The necessity of measuring all the variables related to training process to understand the improvement of the athlete´s performance, has made the quantification of training load (TL) and the study of its relationship with performance raise interest among the scientific community and coaches [1,2]. Moreover, with the irruption of new more accessible technology and software, the use of methods to control and quantify the TL have been spread in different sports [3][4][5]. Furthermore, beyond the improvement of performance perspective, the quantification of the TL can prevent from suffering non-functional overreaching, injuries or illnesses avoiding workload spikes [6][7][8].For quantifying the TL there are different variables which can be categorized as either external (watts, speed, etc.) or internal (physiological and psychological). Traditionally, in endurance sports some internal variables have been used to quantify the TL such as heart rate [9-11], blood lactate and Ratings of Perceived Exertion [12,13]. One of the main reasons for that might be based on the necessity of distinguishing and measuring in an individual way the biological stress imposed by a training session in each athlete. The lack of capacity for measuring the internal work with external training quantification methods makes it impossible to compare the different responses of the athletes in a given training session [12]. In last decades several quantifying training proposals based on training zones have emerged as useful methods for monitoring the TL in endurance sports [2,10,11,14,15]. By means of these different methods, it is possible to compare intra-inter athletes' TL and the relationship between TL and performance. More recently, it has been confirmed the capacity of comparing different endurance sports by an objective method such as the Cejuela-Anta & EsteveLanao´s [10] ECO system [16].