**1. Introduction**

Rate of force development scaling factor (RFD-SF) has been used to quantify the ability to generate force rapidly, which is described as neuromuscular quickness [1]. A large number of studies have reported the RFD-SF as a reliable method for a number of muscle groups such as index finger abductors [1,2], elbow extensors [1,3], knee extensors [1,4] and various hip muscles [5]. However, the relationship between RFD-SF and performance in functional or sports-related tasks has not been ye<sup>t</sup> investigated. It is known that muscle quickness decreases with age [2] or disease [6], while the influence of the specific training history on this ability is still, to a grea<sup>t</sup> extent, unknown.

Explosive and quick release during basketball shot is important to avoid the defender reaction. One of the studies showed positive effects of explosive strength training on the shot percentage level. However, explosive strength training was performed for upper and lower limb; therefore, it is unknown if upper limb strength capacities play important role in basketball shooting performance [7]. We speculate that upper limb strength capacities may be important for accurate shooting performance because it has been reported that an increase in maximum strength of elbow extensors positively affected the shoot accurately in the three-point shot [8].

Basketball shot is among the sports-specific movements in which rapid production of submaximal force by muscles that act across multiple arm joints is considered important. During a basketball throw, the players manipulate their shoulder, elbow, and wrist to generate the optimal ball speed and angular velocity of the joint at the time of the release [9], depending on the distance and the position from the basket. The angular velocity of the upper arm joints and the speed of ball release increase with the shooting distance [10], which suggests that higher submaximal involvement of the major muscle groups is required as the distance increases. The elbow extensors have been suggested as major contributors to release speed in basketball shooting [11,12] as they extend the elbow joint before release, while the activation of the volar flexors is an important component of shooting that optimises impulse applied to the ball at release [13]. Previous studies have reported that the angular velocity of the elbow joint of the shooting arm at release increases with distance from the basket, while the opposite is observed for the wrist [11], suggesting that the roles of the two joints vary with the shooting distance. Some earlier studies reported that players with more training experience had better shooting performance [12,14] and lower average duration of arm muscle activation [15,16]. Based on this, we assumed that junior and senior players might also di ffer in the neuromuscular quickness of the major shooting muscles (i.e., elbow extensors and volar flexors). Furthermore, the relationship between neuromuscular quickness and performance of sport-specific tasks has not ye<sup>t</sup> been investigated. Filling these missing gaps could contribute to better understanding of RFD-SF and its use during routine testing of the athletes and possibly, based on these assessments, to individualized guidance of training programmes (e.g., more emphasis on speed-power training for individuals with lower RTD or RTD-SF).

To contribute our part in clarification of the functional role of the RTD-SF in sport-specific performance, we conducted a study to investigate strength capacities of elbow extensors and volar flexors in two groups of basketball players (juniors and seniors) and their relationship to shooting performance, put into the sport-specific training history. Specifically, the first aim of our study was to investigate the di fferences in the strength capacities (RTD-SF slope (kRTD-SF), maximum torque (TMVC), and peak rate of torque development (RTDPEAK) of elbow extensors (EE) and volar flexors (VF) and the shooting performance between junior and senior basketball players. We hypothesised that senior players, based on their longer training history and complete physical development, have significantly higher strength capacities of elbow extensors and volar flexors and better shooting performance compared to junior players. The second aim of the study was to investigate the relationship between the strength capacities (kRTD-SF, TMVC, and RTDPEAK) and shooting performance. We hypothesised that in both groups, shooting performance would be significantly positively associated with kRTD-SF, TMVC, and RTDPEAK of elbow extensors and volar flexors, at least from the long shooting distance. The third aim of the study was to investigate associations of elbow extensors and volar flexors as previous studies showed positive associations of kRTD-SF ability for di fferent muscle groups, while this association between elbow extensors and volar flexors has not ye<sup>t</sup> been confirmed. We hypothesised that there will be a large and statistically significant association in kRTD-SF between elbow extensors and volar flexors in both groups of players, which might support the idea of a central regulation and upper extremity (not a single joint, i.e., muscle group) related characteristics of RTD-SF ability.

#### **2. Materials and Methods**
