# Lower-Limb Flexibility Profile in 142 Competitive Female Football Players: A Cross-Sectional Study
## 1 Introduction  
The ROM-SPORT is a sport-specific testing battery that measures muscle flexibility via range of motion (ROM) [1]. Recent studies have shown that low ROM values in some tests of this battery are important predictors of the risk of sports injury [2, 3, 4, 5]. Using machine learning techniques, flexibility measures such as hip flexion with the knee passively extended, hip internal and external rotation, hip abduction, knee flexion, and ankle dorsiflexion with the knee flexed and extended, evaluated through the ROM-SPORT method, have emerged as strong predictors of lower-extremity soft tissue injuries in 260 non-elite male youth football players [3], hamstring strain injury in 96 male professional footballplayers [2], and other muscular injuries in 98 male professionals [4]. Traditional statistical analysis has also identified decreased hip abduction ROM as a risk factor for groin strains in 306 male players from Iceland's top divisions [6]. In contrast, in women's football, flexibility is often overlooked in injury risk models, largely because many studies do not include ROM assessments in their protocols [7]. To our knowledge, only one recent study has demonstrated that limited hip internal rotation ROM is associated with an increased risk of anterior cruciate ligament (ACL) injuries in 95 competitive female football players, using binary logistic regression and ROC analysis [5]. Some exceptions exist: a few studies have assessed joint hypermobility [8; 9; 10] and one has linked excessive ankle ROM to ankle injuries in 300 female players [11]. These findings highlight a significant gap in the literature regarding flexibility as a modifiable risk factor for injury in female football. Given the high incidence of non-contact injuries such as ACL ruptures, hamstring strains, and ankle sprains in this population, injuries that are biomechanically linked to deficits or imbalances in flexibility, further predictive research is urgently needed. The ROM-SPORT is a battery that has been used extensively to determine the muscular flexibility profile of the lower and upper extremities of male athletes in individual and collective sports [1; 12; 13]. In the context football, normative values for internal and external rotation of the hip in 90\({}^{\circ}\) flexion, internal rotation of the hip in prone position, flexed knee drop, and abduction of the hip in lateral position were determined in 394 asymptomatic male professional football players aged 18-40 years [14], in 68 male professional football players (25.5 \(\pm\) 5.0 years) from four teams for the hip (flexion with flexed and extended knee, extension, abduction, external and internal rotation), the knee (flexion), and the ankle (dorsiflexion with flexed and extended knee) [13], and in 103 male professional first division footballers and 83 amateur football players for the hip (extension, adduction, abduction, internal rotation and internal rotation). However, only one scientific study was found describing the normal values for hip rotation ROM in 344 individual asymptomatic female football players selected for the Dutch national football teams [15]. In a sense, football professionals and strength and conditioning coaches demand the normative data for flexibility to ensure that women's football players are evaluated on flexibility as well as the other relevant physical abilities that best define the physical demands of competition. This will contribute to enhance decision-making in the design of the flexibility training program. In general, normative data were reported using descriptive statistics, primarily through mean and standard deviation (SD) values [16]. Some studies also categorized these values into five ranges (very low: \(\leq\) -2 SD; low: -1 to -2 SD; normal: within \(\pm\)1 SD; high: +1 to +2 SD; very high: \(\geq\)+2 SD) [14], while others stratified the results by age group [17].