## 1 Introduction  
Running performance depends on the complex interaction of several factors, particularly physiological, as well as biomechanical and psychological [1, 2]. From a physiological point of view, it is well documented that the ventilatory/lactate threshold, maximal oxygen uptake (VO\({}_{2}\)max), and running economy are strong performance indicators, especially when the latter are combined, and these indicators determine the maximal aerobic speed (MAS) [2, 3, 4]. Therefore, running performance could be improved through central adaptations, but also through the ability of athletes to produce more mechanical work for a given energy cost [2, 5]. It is therefore not surprising that increased running performance has been reported when resistance and endurance training are incorporated simultaneously within the same program (e.g., \"_concurrent training_\") [1, 3, 6, 7]. However, if exercise variables such as intensity and volume are not adequately prescribed in a concurrent training session,resistance training-induced fatigue may acutely impair the quality of subsequent endurance training sessions and induce an interference effect on long-term cardiorespiratory adaptations in a phenomenon referred to as \"_resistance training-induced suboptimization on endurance performance_\" (RT-SEP) [8; 9]. For example, [PERSON] et al. [10] reported impaired running time-to-exhaustion at 110% of the second ventilatory threshold six hours after a resistance training session with heavy loads (six repetitions at \(\sim\)80% of the one-repetition maximum [1 RM]) compared to light loads (total work equated with 20 repetitions) in trained male runners. Relatedly, it has been suggested that heavy loads (\(\geq\)80% 1 RM) may increase susceptibility to RT-SEP [9]. Velocity-based training (VBT) may help to assess optimization (e.g., auto-regulation) and individualization of resistance training intensity and volume according to the training readiness of athletes [11; 12], thus reducing chances of RT-SEP [9]. For example, using VBT, [PERSON] et al. [13] found that compared to a moderate (20%) magnitude of velocity loss during resistance training (three full-squat sets at 60% 1 RM), a high (40%) velocity loss resulted in higher metabolic (e.g., greater blood lactate, higher ventilatory equivalents) and mechanical stress (e.g., impaired vertical jump and squat velocity), as well as impaired running performance (e.g., unable to run 10 min at 90% MAS). [PERSON] et al. [14] observed higher running performance (i.e., MAS) following an eight-week concurrent training program with a moderate rather than high velocity loss (15% \(>\) 30%) in the resistance training bouts. Further, 2000 m rowing ergometer time-trial performance was compromised by greater velocity loss in the set (30% vs. 10%), but not by the loading magnitude (60% = 80% of 1 RM) [15]. However, further research is needed to gain a deeper understanding of the acute effects of different concurrent VBT protocols, in terms of loading magnitude (60% vs. 80% of 1 RM) and velocity loss in the set (10% vs. 30%), on running performance. It has been shown that men reported higher velocities than women for the same %1 RM during a variety of resistance training exercises and, consequently, the load-velocity relationship should be sex-specific for a better adjustment of the training intensity [16]. Similarly, it has been reported that recreationally trained men and women can achieve similar increases in strength and power performance following an eight-week VBT program with either 20% or 40% velocity loss, although some results (1 RM strength and velocity attained to low / moderate loads) have indicated that strength and power gains favor using 40% rather than 20% velocity loss in women [17]. Therefore, it seems that women require a greater within-set fatigue than men to maximize strength and power development. These authors also observed that men were more susceptible to acute neuromuscular fatigue than women, but these differences in fatighighity were reduced after the VBT program [18].