Variations in lower body stiffness during sports-specific tasks in well-trained female athletes.

The present study aimed to assess the differences in leg stiffness and the associated performance variables between athletes from various training backgrounds during tasks relevant to athletic training. Forty-seven female participants (20 nationally identified netballers, 13 high-level endurance athletes and 14 age-matched controls) completed a sprint, anticipated sidestep change of direction and unilateral repetitive hopping task to assess leg stiffness and the relationship of stiffness between the different tasks. Leg stiffness and performance variables were evaluated with a 10-camera motion analysis system and force plate, and leg stiffness was derived through the McMahon and Cheng methodology (1990). Significant differences were evident in leg stiffness, and the contributing performance variables between groups across all assessed tasks (p < 0.001-0.017). Furthermore, results indicated the control group displayed no leg stiffness relationship between the evaluated tasks, while the stiffness relationship between tasks within athletic populations reflected training-specific demands of athletes. The results of this study indicated that the athletic training background of individuals may contribute to inherent leg stiffness differences between groups. Furthermore, the stiffness relationship observed between tasks suggests practitioners should take care in the selection of task used to monitor leg stiffness from a performance or injury risk perspective.

The Validity of a Global Navigation Satellite System for Quantifying Small-Area Team-Sport Movements.

Delaney, JA, Wileman, TM, Perry, NJ, Thornton, HR, Moresi, MP, and Duthie, GM. The validity of a global navigation satellite system for quantifying small-area team-sport movements. J Strength Cond Res 33(6): 1463-1466, 2019-The recent development of global navigation satellite systems (GNSS) has improved the availability and signal strength of surrounding satellites compared with traditional global positioning systems, although their ability to quantify rapid changes in speed may still be limited. This study aimed to evaluate the validity of GNSS to quantify the mean speed (m·s) and acceleration (m·s) of movements typical to team sports. One participant completed 9 periods of 4 minutes of activity, separated by 2-minute rest periods, which involved walking, jogging, and running in a variety of directions and patterns, aimed to simulate a team-sport movement profile. Speed and acceleration were quantified from a 10-Hz GNSS unit and compared with a 10-camera, 3-dimensional motion capture system (VICON), from which the movement of both the participant's center of mass (COM) and the location of the GNSS unit (e.g., C7 vertebrae) were calculated. Practical estimates of speed were associated with small differences from both the criterion COM (effect size; ±90% confidence limits = 0.19-0.25; ± ∼0.21) and criterion C7 (0.14-0.22; ± ∼0.13). The corresponding estimates of acceleration derived from raw data were classified as small (0.16-0.22; ± ∼0.15) and small to moderate (0.25-0.35; ± ∼0.24) for the COM and C7, respectively. Software-exported acceleration values exhibited very large mean bias compared with both criterion measures (-3.81 to -3.77; ± ∼0.24). This study demonstrates that 10-Hz GNSS possess acceptable validity for assessing the average demands of movements typical of team-sports training and competition, although caution is recommended when using software-exported measures of acceleration.

Sex Differences in Physical Fitness Characteristics and Match-Play Demands in Adolescent Netball: Should Male and Female Adolescents Co-compete in Netball?

Tissera, KM, Naughton, GA, Gabbett, TJ, Krause, LM, Moresi, MP, and Benson, AC. Sex differences in physical fitness characteristics and match-play demands in adolescent netball: Should male and female adolescents co-compete in netball? J Strength Cond Res 33(3): 846-856, 2019-Sports participation offers multifaceted benefits, especially during adolescence. However, policies relating to male and female adolescents co-competing in team sports can be prohibitive and lack an evidence base. This study aimed to strengthen evidence on coparticipation of male and female adolescents playing recreational netball. Off-court fitness characteristics (power, speed, agility, and high-speed intermittent running) and match-play performances from global positioning system (GPS) and video analysis were compared in adolescent males (n = 34, mean ± SD, age, 15.2 ± 0.8 years) and females (n = 45, mean ± SD, age, 14.9 ± 0.7 years), with previous recreational netball experience. Independent t-tests showed adolescent men outperforming females in all off-court fitness characteristics (p < 0.001). Two-way analyses of variance explored sex-based interactions in match-play (GPS accelerometer data and notational analyses) and type of competition (mixed-/single-sex formats) in forty-two 7-minute matches. Overall, no differences in match-play performances were found between males and females (p > 0.05). Notational skill-based comparisons showed that male skills were better in mixed- than single-sex matches. Conversely, competition format did not alter skills of females. Despite more netball experience in females and superior off-court fitness characteristics in males, on-court performance differences between males and females were minimal in these recreational adolescent netball players. Coparticipation in netball was not detrimental to the performance of either sex.

Lower Body Stiffness Modulation Strategies in Well Trained Female Athletes.

Millett, EL, Moresi, MP, Watsford, ML, Taylor, PG, and Greene, DA. Lower body stiffness modulation strategies in well trained female athletes. J Strength Cond Res 30(10): 2845-2856, 2016-Lower extremity stiffness quantifies the relationship between the amount of leg compression and the external load to which the limb are subjected. This study aimed to assess differences in leg and joint stiffness and the subsequent kinematic and kinetic control mechanisms between athletes from various training backgrounds. Forty-seven female participants (20 nationally identified netballers, 13 high level endurance athletes and 14 age and gender matched controls) completed a maximal unilateral countermovement jump, drop jump and horizontal jump to assess stiffness. Leg stiffness, joint stiffness and associated mechanical parameters were assessed with a 10 camera motion analysis system and force plate. No significant differences were evident for leg stiffness measures between athletic groups for any of the tasks (p = 0.321-0.849). However, differences in joint stiffness and its contribution to leg stiffness, jump performance outcome measures and stiffness control mechanisms were evident between all groups. Practitioners should consider the appropriateness of the task utilised in leg stiffness screening. Inclusion of mechanistic and/or more sports specific tasks may be more appropriate for athletic groups.

The impact of data reduction on the intra-trial reliability of a typical measure of lower limb musculoskeletal stiffness.

Double-leg repeated jumping tasks are commonly used as measures of lower limb stiffness in exercise science research. Within similar stiffness calculations, variation in data-reduction criteria exists. The impact of these varied data-reduction methods on stiffness measures is unknown. Sixteen adolescent female participants from varied physical activity backgrounds performed 15 self-paced, bent-knee continuous jumps (CJb) on two force plates. Leg stiffness was calculated as the ratio of the peak force and the centre of mass displacement for each contact. Using combinations of criteria based on previous literature, 83 data-reduction methods were applied to the raw data. Data reduction suitability was assessed based on intra-trial reliability, the number of participants excluded and the average contacts excluded. Four data-reduction methods were deemed suitable for use with adolescent female populations, with three consecutive contacts within 1 SD of the average jump frequency considered optimal. The average individual stiffness values were not greatly influenced by the data-reduction method; however, for a single participant, a stiffness change of up to 6 kN · m(-1) (30%) was observed. The role and potential impact of data-reduction methods used to evaluate measures of lower limb stiffness during repeated jumping tasks warrants consideration.

The assessment of adolescent female athletes using standing and reactive long jumps.

The aim of this study was to evaluate the reliability of two long jump tasks and their ability to predict 10 m sprint performance in elite adolescent female athletes. Eight junior national-level female track and field athletes completed three standing (SLJ) and reactive long jumps (RLJ) on portable force plates, followed by three 10 m sprints. Intra-class correlation coefficients (ICC) and coefficients of variation (CV) were calculated to examine reliability. Linear regression results identified the best predictor of average and best 10 m sprint time from the jump kinematic and kinetic measures. The ICCs and CVs indicated good reliability for the majority of kinetic measures however, better reliability was reported for the SLJ. The SLJ was a good predictor of best and average 10 m sprint time, with average horizontal power the best predictor of performance (best; R2 = 0.751, p = 0.003, Standard Error of Estimate (SEE)% = 2.2 average; R2 = 0.708, p = 0.005, SEE% = 2.5).