SampEn (SE)

The beat-to-beat time series entropy analysis from continuous ECG recordings, while performing physical activity, may be effective in measuring fitness. 

The SampEn is a good measure of cardiovascular variability which can be related to physical condition and well-being. The sampling entropy is the best for quantifying the complexity of the HRV series.

For sedentary people, entropy decreases during a ST compared to the resting state, for active people, entropy increases, indicating greater complexity in the latter case. The results are reproducible and different entropic measurements provide similar results.

FIGURE 1. (A) SampEn for one subject where the first record belongs to the rest period, the second record to a cardiac stress condition at 3.5 mph and the third measure to a cardiac stress condition at 4 mph. (B) SampEn values for rest and cardiac stress tests of one subject in seven measures. The mean of SampEn at rest is 1.3541 ± 0.187 and at cardiac stress SampEn mean is 0.4344 ± 0. 2475.

The behaviour of entropy is the same for all sedentary, similar to that of Figure 1A

FIGURE 2. Sample entropy values for rest and cardiac stress tests for six young subjects that do regular physical activity.

Entropy values behave similarly (Figure 2) for people that have similar patterns of physical activity independently of their age.

It should be noted that with increasing physical load, the entropy value will decrease.

FIGURE 3. Five time series of active young subjects (red) and five time series of sedentary young subjects (blue) during the stress tests (4 miles per hour). The points represent SampEn values for subseries obtained from the time series with overlapping. For active subjects the average change in sampling entropy is –0.10, and for sedentary subjects is –0.11.

The results are shown in Figure 3, as we can see, the entropy values for active youth are larger than those for sedentary. On average, there is a decrease in entropy in both cases, but such decreases are very small compared to the entropy changes associated with the change in rest-exercise.

The entropy changes not only due to the change in rest-exercise, but also due to fatigue.

By measuring the value of entropy (SE), it is possible to control the load during physical exercises and fatigue after the work done. It is recommended to measure entropy values before and after exercise or in the morning and in the evening to determine fatigue after a working day.

1. https://www.frontiersin.org/articles/10.3389/fphys.2020.00981/full#F4

        2. https://www.mdpi.com/1099-4300/19/10/568/pdf