Nowadays, the heart rate is an extremely well-monitored and reliable indicator for medicine, but also for exercise, to help define your training program and, in some cases, track progress.    
But do you really know what the heart is and how it works to orchestrate the whole machinery of the body?

First of all, the heart is a muscle, along with the striated skeletal muscles (biceps, quadriceps, etc) and the smooth muscles (stomach, blood vessels), and is sometimes called the cardiac muscle.


It is part of the cardiovascular system that includes a pump (the heart), a system of canals (the blood vessels) and a circulating liquid (the blood).


This cardiovascular system is essential to proper body function since it assumes the 6 following major roles :

> Providing oxygen and nutrients

> Eliminating CO2 and metabolic wastes

> Transporting hormones

> Thermoregulation

> Regulating body fluids and acid-base balance

> Immune function

The heart plays an essential role in the blood flow by providing regular blood supply to the body.


The heart is made of 2 atria that receive the blood and 2 ventricles that eject it:
> The right atrium (1) receives the blood filled with metabolic waste.               
> It transfers it to the right ventricle (3) that sends it in the lungs where it is purified and reoxygenated.
> The left atrium (2) receives the oxygenated and nutrient-filled blood from the lungs.
> It transfers it to the left ventricle (4) that sends it to the whole body.

> All these actions are performed by the muscular part of the heart, the myocardium (5). It makes heart contractions possible, therefore enabling the continuous pump action of the heart. 

Montre cardio cardiofrequencemetre Rythme cardiaque Cardio-training Fréquence cardiaque pulsation cardiaque

1 : Right atrium                
2 : Left atrium  
3 : Right ventricle           
4 : Left ventricle              
5 : Myocardium



Red arrow: course of oxygenated and nutrient-filled blood coming from the lungs


Blue arrow: course of deoxygenated blood filled with metabolic waste coming from the body

The heart is able to generate its own contractions with no involvement of the nervous system. It naturally contracts at approximately 100 bpm.       
However, it is also regulated by nervous or hormonal stimuli in order to adapt heart contractions to the physiologic needs.        

To show how significant this regulation is, we can take the example of a cardiac transplant, where the transplanted heart will naturally contract at 70 to 110 bpm because certain self-regulation systems could not be reconnected during surgery.


The heart adapts its number of beats per minute (bpm) based on the body activity an/or external stimuli.When the needs in oxygen and nutrients are high, the heart rate (HR) will increase until it eventually reaches the max HR. On the contrary, during periods of rest, the HR will approach theresting HR. When you are stressed or consume stimulants, such as coffee, the HR may also be increased.


To do so, the body has 3 systems that affect the HR:

> The parasympathetic nervous system can reduce the heart rate and prevails when the HR is below 100 bpm.

> The sympathetic nervous system can increase the heart rate and prevails when the HR is over 100 bpm.

> The endocrine system releases hormones that will also stimulate the HR.


Sport and physical activity result in cardiovascular adaptations. Indeed, an increase in the training burden or intensity implies an increase of the oxygen needs. Therefore, the body adapts to the body needs in oxygen to support the exercise.


Adaptations include, but not limited to:

> An increase in the heart mass and volume.

> A decrease in the resting heart rate.

> A decrease of the HR during moderate/intense exercise.

> An increase in the stroke volume*, and in the maximum cardiac output*.


The easiest device to tracks one's HR is the heart rate monitor, that measures the electrical activity of your heart and shows the number of beats per minute. It helps target your training to the best and track your progress.
Originally developed for medical and professional sport settings, it is now widely used thanks to both its simplicity of use and its purchase price.


The most commonly used technology nowadays is the Bluetooth HRM strap alone (or built in a garment) that is paired with a receptor watch or a smartphone application.      
Optical heart rate watches are also increasingly available. This technology determines your HR at your wrist by measuring the variations in blood pressure in the skin capillaries.


Heart rate monitors being increasingly effective, some of them now also provide heart rate variability (HRV) measurement.          
The HRV refers to the amount of time between two heartbeats, when the HR is fairly stable. This amount of time is slightly irregular and is a reflection of the various systems involved in cardiac regulation.                
A low HRV is associated with significant psychological stress, and is considered as a major factor of increased cardiovascular risk, of cardiac incident and of sudden death. It is also provides some insight on the level of fatigue and the quality of sleep.

Tanguy DAVIN

Research and Development Engineer at Decathlon Sportslab


Stroke Volume (SV): volume of blood ejected by each ventricle when contracting.


Cardiac output: volume of total blood ejected by the ventricle in one minute.

Cardiac output = HR * SV.


- ACHTEN, Juul et JEUKENDRUP, Asker E. Heart rate monitoring. Sports medicine, 2003, vol. 33, no 7, p. 517-538.

- COSTILL, David L. et WILMORE, Jack H. Physiologie du sport et de l'exercice: adaptations physiologiques à l'exercice physique. De Boeck Supérieur, 2006.

- SERVANT, D., LEBEAU, J. C., MOUSTER, Y., et al. La variabilité cardiaque: un bon indicateur de la régulation des émotions. Journal de thérapie comportementale et cognitive, 2008, vol. 18, no 2, p. 45-48.


And now that we briefly explained the heart function, take your HRM watches and measure the impact of your workouts to get a more precise idea!