# Power Profile Index: An Adjustable Metric for Load Monitoring in Road Cycling
###### Abstract  
Workload is calculated from exercise volume and intensity. In endurance sports, intensity has been measured using heart rate or RPE, giving rise to load indexes such as sRPE or TRIMP. In cycling, the advent of power meters led to new indexes, such as TSS. All these indexes have limitations, especially for high intensity exercise. Therefore, a new index for cycling is proposed, the Power Profile Index (PPi), which includes a weighting factor obtained from the relative exercise intensity and stage type. Using power data from 67 WorldTour cyclists and fatigue records in different stage types from 102 road cyclists, weighting factors for intensity and stage type were determined. Subsequently, the PPi was computed and compared to current indexes using data from a WorldTour team during the 2018 Tour de France. The proposed index showed a strong correlation with perceived fatigue as a function of stage type (R\({}^{2}\) = 0.9996), as well as no differences in the load quantification in different types of stage profiles (\(p\) = 0.292), something that does not occur with other indexes such as TSS, RPE, or eTRIMP (\(p\) < 0.001). Therefore, PPi is a new index capable of quantifying the high intensity efforts that produce greater fatigue, as well as considering the stage type. Keywords:WorldTour cyclists; workload quantification; TSS; RPE; TRIMP; type of stage +
Footnote †: journal: _Sciencedence_  
Footnote †: journal: _Sciencedenced_  
Footnote †: _Scienced_
Although HR-based methods are easy to use and HR could be an equally useful variable as PO when planning training, it should be noted that a minimum duration is needed to reach a target HR due to a delay in HR response [11], which is not the case for PO, which is instantaneous. Therefore, despite a large body of published research using HR to analyze the physiologic demands of competition, it has been suggested that HR data is not capable of quantifying high-intensity interval training or non-steady state exercise [12; 13]. In addition, HR is influenced by external variables (e.g., temperature, dehydration, and cardiovascular drift) [14; 15] or stored fatigue, especially at the end of long-duration competitions [16]. In fact, overtraining [17] or acute fatigue may have effects on resting HR [18; 19; 20], submaximal HR [19; 21; 22], and even HR\({}_{\text{max}}\)[23]. Moreover, there can be large differences in HR at the same intensity between race and non-competitive conditions [14]. For these reasons, the usefulness of any kind of HR-based TRIMP equations for quantifying training load may be limited [7; 8; 9; 10]. More recently, heart rate variability (HRV), another HR-based metric, has proven useful for assessing daily fatigue and recovery to monitor training status [24; 25]. Therefore, combined with other methods of load quantification, it can be of great help. To overcome the drawbacks of TRIMP, traditional approaches, such as session-RPE (sRPE) [26], have been used in elite cycling [27]. However, RPE lacks an objective external intensity factor and relies solely on cyclists' perceptions. While RPE represents a reliable method of measuring workloads [13; 28], the convoluted interplay of different factors affecting the personal perception of physical exertion must be considered. Moreover, [PERSON] et al. did not observe a correlation between the average effort scores and the average relative training speed between athletes, suggesting that RPE scales might be useful for comparing or prescribing training intensities individually, but not for comparisons between different athletes [29]. The training load can be divided into two components: internal load (e.g., HR or RPE) and external load (e.g., power) [30], with the ideal being the combined use of both [31]. The introduction of power meters in road cycling allowed for the monitoring of PO. This led to important advances in the real quantification of effort during training or competition, allowing for changes in performance to be examined throughout the season [32], or even along a session or race [33].