The Intense Challenge of Measuring Intensity

Understanding your different intensity zones is key to effective endurance training.

Being an endurance athlete, you are most likely familiar with the four key components of your training program: Frequency, Duration, Intensity and Recovery. How to best determine, measure and implement the “right” workout intensity has been debated within sports scientists and coaches for decades. Measuring intensity is one of the most challenging aspects of endurance exercise.

We all know that training at the proper target intensity is the key to producing the desired stress, physiological response and adaptation and that there should be a well-balanced mix of intensities in our training regimens. Nevertheless many endurance athletes simplify training by using the less complicated “the harder – the better” method. Let’s fix that by providing you with knowledge!

The first step to choosing the proper training intensity begins with understanding what intensity is, how to measure it, how it changes, and how your body responds to it. To help, I break intensity into three categories:

absolute intensity
physiological intensity
subjective intensity

Absolute Intensity

Absolute intensity can be gauged by a number of different parameters, such as speed, pace and power. They are precise, objective, and, to a large degree independent measures of intensity. In addition, these parameters are familiar and practical to use. It is for this reason that many athletes gravitate toward using absolute intensity to determine the difficulty of their workouts and if the workout was successful. However, absolute intensity does not provide insight into the specific physiological response to exercise. For example, is the physiological stress of biking 60 minutes at 250 watts the same when the temperature is 72 degrees with 40% humidity compared with 88 degrees and 70% humidity? I hope the answer is an obvious “no”. For this and similar reasons speed, pace, and power are not ideal for determining workout intensity. It can be very useful information to have though.

Physiological Intensity

Another means of gauging intensity is by the body’s physiological response. I refer to this as Physiological Intensity. The energy expenditure per minute of exercise, (EE, Kcal/min), is the metabolic response to exercise and the “gold standard” for determining exercise intensity. Each individual has a unique and specific EE and metabolic response to exercise that will vary with changes in physical fitness. EE provides an accurate, objective physiological and semi-independent means of determining exercise intensity. Unfortunately, measuring the metabolic response to exercise requires elaborate and expensive equipment along with considerable expertise. This makes monitoring EE impractical for gauging intensity in anything but an exercising testing environment (physiology lab). Heart rate, which is directly correlated to oxygen consumption, is the most convenient, practical and reliable method of measuring physiological intensity during a typical workout. It provides a window into your body to view the stress a workout puts on it. In simplest terms, HR is directly correlated with intensity so, the harder you go, the greater the physiological stress and the higher your heart rate will be. Being aware of factors that affect heart rate during a workout can make it an even more effective training tool: health status, training status, dehydration, temperature, humidity, medication, previous exercise, terrain, time of the day influence HR. Because HR is the resulting physiological response to intensity, it has a delay to changes in exercise workload. Thus heart rate is not a good indicator of intensity shortly after changes in exercise intensity (approximately 1-2 minutes).

Subjective Intensity

Wether you use Absolute or Physiological Intensity, relying too heavily on a fixed number (i.e. heart rate or watts) could over or underestimate your capability, especially when racing. That is why I like to use heart rate as the guide for physiological intensity and integrate the third measure of intensity, Subjective Intensity, as an observation. Subjective intensity is measured by your subjective effort or Rating Perceived Exertion (RPE) during the workout. Interestingly, research has shown that RPE is consistently comparable with physiological data such as heart rate, lactate concentration, respiratory rates and ventilation for a given subject.

To measure your RPE, I use a scale from 1-10:
1 = Very light
3 = Light
5 = Moderate
7 = Hard
9 = Very Hard
10 = Absolute Maximum

Now that you’ve become familiar with different categories of intensity, you may appreciate that there is no right or wrong way of measuring or implementing intensity. The art lies in combining and prioritizing one category over another depending on the session, time point within your season and additional life stressors impacting your training.

By using a combination of absolute, physiological, and subjective intensity, athletes can gain a better understanding of the specific stress and physiological response to their workouts. This can help them to tailor their training programs and choose the right intensity for their workouts, leading to better performance and reduced risk of injury. Additionally, understanding the factors that can affect heart rate and subjective intensity can help athletes to adjust their workouts accordingly and avoid overtraining or undertraining.

Florian Bögge

Head Coach

Keep in mind that intensity is also very much influenced by emotional & mental factors and in training it's just as important to listen to this aspect. On an emotionally rough day, an easy session may feel overwhelming, or on a happy day, a challenging session may feel easy.

Stefanie Sichler

Mental Power Coach

Compare your heart rates with your RPE while also observing speed, pace, and power during your training. The combined feedback of Absolute, Physiological and Subjective Intensity provides you with the most valuable information regarding your training status and whether your session was beneficial to your athletic development.

Marion Summerer

Performance Coach

Nutrition impacts cognitive and physical performance, along with all other influence factors mentioned by Coach Marion. Supporting your physiological adaptations as well as recovery with proper nutrition will help you reach your performance goals. Send me a message and we can chat more about how to dial in your nutrition!

Daniela Salvado

Nutrition Coach

Something for you to try...

For the upcoming 4 weeks use HR as a guide and RPE, speed, pace, and power as an observation. Comparing your heart rates with your RPE while also observing speed, pace, and power during your training provides you with valuable information, such as level of fitness, level of fatigue, mental state, nutritional impact, possible sickness, excitement or de-hydration. Tuning in to what you are feeling while exercising is an “intense” opportunity to train towards your potential!!