Bending Your Own Aging Curve – What to do About Age Related Muscle Loss
Part 2: FAST AND SLOW TWITCH MUSCLE FIBERS
A brief review of Part One “What to do About Age Related Muscle Loss”
https://mewithlauriebb.com/bending-your-own-aging-curve-what-to-do-about-age-related-muscle-loss-part-one/
I wrote about sarcopenia, the term for age related muscle loss and how it begins in our 30’s and accelerates dramatically in those over 60, especially those who are sedentary.
I also wrote that there’s a sure fire way to maintain and even build muscle mass as we age…….exercise with a strong nod towards resistance training.
Resistance training creates muscle strength through progressive overloading of the tissues so that they become more adapted and capable of force production.
Muscle force production allows us to lift, pull, twist, turn, and move heavier things (or even “normal” weighing things like a bag of groceries or our body moving up a set of stairs).
Fast and Slow Twitch Muscle Fibers
At this point in time, science indicates that we are born with a certain number of muscle cells, also known as muscle fibers. It is highly unlikely that we can’t increase the muscle fiber number we are born with, but using progressive overload/strength training it is possible to increase muscle fiber size.
This is muscle hypertrophy. I wrote about it in Part One (see link above).
With the increase in muscle fiber size (hypertrophy) comes that greater force production in the muscles. They get stronger and more capable of doing all the things we need and want to do for quality of life.
Exercise, specifically systematic resistance training, allows us to build strength in our given number of muscle fibers.
Broadly, our muscle mass is made up of slow twitch and fast twitch fibers.
The slow twitch fibers, smaller in size, are the work horses of endurance. They produce low amounts of force, but can maintain that force production for longer periods of time. This makes them more fatigue resistant. Think longer distance activities that require a steady constant output like walking, jogging, hiking, lifting light weights with lots of reps.
The fast twitch fibers, larger in size, are workhorses for generating strength, speed, and explosive power. They produce high amounts of force, but that force production cannot be maintained for long periods of time, so they fatigue quickly. These fibers are good for high intensity activities like sprinting, jumping, swinging a kettlebell, or lifting heavy weights.
Age related muscle mass loss selectively affects the fast-twitch muscle fibers at a higher rate than the slow twitch muscles.
I promise to explain this more, tell you the consequences, but first, some biology….
Trying to Explain some Physiology in Layman’s Terms
Unlike slow twitch muscle fibers, fast twitch muscle fibers have very few blood vessels and mitochondria.
Mitochondria are the energy-producing powerhouses of cells, extracting energy from food through cellular respiration (done with oxygen), which is released as ATP, the energy currency of the cell.
Fast twitch muscle fibers are anaerobic (without oxygen), and with less mitochondria, fast twitch muscles use fuel already present in the body, like glucose.
This isn’t a long term game, which is why fast twitch fibers show up for quick intense activities but aren’t the work horses for endurance.
Slow twitch muscle fibers have lots of blood vessels and mitochondria to fuel them for long periods of time. They are aerobic, using oxygen to generate energy. Remember, they are the workhorses of endurance, of keeping things moving for longer durations. Your body will tap into them before using fast twitch fibers.
Why it’s Essential to Train our Fast- Twitch Fibers for Age Related Muscle Mass
In terms of age related muscle loss, research indicates that we lose a higher ratio of fast twitch muscles fibers relative to slow twitch as we age.
It seems to me from the research I’ve done that scientists aren’t entirely sure whether we really “lose” these muscle fibers. But as we age, the fast twitch fibers are smaller and there are definitely less mitochondria in these tissues. Less mitochondria means less energy to produce force in these fast twitch muscle fibers.
The significance of this is huge for us “goldeners” because this means we lose strength and power capabilities as we age.
Although we all lose muscle strength and mass (sarcopenia), we tend to lose muscle power at a higher rate.
Although you may be thinking, “well, I’m not going to be running a sprint race anytime soon”, these fast twitch muscle fibers are the ones that propel you forward and up from a chair!
Yep, getting up out of a chair is a power move.
Many of the activities of daily living require muscle power.
The fast twitch muscle fibers help us with physical reactivity – getting out of the way, righting ourselves when we lose our balance, reacting quickly behind the wheel of the car, lifting a grandchild up out of the way of harm. These are all power moves requiring not only strength, but a fast “explosive” burst of muscle activity.
Most of you are probably walking for exercise. This is great for maintaining some of our slow twitch capacity because we use slow twitch fibers for “endurance”.
But if we’re not adding some sprinting into that walking time, fast hill walking, jumping, skipping, leaping, then our fast-twitch aren’t getting much stimulation to maintain or grow their size, function, and density of the mitochondria.
OK, SO IS THERE ANY GOOD NEWS IN THIS POST???????
Yes!!!
Just as you can mitigate some of the changes we find with age related muscle mass loss, you can also train to maintain and increase the size of fast-twtich muscle fibers!
Aging mitochondria, the energy producing cells in our muscle fibers, become less efficient at making energy. This may have to do with exposure to free radicals over time. If this theory holds true, eating a diet full of fruits and vegetables, good sleep, and aerobic exercise, some HIIT (high intensity interval training), and regular resistance training are the gold ticket winners!
Because I am a movement specialist, and not a nutrition expert, I’ll get back into my lane.
Here’s what you can do on the movement side of things:
Resistance Training
- This means lifting heavy shit (and “heavy” is different for each of us at this given moment).
- If you are currently lifting and can do a set of 10 – 15 reps of any given movement, then you are currently training slow twitch muscle fiber capacity.
- Begin to increase the weight you are lifting to target fast twitch training and to grow your strength capacity.
- When I back squat with a barbell or deadlift a bar off the ground, I do sets of 3 – 5 reps. In order to train my fast twitch fibers (and progressive strength/hypertrophy) it should be hard for me to finish those 3 – 5 reps.
- Cautionary statement – please work up to heavy weight, it’s incremental and should be progressive overload over time. It’s a commitment to time and consistency to build strength.
Aerobic Training
- Aerobic exercise is beneficial for making new mitochondria through a process called biogenesis.
- How hard should you be working when you train aerobically? Do a bit of research on Zone 2 training. Zone 2 training uses Slow Twitch Muscle Fibers and fosters mitochondrial growth (WE WANT TO GROW OUR MITOCHONDRIAL NUMBERS as we age!).
- A simple way to think about Zone 2 training is this…. Zone 2 should feel like a 5 – 6 out of 10 in terms of perceived rate of exertion (PRE scale) and this is going to be different for all of us depending on what we are currently doing.
- I should be able to hold a conversation while speaking in full sentences for the duration of this workout, but it shouldn’t necessarily feel easy and you will hear me breathing while I am talking.
- Again, as we start the journey to aerobic endurance or add on to what we currently have it is going to be different for each of us – I can jog or walk up a hill and hold a conversation while speaking, but I train Zone 2 jogging and hills almost every week.
- Zone 2 training probably needs to be performed for longer periods of time – 40 minutes or more and probably at least three times a week.
- Zone 2 training is easy to implement for walkers, joggers, runners, cyclists, swimmers… anything that gets your heart moving while you are preforming a repetitious full body activity. Walkers will have to work fairly hard to get to Zone 2, but it’s possible.
Interval Training
- Fast Twitch Muscle Fiber growth and maintenance need to be stimulated not only with strength training, but with activities requiring relatively fast movements – add some run sprints into your jogging, add some sprints on your bike trainer, add hills to your walks and walk up them very rapidly, add some jumping to your work outs (box jumps, jump rope, jumping jacks).
- Personally, I add some jumping into my strength work outs, I add some short sprint intervals to my weekly run, I jog up any hill I come to when I’m walking, I add sprints into my cycling (road or trainer), and I use my concept 2 rower in the garage for training that is considered much higher output than Zone 2.
STATEMENT OF THE OBVIOUS #1
To build and maintain our strength and power as we age we need to do activities that stimulate strength and power!
STATEMENT OF THE OBVIOUS #2
We are all currently moving at our own personal capacity. We must build our capacity, though with slow thorough actions. Please do not read this blog post, put on running shoes, and head out for a 3 or 4 mile run, adding hills and sprints if you haven’t trained your body to run 3 or 4 miles over a period of time! Allow for adaptation.
We live in a society where things are quick and easily accessible… getting stronger and more powerful is not a quick process and while the answer is “easy”, the process of implementing regular strength training, aerobic training, and interval training is not necessarily easy. But it’s sure worth it in terms of bending our own aging curves.
Disclaimer
I am providing information on training slow and fast twitch muscle fibers, but as a matter of health and safety, you are responsible for making choices with you own health and safety in mind. Talk to your Doctor, know your vital statistics and where you’re starting from, what medications you’re on and how they affect balance, heart rate, blood pressure, etc.
To best maintain your fast-twitch fiber size and physical power, you must perform activities that stimulate those muscle fibers.
Two means for effectively stimulating your fast-twitch muscle fibers are exercises that require relatively high resistance and activities that require relatively fast movements. One example of a relatively high resistance would be a strength exercise that you cannot perform for more than 10 repetitions. An example of a relatively fast movement activity would be a 100 meter sprint.
For instance, most of you are probably walking for exercise. This is great for maintaining some of our slow twitch capacity because we use slow twitch fibers for “endurance”.
But if we’re not adding some sprinting into that walking time, fast hill walking, jumping, skipping, leaping, then our fast-twitch aren’t getting much stimulation to maintain or grow their size and function.
Slow twitch muscles have lots of blood vessels and mitochodria to keep them going for long periods of time.
You body will choose to use slow twitch muscle fibers before tapping into fast twitch muscle fibers.
Slow twitch muscles have tons of blood vessels and energy-producing mini cells called mitochondria to help keep them going for long periods of time.
They’re your body’s first choice for muscle use before tapping into fast twitch muscles for shorter, more extreme bursts of energy.
Slow twitch muscles are aerobic muscles, This means that they use oxygen to generate energy in the form of ATP from their high concentration of mitochondria. They can keep you going as long as you get enough oxygen.
