A common misconception is that an endurance athlete will be good at sprinting or that someone who does a lot of high-intensity sprinting will be good at endurance training. In reality, these two forms of exercise use vastly different muscles and energy systems.


One way to think about this is to take the average NFL athlete and compare them to the average professional soccer player. An average player in the NFL weighs 242 lbs. If you remove offensive and defensive linemen from the equation, the average is still 215 lbs. Compare this with the average weight of a professional men’s soccer player which is 170 lbs. Massive differences, right? But why?


How wide the base of the triangle is, is our aerobic base: How long we are able to sustain a workload for — like playing soccer. How high the triangle is, is our anaerobic peak: How much we can exert ourselves at maximum effort — like every snap in football.


As we discussed last week, there are different types of muscle fibers: Type I and Type II. Type I fibers are our slow-twitch; they contract slower, less powerfully, but can keep contracting for long periods of time. Type II fibers are fast-twitch; they are explosive and can generate a lot of force, but they fatigue very quickly. Type II fibers are also much bigger than Type I fibers. An average individual has close to 50% of both fibers in their body (though it can fluctuate based on our genetics and age — if you recall last week’s piece, we lose our Type II fibers much quicker as we age).


Which muscle fiber types are more prevalent in a football player? How about in a soccer player? Now, ask yourself, what are the types of activities you enjoy doing or want to do more of? These are the factors that go into how you should train.


Does this mean that if you want to be lean and muscular, you have to train like a football player? Certainly not. The football player is an example of one end of the spectrum, where a soccer player or elite endurance athlete is at the other end. Many, if not most of us, find ourselves somewhere in the middle.


This brings us back to the metabolic triangle. If our goal is to be metabolically healthy — our cells are using the food we eat for energy by producing more ATP for doing the things we enjoy; not storing that food as fat — we should have a triangle resembling a right triangle.


I can safely tell you, as I learn more about this subject, I am nowhere close to that balance. My base is not wide enough to support my peak. What does this mean? Building a wide metabolic base involves doing something many of us hate… Zone 2 cardio. Zone 2 cardio is picking an exercise like running, swimming, or biking and doing it with a goal of staying in a heart rate zone of 2 for the entire time. 20 minutes, 30 minutes, 60 minutes. It depends on the individual and what their current aerobic capacity is.


It is worth noting this is not the same as steady-state cardio. For a highly trained individual, it might be. If you run marathons, you can probably sustain your zone 2 window at a steady pace for a long period of time. But for most of us, it usually involves low-intensity intervals.


How do you know where your aerobic capacity is? There are a few ways. Personally, I am a massive fan of metabolic testing. If done correctly, it tells you precisely what your five heart rate zones are, and what your aerobic and anaerobic capacities are. From there, you know exactly what kind of training your body needs based on your goals.


Another fairly accurate way is to judge yourself using the Rating of Perceived Exertion (RPE) method. There are five heart rate zones, and if you’re honest with yourself, it’s fairly easy to tell which zone you’re in:


  • Zone 1 — You can easily hold a conversation. Your heart rate is elevated, but you’re barely breaking a sweat.
  • Zone 2 — You can still talk and converse, but it’s much harder. However, you can still sustain your current activity for a long period of time.
  • Zone 3 — You can talk, but not in complete sentences. You can get words out, but you’re gasping for air in between.
  • Zone 4 — You’re able to get one word in, if any. You’re sweating, uncomfortable and exhausted.
  • Zone 5 — You’re likely within 90% of your maximum heart rate. You cannot get a single word out. You feel like we need to sit down or put your hands on your hips. It’s very difficult to control your breathing.


Knowing your perceived exertion, putting together a zone 2 workout involves a little trial and error. For one thing, it takes practice judging your exertion. At first, you’ll find it’s incredibly difficult to avoid zone 3 because it sneaks up on you, then hits you like a brick wall. Often these workouts should and will result in low-intensity intervals where if you’re running, it’s a steady mix of walk, jog, walk, jog. As your aerobic base improves, you’ll find you’re able to jog longer, maybe even forgo walking, and maybe even start running.


What about your triangle’s height? Your anaerobic capacity? This is not strength training; this is getting your heart rate up to its maximum and pushing your body to its physical limit. In the moment, it’s uncomfortable, it’s painful, and it really sucks. But it’s vitally important for our metabolism and our longevity.


As you will learn by listening to this week’s podcast recommendation, high-intensity anaerobic work helps boost your VO2 max — your body’s ability to consume oxygen and produce ATP, our body’s fuel source — and your cardiovascular health. If you’ve been an endurance athlete and hit a plateau where you stopped seeing improvement in your endurance, it’s likely because you weren’t incorporating any sprint work in your training. If you get lightheaded easily during intense workouts, a probable cause is your body is not efficient at using the oxygen you take in to produce ATP.


Moreover, exercising at high intensities helps improve a process called lipolysis, which is our body’s ability to break down stored fat into free fatty acids in the bloodstream which can then be oxidized for energy. In short, high-intensity exercise increases our body’s ability to use stored fat for energy.


As with anything else, doing more high-intensity exercise increases our capacity to do more high-intensity exercise. But how much is too much, and how much is right for you? Again, this is where I cannot recommend metabolic testing highly enough to get your precise recommendation for your current physical condition. Especially given how uncomfortable high-intensity training already is.


Aside from metabolic testing, my first recommendation is to ensure your body is healthy enough, having your heart and lungs tested by your doctor. If you are healthy enough but deconditioned or not used to pushing yourself to peak exertion, even just one time per week for 9 minutes at a time can yield substantial results when paired with other forms of exercise.


In summary, unless we are training for a very precise event that requires us to be at one end of the fitness spectrum or the other, it behooves us to optimize our body for both a wide base and a high peak to our metabolic triangle. It’s very possible to do, but it does take discipline and often doing things we don’t want to do. Coming away from writing this piece, I know exactly what I need to work on. Perhaps you can even expect to see my own metabolic test results in the near future!


What did you come away with? How does this knowledge impact the way you want to train?


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