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Introduction to Heart Rate Training

By Douglas Bush for Inside Triathlon

Training at the proper intensity while swimming, biking, and running is one of the key elements in improving athletic performance and staying injury free. Often times many athletes subscribe to the theory harder is always better mentality during workout, this not the case. The vast majority of workouts should be performed at an easy to moderate intensity.

How do you determine the proper training intensity?
Biking and running with a heart rate monitor is a great way to ensure you are working out at the proper intensity. Training while wearing a heart rate monitor gives the athlete immediate feedback about training effort.

It is essential to develop a strong aerobic base which allows the body to efficiently metabolize stored body fat while sparing stored carbohydrate. During exercise other adaptations that occur during exercise are increased density of capillaries to muscles and connective tissue. These adaptations can only occur when exercising at an easy to moderate intensity and that is why it is very important to develop this aerobic base before doing higher intensity sessions.

One of the most confusing things about using a heart rate monitor during training is to establish heart rate training zones. A number of formulas have been developed to estimate training zones based around maximum heart rate. These formulas are estimates and can be up to 30 to 40 beats off for an individual.

A much more precise method for establishing training zones is to base the zones around the lactate threshold. Lactate threshold is an exercise intensity in which the body can no longer clear one of the by-products of exercise and this by-product begins to accumulate in the blood. This is the burn that is felt in the muscles during hard efforts and races. Elite athletes have been using this method for establishing training zone for quite a long time. More information about lactate threshold can be found on my website by clicking this link.

The most accurate method of determining lactate threshold is through laboratory testing. For more information on threshold testing please go to this LINK. Field tests are another method that the athlete can perform on their own to estimate lactate threshold heart rate. The field tests are a good approximation of lactate threshold heart rate and this is a much more precise method than using the max heart rate formulas.

To do this test you will need a heart rate monitor (one that has a lap function is best but not necessary). The test should be performed for both biking and running as training heart rates can be very different for each sport. Make sure to be very well rested and hydrated for the tests and plan a few days rest between both of the tests.

It is best to retest training zones every 3 – 4 months as lactate threshold heart rate does change dramatically due to changes in fitness.A word of caution. These tests are quite strenuous and you should consult your physician before starting an exercise program.

Testing Protocol:

Make sure to warm up well for 10 to 15 minutes before starting out. The field test is going to be an individual time trial of 30 minutes. The effort should be very hard, but not so hard that you slow down at the end, think race effort of about 10k running or 30k bike time trial effort.

Start the time trial and make sure to press the start button on the heart rate monitor. After the first 10 minutes press the lap button and press the lap button again at 30 minutes. Cool down 5 to 10 minutes easy. The average heart rate over the last 20 minutes is your lactate threshold estimate.

*Note: If your heart rate monitor does not have a lap function look at the watch every minute and make a mental note of average heart rate over the last 20 minutes of the test.

Now that you have your lactate threshold heart rate what do you do with it? Using the chart below calculate your heart rate based upon the lactate threshold heart rate you established in the field test.

% of LT % of LT
Training Zones Lower Upper
1 – Active Recovery <80%
2 – Endurance 80% 89%
3 – Tempo 90% 93%
4 – Subthreshold 94% 99%
5a – Suprathreshold 100% 102%
5b – Aerobic Capacity 103% 105%
5c – Anaerobic Capacity >105

Zone Descriptions:

Zone 1: Active Recovery: Research indicates that after hard workouts, very easy workouts accelerate recovery more than complete rest. Easy aerobic training stimulates circulation which speeds up healing of tissues that have been damaged by hard training. For this purpose, it is absolutely critical to maintain an intensity that is enough to increase blood circulation and to trigger a growth hormone release, but not intense enough to increase the damage from which the athlete must recover.

Zone 2: Aerobic Threshold (AeT): Training at this intensity maximally overloads the slow-twitch muscle fibers, increasing endurance. Since these fibers produce most of the energy and create most of the power for any endurance event lasting four minutes or longer, workouts at this intensity should comprise most of your training. Note that training in this zone is the most effective way to overload the endurance fibers and that training above this intensity is less beneficial for this purpose.

At low intensities, fat is the primary fuel for exercise. Obviously, this is important for body-fat reduction but it is also important when training for events of two hours or longer. The body stores one to two thousand calories as carbohydrate, but even the leanest athlete stores many thousand calories as fat. Carbohydrate will always run out before fat. Therefore, fat is the ideal fuel for long distance racing. Training at this intensity increases fat burning and decreases carbohydrate burning.

Athletes training for shorter events with higher intensity need to perform much of their training at this level to stimulate improvements in the slow-twitch fibers. Performing basic aerobic workouts at too high intensity reduces the effectiveness of harder workouts on subsequent days by fatiguing and/or depleting carbohydrate stores of the fast twitch fibers.

This zone will feel very easy – you may find it hard to believe that this is training at all! For many people, the most difficult part of following a systematic heart-rate training program is keeping the intensity low enough on easy days and long workouts. Staying in zone 2, when appropriate, is critical for everyone. Going too hard on easy days is the #1 cause of overtraining.

Zone 3: Tempo Training In zone 3, the body is still functioning aerobically. The effort is comfortable, conversation is possible, and burning in the legs and shortness of breath are minimal. Still, the intensity is too high for maximal stimulation of the slow-twitch muscle fibers and for fat-burning. As intensity increases from zone 2 to zone 3, the circulatory system cannot get proportionally more oxygen to the muscles. Since it takes more oxygen to burn one calorie from fat than from carbohydrate, more carbohydrate and less fat will be burned.

Zone 3 training does increase glycogen storage in the muscles and has a slight aerobic benefit, but the cost is high for recovery before tomorrow’s workout. Since training in zones 4 and 5 burns nearly 100% carbohydrate, it is critical that carbohydrate stores be full on these hard days. At zone 3 intensity, you really aren’t going hard enough to make yourself faster, but you are going hard enough to deplete yourself for tomorrow’s workout.

Zone 4: Lactate Threshold Lactate Threshold (LT or AT for anaerobic threshold) is the highest intensity at which the body can recycle lactic acid as quickly as it is produced. In zone 4, the aerobic and anaerobic systems are working together in balance to provide energy for exercise. Anaerobic metabolism is slow enough that lactic acid, the substance that makes muscles burn during hard exercise, does not accumulate. At this intensity, the athlete is working very hard, but the exercise can be maintained because lactic acid levels in the blood and muscles are steady, not increasing. Increasing the intensity just slightly causes lactic acid to build up and brings premature fatigue and dramatically delays recovery from the workout.

Training near lactate threshold decreases the amount of lactic acid being produced and increases lactate removal at a given output. At this intensity we train the FOG fibers to produce less lactic acid and we train the slow twitch fibers to burn more acid, both of which raise the speed or wattage of lactate threshold, a primary goal of training. Since lactic acid levels are controlled, recovery from this type of training is quicker than from other high-intensity training methods, therefore Zone 4 training has the best Cost : Benefit ratio of any type of training.

The lower end of Zone 4 is best for long (20-60 minutes) tempo segments at a very steady pace. The primary function of training in low zone 4 is to increase the endurance of the FOG muscle fibers, which extends the duration the athlete is able to maintain anaerobic threshold intensity.

The higher end of Zone 4 is best for cruise intervals or moderately long (12-30 minutes) tempo segments. Cruise intervals are short tempo segments of four to six minutes with one to two minute recovery segments at a lighter intensity between efforts. The primary benefit of high zone 4 training is to increase the power output of the FOG fibers.

Zone 5a: Super-threshold Training: In zone 5a, the energy demand is too high to be met mostly through aerobic metabolism. Anaerobic metabolism increases to the point where lactic acid accumulates in the muscles and blood. At this intensity, lactic acid accumulates slowly, so this intensity may be sustained for a relatively long period. This is effective work since many races, such as a 40K time trial or a 10K running race occur at this intensity. Workouts at this intensity are also effective for increasing lactate tolerance, the ability of the muscle to continue to produce speed and power effectively despite the accumulation of acid.

Zone 5b: Aerobic Capacity Training: In zone 5b, lactic acid builds up quickly, so this intensity cannot be sustained for long periods. At this intensity, the aerobic system is working at 95 – 100% of maximum. This training takes two forms:

• Interval Training, zone 5b efforts of one to three minutes followed by short periods of low level exercise which allow only partial recovery from the repetition. Usually the work to rest ratio is between 1:1 and 2:1.

• Repeat Training, zone 5b efforts of 3 – 7 min with longer periods of low level exercise or rest which allow complete recovery from the repetition. The work to rest ratio is usually below 1:1.

Zone 5 training is a very effective means of increasing endurance performance, but, because lactic acid levels become extremely high, this type of training requires extensive recovery between workouts. Zone 5 training carries a high cost and benefit. Make sure to include these workouts when appropriate, but be just as sure not to overdo them. A little bit goes a long way. Aerobic capacity training is a powerful tool, but a little bit goes a long way.

Zone 5c Anaerobic Capacity Training: While aerobic conditioning is critical to endurance performance, situations arise in races where the energy cost far exceeds the athlete’s aerobic capacity. These situations call for high levels of anaerobic energy production followed by a period of recovery. Training for short durations in zone 5c prepares the athletes for these demands.

In addition to increasing an athlete’s sprint power, training at this intensity will improve an athlete’s economy, or efficiency. Every athlete should take this kind of training seriously as it take a long time to recover from these workouts.

There are numerous books that cover heart rate monitor training in detail and this article is intended to give the basics for heart rate monitor training. For a much more in depth guide to using a heart rate monitor and a great resource in general I recommend reading Joel Friel’s, “Triathlete’s Training Bible”.

Many of the ideas in this article are based upon Joe’s training philosophy.

Thanks to Ken Mierke of Fitness Concepts for allowing me to use his descriptions of training zones.