Last updated
17 October 2009

Heart rate, training zones, and fat burning

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Heart rate - Introduction

As we have already discovered, by reducing your calorie balance to below your maintenance level (TDEE) through a combination of reduced calorie consumption and an increase in activity level, the body uses internal storages of fat as a source of energy supply.

Part of the calorie-weight loss equation is to increase your calories expenditure through increasing you activity level. This usually involves starting an exercise regime.

Whilst you are running on a treadmill, this increases your heart rate as blood is being pumped round the body more quickly to provide your muscles with the energy and oxygen that they require.

You will no doubt understand that exercising burns calories, but given that exercising involves increasing your heart rate, there is also a relationship between heart rate and calorie burning. We will explore this relationship below.

Target heart rate

Heart rate is considered to be the number one method for measuring intensity during aerobic activities.

Depending on what you are looking to achieve from your aerobic activities, be it weight loss, fitness or endurance, it can be useful to aim for a target heart rate when exercising.

The target heart rate (also known as the training heart rate) is calculated as a percentage of a person's estimated maximum heart rate. Sex and age affect the estimated maximum heart rate.

These zones represent the range in which a person can achieve the greatest cardiovascular benefit from aerobic exercise without 'overdoing' it. Target heart rate is measured in beats per minute (bpm).

There is a low and a high range of the target heart rate. Less vigorous exercise will come in the lower end of the zone and will burn fewer calories than more vigorous exercise at the higher end of the zone that will burn more calories. However, staying within these parameters means a person is exercising within the desired target heart rate zone.

Register for free as a Purple Weight Loss member to obtain access to the Purple Weight Loss 'calories burned calculator', part of the exercise diary, which uses metabolic equivalents to estimate the calories you will burn, dependent on your weight for over 600 different activities.

Heart rate training zones

Heart rate training zones are calculated by taking into consideration your Maximum Heart Rate (MHR) and your Resting Heart Rate (RHR). We are currently working on producing these calculators for you to determin your own training zones, so check back here soon.

Warm-up Zone - 50% to 60%

Before starting any exercise, it is advisable to warm up. The warm up should be at 50-60% of the MHR. When walking to work, or shopping, you can achieve this by doing a fast paced walk. This light activity has been shown to help decrease body fat, blood pressure and cholesterol. It also decreases the risk of degenerative diseases and there is very little risk of injury.

The Energy Efficient or Recovery Zone - 60% to 70%

Training within this zone develops basic endurance and aerobic capacity. All easy recovery running should be completed at a maximum of 70%. Whilst exercising in this zone, 85% of calories burned are from fats stored in the body.

The Aerobic Zone - 70% to 80%

Training in this zone will improve your cardiovascular and respiratory system and increase the size and strength of your heart. This is the preferred zone if you are training for an endurance event. More calories per minute are burned than in the energy efficient zone with 50% coming from fat.

The Anaerobic Zone - 80% to 90%

Benefits of this zone include an improved VO2 maximum (the highest amount of oxygen one can consume during exercise) and thus an improved cardio-respiratory system and a higher lactate tolerance ability which means improve endurance and fatigue-fighting ability. This is a high intensity zone burning more calories per minute than the energy efficient or aerobic zones, 15% coming from body fat.

The Maximum or Red Line Zone 90% to 100%

Although this zone burns the highest number of calories per minute, it is very intense. Most people can only exercise in this zone for short periods. You should only train in this zone if you are in very good shape and have been cleared by your doctor to do so.

Learning point: Heart rate variations at given activity intensity levels......

A reduction in heart rate for a given intensity is usually due to an improvement in fitness but a number of other factors might explain why heart rates can vary for a given intensity:

Dehydration can increase the heart rate by up to 7.5%;
Heat and humidity can increase the heart rate by 10 bpm;
Altitude can increase the heart rate by 10 to 20%, even when acclimatised; and
Biological variation can mean the heart rate varies from day to day by 2 to 4 bpm.

What is the fat burning zone?

Gym equipment often refers to the fat burning zone and people often believe that to lose body fat, they must exercise in the fat burning zone......but what is it?

......well, in fact, it is actually a lot of nonsense in reality!

This idea is based on a misunderstanding of the science. It is true that when you exercise at a lower intensity, your body is able to draw more of the energy directly from fat sources on the body, but exercising at a lower intensity will not result in you having lower overall body fat.

There are two reasons as to why you should not really be too concerned about the idea of training within the mythological 'fat burning zone'......

Firstly, it does not matter where the energy comes from while you are exercising; ultimately your body will replenish and rebalance your energy stores on a daily basis. If you refer to the section on weight loss, weight maintenance and weight gain, you will see that your weight attributable to body fat is based entirely on the calorie-weight loss equation. If you consume more calories than you expend, you will increase your body fat and vice versa. The source of the energy expended while you are exercising is therefore irrelevant;
Secondly, the most important thing to consider is really is the total amount of calories you burn, not the proportion that comes from fat. If you exercise at lower intensity, a higher proportion may come from body fat, but this may be a smaller absolute number of calories than had you adopted a safe but more intensive exercise for the same length of time!