## 1 Introduction  
Building muscle endurance takes time and consistency in training in a context in which muscles adapt quickly to exercises and the way they are performed. The way the muscle adapts to resistance training depends on several variables such as the load, volume, frequency of training, speed of contraction, work-to-rest ratios and time under tension [1]. In training, one approach is to base the prescription on the number of repetitions. The number of repetitions left in reserve in a training set is correlated with the level of effort [2]. However, some studies show that there are difficulties in predicting the proximity of momentary task failure [3] or the number of repetitions in reserve [4]. The maximum number of repetition is obtained and maintained due to the intensity, volume and metabolic response to a workload [1, 5]. According to [6, 7, 8], the numbers of possible repetitions prior to failure at the same relative intensity (%1 RM) vary between exercises and individuals. Training to failure and the maximum number of repetitions (MNR) strategy, according to [9, 10], are not optimal for maximizing performance. Additionally, it is difficult to determine the exact number of repetitions left in reserve. So, understanding the physiognomy of the sets can be useful for predicting the number of repetitions left in reserve in a training set. The factors that influence the maximum number of repetitions in the case of bicep curls were analyzed by [PERSON] et al. There is an inverse relationship between MNR and relative intensity, defined by the load ratio per maximum one-repetition attempt, 1 RM [11]. Related to the influence of the training experience upon the MNR, studies that have evaluated the MNR between individuals with different training experience shows little [12] or no influence [13] on this variable. Some strategies were developed in order to increase the MNR and training intensity. [PERSON] et al. [14] showed that a greater number of repetitions with a shorter mean repetition duration were performed in the barbell bench press exercise with an elastic device named the Sling Shot than without it, regardless of the individuals' training experience. The literature also presents special programs dedicated to increasing training intensity: the method of reducing rest periods between sets (e.g., Nubret), based on the traditional training objective which manages the ability to recover between sets [15; 16]; superset training, based on muscle pairs, takes advantage of the contraction of antagonistic muscles and the reduction in rest-on periods, offering very good results for short training times [17; 18; 19]; compound-set training, which is similar to superset training with the exception that it refers to exercises for the same muscle group, reducing the duration of training and high-intensity training, which produces a dramatic increase in intensity (i.e., beyond the point of muscle failure) in terms of volume reduction and training duration reduction [20; 21; 22]. It also seems intuitive to suggest that there may be differences between the repetitions during the entire cycle, in the case of the MNR strategy. [PERSON] et al. presents the problem of morphological differences between the beginning and the end of a repetition, highlighting factors that influence the intensity of a conventional bicep curl; in this case, the critical role of acceleration is highlighted for the first time [23]. [PERSON] et al. presented a three-dimensional musculoskeletal model of the seated bicep curl resistance training exercise in which the influence of small deviations from the ideal trajectory is highlighted [24]. In the literature, there are also references to the models of kinematics, kinetics and muscle activation during explosive upper body movements, focusing on large muscle groups, but in this case, no reference is made to small groups. Based on the literature review, some gaps have been found in this field.