Power has undoubtedly taken over the cycling world as the must-have metric. What started out as an expensive wired contraption that could only be used on a stationary bike has developed into a wide range of increasingly more affordable and portable wireless units with connectivity to multiple devices. Stages was arguably the first to produce a relatively cheap power meter and since then companies like Garmin, PowerTap and Quark have all made efforts to offer a more affordable version of their staple products. This decline in price means that almost everyone from the serious racer to the casual Saturday rider is now tracking and using power in some way. But there was a time before power when heart rate reigned supreme as the invaluable training metric. It’s importance in the world of training has seen a sharp decline since the introduction of the power meter and many riders have opted to abandon heart rate altogether in favour of the absolute and objective watts over the subjective and variable BPM. It’s not uncommon to hear someone on a Saturday group ride proclaim, “I don’t even wear my heart rate strap anymore. I don’t see the point.” So does heart rate still have a place in a world of power?
The short is yes of course it does. It’s still a valuable metric for the same reason it always was a good metric. It tracks what’s actually happening in your body in that moment. Yes HR is delayed when it comes to effort, particularly in short hard efforts, but it nonetheless is tracking a physiological action in your body. Power might be an objective measurement of how hard you are working but it gives no feedback as to what is actually going on in your body and how external and internal forces might be acting on it. Used in conjunction with power, heart rate is great tool for monitoring how the body is coping with stress from not only hard riding but temperature, diet, fatigue, etc.
Heart rate is good indicator of fatigue and predictor of sickness.
We all have those days where we hop on the bike to do some sweet spot or threshold intervals and for some reason we just can’t get the power numbers up to where they should be. It’s especially frustrating if we were able to push out that wattage just a few days or a week prior. There are three main causes for such a thing to occur: the first is fatigue, the second is reduced fitness and the third is that you might be getting sick. The second is only likely if you’ve been off the bike for a significant amount of time. The first and third generally comes with symptoms such as a general feeling of weakness, tiredness, soreness etc. But sometimes they don’t. I can’t begin to count the number of times I’ve had plenty of rest, jumped on the bike thinking I had fresh legs but couldn’t push out the watts I normally do and then two days later I’m in bed with a cold. Often an impending sickness will manifest in poor performance well before any of the symptoms of sickness hit. In this case an elevated heart rate coupled with reduced power can indicate the onset of illness. In the case of fatigue, a reduced or unresponsive heart rate can indicate that more rest is needed. Knowing your heart rate zones and wearing your HR monitor can keep you informed as to how fatigued your body might be. If you are pushing out zone 4 power but your heart rate refuses to climb above zone 3, this can indicate fatigue. It might be best to take a recovery day and ride easy.
Heart rate is affected by temperature and the body’s ability to regulate temperature
Most of the time when riding in cold or hot conditions you know that the temperature is having an affect on your body. In high heat conditions you tend to sweat more, breathe heavier, and feel tired or sluggish. In a long hot race a sudden increase in heart rate can indicate an increased strain on the body’s ability to cope with the heat. This can mean either that the temperature has increased or the body is lacking proper hydration to adequately cool the body. Think of the heart like an engine in a car. All of your vehicle’s primary accessories, A/C, power steering, heat, radio, etc, are all powered by the engine. When you tax one of these systems –such as crank the A/C on a hot day, the engine has to work harder to both power the A/C unit and keep the car moving. In hot weather for example the body has to work harder to combat the heat and stay cool. This increases the workload on the heart. Knowing how your heart responds to heat can help with heat management and to develop strategies for hydration while working hard in extreme temperatures.
Heart rate can indicate endurance capacity
One of the key elements of endurance sports is endurance –the ability to go hard for a long time. If you go out on a long 4-5 hour endurance ride with just power, all you’ll know that is that you’re pushing out x number of watts for x number of hours. This is great but it doesn’t tell you how well your body is able to handle prolonged activity. The phenomenon known as cardiac drift can indicate to an athlete when the body is reaching a point where it’s endurance ability is being stretched. Cardiac drift is when the same effort level starts to produce a higher heart rate. For example, let’s say when you started the ride you were at 200 watts and your heart rate was 130bpm. Now 3 hours into the ride you’re still pushing out 200 watts but your heart rate has climbed to 138bpm. And after another hour its up to 142bpm. The rise in heart rate over time indicates that you probably aren’t conditioned for such prolonged endurance efforts. This is true of any steady state effort, not just long steady distance riding. It’s possible to predict that FTP will increase in the next power test by keeping an eye on heart rate while doing 20 min sweet spot intervals. After adjusting training zones to a new higher FTP, the first few sweet spot workouts will show a gradual rise in heart rate over the 20 minute interval. After a 3 week block of training, when more accustomed to the wattage, heart rate will often stay roughly the same throughout the whole 20 minute block.
Heart rate can save your life
Simply put, power can’t tell you if you’re having a heart attack or experiencing exercise induced arrhythmia. Many age group athletes are well into their 30s, 40s and 50s or higher. In fact in most iron-distance events the largest age group is Men 35-45. While still very young in general, once you hit the big 4-0 the risk of heart-related problems starts to rise. Sometimes even the healthiest people have the worst genetics and this is usually the age that things like arrhythmias can start to manifest. Keeping that heart rate strap on will give you a clear indicator that something is wrong. Even if you don’t recognize it as a problem, just stopping to adjust your strap thinking its an issue with the monitor might be enough to save your life in the event of a heart malfunction. We don’t like to hear it but racing and training hard year after year, especially as we age, can have serious negative effects on the heart. The very activity we do to keep us fit and healthy can also kill us. Repeated hard intervals and racing can thicken the walls of the heart and lead to abnormalities in heart rhythm and function. Many athletes suffer from some form of fibrillation. You might even notice it during your rest weeks. Often athletes notice abnormal skips in their heart-beat when at rest. Wearing your heart rate monitor is good practice for anyone who wants to keep on living.
Heart rate might not be as useful or objective as power when it comes to training or improving performance but it does give us a small window into what’s actually happening in our body when we exercise. And knowing how the heart reacts to different stimuli, whether it be internal or external can help us analyze and develop strategies to make ourselves more efficient and allow us to keep turning those pedals or pounding the pavement. It might also allow us to go on living a little longer.
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