The Magic Behind HR Training

Andrew Jansen Van Rensburg                  www.sportandwellness.co.za

HEART RATE TRAINING

Heart rate training makes use of the fact that the demand for oxygen rises with exercise intensity. As would be expected heart rate has a close relationship to oxygen consumption, especially at exercise intensities between 50 and 90% VO2 max.

Heart rate is easy to monitor and for the majority of athletes it offers a practical measure for assessing exercise intensity, which is why it is so popular.

It’s important to monitor exercise intensity for a number of reasons. Firstly, the specific physiological adaptations to training change depending on what relative work load is employed. It’s fundamental that the athlete or coach understands which type of endurance training (as a reflection of intensity) is best for their sport or phase of training.

Secondly, monitoring the intensity of individual sessions allows the coach or athlete to manipulate the overall program, helping to prevent over training and in order to reach a physical peak for competition.

While heart rate is convenient and practical for most athletes, for many it can be inaccurate in determining the best exercise intensity…

The Limitations of Heart Rate Training

Most heart rate training programs are devised around an estimation of the maximum heart rate. The are two problems with this approach. The first is that maximum heart rate is estimated with the basic formula 220-age. For a significant number of athletes however, this estimation maybe out by as much as 25 beats per minute.

The only way to accurately determine maximum heart rate is perform a short, maximal stress test (to exhaustion). During the test heart rate will rise steadily until a plateau is reached despite the exercise intensity continuing to rise (assuming the individual is fit enough to last until such a time). This is a direct marker that the heart is beating as fast as possible. More detail about this test follows.

The second problem is that, even if maximum heart rate is estimated accurately, prescribing exercise on the back of standardized zones makes no allowances for individual differences. For example, endurance performance improves when lactate threshold as a percentage of VO2 max is increased and it can be improved with training. A standard heart rate zone of 85-90% of the age-predicted maximum is commonly prescribed to improve lactate threshold but this may not be accurate. As with maximal heart rate, the only way to determine the correct heart rate training zone for improvement of lactate threshold is to measure it during laboratory testing. (more explanation later)

Despite these limitations, heart rate training still offers a more objective method for determining exercise intensity.

Other variables: Dehydration (7%), Heat and humidity (7%), Altitude (10%) and natural biological changes of 2 – 4 beats per minute can change daily.

Resting HR

Take while supine resting for longer than 20 min

The heart is a muscle so with regular exercise it will become larger and become more efficient as a pump. As a result you will find your resting heart rate gets lower so you will need to check your RHR on a regular basis (e.g. Monthly).

Types of HR max estimations:

For all examples a 35 year old male will be used working at 65%, Rest HR 60.

• Age based:

220 – AGE

220 – 35

=185

185 x .65 = 121 beats per min

• Karvonen method (all 35 yr olds not same fitness)

220 – AGE

220 – 35

=185

Working HR = HR max – HR rest

185 – 60 = 125

Working HR x intensity =

125 x .65= 81

81 + Rest HR

81 + 60

=141

As you can see this method brings about a higher training zone.

• Sex variation (last of my examples)

Male : 205 – (age/2) = 187.5 x .65 = 122bpm

Female : 211 – (age/2) = 193.5 x .65 = 126bpm

As can be seen the fluctuations are wide, and there are many other methods to use, but to be completely accurate a Max HR test should be carried out by a sports physiologist. Alternatively you can actually carry out a stress test yourself, but please be warned, injury can result if you are not in a fit enough state to carry out this test:

MAX Stress test

Anyone who has undergone a stress test will know that it is not easy. A stress test although relatively short does require you to push your body and your heart to the very limit. Before undertaking a stress test, you should be certain of the following:

• that you have not suffered from any cold, flu, stomach bug or other illness in the last six to eight weeks. The body in this period could still be fighting the last of the infection and the effort of a stress test could leave you prone to a more serious infection. If in any doubt check with your doctor
• that you have not raced in the fourteen days prior to a stress test and at least four to six weeks following a marathon or more if you have not yet fully recovered from your efforts. A tired heart and body will not achieve maximum
• in the final week before a stress test it is important to recovery run – to ensure a max value is possible

Do not undertake a stress test:

• with any hint of an injury. Ensure all old injuries are fully repaired before deciding to undertake stress test
• if you have less than one years running experience and are sport active for less than three hours a week. It is possible you will not be fit enough to take the strain of a stress test let alone achieve a reliable result

Any one who is overweight or over the age of 35 is advised to see their doctor before under going a stress test. I hope that you get the idea that a maximum heart rate stress test is not easy. It is the very limit of your heart and bodies capability and should not be treated lightly.

The tests will require you to wear your heart rate monitor (HRM) and preferable one that is capable of recording your heart rate. It is best to record your heart rate as often as possible – preferable every second or at worst every 5 seconds. If your HRM does not have a record facility, it will be necessary to keep glancing at your monitor to find your highest heart rate. For both these tests, it is important to warm up thoroughly.

Stress Test 1

For this test you need a good hill. The hill needs to take you about two minutes to run up it and of sufficient gradient to ensure you are breathing hard at its summit. The test begins around five minutes running time from the hill. Gradually accelerate towards the hill achieving 85% MHR (for the first time) at the base of the hill. As you hit the hill, maintain your speed by increasing your effort. Your heart rate will rise and you will tire. Without falling over, keep an eye on your monitor and make a mental note of your highest heart rate as you work towards the top of the hill.

Stress Test 2

For those unfortunate enough to live in an area lacking hills it is possible to carry out a test on a flat piece of road or at your local running track. The plan of attack is to run 800 meters very quick. For the first 400 meters run at up to your current 90 to 95% MHR (to be achieved by the end of the first lap) and for the last 400 metres go for it. During this second lap, you must work at 100%. Very fit athletes may have to repeat this test after a few minutes rest (minimum of 65% MHR) to be able to achieve a true maximum. This test is very reliable.

Notes

A stress test should be carried out every six months to ensure ongoing accuracy of your training zones. Many athletes do not achieve their actual MHR at the first attempt as they are either not fit enough or are running tired.

Swimming and cycling have their own max heart rate and as such training zones that need to be followed. A general rule of thumb is to subtract 13 bpm from your HRmax for swimming and 10 bpm for cycling. Cycling HR max can also be tested in a similar manner, but swimming is not necessarily advised as fatigue can cause more serious issues.

Now, for all intensive purposes we have an idea of our HR max and as such can work out certain training zones. . . . . . . What now?

Dependant on the goal of the training, and hence the goals of your sessions will determine the zones in which you should be working. A goal of running a fast 800m is very different to running Comrades or completing Ironman.

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 65%. Another advantage to running in this zone is that while you are training your body to use fat as an energy source, you may lose weight, and you will be allowing your muscles to re-energise with glycogen, which has been expended during those faster paced workouts.

Mark Allen, Legendary triathlete, suggests that many triathletes bodies do not know how to use fat as an efficient energy source, as we tend to go too fast with training sessions. He advises doing most of your endurance work at an intensity of under 70% to train your body to use fat as an energy source, as fat is packed full of ATP and is very useful when going long!

The Aerobic Zone – 70% to 80%

Training in this zone will develop your cardiovascular system. The body’s ability to transport oxygen to, and carbon dioxide away from, the working muscles can be developed and improved. As you become fitter and stronger from training in this zone it will be possible to run some of your long weekend runs at up to 75%, so getting the benefits of an improved aerobic capacity.

The Anaerobic Zone – 80% to 90%

Training in this zone will develop your lactic acid system. In this zone, your individual anaerobic threshold (AT) is found – sometimes referred to the point of deflection (POD). During these heart rates, the amount of fat being utilised as the main source of energy is greatly reduced and glycogen stored in the muscle is predominantly used. One of the by-products of burning this glycogen is lactic acid. There is a point at which the body can no longer remove the lactic acid from the working muscles quickly enough. This is your anaerobic threshold (AT). Through the correct training, it is possible to delay the AT by being able to increase your ability to deal with the lactic acid for a longer period of time or by pushing the AT higher.

The Conconi Test for Measuring Lactate Threshold

As mentioned earlier, the simplest method for determining the lactate threshold is to assume it occurs at 85-90% of the maximum heart rate. An alternative is to use the Conconi test…

In 1982 Conconi et al, stated that the lactate threshold was linked to a deflection point in heart rate data. Heart rate plateaus briefly before rising sharply again and this is said to correspond with a sudden rise in blood lactate concentrations. There are various protocols used to elicit the plateau Conconi and co-workers refer to. Here is an example:

Equipment

• Treadmill (with metric setting – km/hr and meters)
• Heart rate monitor
• Assistant to take recordings

Procedure

• Begin by warming up at a light pace for 5 to 10 minutes. Set the treadmill to a 1% incline.
• The run should last between 2.5km and 4km to allow sufficient data to be collected.
• Gauge your starting speed. Speed is gradually increased every 200m so start too quickly and you won’t last long enough. Start too slowly and you’ll be there all day.
• As a guideline 8 – 10 km/hr is a good starting point.
• Increase the speed every 200m by 0.5 km/hr.
• Record the heart rate and speed at each 200m interval.
• Continue until exhaustion and complete a 10 minute cool down.

You can now plot a simple heart rate graph like the one below and read off lactate threshold:

You can see from the graph above the obvious plateau and deflection in heart rate. It seems to correspond with a heart rate of 172bpm. In theory, then an athlete could train at or just above this heart rate training zone and improve their lactate threshold. However, caution is required when using this test as subsequent research has questioned its validity (7,8). It has been argued that the deflection point occurrs only in a certain number of those tested and that it underestimates the lactate threshold exercise intensity

Heart Rate Training to Increase Lactate Threshold

Here’s a simple heart rate training program to increase lactate threshold…

• Assuming your heart rate at lactate threshold is 170bpm
• Start by completing two 6-10 minute runs approximately 5% below the lactate threshold heart rate. In this case it would be 162bpm.
• Rest for 2-3 minutes between runs and complete this twice a week.
• Gradually build up the length of each run or the number of repetitions (up to 6). Also increase your target heart rate up to your threshold (170bpm).
• The target eventually is to reach a sustained 20minute run at or just above your threshold heart rate.

Complete a thorough cool down at the end of each session. Also re-test every 8 weeks.

The Red Line Zone 90% to 100%

Training in this zone will only be possible for short periods. It effectively trains your fast twitch muscle fibres and helps to develop speed. This zone is reserved for interval running and only the very fit are able to train effectively within this zone.

With a properly designed training program, using heart rate as a guide and perceived exertion to assist you, any goal laid out is possible given enough time and consistent training.

A last word on losing weight and energy systems:

A car with multiple fuel tanks:  Fat vs carbs

You’ll know that our body is capable of using numerous sources of energy during exercise – think of your body as a car with multiple fuel tanks.  The first tank is glycogen, the storage form of carbs in the muscle and liver.  The second is fat (strictly speaking, it is free fatty acids), which is stored in the muscle and in adipose tissue as triglyceride.  This is summarized in the diagram below.

The problem we face is that our body’s glycogen stores are finite – muscle and liver glycogen supply energy for exercise for about two hours (depending, of course, on the intensity, level of training and habitual diet, among other factors), and once they are depleted, hypoglycemia (from liver glycogen depletion) and fatigue are the result.

On the other hand, much to most people’s dismay, fat stores are not limited.   “Infinite” is not the correct word, because they’re not, but in terms of physiology, you have more than enough fat to power exercise for much longer than you can ever exercise, even if you’re an elite athlete.  Most of us are not, and so our objective is to cut down these already abundant fat stores into something a little more “acceptable”!


Burning fat – how fast, how long?

Perhaps the best approach to this topic is to ask when each of the fuel stores is used?  In otherwords, how does your body decide when to use fats versus carbs as a source of fuel, and to ‘fuel’ the discussion by starting with some of the theories around fat burning.

The first theory is that you burn more fat when you exercise at a low intensity.  That is, walking is better than running, and cycling slowly is better than cycling fast, and so on.  The idea is that your body uses carbs more and more as exercise intensity rises – this is the basis for target heart zones and the fat burning zone you see in books and on gym equipment.

Let’s look at that in more detail.  Below is a diagram that shows an example of how the use of fat and carbs are related as exercise intensity rises.

So, on the left, in the pink shaded box, you can see that at low intensities (walking, slow cycling), about 80% of your energy comes from fat, while only 20% comes from that carbohydrate (CHO) “tank”.  As the exercise intensity rises, the relative contribution of fat falls while CHO rises.  The result is that at about 60%, shown by the green zone, the contribution is equal – 50% from fat, 50% from CHO.  This point, at which the contribution from CHO becomes greater than that from fat, was called the Cross-over point by George Brooks, a very famous exercise physiologist, who wrote a great textbook on the field (the book that was prescribed to us in my studies, in fact).

Then, as exercise intensity rises even more, the contribution from fat declines, so that by the time you’re exercising vigorously, between 80 and 90% of the energy comes from CHO, and only about 15% from fat.

Just to comment on how you can measure intensity, my value is calculated as a percentage of VO2max, which is not accessible to many people.  It’s impossible to say exactly what heart rate that corresponds to, because it is very much dependent on the person and the context of exercise.  For some, it’s a one-to-one relationship, so that 50% VO2max is 50% HRmax, whereas for others, heart rate will be higher than VO2max – 50% of VO2max would correspond to say 60% of heart rate max.  I wouldn’t get too hung up about this, for reasons explained below.  I know it sounds simple, but if you’re wondering what 60% corresponds to, it’s 6 out of 10 on a scale of exertion, where 10 is maximum effort.

Note also that the cross-over point, and in fact the whole pattern of the two lines is quite ‘malleable’ in that training, diet and genetic differences affect the relative percentage.  For example, a highly trained athlete burns fat more efficiently than an untrained person, and so they tend to use more fat at a given intensity.  People who habitually eat high fat diets are also shifted to the right, meaning that they burn more fat at a given intensity.  Sympathetic nervous system activity does the reverse, shifting the lines to the left, so that you burn more CHO and less fat at any intensity.  So the point is, the above graph is an example, not an absolute guide.

Low intensity is better, right?
So, what you’re probably thinking is that theory that low intensity exercise is better if you want to burn fat is correct.  Well, think again.  It is true that at low intensity, when you walk, most of your energy comes from fat, and that as you increase the intensity, less and less comes from fat.

But what is missing in this picture is the TOTAL amount of energy.  Let me phrase it this way:  Would you rather have 20% of the money in Rynard Tissinks’ bank account, or 80% of the money in my bank account?

Your answer of course, should be that you don’t know.  And what you should be asking is “How much money is in your bank accounts?”.  The reason is, you’d be pretty annoyed if you took 80% of my money, because my bank account might be empty.  Rynard, on the other hand, might be loaded, and 20% of his money sees you retiring at 40!

So, look at the graph again.  You should not be too pre-occupied with the percentage, but rather the total amount of fat that you are burning, because that 50% that comes from fat in the green zone might be more than the 20% that comes from fat in the pink zone.  For answer to that, we look at a study done many years ago by Romijn.

Below is a graph that I’ve redrawn with some calculated figures, based on Romijn’s study.

So, you’re looking at the same kind of graph as before, showing how much of your energy comes from fat and CHO at different intensities (I’ve further divided it into muscle, liver and adipose sources, but that detail is not vital right now.  Note, however that “Plasma FFA” refers to the fatty acids that originate from the adipose tissue – the triglyceride is broken down into free fatty acids which are used).   This time though, there is also a measure of HOW MUCH total energy is being used, shown by the y-axis (in kCal/hour, for an 80kg man in this case)

So again, at low intensities (25% VO2max), you’ll see again that most of the energy comes from fat (75% in this case), with only 25% from CHO.  Jump to 60% and the fat contribution falls to 48% and then at 85%, fat provides only 20% of the total energy.  This confirms what we saw in the first graph.

But, the key is that the TOTAL energy, shown here on the y-axis, rises as well, and so the 48% of energy from fat that you get at moderate intensity actually adds up to more TOTAL fat use than the 25% did at low intensity.  Think of the y-axis (total energy) as the size of the bank account, if you will.  The green boxes above each bar show the total amount of fat burned in an hour – 24g, 37g and 23g per hour at the three intensities.
What does this all mean?  The role of time and putting it into perspective with diet
So, what this means is that if your goal is maximum fat use, then lower intensities may mean a greater relative contribution, but it is moderate intensity that gives you greater fat use per unit time.

Time is key though, as many of you are no doubt thinking.  If you do a low intensity session, walking (25% VO2max in the above graphs), then while your total fat use per hour is not as high as at say 60%, you might be able to do this exercise for three hours, compared to only one hour at a moderate intensity.  Three hours with 24 g per hour (see figure) beats one hour with 37g.  So duration plays an equally important role.  What I am emphasizing is that for a given time, you will be better off at a moderate intensity somewhere between 50% and 65%.
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Andrew Jansen Van Rensburg

www.sportandwellness.co.za