Your Heart Rate Questions Simplified

Questions about target heart rates are common with P90X and especially Insanity. Shaun T frequently tells people to check their heart rate and to make sure it’s safe, whatever that means. This blog intends to clear up the common questions about heart rates and their effects on exercise.

If you have a short attention span, and don’t care about why, the most important thing to remember is that your body is the best heart rate monitor. Your body will tell you when you need to stop or slow down. That being said, the rest of this article explains this and discusses the broader concepts.

Max Heart Rate

In theory, your body has a maximum heart rate, which is the fastest that heart can theoretically beat. The common estimate for max heart rate is 220-your age. So if you are 20 years old, your max heart rate is 220-20 or 200 beats per minute. If you are 30 years old, your max heart rate is 190. If you are 40, your max heart rate is 180 and so on. This again is just the widely accepted estimate formula of max heart rate. To actually get your maximum heart rate, you have to go to a lab and have your max VO2 measured, where they put a hose in your mouth to measure what's in your breath, and you run on a treadmill to see at what heart rate you stop burning fat.

Biology 101-Your Body Stores Fat, But Not a Lot of Carbs

Before I go on, I should cover a basic, seemingly unrelated, issue. As people know well, your body stores energy as excess fat. Your body does not store any extra protein, and stores a limited supply of carbs, as simple sugar and glycogen, for immediate muscle and brain needs. The average person has about an hour’s worth of carbs stored in their muscles for very hard exercise. If you eat a lot of sugar, insulin converts it to fat as quickly as it can for storage for future needs. If you eat a lot of protein, it too is inevitably converted fat for storage. You will see why this fact is important shortly.

Target Exercise and Heart Rate Zones

Really the discussion about heart rates is irrelevant except as it impacts your exercise. Specifically, there is Aerobic and Anaerobic exercise zones. Aerobic exercise is when your body uses fat as your primary energy source, and Anaerobic exercise where sugar is your primary energy source. Heart rate is what drives your body from Aerobic to Anaerobic exercise zones. Briefly, when your heart beats faster, you move from Aerobic to Anaerobic exercise zones.

Aerobic Exercise

The aerobic exercise range is generally considered when your heart is beating from 60-80% of your max heart rate. So if you are 20 years old, and your max heart rate is 200, your aerobic range is 120-160 beats per minute. This is the range where your body is theoretically burning primarily fat for energy.

You still need carbs to get the process going, but during aerobic exercise, you burn about 80% fat and 20% carbs. Think of carbs as the kindling wood to get a fire going. Given that you have a virtually unlimited fat supply, and are burning carbs slowly, you can exercise for a long period of time.

You can use a heart rate monitor, but the best test is seeing if you can talk while you exercise. If you are exercising aerobically, you should be able to talk while exercising.

Anaerobic Exercise

If you are exercising above 80% of your max heart rate, you are theoretically in your anaerobic range. This means that your body is using sugar, aka carbs, as your primary energy source. When you are in the anaerobic range, you will be breathing heavily and you won’t be able to talk while you exercise. You may be gasping for breath.

The place where you potentially run into a problem with anaerobic exercise, is that as your body has a limited supply of carbs, you can run out of carbs. If you exercise anaerobically for an extended period of time, you can run out of carbs and experience a carb crash. However as was stated, you have about an hour’s worth of carbs in your body, and if you are doing Insanity or P90X, you should be ok.

It is Still Better to Exercise Anaerobically

While most people naturally assume that it is better to burn fat instead of carbs, you still burn more calories in the anaerobic range. The faster your heart rate, the more calories you burn. It is that simple. If you want to burn calories, and push your body to its limits, anaerobic exercise is more effective even though you are not burning as much fat. Your body will begin to convert fat to carbs for energy.

What This Means for Insanity

While it may be controversial, I recommend that people skip the heart rate monitor, and let their body be their monitor. If you are “Digging Deeper!” you will be in the anaerobic range for most of the program. If you try to stay in the aerobic range, you will likely stop every 20 seconds and have to wait for another 20 seconds and barely get a workout in. Insanity wants you to go all out and do it perfectly and stop when you lose your form. That means you need to ignore your heart rate and listen to your body. Of course this assumes that you have a healthy heart, but you shouldn’t be doing Insanity if you don’t.

What This Means for P90X

P90X is very similar to Insanity in most ways. P90X is essentially circuit weight training, which will keep your heart rate in the anaerobic range for much of the workout. There is however more rest during the workouts than with Insanity, so you can sustain the workouts for longer periods of time. You won’t have to worry about your heart rate with Yoga, and you will likely be in the aerobic range for Kenpo X and Cardio X. During Plyo X, you will likely be in anaerobic range for a good portion of the time.

Just in Case

If you do find that you begin to feel lightheaded, develop a halo vision, or become weak during an anaerobic workout, you may be suffering from a carb crash. If that happens, you should take a break and have some recovery drink. This again assumes that you are otherwise healthy and well hydrated. Again, as the workouts always say, you should see a doctor if you have any problems.

Don’t Worry About It

The human race was exercising long before the advent of heart rate monitors, and we seemed to do fine before that. I just don’t want P90X and Insanity to start looking like a 1990s aerobics class, where everyone stops every 5 minutes to check their heart rate and wait until their heart rate goes down. Their hour workouts ended up being 30 minutes, and results went down. Unless you have your Max VO2 measured, you are really just guessing anyway. Just learn to trust your body and you will be fine.