runs. My heart rate in Zone 1 & Zone 2 tops out at 151 & 158, respectively. I've been doing easy runs at 140HR, and Active Recovery runs at 120HR or below. I don't mind 140 for my easy runs, but 120 is so easy that on hot (or hilly) runs I still end up walking some.
MK vetoed that idea, reminding me that training is about more than metabolism alone. Her reply to my inquiry of if I could raise my HR cap on those runs?
MK: "Nope. Just means we can relax on fartleks and go a little harder on 2x2's etc. It's more than metabolism... you know that! We need way more strength and time between the recent hammy incident before I'm going to be comfortable pushing you. Easy days stay easy for now. #buildontbreak"
Once again, MK reminds me of why I need a coach. The data is valuable and will guide her programming, but my metabolism is ahead of my joints & muscles at this point. Left to my own devices, I likely would have started pushing harder and risked injury because my post-baby body hasn't caught up yet. As a tech, I saw far more people with the opposite problem. I remember countless tests with members who were pushing hard all the time in workouts. They could go hard and fast for the test, but their fat-burning metabolism wasn't keeping up. It wasn't uncommon to have a runner who joined a marathon class thinking it would be a sure-fire weight loss strategy, only to be frustrated when the weight didn't drop off. A simple AMA would show that they were burning mostly carbs during exercise, which not only led to little or no weight loss, but could actually increase their appetite post-run. Some simple changes to balance carbohydrate intake with more protein and/or healthy fats often led to better results.
Calories Burned, Fat vs. Carbs:
I was thrilled to see that in zones 1-3, more than 50% of my calories were coming from fat. That's a good sign that my 'engine' is running efficiently, and my aerobic base development is coming along well. In my prior experience as a metabolic tech, I noticed that fat-burning during exercise could be improved much more quickly through nutrition than through changes in training. Both are important, but in many cases, transitioning from a high-carbohydrate diet to a more balanced low or moderate carbohydrate diet would quickly change a runner's metabolism to support better fat burning.
Essentially, if you eat lots of carbs, you can expect to burn mostly carbs during exercise. If you eat fewer carbs, you can expect to burn more fat. That is good news for runners who have weight-loss goals, as well as long-distance runners with performance goals. In events lasting two hours or beyond, being able to utilize more fat during exercise means less reliance on carbohydrate intake during races & training. That reduces the chance of hitting the wall, or experiencing GI distress from taking in more carbs on the run.
As my fitness improves, I'd like to see my fat-burning increase in Zone 1, and hold steady in Zone 2. I wouldn't be surprised if it actually decreases in Zone 3 as my speed improves. It is normal to see some tapering off of fat-burning as a runner approaches AT, and the metabolic demand becomes so strong that the aerobic/ fat-burning metabolism can't keep up. That would be an OK trade-off as long as my paces improve and my fat-burning in Zone 3 stays above 30-40%.
The AMA isn't a true VO2 max test, as that is generally done is a clinical setting. The nature of running to exhaustion is risky, and doesn't provide that much additional value for most members. However, the metabolic cart does measure VO2 peak, which is simply the highest VO2 (volume of oxygen) reading observed during the test. At this point, I don't have the speed endurance to push hard much beyond my AT, so the peak reading was really at the top pace I could sustain. I expect that to improve significantly as my fitness comes back together, as I've had a measurement as high at 68.5 on a past test. That's unusually high, but goes back to my competitive days as a collegiate runner. Anything over 40 is in the 'optimal' category for women in my age group.
Everyone has a unique capacity for VO2max. There is a significant genetic component, but virtually every runner can improve their VO2max with quality training. It also increases directly as body weight decreases, because it is measured relative to body weight (in kg). Within reason, if a runner is able to achieve a more lean yet healthy weight, VO2max would increase.
The AMA printout also comes with a planned warm-up (above) and a workout calendar. I have personalized workouts from MK so I won't be following them precisely, but I enjoy seeing what is prepared for all test participants. Both the warm-up and suggested workouts have a purpose of improving metabolic efficiency, aerobic base and overall aerobic fitness. The test results helped MK confirm that I'm ready to take on a little more intensity on the hard workouts, while I continue the focus on rebuilding my base and core strength. I look forward to testing again in 6-8 weeks to see my progress!
Ironically, between the time I did the test (over a week ago) and published the blog, the baby has gone through a sleep regression. I'm back into sleep-deprivation and coffee-reliance mode, and am no longer complaining about the lower HR workouts. It's hard to even reach 140 when I'm not getting quality sleep, and some of my runs have slowed to a walk, or have even been cut short. MK and I talked on the phone yesterday, and she encouraged me saying "It's been at least 6 weeks since your last rough week, so it's no big deal. Your speed & aerobic base are fine." It's helpful to have that reminder not to freak out over a bad week of training, when my body obviously needs more rest.
Want to learn more about how training & nutrition impact your metabolism? Check out "What should I eat before a workout" and other articles from LifeTime-WeightLoss.com. Stay tuned to my Chasing Potential blog for more posts to come on nutrition and metabolism as well! I'm always tweaking my own nutrition to find out what works best for my body and training, and I plan to share some concepts and recipes along the way.
Enjoy the end of summer as you chase your potential!