# Algorithm-Based Real-Time Analysis of Heart Rate Measures in HIIT Training: An Automated Approach
## 3 Results
### Analysis of HIIT Sessions  
In this section, we present the results obtained by the algorithms applied to three HIIT routines. In all analyzed cases, the automatic identification of the maxima and minima was successful. Based on these, the ascending and descending slopes are calculated, as  
Figure 3: Heart rate signal of five periods of a HIIT routine. (**a**) Smoothed series with marked maximum and minimum values and (**b**) original series. well as the intermediate averages between each pair of maxima and minima (minima and maxima). The proposed algorithm successfully identified the maxima and minima of heart rate signals across all analyzed HIIT sessions. Figures 4-6 illustrate the original signal and its smoothed version, highlighting the detected extrema. The automated detection process proved to be both reliable and consistent, eliminating the need for manual supervision while ensuring precise data extraction. From these detected maxima and minima, we calculated the ascending and descending slopes, as well as the intermediate averages. As shown in Tables 1-3, the ascending slopes indicate how quickly the heart rate increases during high-intensity intervals, while the descending slopes reflect the rate of recovery. The analysis revealed that participants in better physical condition exhibited lower ascending slopes and higher descending slopes, suggesting a more efficient cardiovascular response. In contrast, participants with steeper ascending slopes and shallower descending slopes showed signs of reduced fitness or insufficient recovery between intervals. Additionally, the sequence of maxima and minima was analyzed to determine whether the HIIT sessions followed the expected progressive trend. A well-executed HIIT routine should display an increasing pattern in both the maxima and minima across the intervals, indicating progressive cardiovascular adaptation. Figure 4: Session 1: (**a**) Heart rate signal for a HIIT routine. (**b**) Smooth version of the signal and identification of the maxima and minima. Figure 5: Session 2: (**a**) Heart rate signal for a HIIT routine. (**b**) Smooth version of the signal and identification of the maxima and minima. This trend was observed in most participants, though deviations were noted in cases of early fatigue or improper pacing. The capability of this algorithm to track these variables over multiple sessions enables the creation of an individual performance history. This feature provides a valuable tool for trainers and practitioners to assess progress objectively and adjust the training protocols accordingly. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Maxima (Bpm)** & **Minima (Bpm)** & **Intermediate** & **Ascending (Bpm)** & **Descending** \\ \hline
152.81 & 117.57 & 135.19 & 1196.14 & \(-\)1256.98 \\
160.35 & 126.35 & 143.35 & 1154.06 & \(-\)1532.90 \\
169.19 & 128.10 & 148.65 & 1394.94 & \(-\)1341.29 \\
171.77 & 131.90 & 153.55 & 1732.18 & \(-\)1184.17 \\
177.87 & 140.39 & 154.89 & 1365.24 & \(-\)1781.23 \\
160.55 & 132.52 & 150.47 & 598.79 & \(-\)1332.09 \\
180.61 & 132.52 & 156.56 & 1904.63 & \(-\)1391.11 \\
179.77 & 145.48 & 162.63 & 1357.90 & \(-\)1390.34 \\
150.52 & & & & \\ \hline \hline \end{tabular} Note. Bpm: beats per minute.  
\end{table} 
Table 2: Maxima, minima, and intermediate averages and ascending and descending slopes in Session 2. Figure 6: Session 3: (**a**) Heart rate signal for a HIIT routine. (**b**) Smooth version of the signal and identification of the maxima and minima. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Maxima (Bpm)** & **Minima (Bpm)** & **Intermediate** & **Ascending (Bpm)** & **Descending** \\ \hline
146.94 & 104.45 & 125.69 & 655.51 & \(-\)2044.05 \\
156.00 & 109.09 & 132.54 & 633.31 & \(-\)2193.35 \\
159.12 & 115.38 & 137.25 & 555.70 & \(-\)1813.76 \\
161.47 & 125.53 & 143.50 & 485.21 & \(-\)1588.23 \\
164.29 & 124.71 & 144.50 & 570.07 & \(-\)2001.17 \\
127.24 & & & & \\ \hline \hline \end{tabular} Note. Bpm: beats per minute.  
\end{table}