What is Normal in Netball? A Feasibility Study on Ankle Strength and Countermovement Jump Kinetics in Sub-Elite Athletes

Introduction: Despite regular use of ankle strength and countermovement jump (CMJ) kinetics to support return to play decisions, research paucity limits the clinical application of these assessments among female netball cohorts. Without population and playing position specific data, return to play decision making may be sub-optimal and could increase the likelihood of re-injury or delay return despite physiological readiness. The aim of this feasibility study was to characterise ankle strength and CMJ kinetics of sub-elite female netball athletes. Methods: Pre-season testing of bilateral CMJ without arm-swing (dual force plates) and unilateral maximum isometric ankle inversion and eversion strength (hand-held dynamometer) was undertaken for 23 sub-elite female netball athletes. Eligible athletes were free from injury and participating in the NSW Netball Premier League competition. Maximum CMJ vertical height, left and right limb CMJ kinetics and ankle inversion and eversion peak force were analysed. Between-limb asymmetry was calculated using bilateral asymmetry index (BAI) for CMJ kinetics and percentage difference (PD) for unilateral ankle strength. Players were categorised by position as either non-circle (WA, C, WD) or circle (GS, GA, GD, GK). Descriptive statistics were reported due the study’s preliminary nature. To aid comparisons between position categories, threshold values were calculated as one standard deviation above and below the mean for all asymmetry results. Results: Ten non-circle (19.3±4.4 years, height 174.7±4.6cm, mass 71.8±9.7kg) and 13 circle (18.2±1.8 years, height 180.3±3.8cm, mass 72.4±4.1kg) athletes were assessed. Minimal differences were noted for initial comparisons of CMJ height (non-circle 26.1±4.6cm; circle 26.1±4.2cm), CMJ peak landing force BAI (non-circle 2.1±6.2; circle 1.8±10.8), or ankle strength PD in both inversion (non-circle 11%±5.2%; circle 7.2%±5.3%) and eversion (non-circle 7.6%±5.0%; circle 7.8%±4.9%) directions. When considering the proportion of athletes exceeding asymmetry threshold values, only CMJ peak landing force (non-circle 10%; circle 54%) and ankle inversion strength (non-circle 50%; circle 31%) showed substantial variations between position categories. Discussion: Above threshold between-limb asymmetry was more prevalent in CMJ peak landing force of circle athletes, and ankle inversion strength of non-circle athletes. The circle position specific demand of vertically jumping for ‘rebounds’ following an unsuccessful goal attempt does not appear to be associated with improved performance in jump height but may be associated with landing asymmetries whereby athletes preferentially load a favoured limb. As non-circle athletes more frequently perform short-duration, high-intensity bursts of sprinting along with regular, rapid changes in direction compared to their circle counterparts, the high eccentric loads placed upon the extrinsic inverters of the foot may result in a preferred pivot foot with greater ankle inverter strength developing. Impact/Application to the field:•Irrespective of injury status, clinicians can expect up to 80% of sub-elite female netball athletes to display asymmetries when assessing CMJ kinetics and ankle strength.•Between-limb differences in CMJ kinetics and ankle strength of female netball athletes requires further investigation to determine whether functional asymmetries reflect positional demands or are associated with future injury risk. Declaration: My co-authors and I acknowledge that we have no conflict of interest of relevance to the submission of this abstract.