The Validity of Hawkin Dynamics Wireless Dual Force Plates for Measuring Countermovement Jump and Drop Jump Variables.

Force plate testing is becoming more commonplace in sport due to the advent of commercially available, portable, and affordable force plate systems (i.e., hardware and software). Following the validation of the Hawkin Dynamics Inc. (HD) proprietary software in recent literature, the aim of this study was to determine the concurrent validity of the HD wireless dual force plate hardware for assessing vertical jumps. During a single testing session, the HD force plates were placed directly atop two adjacent Advanced Mechanical Technology Inc. in-ground force plates (the "gold standard") to simultaneously collect vertical ground reaction forces produced by 20 participants (27 ± 6 years, 85 ± 14 kg, 176.5 ± 9.23 cm) during the countermovement jump (CMJ) and drop jump (DJ) tests (1000 Hz). Agreement between force plate systems was determined via ordinary least products regression using bootstrapped 95% confidence intervals. No bias was present between the two force plate systems for any of the CMJ and DJ variables, except DJ peak braking force (proportional bias) and DJ peak braking power (fixed and proportional bias). The HD system may be considered a valid alternative to the industry gold standard for assessing vertical jumps because fixed or proportional bias was identified for none of the CMJ variables (n = 17) and only 2 out of 18 DJ variables.

Kinetics and Kinematics of the Free-Weight Back Squat and Loaded Jump Squat.

ABSTRACT: Thompson, SW, Lake, JP, Rogerson, D, Ruddock, A, and Barnes, A. Kinetics and kinematics of the free-weight back squat and loaded jump squat. J Strength Cond Res 37(1): 1-8, 2023-The aim of this study was to compare kinetics and kinematics of 2 lower-body free-weight exercises, calculated from concentric and propulsion subphases, across multiple loads. Sixteen strength-trained men performed back squat 1 repetition maximum (1RM) tests (visit 1), followed by 2 incremental back squat and jump squat protocols (visit 2) (loads = 0% and 30-60%, back squat 1RM). Concentric phase and propulsion phase force-time-displacement characteristics were derived from force plate data and compared using analysis of variance and Hedges' g effect sizes. Intrasession reliability was calculated using intraclass correlation coefficient (ICC) and coefficient of variation (CV). All dependent variables met acceptable reliability (ICC >0.7; CV < 10%). Statistically significant 3-way interactions (load × phase × exercise) and 2-way main effects (phase × exercise) were observed for mean force, velocity (30-60% 1RM), power, work, displacement, and duration (0%, 30-50% 1RM) ( p < 0.05). A significant 2-way interaction (load × exercise) was observed for impulse ( p < 0.001). Jump squat velocity ( g = 0.94-3.80), impulse ( g = 1.98-3.21), power ( g = 0.84-2.93), and work ( g = 1.09-3.56) were significantly larger across concentric and propulsion phases, as well as mean propulsion force ( g = 0.30-1.06) performed over all loads ( p < 0.001). No statistically significant differences were observed for mean concentric force. Statistically longer durations ( g = 0.38-1.54) and larger displacements ( g = 2.03-4.40) were evident for all loads and both subphases ( p < 0.05). Ballistic, lower-body exercise produces greater kinetic and kinematic outputs than nonballistic equivalents, irrespective of phase determination. Practitioners should therefore use ballistic methods when prescribing or testing lower-body exercises to maximize athlete's force-time-displacement characteristics.

Predicting Weight Category-Specific Performance Zones for Olympic, World, and European Weightlifting Competitions.

ABSTRACT: Chavda, S, Comfort, P, Lake, JP, Bishop, C, and Turner, AN. Predicting weight category-specific performance zones for Olympic, World, and European weightlifting competitions. J Strength Cond Res 37(10): 2038-2045, 2023-Understanding the total likely required weight category to achieve a specific rank within a specific competition can aid in the long-term and short-term preparation and tactics for performance teams. The primary objective of this investigation was to develop a set of predictive models for new weight categories across 5 performance zones for 3 major weightlifting competitions. Performance total (Ptot) data for top 15 male athletes were obtained from the International Weightlifting Federation website from 1998 to 2020 across the Olympics, and World and European Championships. A second-order polynomial regression was conducted with 95% confidence, and predictive intervals were calculated. The average of the newly contested body mass was then used as the intercept. Predictions were compared against current performances of the new weight categories up to the 2020 Olympics. Results revealed that the models for all competition types varied in their predictive ability for each performance zone, across each new weight category. On average, predicted Ptot displayed a difference from actual Ptot of 3.65 ± 2.51% (12.46 ± 9.16 kg), 0.78 ± 3.29% (2.26 ± 10.08 kg), and -1.13 ± 3.46% (-4.32 ± 11.10 kg) for the Olympics, and World and European Championships, respectively. The results suggest that the predictive models may be a good indicator of future performances; however, the models may have greater efficacy in some weight categories and performance zones than others.

Effects of 56-Kilogram Kettlebell Swing Endpoint on Total Body Mechanics.

ABSTRACT: Ross, JA, Keogh, JWL, Lorenzen, C, and Lake, J. Effects of 56-kilogram kettlebell swing endpoint on total body mechanics. J Strength Cond Res 37(12): 2333-2338, 2023-In the past 2 decades, kettlebell training popularity has increased and the range of kettlebells has expanded to 2-92 kg. However, commercially available kettlebells above 56 kg have 12 kg increments, so alternatives to load are required to provide a suitable way of increasing training stimulus until the athlete is strong enough for a load increase. This study aimed to determine the differences in the force plate-derived biomechanical characteristics of heavy kettlebell swings to 3 different heights, as altering the height of the kettlebell swing may be one way to alter the mechanical demands with the same kettlebell mass. Fifteen resistance-trained men performed the kettlebell swing to acromion process height (AH), acromion process height + 20% (AH+20), and acromion process height-20% (AH-20). Swing height significantly affected vertical braking and propulsion phase net impulse and displacement, vertical braking velocity, and braking and propulsion work but not braking and propulsion duration. Altering kettlebell swing trajectory endpoint is a method to regress/progress the demands of kettlebell training. Coaches may be able to alter the acute demands and likely chronic adaptations of kettlebell training by prescribing different swing heights and kettlebell masses to their athletes.

Agreement in Squat Jump Force-Time Characteristics Between Smith Machine and Free-Weight Squat Jump Force-Time Characteristics.

ABSTRACT: Kotani, Y, Lake, J, Guppy, SN, Poon, W, Nosaka, K, and Haff, GG. Agreement in squat jump force-time characteristics between Smith machine and free-weight squat jump force-time characteristics. J Strength Cond Res 37(10): 1955-1962, 2023-The purpose of this study was to determine whether squat jump (SJ) force-velocity (FV) and load-velocity (LV) profiles created using free-weights agree with profiles created with a Smith machine. Fifteen resistance-trained male subjects (age = 26.4 ± 2.5 years; height = 1.75 ± 0.09 m; body mass = 82.6 ± 13.4 kg) participated in this study. All subjects completed 2 familiarization and 2 experimental sessions using both the Smith machine and free-weight SJs each separated by 48 hours. During the experimental trials, progressively loaded SJs were performed in a quasi-randomized block order with loads between 21 kg and 100% of the subject's body mass. Agreement between exercise mode was determined with a weighted least products regression analysis. No fixed or proportional bias was noted between exercise modes when using peak velocity (PV) and mean velocity (MV) to create an FV profile. There was no fixed and proportional bias present for the LV profile when the profile was created with PV. When the LV profile was calculated from MV, fixed and proportional bias were present, indicating that MVs were significantly different between exercise modes. In addition, the free-weight FV and LV profiles exhibited poor to good relative and good to poor absolute reliability. Furthermore, when created using the Smith machine, both profiles exhibited poor to moderate relative and absolute reliability. Based on these data, caution should be used when interpreting LV and FV profiles created with these 2 methods.

Bilateral vs. Unilateral Countermovement Jumps: Comparing the Magnitude and Direction of Asymmetry in Elite Academy Soccer Players.

ABSTRACT: Bishop, C, Abbott, W, Brashill, C, Turner, A, Lake, J, and Read, P. Bilateral vs. unilateral countermovement jumps: comparing the magnitude and direction of asymmetry in elite academy soccer players. J Strength Cond Res 36(6): 1660-1666, 2022-The aims of this study were to compare the magnitude and direction of asymmetry in comparable bilateral and unilateral countermovement jumps (CMJs). Forty-five elite academy soccer players from under-23 (n = 15), under-18 (n = 16), and under-16 (n = 14) age groups performed bilateral and unilateral CMJs as part of their routine preseason fitness testing. For the magnitude of asymmetry, no significant differences were evident for any metric between tests. However, the eccentric impulse asymmetry was significantly greater than mean force and concentric impulse in both bilateral and unilateral tests (p < 0.01). For the direction of asymmetry, Kappa coefficients showed poor levels of agreement between test measures for all metrics (mean force = -0.15, concentric impulse = -0.07, and eccentric impulse = -0.13). The mean jump data were also presented relative to the body mass for each group. For the bilateral CMJ, significant differences were evident between groups but showed little consistency in the same group performing better or worse across metrics. For the unilateral CMJ, eccentric impulse was the only metric to show meaningful differences between groups, with the under-18 group performing significantly worse than under-23 and under-16 players. This study highlights that despite the magnitude of asymmetry being similar for each metric between comparable bilateral and unilateral CMJs, consistency in the direction of asymmetry was poor. In essence, if the right limb produced the larger force or impulse during a bilateral CMJ, it was rare for the same limb to perform superior during the unilateral task. Thus, practitioners should be aware that bilateral and unilateral CMJs present different limb dominance characteristics and should not use 1 test to represent the other when measuring between-limb asymmetries.

Intra- and Interday Reliability of Weightlifting Variables and Correlation to Performance During Cleans.

ABSTRACT: Sorensen, AM, Chavda, S, Comfort, P, Lake, J, and Turner, AN. Intra- and interday reliability of weightlifting variables and correlation to performance during cleans. J Strength Cond Res 36(11): 3008-3014, 2022-The purpose of this investigation was to examine intra- and interday reliability of kinetic and kinematic variables assessed during the clean, assess their relationship to clean performance, and determine their suitability in weightlifting performance analysis. Eight competitive weightlifters performed 3 sets of single repetition cleans with 90% of their 1-repetition maximum (1RM). Force-time data were collected via dual force plates with displacement-time data collected via 3-dimensional motion capture, on 3 separate occasions under the same testing conditions. Seventy kinetic and kinematic variables were analyzed for intra- and interday reliability using intraclass correlation coefficients (ICCs) and the coefficient of variation (CV). Pearson's correlation coefficients were calculated to determine relationships between barbell and body kinematics and ground reaction forces, and for correlations to be deemed as statistically significant, an alpha-level of p ≤ 0.005 was set. Eleven variables were found to have "good" to "excellent" intra- and interday ICC (0.779-0.994 and 0.974-0.996, respectively) and CV (0.64-6.89% and 1.14-6.37%, respectively), with strong correlations ( r = 0.880-0.988) to cleans performed at 90% 1RM. Average resultant force of the weighting 1 (W1) phase demonstrated the best intra- and interday reliability (ICC = 0.994 and 0.996, respectively) and very strong correlation ( r = 0.981) to clean performance. Average bar power from point of lift off to peak bar height exhibited the highest correlation ( r = 0.988) to clean performance. Additional reliable variables with strong correlations to clean performance were found, many of these occurred during or included the W1 phase, which suggests that coaches should pay particular attention to the performance of the W1 phase.

Countermovement Jump Standards in Rugby League: What is a "Good" Performance?

ABSTRACT: McMahon, JJ, Lake, JP, Dos'Santos, T, Jones, PA, Thomasson, ML, and Comfort, P. Countermovement jump standards in rugby league: what is a "good" performance? J Strength Cond Res 36(6): 1691-1698, 2022-The countermovement jump (CMJ) is considered an important test in rugby league, and the force platform is the recommended tool for assessing CMJ performance in this cohort. Because of inconsistent methods applied across previous studies, there is currently a lack of understanding of what constitutes a "good" CMJ performance, with respect to the typical CMJ metrics that are reported for rugby league players. The purpose of this study was, therefore, to produce a scale of reference values for the jump height (JH), reactive strength index modified (RSImod), and mean (PPmean) and peak (PPpeak) propulsion power (relative to body mass) for top-level senior rugby league players competing in the global "forward" and "back" positional groups. One hundred four players (55 forwards and 49 backs) from the top 2 tiers of English rugby league performed 3 CMJs on a force platform at the beginning of pre-season training. The JH, RSImod, PPmean, and PPpeak were calculated using criterion methods, and a scale of norm-referenced values (percentiles) was produced for each positional group. The backs outperformed the forwards for each CMJ metric reported, thus supporting the production of position-specific norm-referenced values. When each positional group was separated into quartile subgroups, the respective JH, RSImod, PPmean, and PPpeak values were mostly largely and significantly different both within and between positions. The presented scale of reference values can, therefore, be used to determine the performance standards of rugby league forwards and backs with respect to the most commonly reported CMJ-derived variables for this cohort.

Reliability of the Squat Jump Force-Velocity and Load-Velocity Profiles.

ABSTRACT: Kotani, Y, Lake, J, Guppy, SN, Poon, W, Nosaka, K, Hori, N, and Haff, GG. The reliability of the squat jump force-velocity and load-velocity profiles. J Strength Cond Res 36(11): 3000-3007, 2022-The purpose of this study was to investigate the between-session reliability of the squat jump force-velocity (FV) and load-velocity (LV) profiles. Eighteen subjects (age = 28.1 ± 4.8 years; height = 1.7 ± 9.7; body mass = 74.7 ± 12.8) who could back squat >1.5 times body mass participated in this study. Each subject completed a familiarization session, followed by 2 experimental sessions each separated by 72 hours. Subjects performed a series of squat jumps on a force plate against external loads between 0 and 100% of their body mass in a quasi-randomized block order. Intraclass correlation coefficient (ICC) and coefficient of variation (CV) were used to examine the between-session reliability. Peak velocity (PV) and mean velocity (MV) at each load were highly reliable (ICC >0.80, CV% <7.41, SEM <0.13 m·s -1 , smallest detectable difference [SDD] <0.31 m·s -1 , ES <0.21). Force-velocity profiles created with peak force and relative peak force resulted in poor to excellent reliability (ICC = 0.34-0.92, CV% = 11.9-26.3). When mean and relative mean forces were used to create FV profiles, there was poor to good reliability (ICC = 0.03-0.85, CV% = 18.1-39.4). When the LV profile was calculated with PV (ICC = 0.60-0.90, CV% = 7.9-16.9) or MV (ICC = 0.49-0.91, CV% = 11.1-23.4), there was poor to excellent reliability. There was no time effect found between sessions for both FV and LV profiles. The squat jump FV and LV profiles established with a force plate are not reliable. Therefore, these profiles are not recommended to be used to inform programming decisions.

A Novel Approach for Athlete Profiling: The Unilateral Dynamic Strength Index.

ABSTRACT: Bishop, C, Read, P, Lake, J, Loturco, I, and Turner, A. A novel approach for athlete profiling: The unilateral dynamic strength index. J Strength Cond Res 35(4): 1023-1029, 2021-The Dynamic Strength Index (DSI) provides a ratio of the peak force an athlete can produce in both isometric and ballistic tasks. Although the DSI measured during bilateral tests has been examined, unilateral DSI scores have not been reported to date and thus was the aim of the present study. Twenty-eight recreational sport athletes performed 3 trials of a unilateral isometric squat and countermovement jump (CMJ) to measure peak force in each task across 2 separate test sessions. The unilateral DSI was calculated using both left vs. right and dominant vs. nondominant limbs. Good to excellent reliability was shown in the isometric squat (intraclass correlation coefficient [ICC] = 0.86-0.96; coefficient of variation [CV] ≤ 5.7%) and the CMJ (ICC = 0.83-0.93; CV ≤ 5.8%) on both limbs. The DSI showed moderate to good reliability (ICC = 0.71-0.79; CV = 7.54-11.9%). Dynamic Strength Index scores of 0.52-0.55 and 0.55-0.59 were reported on the left and right limbs, respectively, with no significant differences reported between limbs. A significant difference (p = 0.04) was seen for the CMJ between left and right during the second test session only. The dominant and nondominant limbs reported mean DSI scores of 0.53-0.57, and significant differences were evident between limbs in both the isometric squat and CMJ (p < 0.01). This study provides normative data for the unilateral DSI and indicates acceptable levels of reliability, whereas the consistency of individual measures of peak force can be considered good when quantified unilaterally.

Relationship Between Reactive Strength Index Variants in Rugby League Players.

ABSTRACT: McMahon, JJ, Suchomel, TJ, Lake, JP, and Comfort, P. Relationship between reactive strength index variants in rugby league players. J Strength Cond Res 35(1): 280-285, 2021-Two reactive strength index (RSI) variants exist, the RSI and RSI modified (RSImod), which are typically calculated during the drop jump (DJ) and countermovement jump (CMJ), respectively. Both RSI variants have been used to monitor athletes' ability to complete stretch-shortening cycle actions quickly, but they have never been compared. The purpose of this study was to determine whether they yield relatable information about reactive strength characteristics. Male professional rugby league players (n = 21, age = 20.8 ± 2.3 years, height = 1.82 ± 0.06 m and body mass = 94.3 ± 8.4 kg) performed 3 DJs (30 cm) and CMJs on a force plate. Reactive strength index and RSImod were subsequently calculated by dividing jump height (JH) by ground contact time (GCT) and time to take-off (TTT), respectively. All variables were highly reliable (intraclass correlation coefficient ≥0.78) with acceptable levels of variability (coefficient of variation ≤8.2%), albeit larger variability was noted for DJ variables. Moreover, there was a large relationship between RSI and RSImod (r = 0.524, p = 0.007), whereas very large relationships were noted between JHs (r = 0.762, p < 0.001) and between GCT and TTT (ρ = 0.705, p < 0.001). In addition, RSI (0.90 ± 0.22) was largely and significantly (d = 2.57, p < 0.001) greater than RSImod (0.47 ± 0.08). The DJ-derived RSI yields much larger values than the CMJ-derived RSImod and although a large relationship was noted between them, it equated to just 22% shared variance. These results suggest that the 2 RSI variants do not explain each other well, indicating that they do not assess entirely the same reactive strength qualities and should not be used interchangeably.

Jumping Asymmetries Are Associated With Speed, Change of Direction Speed, and Jump Performance in Elite Academy Soccer Players.

ABSTRACT: Bishop, C, Brashill, C, Abbott, W, Read, P, Lake, J, and Turner, A. Jumping asymmetries are associated with speed, change of direction speed, and jump performance in elite academy soccer players. J Strength Cond Res 35(7): 1841-1847, 2021-The aim of this study was to establish interlimb asymmetries across different age groups in elite academy male soccer players and to examine any relationships between asymmetry and measures of physical performance. Fifty-one players from an English Premier League soccer academy were split into under-23 (n = 21), under-18 (n = 14), and under-16 (n = 16) groups and performed bilateral and unilateral countermovement jumps, 5-, 10-, and 20-m sprints, and a 505 change of direction speed tests. All tests showed low variability (coefficient of variation ≤ 2.5%) and good to excellent reliability (intraclass correlation coefficient = 0.80-0.99). A 1-way analysis of variance showed that the under-23 group was significantly faster than the under-16 group during the 20-m sprint (2.90 vs. 2.98 s; p = 0.02; effect size = 0.94). No other significant differences were present between groups. Interlimb asymmetry was quantified from the single-leg countermovement jump, and no significant differences in the magnitude of asymmetry were present between groups. However, multiple significant correlations were present in each age group between asymmetry and physical performance tests, all of which were indicative of reduced athletic performance. Results from this study show that although interlimb asymmetry scores are comparable across age groups in elite academy soccer players, differences as low as 5% are associated with reduced physical performance during jumping, sprinting, and change of direction speed tasks. This study suggests the importance of monitoring jump height asymmetries in elite academy soccer players.

Interlimb Asymmetries: The Need for an Individual Approach to Data Analysis.

ABSTRACT: Bishop, C, Lake, J, Loturco, I, Papadopoulos, K, Turner, A, and Read, P. Interlimb asymmetries: the need for an individual approach to data analysis. J Strength Cond Res 35(3): 695-701, 2021-It has been shown that the magnitude of interlimb asymmetries varies depending on the test selected; however, literature relating to whether asymmetries always favor the same limb is scarce. The aim of this study was to determine whether interlimb asymmetries always favored the same side for common metrics across unilateral strength and jumping-based tests. Twenty-eight recreational sport athletes performed unilateral isometric squats, single-leg countermovement jumps, and single-leg broad jumps with asymmetries in peak force compared across all tests, and eccentric and concentric impulse asymmetries compared between jumps. Mean asymmetries for all tests were low (≤-5.3%), and all interlimb differences for jump tests favored the left limb, whereas asymmetries during the isometric squat favored the right limb. Despite the low mean asymmetry values, individual data highlighted substantially greater differences. Levels of agreement for asymmetries were computed through the Kappa coefficient and ranged from slight to substantial (<0.01-0.79), although concentric impulse asymmetries for jump tests was the only comparison with result in substantial levels of agreement. With asymmetries rarely being present on the same side across tests, these results show that a more individual approach to reporting asymmetries is required, which should help practitioners when designing targeted training interventions for their reduction.

Effects of a Competitive Soccer Match on Jump Performance and Interlimb Asymmetries in Elite Academy Soccer Players.

ABSTRACT: Bromley, T, Turner, A, Read, P, Lake, J, Maloney, S, Chavda, S, and Bishop, C. Effects of a competitive soccer match on jump performance and interlimb asymmetries in elite academy soccer players. J Strength Cond Res 35(6): 1707-1714, 2021-The purpose of this study was to investigate the effects of a competitive soccer match on jump performance and interlimb asymmetries over incremental time points during a 72-hour period. Fourteen elite adolescent players from a professional English category 3 academy performed single-leg countermovement jumps pre, post, 24-, 48-, and 72-hour post-match on a single force platform. Eccentric impulse, concentric impulse, peak propulsive force, jump height, peak landing force, and landing impulse were monitored throughout. Interlimb asymmetries were also calculated for each metric as the percentage difference between limbs. Significant negative changes (p < 0.05) in jump performance were noted for all metrics at all time points, with the exception of jump height. Interlimb asymmetries were metric-dependent and showed very large increases, specifically post-match, with a trend to reduce back toward baseline values at the 48-hour time point for propulsive-based metrics. Asymmetries for landing metrics did not peak until the 24-hour time point and again reduced toward baseline at 48-hour time point. This study highlights the importance of monitoring distinct jump metrics, as jump height alone was not sensitive enough to show significant changes in jump performance. However, interlimb asymmetries were sensitive to fatigue with very large increases post-match. More frequent monitoring of asymmetries could enable practitioners to determine whether existing imbalances are also associated with reductions in physical performance or increased injury risk.

Effect of Barbell Load on Vertical Jump Landing Force-Time Characteristics.

ABSTRACT: Lake, JP, Mundy, PD, Comfort, P, McMahon, JJ, Suchomel, TJ, and Carden, P. Effect of barbell load on vertical jump landing force-time characteristics. J Strength Cond Res 35(1): 25-32, 2021-The aim of this study was to quantify the effect that barbell load has on the jump height and force-time characteristics of the countermovement jump (CMJ). Fifteen strength-trained men (mean ± SD: age 23 ± 2 years, mass 84.9 ± 8.1 kg, and height 1.80 ± 0.05 m) performed 3 CMJs with no additional load, and with barbell loads of 25, 50, 75, and 100% of body mass on 2 force plates recording at 1,000 Hz. Propulsion and landing force-time characteristics were obtained from force-time data and compared using analysis of variance and effect sizes. Jump height decreased significantly as load increased (26-71%, d = 1.80-6.87). During propulsion, impulse increased with load up to 75% of body mass (6-9%, d = 0.71-1.08), mean net force decreased (10-43%, d = 0.50-2.45), and time increased (13-50%, d = 0.70-2.57). During landing, impulse increased as load increased up to 75% of body mass (5 to 12%, d = 0.54-1.01), mean net force decreased (13-38%, d = 0.41-1.24), and time increased (20-47%, d = 0.65-1.47). Adding barbell load to CMJ significantly decreases CMJ height. Furthermore, CMJ with additional barbell load increases landing phase impulse. However, while mean net force decreases as barbell load increases, landing time increases so that jumpers are exposed to mechanical load for longer. Practitioners should exercise caution when implementing loaded CMJ to assess their athletes.

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

ABSTRACT: 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.

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

ABSTRACT: 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.

Unilateral Isometric Squat: Test Reliability, Interlimb Asymmetries, and Relationships With Limb Dominance.

ABSTRACT: Bishop, C, Read, P, Lake, J, Loturco, I, Dawes, J, Madruga, M, Romero-Rodrigues, D, Chavda, S, and Turner, A. Unilateral isometric squat: Test reliability, interlimb asymmetries, and relationships with limb dominance. J Strength Cond Res 35(2S): S144-S151, 2021-The aim of this study was to determine test reliability, establish interlimb asymmetries and their associations with force production capability on the dominant (D) and nondominant (ND) limbs during the unilateral isometric squat test. Twenty-eight recreational sport athletes attended a single-test session after familiarization and performed 3 trials on each limb with 140° of hip and knee flexion, to assess peak force (PF), rate of force development (RFD), and impulse at different time intervals. Reliability, interlimb asymmetries, and Pearson's r correlations were computed thereafter. Test reliability was metric-dependent with only PF showing good levels of reliability on both limbs (coefficient of variation = 5.44-5.70; intraclass correlation coefficient = 0.93-0.94). Interlimb asymmetries ranged from 8.36 to 25.46%, with a tendency for RFD and impulse asymmetries to reduce as time intervals increased. Three significant negative relationships of a possible 49 (r = -0.43 to -0.47; p < 0.05) were found between asymmetries and performance on the D limb. However, 31 significant negative correlations (r = -0.42 to -0.71; p < 0.05) were found between asymmetries and performance on the ND limb. These findings demonstrate that practitioners may only be able to use PF as a reliable test metric during a unilateral isometric strength test. Furthermore, the negative association between asymmetries and strength performance on the ND limb may indicate that the reduction of imbalances through targeted training interventions may be warranted.

Antibiotic Duration, but Not Abscess Size, Impacts Clinical Cure of Limited Skin and Soft Tissue Infection After Incision and Drainage.

Antibiotics are frequently prescribed following incision and drainage of cutaneous abscesses. In subgroup analyses from a recent clinical trial, we observed higher likelihood of cure with antibiotic courses beyond 5 or 7 days (up to 10). Among this cohort, for abscesses ≤5 cm, size did not modify the antibiotic effect.

Isometric Midthigh Pull Characteristics in Elite Youth Male Soccer Players: Comparisons by Age and Maturity Offset.

Morris, RO, Jones, B, Myers, T, Lake, J, Emmonds, S, Clarke, ND, Singleton, D, Ellis, M, and Till, K. Isometric midthigh pull characteristics in elite youth male soccer players: Comparisons by age and maturity offset. J Strength Cond Res 34(10): 2947-2955, 2020-The purpose of this study was to (a) provide comparative isometric midthigh pull (IMTP) force-time characteristics for elite youth soccer players and (b) determine the effect of age and maturation on IMTP force-time characteristics. Elite male youth soccer players (U12 n = 51; U13 n = 54; U14 n = 56; U15 n = 45; U16 n = 39; and U18 n = 48) across 3 maturity offset groups (Pre n = 117; circa n = 84; and Post-peak height velocity n = 92) performed 2 maximal IMTP trials on a portable force platform (1,000 Hz). Absolute and relative values for peak force (PF) and impulse over 100 and 300 ms were analyzed. A full Bayesian regression model was used to provide probable differences similar to that of a frequentist p value. Advanced age and maturation resulted in superior IMTP force-time characteristics. Peak force demonstrated high probabilities of a difference between all consecutive age groups (p > 0.95). For absolute and relative impulse (100 and 300 ms), only 2 consecutive age groups (U14-15's and U16-18's) demonstrated high probabilities of a difference (p > 0.95) with large effects (d = 0.59-0.93). There were high probable differences between all maturity offset groups for PF and impulse with medium to large effects (d = 0.56-3.80). These were also reduced when expressed relative to body mass (relative PF and relative impulse). This study provides comparative IMTP force-time characteristics of elite male youth soccer players. Practitioners should consider individual maturation status when comparing players given the impact this has on force expression.