More Zone 2 Training - Sometimes Slower (and longer) is Better
New Research—and Realizations
Now that I’ve taken a fresh look at new research about High-Intensity Interval Training (HIIT) let’s circle back and take a deeper dive into Zone 2 training. Despite the dramatic evidence we encountered promoting HIIT as a proven longevity enhancer, Zone 2 training (lower-level, longer aerobic movement) is still the mainstay of any health and longevity program. This should make up about 80% of our aerobic activities, with the remaining 20% being HIIT work. And as tempting as it is to speed up this lower-level work, there are probably more benefits to be had in staying in Zone 2 range for longer and not pushing that hard. Here is the underlying metabolism of this.
Zone 2 makes up your aerobic base, whether you regularly walk, run, bike, or do some other type of aerobic exercise. It reflects the day-to-day movement that our ancestors spent most of their waking time doing to acquire food. We mimic it today mostly by walking, as well as in the gym and elsewhere with biking, rowing, cross-country skiing, swimming, working out on treadmills or other gym machines, taking dance classes, and lots of other forms of movement.
Zone 2 is sometimes called the fat-burning speed. You do an aerobic activity (walking, biking, or whatever) at a speed that gets your heart pumping at roughly 2/3 of your maximum heart rate. How can you figure that out? Start with 180 minus your age for a rough Zone 2 heart rate estimate. For example, if are 65 years old, the math would look like this: 180 – 65 = 115. In Zone 2, you would be working at the fat-burning speed when you maintain a heart rate of about 115 beats/minute during your aerobic activity. (This should be about 2/3 of your maximum heart rate.)
Zone 2 is not an easy stroll, that’s Zone 1. It is energetic yet relaxed and sustainable. The other way to know if you are staying at Zone 2 speed is that you can hold a conversation comfortably and you can breathe through your nose comfortably. Above this speed our bodies begin to burn glucose as fuel instead of the fat we burn in Zone 2. When you start to breathe more heavily walking up a hill, that’s your body switching from burning fat to burning glucose for extra energy. Yes, we are magnificent hybrid machines, able to switch fuels when extra energy is needed!
Fat burning is an overlooked subject, but it is where things get interesting for me. Most of our day-to-day muscle energy is sourced from fat, or should be, and not glucose (or sugar, fructose, or any of the derivatives). I say “should be,” because it depends on our Zone 2 activity and levels of aerobic fitness to make fat burning the primary source for sustained muscle energy.
Inside each of our cells are numerous mitochondria, the energy providers of life throughout our bodies. This is where the small molecules known as ATP that power each and every one of our cells get made, from either fat or glucose. Healthy mitochondria mean lots of energy and are increasingly linked to longevity and health span. But the real, immediate benefit is that if you increase the health of your mitochondria, you will have more energy every day.
Mitochondria prefer fat as a fuel. It is how we evolved to move around. Our fat supplies are virtually limitless, whereas glucose is only stored in smaller quantities, mostly in our muscles and liver for intense activity related to danger or hunting. Fat also burns cleanly with only two end products: water and carbon dioxide (CO2). Excess water and CO2 are easily eliminated, in our breathing and when we go to the bathroom. (When we lose weight, we are literally exhaling those pounds as burned up fat.) Burning glucose, on the other hand, produces waste products like lactic acid, which impede cellular functioning. You only want to burn glucose when you have to, such as in dangerous or stressful situations (or to mimic them with HIIT work.)
The other thing that happens in this glucose burning “fight or flight” mode, is that your body prioritizes dealing with the stress or danger. It sends blood and energy to your brain and muscles for a short-term spike, and it temporarily suppresses regular activities like digestion and the immune system. Staying in the fat-burning zone gently increases circulation and enhances these functions.
Interestingly, new findings have linked poorly functioning mitochondria to metabolic disfunction, insulin resistance, and diabetes. It makes sense. Due to a lack of exercise, coupled with poor, processed, carbohydrate-based diets, our mitochondria have lost their robustness as well as their diversity. Stressful lives, which artificially induce glucose burning and the release of adrenalin and cortisol, are also big factors affecting mitochondria.
Zone 2 activity and training fixes all this. When we participate in Zone 2 activities, our bodies require more lower-level energy for extra activity, so more mitochondria are formed in each cell. In addition, the mitochondria tune themselves up to burn fat more efficiently as well as raise the threshold where they need to switch to glucose for more taxing anaerobic work, like HIIT workouts. This is why an elite marathoner can primarily burn fat at 70% of their maximum heart rate [PR1] and save their glucose and glycogen reserves for an end-of-race sprint to the finish line. Well-tuned mitochondria can even burn up the lactate or lactic acid, the waste product of burning glucose.
This science-oriented discussion is based on my hours of research and reading. As I noted, I find this fascinating! If you are scratching your head and wondering how you can apply this information in your life—and in your Zone 2 training—the following paragraphs regarding my own experimentation might give you some ideas to try.
My Own Experimentation
Lately, I’ve been increasing the length of my Zone 2 workouts and am careful not to exceed the fat-burning threshold. I used to do 40-60 minutes of Zone 2 aerobic activity, followed by yoga or a strength workout. I now do some sessions of 90 to 120 minutes of pure Zone 2. They are “easy” to do, in that they are not as strenuous as HIIT workouts or strength training. I don’t leave the gym or come home from a walk or bike ride fatigued the way I do when I push myself.
The hardest part of doing a longer Zone 2 session is that it takes time! I need to allow 1½ to 2 hours, and sometimes I get bored. I often listen to music, but mostly feeling the endorphins and knowing that what I’m doing is so good for me fixes any boredom. I have also discovered that being in Zone 2 is a good speed for contemplation and even some light meditation, or at least concentrating on my breath. You might say I really am “in the zone”!
Staying on the slower side is key to these workouts. Rather than pushing myself, I slow down if my heart rate increases, like if I’m riding my bike up a hill. I resist the temptation to prove to myself how fit I am, knowing that the benefit of doing an extended lower-level Zone 2 session is in the mitochondria. If I feel the need to exert myself, I save it for the end of my Zone 2 workout.
The first time I did a 90-minute Zone 2 workout (instead of my usual 60 minutes) I had a pleasant surprise the next morning. My heart rate variability had increased by about 10%, and my resting heart rate had decreased a few beats per minute. In addition, there was no muscle stiffness, because I had stayed below the lactate threshold. (I didn’t push hard enough to burn glucose, so there was no lactate by-product, which can cause muscle stiffness.) So far, this Zone 2 aerobic routine feels like the right thing to be doing, and I’ve even felt a slight increase in energy. I am keen to see where it takes me.
What is your favorite aerobic activity? Do you prefer to walk or run? Swim or spin? Bike or hike? Try staying “in the zone” with Zone 2 training for a full 90 minutes. Do this several times over the next few weeks, then check in with how you feel and your health numbers. If they reflect my experience, you will be pleasantly surprised, and on your way to better health, more energy and mightier mitochondria.
