Your Heart Rate and Your Workout
As our bodies engage in strenuous activity, our heart rate tends to speed up. The heart is a powerful muscle that pumps blood to our lungs and delivers oxygen to the tissues of our muscles, bones and organs. As physical activity increases, so does the oxygen demand of each body cell, specifically the cells of our hardworking muscles. So our heart rate has to accelerate in order to keep pace.
And body cells don’t just need oxygen; they also need fuel in the form of carbohydrates and burnable fat. A rapid heart rate keeps blood surging not just through the lungs, but also through the liver, where it picks up vital nutrients and energy to deliver to our body systems.
This might seem like a simple equation: Physical activity speeds up the depletion of cell nutrients, causing the heart rate to rise so nutrient delivery can keep up with increasing demand. But our bodies are complex. And in fact, as physical activity continues and heart rate increases, nutrient delivery doesn’t just speed up, it also starts happening in different ways. Some of these changes can have an impact on our workout goals.
Measuring Your Heart Rate
To determine your heart rate, place two fingers on your wrist or the large artery in your throat, just below your jaw. Count the number of pulses you feel during a period of six seconds, then multiply that number by ten to calculate your heart rate for a full minute.
Do this at a period of peak activity when your heart rate is as high as it’s likely to go. A healthy maximum heart rate should usually equal 220 minus your age. So if you’re 34, your peak heart rate should be 220 – 34 = 186. Your resting heart rate, or your heart rate at your lowest activity level, should be your peak heart rate minus 70, or 186 – 70 = 116.
This means that if you’re 34, your heart rate should vary between 116 (slowest) and 186 (fastest). We’ll base our information and advice on these numbers. (If your peak or resting heart rate varies widely from this model, consult a doctor before you make your workout plans.)
Peak Heart Rate (PHR=220-Age)
Resting Heart Rate (PHR-70)
Fat Burning Zone (70% of PHR)
|Cardio Zone (+70% of PHR)||137+||130+||123+||116+|
Heart Rate Zones: The Cardio Zone Versus the Fat Burning Zone
As our workout begins and our heart rate starts to accelerate, the fuel delivered to our cells comes primarily from burnable fat. This slightly elevated heart rate zone is called the fat burning zone.
As activity becomes more intense and heart rate rises, our bodies switch over to a different delivery system, in which cells consume more carbohydrates than fat. This highly accelerated heart rate zone is called the cardio zone.
The Fat Burning Zone
We remain in the fat burning zone as long as our heart rate stays between 50 and 70 percent of our maximum heart rate. That means a 34 year old person will burn primarily fat for energy as long as his or her heart rate stays below 130. While you occupy this fat burning zone, your muscles depend on a form of fuel that’s consumed in the presence of oxygen. This is also sometimes called the aerobic, or oxygen-dependent zone. Is this a better place to be if your workout goals are focused on fat loss? Not exactly, since fat loss comes from overall calories burned regardless of what form those calories take. But all activity burns calories, so this is a good place to start.
Activities in the fat burning zone can include brisk walking, jogging, easy cycling and low impact activities with moderate resistance. The fat burning zone offers an easier workout starting point for those who are out of shape or overweight. But to get the most out of the fat burning zone, activities at this heart rate need to be sustained for a longer period of time.
The Cardio Zone
We enter the cardio zone as our heart rate rises above 70 percent of the maximum. For a 34 year old person, muscle activity that keeps the heart rate at or above 130 beats per minute becomes anaerobic, or non-oxygen dependent, and fuels body cells using carbohydrates more than fat. Activity in the cardio zone actually burns calories faster than activity in the fat burning zone, which can put us on a faster path to weight loss. (The names of the zones can be misleading).
Heart Rate Zones and Workout Goals
Moving back and forth between the cardio zone and the fat burning zone, often called interval training, can provide some great workout benefits.
First, varying our heart rate like this can allow us to spend more overall time at the highest levels of intensity. The more our heart rate drops below the cardio zone and then rises back up, the more time we spend in the cardio zone during an average workout session. It’s far more difficult to stay in the cardio zone if we try to do it continuously.
Second, interval training keeps our bodies in motion longer. When we vary our heart rate zones, most of us seem better able to sustain a level of continuous focus on intense activity without getting exhausted or bored. Interval workouts stay engaging and keep us goal-oriented in ways other workouts don’t.
Heart Rate Zones: Considerations
Keep these considerations in mind as you work heart rate intervals into your exercise plans:
The longer you stay in the anaerobic cardio zone, the more work your oxygen-depleted cells will need to do in order to recover afterward. Work burns calories, so consistent cardio zone training can help you burn more calories during non-workout hours.
The stronger your heart becomes, the more force it will generate with each beat. This means that over time, your resting heart rate will drop, and your agile heart will move more rapidly between the resting zone, fat burning zone, and cardio zone. You’ll need to adjust your calculations now and then to account for this.
Remember, time spent in both heart rate zones will burn calories, which means accelerated weight loss (as long as your caloric intake doesn’t rise). Time spend in both zones also conditions muscles and increases strength. In the cardio zone these things happen faster, but it’s fluctuation between the two heart rate zones that will contribute most to your success.