Reliability and measurement of inter-limb asymmetries in four unilateral jump tests in elite youth female soccer players

Purpose: The purpose of this study was to determine the within and between-session reliability, and inter-limb asymmetries, in four unilateral jump tests in elite youth female soccer players. Given the low plyometric training age and paucity of data for this population, this research study was warranted. Methods: Nineteen elite youth female soccer players (age: 10 ± 1.1 years; height: 141 ± 7.9 cm; body mass: 35 ± 7.1 kg) were recruited from an elite Tier 1 Regional Talent Centre of a professional soccer club. Tests included the single leg countermovement jump (SLCMJ), single leg hop, triple hop, and crossover hops for distance with reliability quantified via the coefficient of variation (CV), intraclass correlation coefficient (ICC), and standard error of the measurement (SEM). Inter-limb asymmetries were also calculated. Results: Both test sessions resulted in excellent within-session reliability (ICC range = 0.81-0.99; SEM range = 0.11-0.49; and CV range = 2.6-6.0%). Between-session reliability was deemed good to excellent (ICC range = 0.72-0.99 and pooled CV = 2.7-5.7%). Asymmetries were deemed small across both test sessions with the highest value reported in the SLCMJ (6.12%). Conclusion: Results highlight that unilateral jump tests can be considered a reliable test protocol in elite youth female soccer players, which is important considering youth athletes likely do not have a vast plyometric training age. Furthermore, inter-limb differences appear small in the present sample which may also be explained by their limited training age, given that asymmetries have previously been highlighted to be a product of limb function over time

A comparison of dynamic strength index between team-sport athletes

The purpose of this study was to examine the differences in countermovement jump peak force (CMJ-PF), isometric mid-thigh pull peak force (IMTP-PF), and resultant dynamic strength index (DSI) values between team-sport athletes. One hundred and fifteen male and female team-sport athletes performed the CMJ and IMTP to determine peak force (CMJ-PF and IMTP-PF, respectively). Statistically and practically significant differences (p ≤ 0.050; d = 0.49–1.32) in CMJ-PF were evident between teams. Specifically, the greatest CMJ-PFs were produced by the male cricket players and were followed in order by the male basketball, male soccer, female netball, female cricket, and female soccer players. Statistically and practically significant differences (p ≤ 0.045; d = 0.64–1.78) in IMTP-PF existed among sports teams, with the greatest IMTP-PFs were produced by the male soccer players and were followed in order by the male cricket, male basketball, female netball, female soccer, and female cricket players. Statistically and practically significant differences (p ≤ 0.050; d = 0.92–1.44) in DSI were found between teams. These findings demonstrate that CMJ-PF, IMTP-PF, and DSI differ between sports teams and provide normative data for ballistic and isometric PF measures. Strength and conditioning coaches should consider relative changes in CMJ-PF and IMTP-PF when assessing DSI ratios

Comparison of change of direction speed performance and asymmetries between team-sport athletes : application of change of direction deficit

The purpose of this study was twofold: (1) to examine differences in change of direction (COD) performance and asymmetries between team-sports while considering the effects of sex and sport; (2) to evaluate the relationship between linear speed, COD completion time, and COD deficit. A total of 115 (56 males, 59 females) athletes active in cricket, soccer, netball, and basketball performed the 505 for both left and right limbs and a 10-m sprint test. All team-sports displayed directional dominance (i.e., faster turning performance/shorter COD deficits towards a direction) (p ≤ 0.001, g = −0.62 to −0.96, −11.0% to −28.4%) with, male cricketers tending to demonstrate the greatest COD deficit asymmetries between directions compared to other team-sports (28.4 ± 26.5%, g = 0.19–0.85), while female netballers displayed the lowest asymmetries (11.0 ± 10.1%, g = 0.14–0.86). Differences in sprint and COD performance were observed between sexes and sports, with males demonstrating faster 10-m sprint times, and 505 times compared to females of the same sport. Male soccer and male cricketers displayed shorter COD deficits compared to females of the same sport; however, female court athletes demonstrated shorter COD deficits compared to male court athletes. Large significant associations (ρ = 0.631–0.643, p < 0.001) between 505 time and COD deficit were revealed, while trivial, non-significant associations (ρ ≤ −0.094, p ≥ 0.320) between COD deficit and 10-m sprint times were observed. In conclusion, male and female team-sport athletes display significant asymmetries and directional dominance during a high approach velocity 180° turning task. Coaches and practitioners are advised to apply the COD deficit for a more isolated measure of COD ability (i.e., not biased towards athletes with superior acceleration and linear speed) and perform COD speed assessments from both directions to establish directional dominance and create a COD symmetry profile

Assessing muscle strength asymmetry via a unilateral stance isometric mid-thigh pull

Purpose: The purpose of this study was to investigate the within-session reliability of bilateral and unilateral stance isometric mid-thigh pull (IMTP) force-time characteristics including peak force (PF), relative PF and impulse at time bands (0-100, 0-200, 0-250 and 0-300 ms); and to compare isometric force-time characteristics between right and left and dominant (D) and non–dominant (ND) limbs. Methods: Professional male Rugby league and multi-sport collegiate male athletes (n=54, age 23.4 ± 4.2 years, height 1.80 ± 0.05 m, mass:88.9 ± 12.9 kg) performed 3 bilateral IMTP trials, and 3 unilateral stance IMTP trials per leg 60 on a force plate sampling at 600 Hz. Results: Intraclass correlation coefficients (ICC) and coefficients of variation (CV) demonstrated high-within session reliability for bilateral and unilateral IMTP PF (ICC =.94, CV = 4.7–5.5%). Lower reliability measures and greater variability were observed for bilateral and unilateral IMTP impulse at time bands (ICC =.81-.88, CV =7.7-11.8%). Paired sample t-tests and Cohen’s d effect sizes revealed no significant differences for all isometric force-time characteristics between right and left limbs in collegiate male athletes (p &gt;.05, d ≤0.32) and professional rugby league players (p &gt;.05, d ≤0.11), however significant differences were found between D and ND limbs in male collegiate athletes (p &lt;.001, d = 0.43–0.91) and professional rugby league players (p &lt; .001, d = 0.27–0.46). Conclusion: This study demonstrated high within-session reliability for unilateral stance IMTP PF;revealing significant differences in isometric force-time characteristics between D and ND limbs in male athletes

The application of change of direction deficit to evaluate cutting ability

The purpose of this study was to examine the application of the change of direction deficit (CODD) to a 90° cut test in order to examine whether CODD provides a unique evaluation of an individual’s cutting ability. Thirty-six male collegiate team–sport (23 Rugby/ 13 Soccer) athletes (age: 20 ± 1.4 years; height: 1.80 ± 0.08 m; mass: 83 ± 13.2 kg) participated in the study. Each athlete performed 3 trials of a 20 m sprint (with 5 m and 10 m splits) and 2 change of direction [COD] tests (90° cut and 505 tests) cutting/ turning from both limbs. Completion times for all sprint and COD tests were measured using timing cells. For both COD tests, CODD was determined (COD completion time – 10 m sprint time). Pearson’s correlation was used to explore relationships between sprint times and CODD and completion times. Significant (P 0.05) trivial to small correlations (r ≤ 0.199) were found between sprint variables and 90° cut CODD. Significant (P < 0.001) large to very large correlations (r ≥ 0.531) were revealed between left and right 90° cut and 90° cut CODD. The results suggest the CODD could be applied to isolate and assess cutting ability in COD speed tests that involve a single cutting maneuver. Failure to inspect CODD could lead to incorrect evaluation of an athletes cutting or COD ability

The effect of angle and velocity on change of direction biomechanics : an angle-velocity trade-off

Changes of direction (CODs) are key manoeuvres linked to decisive moments in sport and are also key actions associated with lower limb injuries. During sport athletes perform a diverse range of CODs, from various approach velocities and angles, thus the ability to change direction safely and quickly is of great interest. To our knowledge, a comprehensive review examining the influence of angle and velocity on change of direction (COD) biomechanics does not exist. Findings of previous research indicate the biomechanical demands of CODs are ‘angle’ and ‘velocity’ dependent and are both critical factors that affect the technical execution of directional changes, deceleration and reacceleration requirements, knee joint loading, and lower limb muscle activity. Thus, these two factors regulate the progression and regression in COD intensity. Specifically, faster and sharper CODs elevate the relative risk of injury due to the greater associative knee joint loading; however, faster and sharper directional changes are key manoeuvres for successful performance in multidirectional sport, which subsequently creates a ‘performance-injury conflict’ for practitioners and athletes. This conflict, however, may be mediated by an athlete’s physical capacity (i.e. ability to rapidly produce force and neuromuscular control). Furthermore, an ‘angle-velocity trade-off’ exists during CODs, whereby faster approaches compromise the execution of the intended COD; this is influenced by an athlete’s physical capacity. Therefore, practitioners and researchers should acknowledge and understand the implications of angle and velocity on COD biomechanics when: (1) interpreting biomechanical research; (2) coaching COD technique; (3) designing and prescribing COD training and injury reduction programs; (4) conditioning athletes to tolerate the physical demands of directional changes; (5) screening COD technique; and (6) progressing and regressing COD intensity, specifically when working with novice or previously injured athletes rehabilitating from an injury

Effect of low-pass filtering on isometric midthigh pull kinetics

The purpose of this study was to investigate the effect of low-pass filtering on isometric mid-thigh pull (IMTP) kinetics, including body weight (BW), onset threshold force, time-specific force values (50, 100, 150 and 200 ms) and peak force (PF). Forty IMTP trials from twenty-four collegiate athletes (age: 21.2 ± 1.8 years, height: 1.72 ± 0.09 m, mass: 79.4 ± 8.2 kg) were analyzed and compared using unfiltered (UF) and low-pass filtered (LPF) (Fourth-order Butterworth) with cut-off frequencies of 10 (LPF10) and 100 (LPF100) Hz. Significantly lower (p < 0.001, g =-0.43 to- 0.99) onset threshold forces were produced when force data were LPF. This led to significant (p < 0.001, g = 0.05-0.21) underestimations of time-specific force values when LPF10 compared to UF, displaying unacceptable percentage differences (1.2-3.3%) and unacceptable limits of agreement (LOA) (-25.4 to 100.3 N). Although significantly different (p ≤ 0.049), trivial (g ≤ 0.04) and acceptable percentage differences (≤0.8%) and acceptable LOA (-28.0 to 46.2 N) in time-specific force values were observed between UF and LPF100. Statistically significant (p < 0.001), yet trivial (g ≤ 0.03), and acceptable percentage differences (≤0.7%) and acceptable LOA (-4.7 to 33.9 N) were demonstrated in PF between filtering conditions. No significant differences (p = 1.000) and identical BW values were observed between filtering conditions. Low-pass filtering results in underestimations in IMTP kinetics; however, these differences are acceptable between LPF100 and UF, but unacceptable between LPF10 and UF (excluding PF). Filtering procedures should be standardized when longitudinally monitoring changes in IMTP force-time characteristics to allow valid comparisons; with analysis of UF data recommended

Role of the penultimate foot contact during change of direction : implications on performance and risk of injury

Most change of direction biomechanical investigations and current technique guidelines focus on the role of the final foot contact (plant foot contact). However, it is evident that the braking characteristics during the penultimate foot contact play an integral role in deceleration prior to directional changes ≥ 60°; and can therefore, be described as a “preparatory step”. In this review, we examine the role of the penultimate foot contact on change of direction performance and associated biomechanical injury risk factors, and provide technical guidelines for coaching the “preparatory step” during change of direction, to enhance performance and reduce risk of injury