## 4 Experiments and Results
### Results
#### 4.1.2 Case Study 1: Results of the Professional Cyclist  
In Case Study 1, a professional cyclist was invited to implement a proposed interval training session as presented in Algorithm 4. The interval training session was estimated  
Figure 3: Implementation of the interval training session with the depiction of the digital twin prediction on a Raspberry Pi computer. by a sport trainer as moderate, because it consisted of 10 repeats of the speed/recovery intervals, where the speed interval lasts 1 min at an intensity of 150 bpm (i.e., the tempo HR zone), while the recovery one lasts 2 min at an intensity of 90 bpm (i.e., the active recovery HR zone). Research Question 1 (RQ-1) in the Case Study 1 was set as: \"How to determine that the cyclist implementing the interval training session is a professional by using the DT in cycling?\". The average efficiency of the implementation was measured and recorded by the DT. The experimental period was of duration \(10\times 3\) min = 30 min, where 10 denotes the number of experimental phases and 3 is duration of one speed/recovery interval. Normally, the implementation of the sport training session was conducted 2 h after eating. Here, a time series analysis was performed for the participant and the results of the analysis were visualized. The following criterion was asserted for accepting the proposition: \"If the efficiency of the implemented interval training session is higher than 90%, then the cyclist is a professional cyclist\". The implementation of the interval training session was performed in sunny and calm weather at 24\({}^{\circ}\), while a straight round track with little traffic was selected for the implementation. Consequently, the cyclist can be focused only on his riding on the track. The results of the implementation of the interval training session are illustrated graphically in Figure 4, which is divided into 10 speed/recovery intervals, displayed according to the overcoming time (x-axis) by the heart rate (y-axis). Actually, there are two different heart rate curves drawn: the proposed \(\overline{HR}_{spe}\) or \(\overline{HR}_{rec}\), and the measured \(\overline{HR}\). Thus, the proposed heart rate curve is drawn in red, while the measured one in blue. As can be seen in the diagram, the cyclist's measured \(\overline{HR}\) tries to follow the proposed \(\overline{HR}_{spe}\) or \(\overline{HR}_{rec}\) as closely as possible. Interestingly, only in speed intervals 1, 4, and 6, the measured \(\overline{HR}\) overcomes the proposed \(\overline{HR}_{spe}\) substantially, while, in the other cases, the \(\overline{HR}\) is near to or below the proposed \(\overline{HR}_{spe}\). When the recovery intervals are observed, it can be concluded that the prominent valleys overcoming the proposed \(\overline{HR}_{rec}\) arose in the recovery intervals 1, 3, 6, and 10. In the other recovery intervals, the measured \(\overline{HR}\) is near to the proposed \(\overline{HR}_{rec}\). Let us emphasize that the prominent peaks and valleys are a necessary condition for achieving the average for either \(\overline{HR}_{spe}\) or \(\overline{HR}_{rec}\). Although the diagram in Figure 4 illustrates explicitly how the measured \(\overline{HR}\) adapts to the proposed \(\overline{HR}_{spe}\) and \(\overline{HR}_{rec}\) based on the predicted \(\overline{HR}_{pred}\) online, we are interested in how efficient was the implementation of the interval training sessions in the sense of the training load indicator TRIMP. In line with this, the \(TRIMP_{spe}\) and \(TRIMP_{rec}\) are calculated for each speed and recovery interval, respectively. The calculated results for the speed intervals are presented in Table 3, which is divided into more columns denoting the proposed average TRIMP for the speed interval \(\overline{TRIMP}_{spe}\), the measured TRIMP in the same interval \(TRIMP_{spe}\), the difference between the proposed average and measured speed intervals \(\Delta TRIMP_{spe}\), and the corresponding efficiency \(SR_{spe}\). Figure 4: Professional sport training.