# Single-Leg Squat Performance and Reported Pain within Youth Softball Players
## 1 Introduction  
Baseball and softball combined is the fourth most played high school sport in the United States [1]. Along with the sport's popularity comes the prevalence of and susceptibility to injury. Contrary to the lack of injury-prevention research in softball compared to baseball, softball injury rates have been found to be at least comparable to, if not higher than, those of baseball [2, 3]. Additionally, injury patterns have been shown to vary between the sports [2, 3, 4]. While the majority of injuries in softball and baseball are to the upper extremity, softball players reportedly experience proportionally higher rates of injury to the lower extremity than baseball players [5]. Moreover, a greater proportion of softball injuries have been classified as a major injury or season-ending injury, compared with baseball and other female sports [5], thus suggesting injury susceptibility in the sport of softball could be greater than that reported in baseball. Likewise, softball athletes have been observed to suffer a greater proportion of sprains and dislocations than baseball athletes [5]. Such overuse injuries like sprains have been commonplace in youth athletics, as overuse injuries account for at least 50% of all youth sport-related injuries [6]. Injury severity and incidence data in youth softball suggest that most injuries are related to chronic mechanical deficiencies rather than acute trauma. With the high prevalence of severe and overuse injury in youth softball, injury prevention should be of high concern for sports medicine personnel; parents; and coaches. Youth softball athletes are required to complete numerous near maximal effort overhead throws during practice and games. Such high repetition of a singular movement pattern may lead to overuse injury. Throwing is a complex dynamic movement that requires efficient use of the kinetic chain [7; 8]. For the body to function as a kinetic chain, interdependent segments must work synchronously in a proximal to distal fashion. Specifically, force is generated in the proximal lower extremity and then transferred thorough the lumbopelvic-hip complex (LPHC), to the distal upper extremity, and on to the ball at release. Trunk musculature contributes to LPHC stability during the overhead throwing motion is important not only for postural control but to also generate and transfer force from the lower extremity to the upper extremity [8]. Due to the unilateral nature of the overhead throw, structural and mechanical asymmetries develop in overhead throwing athletes; meanwhile, such asymmetries may place athletes at a greater risk of injury. When considering the overhead throwing motion as a total body dynamic activity, awareness of segmental asymmetries that could result in kinetic chain alterations is needed. As any alteration in the kinetic chain could result in compensations and ultimately injury to the more distal segments in the chain [8]. One of the most documented segmental compensations within the kinetic chain is LPHC instability [8; 9; 10; 11; 12]. The LPHC serves as the connection between the lower and upper body and is a key component of energy transfer through the body, meaning pathomechanics at the LPHC may be a shared risk factor for upper and lower extremity injuries. Trunk and lower extremity pain have been correlated with upper extremity pain in youth baseball, softball, handball, tennis, badminton, and volleyball athletes [13], suggesting that the lower and upper extremities share injury risk factors. Due to the impact of the LPHC on not only the efficiency of the kinetic chain but also in pain and injury susceptibility, assessment of LPHC stability could prove valuable in injury-prevention strategies for throwing athletes. Clinically, LPHC stability has been assessed and validated through the use of a single-leg squat (SLS) [7; 14]. When considering the ability of the LPHC to stabilize both the lower extremity and trunk, clinicians commonly rely on the assessment of the SLS [15; 16].