This article is from the 'Science of Endurance' column featured in the New Zealand Triathlon and Multisport Magazine
Until recent times portable heart rate monitors were a tool only accessible to elite athletes. Now heart rate monitors are readily available and it is rare to meet an endurance athlete who does not monitor their heart rate during training. The majority of athletes that I consult with do not fully understand why they measure heart rate during training and only a small percentage train effectively using heart rate zones. With this in mind, this article aims to provide some back ground on why it is useful to measure heart rate during training, an insight into different methods of setting heart rate training zones and some limitations of heart rate for gauging training intensity.
Heart rate (the number of times your heart beats per minute) is a useful monitoring tool for endurance athletes because the relationships between heart rate and other variables such as oxygen consumption (VO2) and some metabolic processes during exercise are well known. During exercise we are not interested so much in heart rateper se. It is more that heart rate provides a convenient window into the body through which we can use known relationships to indirectly measure what energy systems (aerobic/ anaerobic) an individual is using. Using this information it is possible then to train at an intensity (with the guidance of a heart rate monitor) which targets the specific aspect of the energy system you want to train and in doing so taking some of the guess work out of your training.
Heart rate training zones have long been used to guide athletes training intensity. Most people are familiar with heart rate training zones that specify the heart rate an individual should be training at for active recovery, aerobic development, tempo, threshold and high intensity training sessions. However, there is a lot of mixed information about what any given individuals heart rate should be for these training zones. Below is an outline of four different methods that are commonly used to determine heart rate training zones and some of the pros and cons of each method.
Percentage of Max HR
One of the most common ways to determine heart rate training zones is as percentages of age predicted maximum heart rate. This can easily be calculated via taking 220 and subtracting the individuals age. This equation is based on the approximately linear relationship heart rate has with VO2 and the assumption that max heart rate decreases one beat per minute each year. While this method is simple to use, the relationships and assumptions the equations are based on often do not hold true for athletes. One way that this method can be improved is through the determination of actual maximum heart rate. This can be determined in a sport science lab or during a maximal exercise protocol outdoors. Achieving a ‘true’ maximal heart rate is difficult to do, as it requires a lot of motivation and is very stressful, so it is not appropriate for some individuals.
Heart Rate Range
Another equation that is somewhat more accurate than the above equation is that of heart rate range (aka, heart rate reserve). This equation takes into account an individual’s resting heart rate as well as their maximum heart rate (actual or age predicted)
Heart rate range= (HRmax – HRRest)*(% of training zone) + (HRRest).
From these equations percentages of heart rate range are calculated to determine specific training zones. While this method is an improvement on the percentage max heart rate method there are still a number of assumptions made in these calculations.
Anaerobic threshold testing (aka, Lactate testing) in a sport science lab is one of the most accurate ways to determine individualised heart rate training zones. During such a test an individual’s metabolic (lactate) and cardiovascular (heart rate) response profile to different work rates (power or speed) is determined. From this profile key aspects relating to the response of lactate accumulation in the blood allows individualised heart rate training zones to be calculated. This method provides accurate individualised training zones based on the athletes underlying metabolic processes. These tests however, can be relatively expensive compared to the other methods due to the specialised equipment and expertise required.
Field testing can be used as an alternative to lab base anaerobic threshold testing to provide sport specific individualised heart rate training zones. A simple test that can be performed is a maximal work trial over approximately 20-30 min. The average heart rate and athletes holds over this work trial approximately represents their anaerobic threshold. Using this value along with some assumptions about heart rate and lactate, training zones can be calculated relatively accurately.
All of the above methods have pros and cons. Table 1 outlines a summary of the four different methods described here and what the different training zones are based on. Furthermore, Table 2 provides an example of the large variation in heart rate training zones calculations between the different methods described above.
It should be noted that heart rate at any given intensity is different for different disciplines. Posture, size of the exercising musculature and technique all affect exercising heart rate. With this in mind, for the greatest accuracy triathletes and multisporters should determine heart rate training zones for each of their separate disciplines.
While heart rate is a useful training tool for endurance athletes it is important that its limitations are acknowledged. Many factors including the heat, altitude, hydration status, emotions, exercise mode, illness and fatigue all effect heart rate. Therefore, it is important that heart rate is interpreted carefully and used in conjunction with perceived exertion i.e. how hard you feel you are exercising.
If you have any questions or suggested topics for the next instalment of the ‘Science of Endurance’ please contact me with them.