|Muscle Fibers 101|
There are entire books written on the differences between Muscle Fibers, delving into how they’re triggered, the mechanisms by which they fire based on the activity we’re engaged in, and a variety of other fascinating physiological components involving their functionality. For our purposes here, we’re providing the simplest of overviews, breaking them down into their two primary classifications: Slow-twitch and Fast-twitch. Slow-twitch muscle fibers, also known as Type 1, are used for activities that require no bursts of speed. Moving around in a chair, walking, or even steady-state cardio activities like jogging and low intensity rowing, biking, and swimming. When operating within this non-strenuous state, we rely exclusively on these slow-twitch fibers.
Fast-twitch muscle fibers are composed of two subtypes: Type 2A and Type 2B. Type 2A fast-twitch fibers activate when we take things up a notch and our Type 1’s need a bit of help to meet the energy demand. Type 2B fibers kick into gear once we’re in overdrive. It’s easy to think of the difference between each as they relate to running. A marathon runner will be relegated to Type 1 usage only. Someone running an 800m race or seeking to hit their PR in a one mile run will be relying primarily on Type 2A fibers. You guessed it, a sprinter will begin tapping into their Type 2B fibers the moment the body realizes its exceeding its Type 1 and Type 2A limitations.
Where The Rubber Meets The RoadSeeking to improve the health of our mitochondria is a no-brainer, seeing how vital it is to our well being and to our ability to age well. Exercise also correlates directly with better health, in some way or another in all of its various forms. But is there a union where the two intersect, that where a certain type of exercise can maximize the mitochondrial strengthening we yield from the activity? It turns out that there is.
Type 1 muscle fibers (our “slow-twitch” fibers used for lower exertion activities) have the highest amount of mitochondrial content versus the other two types. But simply walking all day (though far superior to remaining sedentary all day) doesn’t push those slow-twitch muscle fibers to their limits, and that’s truly where the most potent benefits lie. This takes us back to Zone 2 training. Boiled down, Zone 2 is the place where your mitochondria are producing the maximum amount of ATP under purely aerobic conditions, using only Type 1 muscle fibers. When going a bit harder, entering us into Zone 3, we experience an uptick in lactic acid production as a result of tapping into our glycogen, compelling us to begin burning more carbohydrates versus fat. It also turns out that fat can only be burned within the mitochondria. Therefore, with Zone 2 training we’re able to exercise our mitochondria to their fullest extent while preferentially converting fat into energy.
(It’s worth noting that there is plenty of room for exercise in those upper zones. Like a balanced diet consisting of a variety of macronutrients like fats, carbohydrates, and protein, a balanced exercise protocol may also consist of a variety of training types. For a refresher on the benefits of those upper zones, refer to our prior Health Hack here, where we provided some useful guidance on how to use glycogen-dependent exercise to best mitigate the effects of falling off of the diet wagon during a holiday gorge. For those planning an uncharacteristically decadent Easter meal tomorrow, this past article would be right up your alley. But gorging aside, benefits exist across all zones of exercise, and we’ll delve more deeply into some of those other zones down the road.)
The Best Ways To Enjoy Zone 2 TrainingMy largest gripe with Zone 2 training was always the boredom piece. There was a perpetual “when is this going to end” aspect to any jogging session. Then I discovered the bike. While biking, I was moving outdoors, able to get a taste of nature and sunlight. Then when the winter months set in and I converted to a stationary bike, it became an opportunity to detach, throw the phone on airplane mode and tune into a podcast. Once spring came near I came upon trail running, which took the aspects I enjoyed most about biking and brought them to the type of exercise I’d always resented the most, which was jogging. But in its new form, it had a whole new life. Having come to enjoy jogging in the woods, quickly jogging in general became enjoyable, without any headphones or podcasts. It’s fascinating how I’m suddenly eager to go for a jog, even on a lousy day. I’m sure that learning of the laundry lists of benefits that mitochondrial training possesses had plenty to do with it, but there’s also the aspect of learning to enjoy movement without complete and utter mental devotion to the task at hand. The mind has a hard time wandering when the task at hand (such as sprinting) is so grueling and demanding. But when it’s an activity (like jogging) that can exist almost in the background, suddenly it’s an opportunity to think, reflect, and in some cases even learn (with a podcast playing while enjoying a bike ride) while moving, and there’s something soothing and therapeutic about that.
If you own stationary equipment at home such as treadmills, bikes, rowing machines - lucky you. These machines are Zone 2 Heaven, and the gyms where we typically find them in abundance are still closed. And a helpful tip - if the talk test is deceiving you and you’re not about to start pricking your finger mid-workout to measure your lactate, there’s another way that closely approximates if you’re in the zone. If the machine you’re using has a Heart Rate Sensor or if you have access to one via an app on your phone, a general approximation for determining Zone 2 is to subtract your age from 180. At 35 years old, I would be aiming for a consistent heart rate at or near 145. This is far from precise, but it’s a helpful guide when available.
With most of us still restricted to our homes most of the day, this is actually a nice opportunity to explore forms of Zone 2 training in the outdoors, while remaining conscious of proper social distancing. We can reap the ever-important Sunshine Vitamin while earning a brief reprieve from quarantine. While employing the criteria listed above for knowing when you’re fitting snugly into that Zone 2 status, any of the following exercise practices can be deployed:
• Jogging (indoors, outdoors, on a track, on a trail)
• Biking (stationary or live)
• Rowing (all forms)
• Hiking (the moderately intense version)
The list goes on and on. It’s best to choose the types that most suit your fancy, and set realistic targets. For the sweet spot within the sweet spot, aim for 2-3 hours per week of straight Zone 2 training.