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Thursday 150326 - Rest Day/Open Gym

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Tammy and Morgan cranking out Thrusters on Wednesday morning.
Rest Day Reading

Editor's Notes: This one is from deep in the Sanctify blog archives and deserves to be re-run. Some good nuggets here, especially for you nerd types. Enjoy!


Exercise Physiology 101, Part 1
by Josh Earleywine


If you haven’t figured it out yet, I’m of the opinion that if you want to really reach your fitness potential then you need to not simply workout and exercise but start to understand the why/how/what of exercise. Therefore, in an attempt to help you get the most out of these workouts and understand how your body responds to them and improves, I’m going to start providing some additional info with each workout. Instead of just posting what we’re doing, I’ll also post what it should be training, that is, strength, power, speed, stamina, endurance, technique, etc. In order for what I say to make sense, we need to go over a little terminology and some basic exercise physiology (emphasis on the basic part). Don’t freak out now, I know that some of you are only marginally interested in this stuff, so I will be keeping it as easy to understand as possible. Honestly, I wouldn’t waste your time or mine explaining this if I didn’t really believe it could help you. So…

Exercise Physiology 101

Every time one of our muscles contracts, it does so using a fuel called ATP (adenosine triphospate). Yes, we eat carbs, fats, and protein for energy, but our muscles can’t use that stuff directly; those nutrients must first be converted into ATP to actually power muscle contraction. Think of it this way: ATP is like cash for our muscles. In life, when you receive a paycheck you can’t take that paycheck directly to the store and buy groceries (ok, maybe you can in some situations, but let’s not get cheeky here, stay with me). You first have to go to the bank, cash the check, then take the cash to said grocery store. Food is like a paycheck. In order to “spend” it at the muscle store it first has to be “cashed” via digestion and converted into ATP which is the only form of currency the muscles can use.

Unfortunately, muscles only have a limited supply of ATP (kinda like our cash in real life huh?). If the supply was unlimited, we could do cool things like run full bore, never tire, and win the CrossFit Games, but alas, it doesn’t work that way. When a muscle uses its stored ATP, it has to get replenished via our energy systems. There are 3 energy systems that our bodies use to recreate ATP. Two of them are anaerobic energy systems, meaning they work without oxygen present, and the third one is an aerobic energy system, meaning it functions in the presence of oxygen.

Aerobic Energy System

The easiest one to understand is the aerobic energy system. When we exercise we are either at an anaerobic or aerobic intensity level. That is, we’re either going to be using oxygen in our muscles faster than we can take it in through breathing (that’s anaerobic) or we’ll be using oxygen at a rate equal or lesser to the rate we can take it in (aerobic). When we’re exercising at an aerobic level, usually low to moderate intensity, our aerobic energy system can produce ATP for our muscles as fast as our muscles are using it. That means we could theoretically exercise in an aerobic state indefinitely; as fast as we’re using ATP we’re also reproducing it, so it’s all good.

If we classified all physical activity on a scale of 1 to 10, with 1 being absolute low-level walking type of stuff, and 10 being all-out, eyes-bulging maximal effort, aerobic activities would occur somewhere below a 6 or 7. Anything at an intensity greater than that would be anaerobic in nature. The easiest way to decide whether an activity is aerobic or not is to look at how long the activity lasts. The longer an activity lasts, the more aerobic it is. How long can you hold your breath for? 30 seconds? A minute? Maybe if you’re really good, two minutes tops? Well, that’s about how long you can function in an anaerobic state, so anything longer than that is going to have to be aerobically powered. Examples of aerobic activity: an Ironman, walking your dog, an easy bike ride on a Sunday afternoon, eating, even sleeping. Basically, anything that you could do indefinitely without tiring is aerobic in nature. How about trickier ones, like a recent workout I did:

10 rounds of:
Run 30 seconds @ 80% effort
Rest 30 seconds
Burpees for 30 seconds @ 80% effort/speed
Rest 30 seconds

Running for 30 seconds at 80% effort was definitely anaerobic for me; there’s no way I could have kept that pace much longer than 60 seconds at the most. Same thing for the burpees.  But if we look at the sum total of the workout, we’ll see that it had to have a strong aerobic component because the whole thing lasted 20 minutes. Yes, the individual components were anaerobic, but the fact that there was rest built in there allowed me to keep that pattern of work and rest going for a full 20 minutes. Take the rest out and I would have lasted a minute, maybe two at most. So you can see that if you want to assess the nature of an entire workout, you have to look at not only its parts, but also the sum of its parts.

Lastly, maybe this is obvious, but why should we want a strong aerobic energy system? For one, the majority of things that we do in life are aerobic in nature. As I sit here typing this article, guess what? I’m functioning aerobically. And from a workout standpoint, the people that tend to do the best on traditional CrossFit workouts, the ones whose third round of Helen isn’t drastically slower than the first and who keep a strong pace throughout a 2k row, have an aerobic system that can sustain them throughout efforts like that. It’s also the system that helps us recover between sets of heavy lifting in a couple of minutes and also between workouts in a day or two. Despite the bad rap the aerobic system gets from a lot of the CrossFit world (editors note: back when this was originally written, aerobic training was kinda poo-poo’d in the CrossFit world; I’d say that’s less the case now and people are realizing how important aerobic training really is), it really is foundational for almost everything we do. Oxygen is not a crutch.

So to summarize
  • Muscles need ATP in order to contract
  • There is a limited supply of ATP within muscles
  • Our energy systems produce ATP for our muscles
  • The aerobic energy system and therefore aerobic activities occur in the presence of oxygen
  • Intensity and duration dictate whether an activity will be aerobic or anaerobic
  • Generally, activities below 70% effort and longer than 2 minutes will be predominantly aerobic
  • The aerobic system plays a bigger role in most physical activities – both daily activities and workouts – than we realize
Stay tuned for part 2 where I’ll discuss the anaerobic energy systems. Until then, post any questions or thoughts you have to comments. Keep learning.

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