How Heart Responds to Physical Activity

In those wonderful days when I didn’t run marathons, I was already concerned about what our bodies tell us. I did some scientific work exploring the relationship between heart rate and physical activity. Here is what I discovered.

A Minute of Theory

You, me, and the sexy girl next door — we are all biological systems. When biosystems have mechanisms to maintain the stability of their own state, (homeostasis) they are also open to external impacts that are fundamentally necessary for their existence. In response to every external impact, a biological system starts its adjustment mechanisms for self-preservation.

If an external impact is constant and continuous, the adjustment reaction should look like this:

First, there is a steady condition before the impact (1). Then some transitional peak process occurs in response to the start of the impact (2). While impact is still in effect, the steady process sets in (3). Finally, there is the recovery process during post-impact time (4).

The form, the lasting, the maximum value of the process (2), and the lasting of the process (4) depends on the system’s inner condition as well as the external impact value.

It doesn’t matter what the specific biosystem is under the loop or what the units of impact are. It is important to know that the adjustment reaction is typical. Almost every biological system works the same.

When we talk about physical activity, the impact is a physical load. The biological system in this case is our cardiovascular system. The adjustment reaction on a physical load is the changing in our heart rate. Heart rate values depend on body fitness and on the physical load value the body is faced with.

Time for Action

Science is boring when it’s on paper. Let’s do some experiments. For a while I was trying to find a perfect lab rat, but then realized… it’s me! Not-the-newest-one heart rate monitor with a strap placed on a chest, a stopwatch, and I’m ready.

I’ve taken HR measurements while walking, running, and cycling. I’ve performed several training sets with each duration being 10 minutes (pre-training resting time, training, post-training resting time). Walking and running were outdoors. Cycling was indoors. Cycling on a stationary bike. Boring, but it allowed me to set the required load. The results are shown below.

Heart rate changes in response to different load testing

As seen, the adjustment process could be perfectly identified on the graphs: constant heart rate while resting (1), transition process with achieving maximum HR level (2), steady HR level stage while training (3), recovery process to get the heart rate to the resting level (4). By the way, for high-load training (running and biking) the heart rate tends to increase during the entire course of the training.

By comparing the data, we can draw the following conclusions.

  • The higher the load, the longer the maximum heart rate is achieved.
  • Accordingly, the longer the stage of the transition process (2).
  • If the duration of the transition process (2) is longer, the duration of the steady heart rate stage is shorter (3).
  • The higher the load, the longer it takes to return to the resting heart rate level (4).
Hello!

Although I found the stationary bike boring, I’ve needed to take more measurements on it…

I did one training session at almost one hour in duration. It was divided into 5 sets with an increasing load in each set, and with resting time between.

Stepped increasign load test on stationary bike

This stepped increasing load test perfectly shows what overworking is. My resting HR level of 80 BPM was not reached even after the fourth phase (I still remember that feeling). This kind of load testing is widely used in sports medicine.

Putting each set on one time frame we can observe and draw the same conclusions early. The higher load causes a higher maximum HR, a longer time to achieve it, and a longer recovery time.

So What?

Arising pathological processes in a biosystem change the adjustment reactions in many cases. This is reflected in the changes in shape, intensity, and duration of the transition process. When these signs of adjustment reaction depend on the biosystem’s state of health, they are thus diagnostically significant.

It means that the deterioration of the system could be detected knowing these signs. For example, the intensity and duration of a transition process increases when the pathological state of the system grows.

In the case of heart diseases, a diagnosis knowing the adjustment reaction on a physical load gives doctors the opportunity to identify the pathology. In other words, from knowing only the heart rate and physical activity, we can diagnose abnormalities.

Understanding what is described above, we have started working on Heedio — a device for continuous heart monitoring. The device type and sensor technology could be different: a stylish ring with an optical sensor, wristbands (well-known today), or adhesive patches with ECG. The challenge here is to create as much of an invisible sensor as possible while still measuring as accurately as possible. But the importance of heart rate data is priceless.


Besides exploring basic physiology processes over nights, I’m experienced designing interfaces for web/mobile applications as well as for hardware devices. Portfolio on Behance.

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