Understanding and advancing female adolescent football performance: validating the HumanTrak movement analysis system and longitudinally investigating maturation effects in female adolescent players

IntroductionTracking performance metrics in relation to biological maturation (BM) in male football has beenwidely researched, however, is lacking in female football. To track performance, applied sportscientists rely on specialised equipment. Marker-less camera systems to assess functional movementsare becomingly increasingly popular, however, there is an absence of information surrounding thevalidity of the HumanTrak Movement Analysis System.PurposeChapter Three investigated the validity of the HumanTrak Movement Analysis System against the goldstandard Vicon Motion Capture System through single- and double-leg squat movements. ChapterFour tracks the longitudinal effects of BM on functional movements and performance metrics inadolescent female football players.MethodsChapter Three involved 20 participants (10 male and 10 female; age, 24±3years, body mass;72.9±15.8kg, height; 172.1±9.9cm) completing an overhead squat (OHS) and single-leg squat (SLS)whilst using the HumanTrak system against the gold standard Vicon motion capture system. Kneeflexion values were obtained from OHS and SLS and knee varus/valgus values obtained from SLS.Spearman’s correlation coefficients were used to report relationships between the two systems andBland-Altman plots with 95 % CI to depict levels of agreement for knee angles. Chapter Four involved95 academy female footballers (age 14±2years) completing four functional movements (single-legbalance, single-leg squat, overhead squat and forward lunge), a countermovement jump (CMJ), 30 msprint and 1.4 km maximal aerobic speed (MAS) at baseline, 6 and 9-months. Repeated measuresanalysis of variance were used to determine changes in performance metrics across the threetimepoints, Pearson’s coefficients to determine the relationship between maturity offset andperformance metrics and Independent t-tests to assess differences between pubertal developmentand performance metrics.ResultsA significant correlation was found between the two systems for knee flexion during both OHS (r =0.843, p < 0.001) and SLS (r = 0.683, p < 0.001). No significant correlation was reported for kneevarus/valgus during SLS (r = 0.104, p = 0.663). Performance metrics measured over a longitudinalperiod against BM had no significant effect (p > 0.05), however, when assessing each variable atindividual timepoints, significant relationships between BM and performance metrics were noted forsingle-leg right knee varus/valgus ( r = 0.382, p < 0.05) and CMJ (r = 0.275, p < 0.05) at timepoint A, 30m sprint time at all three timepoints (A: r = -0.628, p < 0.001; B: r = -0.556, p < 0.001; C: r = -0.596, p <0.001) and 1.4km MAS at timepoint C (r = 0.382, p = 0.012). No significant effects of BM on all otherperformance metrics at all three timepoints were observed (p > 0.05). Post-menarche pubertaldevelopment scores were significantly lower at all three timepoints for 30 m sprint (A: p = 0.013; B: p= 0.006; C: p = 0.003). All other performance metrics at all timepoints were not significant (p > 0.05).ConclusionMarker-less cameras can accurately report knee flexion values with varus/valgus values noted asinvalid. Performance metrics are affected by BM, with the longitudinal effects of BM beinginsignificant in this study.