This will be the final segment of my series on Metabolic Efficiency. In Part 1, I discussed the history and gave a description of the Metabolic Efficiency Test (MET) and then in Part 2, I gave you a recap of what the test actually consisted of. So to wrap things up, I’m going to show you my results and tell you what they mean. The team at FitnessRx did a wonderful job of summarizing my test results and giving me lots of charts and graphs…which you know I LOVE!
There were several things that I wanted to take away from this test, but the biggest was to learn at what intensity I switched from burning mostly fats as fuel to burning carbohydrates. This point is known as the crossover point. Even though we burn a mix of both carbohydrate and fat to fuel exercise up to maximal intensities, as the intensity of your exercise increases, your body prefers to use more carbohydrate for fuel. This point will tell me at what speed (running) and heart rate I need to start including carbohydrates into my race nutrition. The chart below shows where my crossover point occurred.
This crossover point is also know as a Metabolic Efficiency Point (MEP). For me, it occurred at a pace of 7:36 minutes per mile, a heart rate of 162 and a perceived effort of 6. This means that I am efficient at using internal fat stores for energy at a pace less (slower) than 7:36 and a heart rate of less than 162. I was at at 49% carb burn and 52% fat burn at 7:36 min/mile but 59% carbs/42% fat at 7:19 so in all actuality, the crossover occurred somewhere between these two paces but much closer to the 7:36 min/mile. The goal of improving Metabolic Efficiency training is to try and move this crossover point to the right. If I can move it, it means that I have continued to teach my body to use more fat (and therefore less carbohydrate) at higher intensities (higher heart rate). This only tells me part of what I need to know though. The other big question is HOW MANY calories of fat and carbohydrate am I burning at these different intensities?
This next chart shows a breakdown of my “10-30%” calorie intake needs. It is now known that while exercising, you can only digest and use approximately 10-30% of your calorie expenditure. This chart shows me, at different efforts, how many calories I am able to consume and use while exercising. This graph will help me plan my nutrition for a long training session or race. It is important to keep in mind here that most people do not aim to replace their total calorie expenditure unless an athlete is truly too thin. Most athletes are not interested in replacing the calories expended through fat.
So if I take my 8:13 min/mile pace as an example (close to my aerobic zone heart rate), you can see that while I am burning a total of 987 calories per hour at this pace (black text at the top of the red/blue bar), I can only digest and actually use 10-30% (99-296 cal/hr) of these.
So the next obvious question is…what type of calories should I be taking in as I’m exercising? Should they be carbohydrates or fats? Many athletes consume their calories based on carbohydrates only. For example, a typical gel will have 100 carbohydrate calories or 25 grams. So based on my results, if I was going out for a long run in my aerobic heart rate zone (8:13 pace), I would burn 987 calories/hour but only 415 of these are carb calories. So with the 10-30% rule, I need approximately 42-124 carb calories/hour. This may seem like a pretty big range of calories, but it tells me that I definitely need less than the 300-400 calories per hour that most “experts” recommend consuming during long periods of moderate exercise. This is a perfect example of why there is no such thing as a “one size fits all” nutrition plan.
So now that I know how many calories I need to try and replace during endurance events (like Ironman), I can dial in my nutrition plan and practice it during some of my longer training rides and runs. But what about shorter races where my heart rate is above my aerobic zone? Having this test done has taken out all of the guess-work for nutrition during those races as well. The chart below gives me details on how many calories I need to try and replace at various intensities, paces and heart rates…this is important information!
I wish that I would have referenced this data before doing back-to-back races this past Saturday. I clearly did not consume enough calories during the two races and ended up bonking on the run of the second race. Looking back at my race data, based on my heart rate and perceived effort, I should have been taking in between 150 and 200 calories per hour…instead of the 100 calories or so that I did. From now on, I will reference this chart when thinking up my nutrition plan for any race.
This is just some of the data that I was given following my test at FitnessRx. Although I had a pretty good handle on where my heart rate and pace zones were, I had no idea how many calories I was burning and at what heart rate and pace I needed to start replacing calories in order to sustain the effort. I’m all about controlling as many variables as I can on race day. A solid nutrition plan is often a variable that people don’t pay much attention to, but it can make or break your race.
I highly recommend getting this test done if you want to perform at your best! I plan to continue to try and improve my Metabolic Efficiency through both diet and exercise and will likely have another test done just prior to Ironman Louisville in October so that I can dial things in leading up to race day.
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