# Algorithm-Based Real-Time Analysis of Heart Rate Measures in HIIT Training: An Automated Approach
## 2 Materials and Methods
### Procedures  
All testing sessions were conducted in a climate-controlled indoor cycling facility maintained at 21 \(\pm\) 1 \({}^{\circ}\)C and 50 \(\pm\) 5% relative humidity. Each participant completed six sessions, a preliminary assessment and familiarization session, and three standardized HIIT protocol sessions. The sessions were separated by at least 48 h but not more than seven days to minimize the effects of training adaptations while ensuring recovery between sessions. The preliminary session included anthropometric measurements (height and weight), resting heart rate assessment after 10 min of seated rest, and completion of the PAR-Q+ questionnaire. The participants were then familiarized with the indoor cycling bicycles, the equipment, and the HIIT protocol.  
For the experimental sessions, the participants arrived at the laboratory in a rested state and were fitted with the Garmin heart rate band and WIMU PRO device. After a 5 min seated rest period to establish baseline heart rate, the participants completed a 10 min standardized warm-up on the cycling bikes, consisting of 5 min of light cycling (RPE 3-4 on a 10-point scale) followed by 5 min of progressive intensity increases, including three 20 s accelerations to prepare for the high-intensity intervals. The HIIT protocol consisted of three standardized sessions that all participants completed, including Session 1 with five intervals, Session 2 with eight intervals, and Session 3 with eleven intervals. Each session included HIIT intervals at high intensity (85-90% of estimated maximum heart rate) interspersed with active recovery periods (60-65% of estimated maximum heart rate).  
Participants were instructed to maintain cadence between 85 and 95 rpm during high-intensity intervals and 60-70 rpm during recovery intervals, with the resistance adjusted individually to achieve the target heart rate zones. As shown in Figure 2, the indoor cycling facility was equipped with stationary bikes arranged to allow instructor supervision, and a large display screen mounted on the wall provided participants with real-time visual feedback on their current heart rate, exercise zones, and time remaining in each interval. Verbal encouragement was standardized throughout the sessions.  
Figure 2: Indoor cycling facility setup for HIIT sessions. Participants performing the standardized protocol on stationary bikes with heart rate monitoring and real-time feedback displayed on the wall screen.  
Following the HIIT intervals, the participants completed a 10 min cool-down consisting of low-intensity cycling with gradually decreasing resistance. Heart rate data were recorded continuously from the beginning of the warm-up until the end of the cool-down period. Only the data of the main part of the session (HIIT intervals) was utilized for further analysis. Throughout all sessions, a certified indoor cycling instructor supervised the protocol to ensure correct execution, and a researcher monitored heart rate responses to verify that the participants were reaching the intended intensity zones.