Heart Rate, Heart Health, and How to Train with Heart Rate Zones

We each only have 24 hours in a day and there are many different priorities that levy for that time - Our families, careers, friends, obligations and projects - sometimes our fitness can take a back seat to it all. Recognizing that to maintain a healthy body requires activity is the first step to wellness; and there is a large body of evidence to suggest that this is true. But, regardless of whether we have read the case studies or not, I think we all intuitively know that exercise is good for us; we just don’t know how best to do it or how to make time for it. Once we have decided that making time to exercise is important the next step is deciding how much time to set aside for it and which exercises to do.

A great place to start is with activities that stress your cardiovascular system, ie. cardio. Cardio gets a bad rap, mainly because it’s hard and because the results are a little less external than its more buff cousin, strength training. What makes cardio great though, and why I recommend it before weightlifting, is that it’s very applicable in day-to-day living. Having a healthy cardiovascular system means you can jump longer with your kids on the trampoline, enjoy hiking with your friends more, and outrun the competition in a pickup basketball game. In addition to increasing our enjoyment of daily activities, cardio also burns more calories per hour than weightlifting, meaning you shed weight faster and can fit into those jeans that you haven’t had the heart to give away yet. Speaking of heart; It also strengthens your heart, which is important when you are living in a country where heart disease is the number one cause of death. All this isn’t to say that strength training isn’t necessary, because it certainly is, but cardio is a great place to start when looking to get into shape.

So, we’ve decided that exercise is important, and that we want to start with cardio, but what does that mean? A lot of different activities fall under the umbrella of cardio: running stairs like Rocky, going on a long leisurely hike, running, high intensity interval training (like some Crossfit workouts and Orange Theory), eating cheese on the couch - just checking to see if you’re paying attention! All these are options, but which to choose?

There are 4 Main Types of Cardio

There are 4 main types of cardio. There is all-out, max effort, cardio which occurs during sprints. Then there’s the intensity that is extremely difficult and can only be sustained for 20 minutes to 1 hour (depending on your fitness level). Below that is the intensity that you could maintain for a couple hours, such as hiking or riding a bike. And then last, but not least, is a pace that you could sustain with minimal effort for an extended period of time, like walking. Each of these intensities is correlated with different physiological barriers, which is how we differentiate between the different levels.

Type I: Vo2 Max

The first type we talked about, the-all out effort, is correlated with the measurement of how much air your body can process. At full tilt the limiting factor to your performance is how much oxygen you can get to the cells doing the work. This measurement you may have heard of before, it’s called your V02 max, or more specifically your aerobic capacity. You probably don’t think much about your V02 max except when sprinting in a footrace or running a football into an end zone - and then you become acutely aware of it! Training at this maximum intensity is important if you want to be an elite athlete but, if the other systems in your body aren’t also tuned up to handle running at a sprint, you can risk injury. I wouldn’t recommend incorporating max-effort sprints into your workouts until you have also incorporated weightlifting and stretching, ensuring that your body is ready to handle the increased forces.

Type II: Anaerobic Threshold

The next level of intensity, the one you can sustain for 20-60 minutes, is correlated with your anaerobic threshold. Your anaerobic threshold is the intensity level at which your body is burning more of its glycogen stores than its fat stores (because it’s easier for your body to quickly turn glycogen into energy as opposed to fat). Additionally, at this intensity, your body is unable to evacuate the lactate being produced by your muscles at the rate it is produced, which is why you’ll often hear anaerobic threshold and lactate threshold used interchangeably. If you wanted to know your anaerobic threshold you could go to a sports science clinic and get evaluated (where they put you on a treadmill with a mask over your face to measure your oxygen burn and lactate levels) but, for the most of us, that’s not really necessary. We can determine our own aerobic capacity based on feel. You’ll know when you are at your aerobic threshold because there is a distinct amount of suffering involved: If a 10 was max effort and a 1 is a slow walk, most people find their anaerobic threshold to be around a 7. Not max speed, but at a pace that isn’t sustainable for long and definitely hurts. Exercising at this pace is good, because it can help push our anaerobic ceiling higher, and there is evidence to show that your body’s metabolism is increased after intense workouts, meaning you burn extra calories in the hours following a anaerobic threshold workout, which is pretty cool. If the amount of time you can spend exercising each day is limited to 30 minutes or less then including high-intensity workouts is a good way to make the most of your time. However, for most people, it’s best to incorporate these workouts in maybe once per week (about 10% of your total training volume). I recommend this for two reasons; first, the soreness you feel after these workouts often limits your ability to exercise in the days following and, secondly, because the benefits from longer, easier workouts, is often preferable.

Type II: Aerobic Threshold

The level of intensity below your anaerobic threshold his called your aerobic threshold. Sounds similar to anaerobic, but the difference is that during aerobic exercise your body is performing at a level that allows it to burn both fat and glucose, meaning you can train longer, with less pain, and burn more fat. Your body can only store a limited amount of energy as glucose (glycogen), and once the energy stored in the blood and liver is consumed the body relies on fat to continue operating. Burning through those glycogen reserves usually takes around 2 hours, although it varies from person to person. Once you breach the two-hour mark you really start to make a dent in your fat stores. Burning through those first energy stores slowly is critical to being able to sustain a long effort; otherwise your body will run out of energy faster than it can transition to burning fat stores. This phenomenon goes by many names: hitting the wall, bonking, blowing up… and it’s not a pleasant experience. Maybe you have seen those videos of marathon runners crawling over the finish line because their legs will no longer support them? That’s bonking, and it happens when you train too hard for too long. To avoid this, don’t train at an intensity beyond your aerobic threshold for longer than a couple hours. I recommend that people train mostly at or just below their aerobic threshold, for about 90% of their training, because it gives the best results, isn’t too unpleasant (think of going for a long hike or a couple hour bike ride) and is accessible to everyone (you don’t need a membership to a fancy gym to train at this intensity).

Type IV: Low Intensity

The final level of intensity is that easy, “I-could-do-this-all-day”, type of workout. For people with injuries or older folks that can’t train at a higher intensity, this is the best (and only) way to exercise. But, because most of us don’t have all day to exercise, and want to a good bang for our buck, we’ll skip this one.

Understanding Heart Rate Zones

Okay, so we know we want to do cardio, 90% at aerobic threshold and 10% at anaerobic threshold, a great start. But, how do we know if we are training at the right intensity? There are 2 ways to determine workout intensity. The easiest and cheapest way is by feel: Anaerobic workouts rank around 7/10 on the difficulty scale and aerobic workouts feel about a 3/10. You’ll know if you are at the right intensity based on the duration that you can sustain the intensity as well. Anaerobic should only be sustainable for less than an hour, but longer than 20 minutes and aerobic workouts should be sustainable for many hours, but not easy either. The second, more scientific way to measure our intensity level is by using our heart rate. The rate that our hearts beat at is directly correlated to the amount of stress we are putting on the body (with certain exceptions; an elevated resting heart rate is known as tachycardia). As intensity goes up, so does the heart rate, and thus we can use it to gauge our intensity level. In the olden-days the rule of thumb was to take your age and subtract it from 220 and then do some math to figure out what your heart rate zones were… but c’mon, it’s 2019! We have better methods at our disposal! The “easiest” way to find what your heart rate zones is to get an activity watch that measures heart rate and do a test. And I put easiest in quotes because it’s the easiest way to get an accurate result, but it’s certainly not easy.

The protocol is as follows: Find a flat trail or track that you can run uninterrupted on. Set out at a pace that you can barely sustain for 30 minutes and run as fast as you can for a half hour. It’s not going to be fun, but the harder effort you put in, the better data you will get. Once finished, pull out your phone and find the average heart rate of the last 20 minutes of the run (we discard the first 10 minutes because it takes a while for the heart rate to normalize at this intensity). Then subtract 5% (av. hr x 95%) and you have your anaerobic threshold heart rate. Now, anytime you want to work out at your anaerobic threshold you just run/ bike until the heart rate on your watch matches your calculated anaerobic threshold heart rate. To calculate your aerobic threshold (the intensity that we will use for 90% of our workouts), subtract 30 beats per minute from your anaerobic threshold heart rate and voila; you will have your aerobic threshold heart rate. Knowing this will help you keep your intensity consistent, helping you start at the right pace (it’s a common mistake to start too fast and burn out) and finish strong during those long workouts.

Putting It All Together

The next step, now that you know how to calculate the intensity of your workouts and how to divide your time over these differing intensities, is to determine how much time to spend and how regimented you want to be. The answer to this question is unique for everyone, depending on goals and available time. If your goal is to complete an Ironman distance event, then you will need to set aside a significant amount of time to train and will want a well scheduled and documented training plan. But, if you just want to be healthy and enjoy strenuous activities, then you can afford to be more lax with your training. Regardless of your end goal though, it’s a good rule of thumb to not increase training volume more than 10% each week. Increasing total load more quickly has been shown to result in a higher chance of injury and burnout.

This blog post only scratches the surface of workout intensity levels and exercise planning. To learn more about these topics some helpful resources are The Triathletes Training Bible by Joe Friel (how to train using science), and Finding Ultra by Rich Roll (a memoir about Rich Roll discovering his true potential through endurance sports). My hope is that this article helps you become more educated about sports science, so that you can train smarter, harder and in a way that is enjoyable and fits your lifestyle. Now go lace up those tennies’ and get out there!