All PKRS.AI workouts (aside from swimming) are based on Heart-rate (HR). Heart-rate is an excellent guide to the stress created by a workout and also the intensity of the workout. By training in carefully calculated HR zones, each training session is made specific to your needs and physiology. There are 6 main training zones and each zone has a specific purpose.





How it feels





Active recovery 

Very easy



Endurance development & fat burning

Easy & conversational





Strength and aerobic conditioning


Stage race




Developing sustainable race pace






Speed and aerobic capacity

Very hard






Maximal effort




Some coaches feel that heart-rate is not the best source of monitoring intensity since it fluctuates often. We however believe that it is for this reason exactly that we value heartrate above all other gauges of intensity, most of the time. Here are some factors that affect your heart-rate and what you can do when you experience them :

Cardiac Drift is when your heart-rate increases over time despite staying at the same pace/ intensity. This is very common and mostly due to an increase in body temperature and some fluid loss. A tactic to work with it is to start the session at lower end of the training zone, monitor your perceived exertion and maintain hydration throughout.

In the Heat heart-rate can be up to 30 beats per minute higher than usual. This is a reflection of significant stress on your system. In this situation, train using your normal heart-rate zones which will mean an easing off in power or pace and maintain hydration with not only water but also carbohydrate and electrolytes. Keep the skin wet to help heat dissipate from your body and be sure to use sunscreen, a hat and sunglasses to further reduce the heat’s impact on you. In cold weather you may find that your heart-rate stays lower than expected. Here rather than trying to force the heart-rate up, instead train in the lower part of the zone and also use perceived exertion to help guide the intensity.

What Does Your Heart Rate Say About Your Health? | Tri City Cardiology

Sometimes you will find that your heart-rate just won’t rise like it normally does. If at the start of a session you notice that you are having to work harder than usual to bring the heart-rate up and at the same time it does actually feel harder, then this is a sure sign of underlying fatigue. On days like this, back off into recovery mode and shorten the session. If during a longer session or race (such as a Marathon, Ironman or Ultra), you notice your heart-rate starting to drop despite maintaining the same effort then this is a sign that you are heading for the dreaded “bonk” and that your body needs carbohydrate calories and fast. 

On race day, adrenalin and nerves can reveal much higher heart-rates than you are used to seeing. Use this as a trigger to bring your focus to internal thoughts such as smooth breathing, rhythmical movement and a conscious effort to “let go”. Use power on the bike and pace on the run combined with your perceived exertion while being sure to stay on top of your calorie consumption.

For interval training, especially short intervals that are less than 3 minutes long, we suggest using power on the bike and pace on the run to guide the initial intensity of each interval. This will allow your heart-rate to gradually come up to the correct zone and prevent you from flooding your body with lactate from trying to raise the heart-rate too quickly. Always use the lap button at the start and end of each interval. The interval starts when you start the higher intensity effort.

As you can see, heart-rate gives you plenty of key information to help you get the most of your training and racing. It always tells you something and the key is to listen to what it’s saying and use your knowledge to react appropriately.


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We are excited to have you on board. Proudly considered as the official platform for Ironman and Haute Route, you are in reliable hands.

Seamlessly sync your fitness tool of choice such as Garmin, Suunto, and Strava to PKRS.AI and let us create an adaptable training plan tailor-made just for you, and have your data be expertly evaluated by our AI coach, all for less than $1 a day. And for less than $3 a day, you also get access to a coaching dream team consisting of your own head coach, nutritionist, and strength trainer, with lots more to offer.

PKRS.AI is ready for you. Available for both Android and iOS devices, download PKRS.AI today and enjoy your 7-day free trial.