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I got got asked an awesome question the other day related to a video that’s been bouncing around Instagram about how “too much HIIT can damage our mitochondria.” While HIIT can be fantastic for our health, it’s important to understand when and how much to implement it ESPECIALLY as women who cycle through hormonal phases (some of which do not respond well to HIIT, aka turning on fat storage from the stress).
Link to the IG post:
The question that followed was: “What’s considered the divide between moderate and high intensity?”
Let’s unpack it…
It comes down to our heart rate zones. Simply speaking, the divide between moderate and high intensity can be determined by our ability to converse comfortably. If we aren’t able to hold a conversation comfortably, we are likely in a high intensity heart rate zone.
Our heart rate (the effort our body is exerting) determines what our body uses for fuel, fat or glycogen (carbs). This is why it’s important to understand our heart rate zones, so that we know where we need to be in alignment with our goals.
The more familiar we are with our HR zones, the better we can understand wants happing to our body’s in each zone + how to efficiently train towards our goals and prevent unnecessary stress to our body (i.e. by being in too high of a zone for too long).
We’ve got 5 zones that range anywhere from 50%-100% of our max heart rate. Before we can understand each zone, we must first know what our max heart rate is. The easiest way to determine our maximum heart rate is by using one of these formulas:
220 – Age – most common and widely used maximum heart rate formula
207 – (0.7 x Age) – more precise formula, adjusted for people over the age of 40
211 – (0.64 x Age) – slightly more precise formula, adjusted for generally active people
If we aren’t wearing a heart rate monitor (Fitbit, Apple Watch, Whoop, Garmin), we can determine our heart rate zones by subtracting our age from 220. (Keep in mind, 220 is a very general max heart rate, and 220 minus your age is a rough average compared to the same age group but NOT taking into account your physical fitness level). Then, multiply that number by the percentage of the heart rate zone we are aiming to be in.
Also important to note, our heart rate zones can change (zone ranges can increase) the more we train and the more our body has to adapt to challenge.
Let’s dig into what’s going on in each heart rate zone…
HR Zone 1:
50-60% of your HR max
Known as the “recovery zone”
Should be able to converse easily
HR Zone 2:
60-70% of your HR max
Lowest “training zone”, just below aerobic
Should still be able to hold a conversation (ideally for 30 + min)
Benefits of training in Zone 2:
Higher cardiac output + lower resting heart rate
Increased VO2 max (the maximum amount of oxygen your body can import, transport and utilize per min of intense activity — higher VO2 = more conditioned/ in shape)
Ability to sustain aerobic capacity without lactic acid build up
Helps bring body to a parasympathetic state vs. sympathetic (fight or flight) — optimal for rest & recovery
Increased endurance
Helps teach your body to use fat as fuel (and save glycogen (carbs) for high intensity bursts)
HR Zone 3:
70-80% of your HR max
Not a conversational zone for talking
Think: HIIT, Orange Theory, Barry's +
Benefits of training in Zone 3:
Helps improve your anaerobic threshold (ability to be at higher intensity longer)
*Why do you burn less fat the harder you workout?
“Once your heart rate increases, you’re not taking in as much oxygen. You can’t oxidize fat fast enough. Your body turns to another, more readily available energy source to provide fuel for you — glycogen, also known as carbohydrates.”
HR Zone 4:
80-90% of your HR max
Crossed over the “threshold” from aerobic to anaerobic *Aerobic exercise involves continuous movement fueled by oxygen from the air you breathe. Anaerobic exercise involves short bursts of high-intensity movement fueled by energy stored in your muscles.*
Benefits of training in Zone 4:
Lactic acid threshold increases
Body will be burning through carbs
Uses more muscle fibers (think sprint interval training), which creates the proteins required to build strong mitochondria cells (which contain most of our energy) *Strong mitochondria = better energy and focus, and greater ability to sustain high levels of activity without fatiguing.*
HR Zone 5:
90-100% of your HR max
Only able to sustain for a VERY short amount of time (all out, quick sprints)
Zone 5 has passed the lactate threshold (lactic acid build up) *Lactic acid build-up happens when our bodies have turned glucose into energy as a final “Hail Mary”. On top of that, it usually happens when we cannot get enough oxygen in to utilize for what we are doing.*
Puts body into a sympathetic state (fight or flight), ability to recover lessens
Knowing our heart rate zones, helps us have a better understanding of what kind of training is actually going to benefit us (in alignment with our goals). If we already train, it gives us insight as to where and how we can improve and optimize our training!
If you’re sick of guessing how to train for your goals and looking for coaching that’s going to meet you where you are and support you to your goals holistically, don’t hesitate to reach out!
Pursue Your Best,
Candice