Single-leg Countermovement Jumps Research Articles

Train the Engine or the Brakes? Influence of Momentum on the Change of Direction Deficit.

Currently, it is unclear which physical characteristics may underpin the change of direction deficit (COD-D). This investigation sought to determine if momentum, speed-, and jump-based measures may explain variance in COD-D. Seventeen males from a professional soccer academy (age, 16.76 [0.75]y; height, 1.80 [0.06]m; body mass, 72.38 [9.57]kg) performed 505 tests on both legs, a 40-m sprint, and single-leg countermovement and drop jumps. The regression analyses did not reveal any significant predictors for COD-D on either leg. "Large" relationships were reported between the COD-D and 505 time on both limbs (r = .65 to .69; P < .01), but COD-D was not associated with linear momentum, speed-, or jump-based performances. When the cohort was median split by COD-D, the effect sizes suggested that the subgroup with the smaller COD-D was 5% faster in the 505 test (d = -1.24; P < .001) but 4% slower over 0-10 m (d = 0.79; P = .33) and carried 11% less momentum (d = -0.81; P = .17). Individual variance in COD-D may not be explained by speed- and jump-based performance measures within academy soccer players. However, when grouping athletes by COD-D, faster athletes with greater momentum are likely to display a larger COD-D. It may, therefore, be prudent to recommend more eccentric-biased or technically focused COD training in such athletes and for coaches to view the COD action as a specific skill that may not be represented by performance time in a COD test.

Higher Vertical Jumping Asymmetries and Lower Physical Performance are Indicators of Increased Injury Incidence in Youth Team-Sport Athletes.

Fort-Vanmeerhaeghe, A, Milà-Villarroel, R, Pujol-Marzo, M, Arboix-Alió, J, and Bishop, C. Higher vertical jumping asymmetries and lower physical performance are indicators of increased injury incidence in youth team-sport athletes. J Strength Cond Res 36(8): 2204-2211, 2022-To date, the literature about the association between injury-risk factors and actual injury incidence in young elite team-sports athletes is scarce. The main objective of this study was to examine how modifiable factors may affect injury incidence. Eighty-one young elite team-sports athletes (age: under-14 to under-18) performed the countermovement jump (CMJ), a single leg CMJ (SLCMJ), the one-legged hop test (OLHT), a 30-m sprint test, the V-cut test, a repeated sprint ability, and the 30-15 intermittent fitness test (IFT) during the pre-season period. Interlimb asymmetries were calculated for SLCMJ and OLHT. Injuries were recorded prospectively for the entirety of the 2017-2018 season. Comparison of injury and noninjury data was performed using a two-way analysis of variance (ANOVA). Results of the ANOVA according to injury showed significant differences in CMJ ( p = 0.01), SLCMJ on the lowest performing limb ( p = 0.03), and SLCMJ asymmetry (<0.001). Sex × injury interaction was significant from CMJ ( p = 0.018) and 30-15 IFT ( p = <0.001). In conclusion, this study indicated that athletes with greater interlimb asymmetries, less vertical jump capacity, and lower intermittent aerobic fitness had a greater predisposition to injury. Therefore, monitoring CMJ, aerobic performance, and interlimb asymmetries is recommended given their sensitivity to detect significant differences between injured and healthy youth athletes.

The effect of a school based injury prevention program on physical performance in youth females

Injury prevention (IP) programs can reduce injury in youth, however, little is known about their impact on athletic performance, especially in females. The purpose of this study was to examine the effects of a school curriculum IP program on movement skill and athletic performance in youth females. Ninety-two female students (age 14.0 ± 0.6 y, height 162.5 ± 5.8 cm, mass 57.1 ± 9.3 kg, intervention (INT) n = 43, control (CON) n = 49) participated in this study. The INT group completed a 23 week IP program whereas the CON group continued normal physical education class. Sprint, countermovement jump (CMJ), isometric mid-thigh pull (IMTP), y-balance, back squat assessment (BSA), and drop vertical jump (DVJ) were assessed. An independent-samples t-test revealed that the INT group performed significantly better on all tests at baseline (p = &lt;0.05), except single-leg CMJ power. Ordered regression models showed the INT group were more likely to improve their score on the BSA and DVJ (OR = 0.14 and 0.20) compared to the CON group. Marginal analysis revealed a significantly greater increase in y-balance composite measures for the INT group [mean difference (95% CI) = 2.07 (0.48 to 3.66) and 2.66 (1.03 to 4.29), p &lt; 0.05] and relative IMTP for the CON group [mean difference (95% CI) = −0.34 (−0.60 to −0.08), p &lt; 0.05). These findings highlight that a long-term IP program integrated into the school curriculum can improve movement skill and balance in youth females.

A Comparison of Bilateral vs. Unilateral-Biased Strength and Power Training Interventions on Measures of Physical Performance in Elite Youth Soccer Players

Stern, D, Gonzalo-Skok, O, Loturco, I, Turner, A, and Bishop, C. A comparison of bilateral vs. unilateral-biased strength and power training interventions on measures of physical performance in elite youth soccer players. J Strength Cond Res 34(8): 2105-2111, 2020-The aim of the present study was to compare the effects of bilateral and unilateral-biased strength and power training programs on measures of physical performance in male youth soccer players. Twenty-three elite youth players (age: 17.6 ± 1.2 years) were randomly assigned to either a unilateral (n = 11) or a bilateral (n = 12) group, who completed a strength and power intervention, twice per week for 6 weeks. The unilateral group completed rear foot elevated split squats (RFESS), single-leg countermovement jumps (SLCMJs), single-leg drop jumps (SLDJs), and single-leg broad jumps (SLBJs). The bilateral group intervention performed back squats, CMJs, drop jumps (DJ), and broad jumps (BJ). A 2 × 2 repeated measures analysis of variance showed no between-group differences. However, within-group differences were evident. The bilateral training group showed significant (p < 0.05) improvements in back squat strength (d = 1.27; %Δ = 26.01), RFESS strength (d = 1.64; %Δ = 23.34), BJ (d = 0.76; %Δ = 5.12), 10-m (d = -1.17; %Δ = 4.29), and 30-m (d = -0.88; %Δ = 2.10) performance. The unilateral group showed significant (p < 0.05) improvements in RFESS strength (d = 1.40; %Δ = 33.29), SLCMJ on the left leg (d = 0.76; %Δ = 9.84), SLBJ on the left leg (d = 0.97; %Δ = 6.50), 10 m (d = -1.50; %Δ = 5.20), and 505 on the right leg (d = -0.78; %Δ = 2.80). Standardized mean differences showed that bilateral training favored improvements in back squat strength and unilateral training favored improvements in RFESS strength, SLDJ on the right leg and 505 on the right leg. These results show that although both training interventions demonstrated trivial-to-large improvements in physical performance, the notion of training specificity was evident with unilateral training showing greater improvements in unilateral test measures.

Using machine learning to improve our understanding of injury risk and prediction in elite male youth football players

ObjectivesThe purpose of this study was to examine whether the use of machine learning improved the ability of a neuromuscular screen to identify injury risk factors in elite male youth football players. DesignProspective cohort study. Methods355 elite youth football players aged 10–18 years old completed a prospective pre-season neuromuscular screen that included anthropometric measures of size, as well as single leg countermovement jump (SLCMJ), single leg hop for distance (SLHD), 75% hop distance and stick (75%Hop), Y-balance anterior reach and tuck jump assessment. Injury incidence was monitored over one competitive season. Risk profiling was assessed using traditional regression analyses and compared to supervised machine learning algorithms constructed using decision trees. ResultsUsing continuous data, multivariate logistic analysis identified SLCMJ asymmetry as the sole significant predictor of injury (OR 0.94, 0.92–0.97, p<0.001), with a specificity of 97.7% and sensitivity of 15.2% giving an AUC of 0.661. The best performing decision tree model provided a specificity of 74.2% and sensitivity of 55.6% with an AUC of 0.663. All variables contributed to the final machine model, with asymmetry in the SLCMJ, 75%Hop and Y-balance, plus tuck jump knee valgus and anthropometrics being the most frequent contributors. ConclusionsAlthough both statistical methods reported similar accuracy, logistic regression provided very low sensitivity and only identified a single neuromuscular injury risk factor. The machine learning model provided much improved sensitivity to predict injury and identified interactions of asymmetry, knee valgus angle and body size as contributing factors to an injurious profile in youth football players.

Jump and Change of Direction Speed Asymmetry Using Smartphone Apps: Between-Session Consistency and Associations With Physical Performance.

Bishop, C, Perez-Higueras Rubio, M, Gullon, IL, Maloney, S, and Balsalobre-Fernandez, C. Jump and change of direction speed asymmetry using smartphone apps: between-session consistency and associations with physical performance. J Strength Cond Res 36(4): 927-934, 2022-The aims of this study were to (a) quantify the magnitude and direction of asymmetry from jump and change of direction speed (CODS) tests and (b) determine the relationship between these asymmetries and jump and CODS performance, in a test-retest design. Thirty Spanish national-level youth basketball athletes performed single leg countermovement jumps (SLCMJs), single leg drop jumps (SLDJs), and 505 CODS tests, all assessed using the My Jump 2 and CODTimer smartphone applications. All tests showed good to excellent reliability, with no significant differences identified between test sessions in jump, CODS, or asymmetry data. The direction of asymmetry showed substantial levels of agreement between test sessions for jump height during the SLDJ (Kappa = 0.72), but only fair levels of agreement for reactive strength during the SLDJ (Kappa = 0.25), fair levels of agreement for jump height during the SLCMJ (Kappa = 0.29), and slight levels of agreement for total time during the 505 test (Kappa = 0.18). Jump height asymmetry from the SLDJ was significantly associated with reduced jump height (ρ = -0.44), reactive strength (ρ = -0.46) and 505 times (ρ = 0.45-0.48) in test session 1, and reactive strength (ρ = -0.42) and 505 times (ρ = 0.40) in test session 2. These data show that jump height asymmetry from the SLDJ was associated with reduced jump and CODS performance in youth basketball athletes during repeated test sessions. In addition, the same asymmetry metric was the only one to show substantial levels of agreement between test sessions. Owing to the consistency of these data, SLDJ height asymmetry may be a useful metric to measure when monitoring interlimb asymmetries.

Effects of Soccer Match-Play on Unilateral Jumping and Interlimb Asymmetry: A Repeated-Measures Design.

Bishop, C, Read, P, Stern, D, and Turner, A. Effects of soccer match-play on unilateral jumping and interlimb asymmetry: a repeated-measures design. J Strength Cond Res 36(1): 193-200, 2022-The aims of this study were two-fold: (a) determine the effects of repeated soccer match-play on unilateral jump performance and interlimb asymmetries and (b) examine associations between asymmetry and commonly reported external load variables collected during competition. Single-leg countermovement jumps and drop jumps were collected before and immediately after 5 soccer matches in elite academy soccer players. Global positioning system data were also collected during each match as part of the routine match-day procedures. Single-leg countermovement jump height and concentric impulse showed significant reductions after matches (p < 0.01; effect size [ES]: -0.67 to -0.69), but peak force did not (p > 0.05; ES: -0.05 to -0.13). Single-leg drop jump height and reactive strength also showed significant reductions after matches (p < 0.01; ES: -0.39 to -0.58). No meaningful reductions in asymmetry were present at the group level, but individual responses were highly variable. Significant associations between postmatch reactive strength asymmetry and explosive distance (r = 0.29; p < 0.05), relative explosive distance (r = 0.34; p < 0.05), high-speed running (r = 0.35; p < 0.05), and relative high-speed running (r = 0.44; p < 0.01) were observed. These findings show that unilateral jump tests are more appropriate than asymmetry to detect real change after soccer competition, and practitioners should be cautious about using asymmetry to inform decision-making during the temporal recovery period.

Povezanost varijabilnosti položaja stopala nedominantne noge sa ubrzanjem i agilnošću rukometaša

The horizontal acceleration and agility are both an essential part of sports performance in handball. The foot placement variability has been shown to vary between differences in speed and direction of running. However, no studies have considered the connection between the foot placement variability, forward acceleration and agility performance. In the present study, a proposed repetitive single leg countermovement drift test was analyzed as a measure of the foot placement variability and correlated with forward sprinting and agility performance in handball players. Twenty-three male handball players performed a series of 10 consecutive single leg countermovement jumps, 10 m forward acceleration sprint, a handball adapted T-agility test and a single leg countermovement jump test. Correlations between the drift area, T-agility test duration, acceleration performance are measured as well as the time used to accelerate at a 5 m and 10 m distance and the height of the single leg countermovement jump. The drift area for the non-dominant leg had high and significant negative correlations with the first 5 m of forward acceleration sprinting and a positive correlation with the T-agility test to the non-dominant side. The countermovement jump height had no significant correlation to any other parameters. This data indicates that the foot placement variability of the jumps performed on the non-dominant leg could be an indicator of the ability to control stability during short forward acceleration sprints and a quick change of direction. On the contrary, these correlations disappeared when the direction change was performed under reaction time conditions.

Inter-device reliability of wearable technology for quantifying jump height in collegiate athletes.

The purpose of this study was to evaluate the inter-device reliability of three VERT devices (Mayfonk Athletic, Florida, USA) when worn on the waist (W), left-hip (LH), and right-hip (RH) during single- and double-leg counter movement jumps (CMJ) in collegiate athletes. Thirty-two female and twenty-eight male NCAA Division II athletes (n = 60) participated in the present study. Jump height (JH) values for double-leg CMJs were analyzed by each device using a one-way repeated measures ANOVA whereas a 2 (jump leg) x 3 (wear location) repeated measures ANOVA was employed to evaluate single-leg CMJs. Reliability of the VERT devices were based upon intraclass correlation coefficients (ICC). Double-leg CMJs revealed an excellent ICC between all three VERT devices (ICC = 0.969). However, JH for RH and LH (45.69 ± 9.84 and 45.82 ± 10.45 cm, respectively) were on average lower than W (50.44 ± 12.37cm; both p < 0.001). The ICCs were excellent for right- and left-leg CMJs (ICC = 0.939 and 0.941, respectively). However, an interaction was observed (p < 0.001). No differences existed for left- or right-leg when VERT was worn on the waist. However, JH was higher when VERT devices were worn on the opposite hip of the jump leg (i.e., LH>RH for right-leg CMJs; RH>LH for leftleg CMJs; all p < 0.001). Results suggest that LH and RH are interchangeable for double-leg CMJs, but not with waist despite excellent reliability. In addition, all wear locations provided excellent ICCs for single-leg CMJs. However, waist provides more consistent JH values for right- and left-leg CMJs while RH and LH show more variability.

Leg asymmetry and muscle function recovery after anterior cruciate ligament reconstruction in elite athletes: a pilot study on slower recovery of the dominant leg.

The aim of this study was to examine performance in hopping tests in male athletes after anterior cruciate ligament reconstruction (ACLR) in the 4-to-6 months post-surgery period. A total of 36 athletes (24 ACLR and 12 controls) participated in this study. The ACLR group consisted of athletes who had undergone an ACLR on their dominant side (ACL DG n=16) or non-dominant side (ACL NDG n=8). Participants completed the following functional tests: a single-leg hop (SLH), single-leg triple hop (SL3H) and single-leg counter movement jump (SLCMJ), then the limb symmetry index (LSI) was calculated. There were no significant differences between the dominant and the non-dominant legs for all functional tests when comparing the ACL DG and the ACL NDG at 6 months after surgery. At 6 months after ACLR, the LSI of the two legs was within acceptable values, whether the athlete had the operation on their dominant or non-dominant leg (except the mean LSI for the ACL DG in the SLCMJ test). Furthermore, the control group showed higher performances as compared to the ACL group for all variables at 6 months after surgery, despite acceptable LSI. We concluded that an early return to “full participation to training” is not recommended in participants who have undergone an ACLR with patellar tendon grafts.

Seasonal variation in neuromuscular control in young male soccer players

ObjectiveDetermine how lower limb neuromuscular control changes over the course of a competitive soccer season. DesignRepeated measures. SettingAcademy soccer club. Participants43 male youth soccer players (age 13.1 ± 2.2 yr; height 160.1 ± 15.7 cm; body mass 49.4 ± 14.3 kg; maturity offset 0.2 ± 1.9 yr). Main outcome measuresPre-, mid- and end of season assessments of peak landing forces during single leg 75% horizontal hop and stick (75%HOP) and a single leg countermovement jump (SLCMJ), single leg hop for distance (SLHD), knee valgus during the tuck jump assessment (TJA) and inter-limb symmetries. ResultsHop distance increased significantly. Absolute peak landing forces in the left leg during the SLCMJ and 75%HOP increased significantly, with significant increases also present in the same leg for SLCMJ relative peak landing force. TJA knee valgus score was reduced in the right leg, but remained at a ‘moderate’ level in the left knee. ConclusionNeuromuscular control, as evidenced by increased absolute and relative peak landing forces, appears to reduce over the course of a competitive season. Young soccer players should engage in neuromuscular training throughout the season to offset any decrements in neuromuscular control and to facilitate appropriate landing strategies.

Handball injuries and their prevention

Handball is one of the most popular team sports in Germany, as well as one of the most dangerous ones. Injury rates in Germany are higher amongst handball professionals than in soccer, with the knee being the most commonly injured joint. To prevent injuries, afunctional inert stability is necessary, but definitions and objective measures are lacking. Establishing valid reference data of functional knee stability in amateur handball players with use of an established test battery giving objective measures METHODS: 261 athletes (f:130; m:131), mean age 25.1 ± 5.8 y were screened during the preseason. The test battery consisted of double and single-leg counter movement jumps, balance tests, agility, parkour, quick feet test and plyometric jumps. Significant differences between males and females were noted in regard to balance scores (favour for females p ≤ 0.001), as well as jump height, agility and speed tests (favour for males [p ≤ 0.002-0.001]). The noted differences once again bring focus to the interindividual presence of risk factors, because female and male handball athletes have gender-specific ground levels. These attributes have to be considered in further screening and prevention programs, as well as in the context of the return-to-sports decision after injury. The given data may serve as objective reference measures.

Relationship Between Interlimb Asymmetries and Speed and Change of Direction Speed in Youth Handball Players.

Madruga-Parera, M, Bishop, C, Beato, M, Fort-Vanmeerhaeghe, A, Gonzalo-Skok, O, and Romero-Rodríguez, D. Relationship between inter-limb asymmetries and speed and change of direction speed in youth handball players. J Strength Cond Res 35(12): 3482-3490, 2021-The aims of the present study were to quantify interlimb asymmetry from jumping, change of direction speed (CODS), and iso-inertial tests and to establish the association between those asymmetry scores and performance during speed and CODS tests in youth handball athletes. Twenty-six youth handball players (age: 16.2 ± 0.9 years) volunteered to participate in this study and performed single-leg countermovement jumps, single-leg broad jumps, single-leg lateral jumps, CODS tests at 180° (CODS180) and 90° (CODS90), change of direction actions with iso-inertial overload (crossover step [CRO] and lateral shuffle step), and a 20-m sprint test. Excellent intraclass correlation coefficient (ICC) values were found for all tests (ICC = 0.96-1.00) with the exception of the dominant limb during the CODS90 test (ICC = 0.69). Interlimb asymmetry scores ranged from 3.66 to 12.67%. Iso-inertial asymmetry values were higher than those found during jumping tasks (9.8-12.7% vs. 3.66-8.76%). Spearman's r correlations showed significant relationships between CRO asymmetry and CODS90 performance on both limbs (r = 0.48-0.51; p < 0.05) and CODS180 (r = 0.41-0.51; p < 0.05) and a sprint test (r = 0.46; p < 0.05). These results show the test-specific nature of asymmetries in youth handball players, with iso-inertial device and CODS deficit presenting the greatest magnitude of asymmetries. Furthermore, interlimb differences during iso-inertial device (CRO) were associated with reduced CODS and sprint performance. These results suggest that the use of iso-inertial devices for the detection of interlimb asymmetry may be more effective than the total time during traditional CODS tests and that larger imbalances are associated with reduced athletic performance in youth handball players.

Effects of Maturation on Lower Limb Neuromuscular Asymmetries in Elite Youth Tennis Players.

Neuromuscular asymmetries have been previously associated with reduced performance. Similarly, maturation has shown that youth athletes may experience a loss of motor control, which could also lead to compromised physical performance. The present study aimed to evaluate and quantify the level of asymmetry among chronological and maturational groups. Forty-one youth tennis players performed the single leg countermovement jump (SLCMJ), star excursion balance test (SEBT) and a change of direction speed (CODS) test. Differences were found between the strongest and weakest limbs across all tests (p < 0.001), and also for SEBT in the posteromedial direction (p = 0.02), SEBT composite score (p < 0.01) in maturation groups, and for SEBT posterolateral direction (p = 0.03) and SEBT composite score (p = 0.01) in chronological groups. The SLCMJ showed the largest inter-limb asymmetries for the circa peak height velocity (PHV) group (19.31 ± 12.19%) and under-14 (U14) group (17.55 ± 9.90%). Chronological and maturation groups followed similar trends for inter-limb asymmetries, but the biological index showed larger asymmetry scores in the jumping test at PHV compared to that found in the chronological group (U14). These results show that inter-limb differences may be heightened during PHV. Practitioners can use this information to inform the decision-making process when prescribing training interventions in youth tennis players.

Interlimb Asymmetries in Youth Tennis Players: Relationships With Performance.

Madruga-Parera, M, Bishop, C, Fort-Vanmeerhaeghe, A, Beltran-Valls, MR, Gonzalo-Skok, O, and Romero-Rodríguez, D. Interlimb asymmetries in youth tennis players: relationships with performance. J Strength Cond Res 34(10): 2815-2823, 2020-Change of direction speed (CODS) has been highlighted as a critical component of tennis. Interlimb asymmetries have been commonly studied in jump tests, but less attention given to the topic during CODS. The aim of this study was to quantify interlimb asymmetries in jumping and CODS (during traditional and isoinertial tests) and establish their relationship with measures of physical performance. Twenty-two elite youth tennis players (16.3 ± 1.4 years) performed single-leg countermovement jump (SLCMJ), single-leg broad jump, and single-leg lateral jump, a double 180° turn CODS test, and shuffle lateral step and crossover step with an isoinertial resistance device. Paired-samples t-tests revealed significant differences between limbs for all tests (p < 0.05). Interlimb asymmetry scores ranged from 1.83 to 15.03%, and a 1-way repeated-measures analysis of variance showed significant differences between interlimb asymmetry scores across multiple tests (p < 0.05). Spearman's rank order r correlations showed significant negative relationships between CODS asymmetry and SLCMJ performance on both limbs (r = -0.50; p = 0.02 and r = -0.53; p = 0.01) and CODS performance on both limbs (r = 0.50; p = 0.02 and r = 0.63; p = 0.002). These results show the test-specific nature of asymmetries in youth tennis athletes, with the SLCMJ presenting the greatest magnitude of asymmetry. Furthermore, interlimb differences during CODS were associated with reduced performance during jumping and CODS tests, suggesting the monitoring of asymmetries within this population may therefore be warranted.

Effects of Interlimb Asymmetries on Acceleration and Change of Direction Speed: A Between-Sport Comparison of Professional Soccer and Cricket Athletes.

Bishop, C, Read, P, Brazier, J, Jarvis, P, Chavda, S, Bromley, T, and Turner, A. Effects of interlimb asymmetries on acceleration and change of direction speed: a between-sport comparison of professional soccer and cricket athletes. J Strength Cond Res 35(8): 2095-2101, 2021-The first aim of this study was to quantify and compare asymmetries among professional soccer and cricket athletes. The second aim was to examine the association between asymmetries and performance within both groups. Professional soccer (n = 18) and cricket (n = 23) athletes performed single-leg countermovement jumps, single-leg drop jumps (SLDJs), a 10-m sprint, and 505 change of direction speed (CODS) tests. Interlimb asymmetries were calculated as a standard percentage difference, Mann-Whitney U tests conducted to establish systematic bias between groups, and Spearman's r correlations used to establish the relationship between asymmetry scores and speed and CODS performance. Soccer athletes sprinted faster, jumped higher, and had a greater reactive strength index (RSI) score than cricket athletes (p < 0.05). However, cricketers showed reduced ground contact times compared with footballers during the SLDJ (p < 0.05). The cricket group showed significantly greater jump height (asymmetry = 11.49 vs. 6.51%; p = 0.015) and RSI (asymmetry = 10.37 vs. 5.95%; p = 0.014) asymmetries compared with soccer players. These metrics were also associated with slower 505 times in the cricket group only (r = 0.56 -0.74; p < 0.01). These results show that between-limb asymmetries exhibit no association with speed and CODS in elite soccer players but are associated with reduced CODS in elite cricketers. Thus, the reduction of interlimb asymmetries may be of greater consideration when working with cricket vs. soccer athletes.

Acute Effect of Repeated Sprints on Interlimb Asymmetries During Unilateral Jumping.

Bishop, C, McAuley, W, Read, P, Gonzalo-Skok, O, Lake, J, and Turner, A. Acute effect of repeated sprints on interlimb asymmetries during unilateral jumping. J Strength Cond Res 35(8): 2127-2132, 2021-The aim of this study was to investigate the effects of multiple repeated sprints on unilateral jump performance and interlimb asymmetries. Eighteen recreationally active men performed 3 single-leg countermovement jumps (SLCMJ) as baseline data. The repeated sprint protocol was 6 × 40 m with 20 seconds of passive rest between each sprint. This protocol was conducted 4 times, each set separated by 4 minutes of rest. Within that rest period, subjects performed one SLCMJ on each limb after 2 minutes of rest. A 1-way analysis of variance showed significant reductions (p < 0.05; effect size [ES] = -0.52 to -0.99) in jump height on both limbs after each set relative to baseline. Interlimb asymmetries increased at each time point and ranged from 7.62 to 14.67%, with significant increases in asymmetry seen after sets 3 (p = 0.046) and 4 (p = 0.002). Significant increases in sprint time were shown between sprints 1 and 6 in each set (p ≤ 0.01). A fatigue index (%) was also calculated and showed an exponential increase from 5.74% (set 1) to 13.50% (set 4), with significant differences between all sets (p < 0.001) with the exception of sets 3 and 4. Results from this study show that a 6 × 40-m repeated sprint protocol is a sufficient dose for implementing acute fatigue in recreationally active subjects. This was manifested by reductions in jump height at all time points and jump height asymmetries after the third and fourth sets. These findings indicate that jump height from unilateral jump testing may be a useful metric to use during the monitoring process in recreationally trained athletes.

Bilateral Deficit During Jumping Tasks: Relationship With Speed and Change of Direction Speed Performance.

Bishop, C, Berney, J, Lake, J, Loturco, I, Blagrove, R, Turner, A, and Read, P. Bilateral deficit during jumping tasks: relationship with speed and change of direction speed performance. J Strength Cond Res 35(7): 1833-1840, 2021-Research to date has investigated the phenomenon of the bilateral deficit (BLD); however, limited research exists on its association with measures of athletic performance. The purpose of this study was to investigate the magnitude of the BLD and examine its relationship with linear speed and change of direction speed (CODS) performance. Eighteen physically active and healthy university students performed double- and single-leg countermovement jumps (CMJs), drop jumps (DJs), and standing broad jumps (SBJs) to calculate the BLD across jump tasks. Subjects also performed 10- and 30-m sprints and a 505 CODS test, which were correlated with all BLD metrics. Results showed varying levels of BLD across CMJ metrics (jump height, peak force, eccentric impulse, concentric impulse, and peak power), DJ metrics (ground contact time and flight time), and the SBJ (distance). However, a bilateral facilitation was shown for jump height and reactive strength index during the DJ test. The main findings of this study were that: (a) a larger BLD in CMJ height related to a faster 505 COD (left leg) (r = -0.48; p = 0.04), 505 COD (right leg) (r = -0.53; p = 0.02), and COD deficit (right leg) (r = -0.59; p = 0.01), (b) a larger BLD in CMJ concentric impulse related to faster 505 COD (left leg) (r = -0.51; p = 0.03), 505 COD (right leg) (r = -0.64, p = 0.01), and COD deficit (right leg) (r = -0.60; p = 0.01), and (c) a larger BLD in DJ flight time related to a faster 505 COD (left leg) (r = -0.48; p = 0.04). These results suggest that a larger BLD is associated with faster CODS performance, but not linear speed. This highlights the individual nature of the BLD and may support the notion of developing movement competency on one limb for enhanced CODS performance.

Vertical and Horizontal Asymmetries Are Related to Slower Sprinting and Jump Performance in Elite Youth Female Soccer Players.

Bishop, C, Read, P, McCubbine, J, and Turner, A. Vertical and horizontal asymmetries are related to slower sprinting and jump performance in elite youth female soccer players. J Strength Cond Res 35(1): 56-63, 2021-Interlimb asymmetries have been shown to be greater during vertical jumping compared with horizontal jumping. Notable interlimb differences have also been established at an early age in male youth soccer players. Furthermore, given the multiplanar nature of soccer, establishing between-limb differences from multiple jump tests is warranted. At present, a paucity of data exists regarding asymmetries in youth female soccer players and their effects on physical performance. The aims of this study were to quantify interlimb asymmetries from unilateral jump tests and examine their effects on speed and jump performance. Nineteen elite youth female soccer players performed a single-leg countermovement jump (SLCMJ), single, triple, and crossover hops for distance, and a 20-m sprint test. Test reliability was good to excellent (intraclass correlation coefficient = 0.81-0.99) and variability acceptable (coefficient of variation = 1.74-5.42%). A 1-way analysis of variance highlighted larger asymmetries from the SLCMJ compared with all other jump tests (p < 0.05). Pearson's correlations portrayed significant relationships between vertical asymmetries from the SLCMJ and slower sprint times (r = 0.49-0.59). Significant negative relationships were also found between horizontal asymmetries during the triple hop test and horizontal jump performance (r = -0.47 to -0.58) and vertical asymmetries during the SLCMJ and vertical jump performance (r = -0.47 to -0.53). The results from this study highlight that the SLCMJ seems to be the most appropriate jump test for identifying between-limb differences with values ∼12% showing negative associations with sprint times. Furthermore, larger asymmetries are associated with reduced jump performance and would appear to be direction specific. Practitioners can use this information as normative data to be mindful of when quantifying interlimb asymmetries and assessing their potential impact on physical performance in youth female soccer players.

A prospective investigation to evaluate risk factors for lower extremity injury risk in male youth soccer players.

There is an inherent risk of injury in male youth football; however, pertinent risk factors for injury have yet to be examined. This study used a prospective cohort design with 357 elite male youth football players (aged 10-18years) assessed during the preseason period and then monitored during the season recording all non-contact lower extremity injuries. Screening tests included single leg hop for distance (SLHD); 75% of maximum hop and stick (75%Hop); single leg countermovement jump (SLCMJ); and the tuck jump assessment (TJ). Players were divided into subgroups based on chronological age. SLCMJ peak landing vertical ground reaction force (pVGRF) asymmetry was the most prominent risk factor (U11-U12s, OR 0.90, P=.04; and U15-U16s, OR 0.91, P<.001). Maturational offset (OR 0.58, P=.04), lower right leg SLCMJ pVGRF relative to body weight (OR 0.36, P=.03), and advanced chronological age (OR 3.62, P=.04) were also significantly associated with heightened injury risk in the U13-U14s, U15-U16s, and U18s, respectively. Univariate analyses showed combinations of anthropometric and movement screening risk factors were associated with heightened risk of lower extremity injury; however, there was variability across the different chronological age groups. Greater SLCMJ pVGRF asymmetry, lower right leg SLCMJ pVGRF %BW, later maturation, and advanced chronological age are potential risk factors for injury in elite male youth football players, although the strength of these relationships was often low to moderate. In addition, risk factors are likely to change at different stages of development.