Monitoring your training load is a great way to keep track of what you have been doing and identify what has worked for you and what hasn’t.
Previously, weekly distance (kilometres covered in training) and hours spent training have been used to quantify training. However, both of these training load metrics (distance and duration) ignore training intensity. Training intensity is a major component of training load and failing to monitor it could reduce the quality of your training programme. The most direct measure of cycling intensity is power output. It is not influenced by external factors and cycling is one of only a handful of sports where power output can be measured during both training and racing. Power meters have become increasingly more affordable, but may still be out of reach for most cyclists.
Heart rate has been used to monitor training intensity since the 1980s and the affordable nature of heart rate monitors has made them common training tools. Ensuring that you are training a the correct exercise intensity will play a major role in your favourable response to a training programme. One common method used to devise heart rate based training zones is simply to train at relative percentages on your maximal heart rate. These percentages are often based off an age-predicted maximal heart rate (220 – age = maximal HR). Predicting your maximal heart rate using this equation may be accurate for some, but for others, it could greatly under- or over-estimate their maximal heart rates. In addition, using relative percentages of your maximal heart rate to set your training zones does not take into account individual metabolic differences between cyclists. When you or your coach are designing a training programme, you will aim to target certain energy systems (oxidative vs glycolytic metabolism as examples) during specific training sessions. It is hard to target these energy systems if you do not know at what intensity (heart rate range) they occur.
It is recommended that you perform a maximal incremental exercise test at a recognised facility to help determine your personal training zones. Two recent studies have shown that training with individualised training zones results in superior training adaptations compared to training at percentages of a (predicted)
maximal heart rate (1, 2). Training according to specific training zones, which are based on your metabolic thresholds, will improve both the specificity and quality of your training. You can’t exercise below, at or above your specific threshold intensity if you don’t know at which heart rate range it occurs.
It is important to remember that heart rate can be influenced by external factors when training. Fatigue will typically result in a suppressed heart rate and this will manifest as a slow rise in heart rate despite an increase in effort. Environmental temperatures will also influence heart rate. As our body temperatures rise, we send more blood to the skin to help cool our bodies down. The skin and muscles are now both competing for blood flow, so the heart beats faster to match the increased demands. Finally, it is CRITICAL to remember that your heart rate will be elevated during a race when compared to similar intensities (power outputs) in training, so you should never use your heart rate to pace yourself during a race. It will most likely result in an over-conservative approach and a poor performance. These factors do affect heart rate data, but heart rate is still a very effective tool for monitoring training intensity.