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The aim of this study was to assess the agreement of three different automated methods of identifying force-onset (40 N, 5 SDs, and 3 SDs) with manual identification, during the isometric mid-thigh pull (IMTP). Fourteen resistance-trained participants with >6 months experience training with the power clean volunteered to take part. After three familiarisation sessions, the participants performed five maximal IMTPs separated by 1 min of rest. Fixed bias was found between 40 N and manual identification for time at force-onset. No proportional bias was present between manual identification and any automated threshold. Fixed bias between manual identification and automated was present for force at onset and F150. Proportional but not fixed bias was found for F50 between manual identification and all automated thresholds. Small to moderate differences (Hedges g = −0.487- −0.692) were found for F90 between all automated thresholds and manual identification, while trivial to small differences (Hedges g = −0.122—−0.279) were found between methods for F200 and F250. Based on these results, strength and conditioning practitioners should not use a 40 N, 5 SDs, or 3 SDs threshold interchangeably with manual identification of force-onset when analysing IMTP force–time curve data. [ABSTRACT FROM AUTHOR]

This study aimed to assess the validity and reliability of a commercially available inertial measurement unit (Enode) for measuring barbell kinematics and kinetics during a snatch. In order to assess validity and within- and between-session reliability, thirteen competitive weightlifters conducted two snatches on two separate occasions at 85% of their one-repetition maximum. The Enode sensor was attached to the barbell, with each lift recorded via the device's native application concurrently with an 11-camera motion capture system. Passing–Bablok regression indicated fixed and proportional bias in some horizontal measures of barbell mechanics but showed no bias in all but one vertical variable. Collectively, this suggests that the Enode is a valid tool in the measurement of vertically derived, but not horizontally derived, variables from barbell kinematics. Within- and between-session reliability showed moderate to excellent ICCs, with trivial to small differences between repetitions and between sessions. However, between-session reliability showed lower levels of variability and, thus, may help coaches identify changes in technique over time (between sessions) with good accuracy. Overall the Enode offers a practical and affordable option for coaches seeking to monitor weightlifting technique in training environments. [ABSTRACT FROM AUTHOR]

The aim of this study was to explore the kinetics and kinematics across incremental loads with the push press (PP), push jerk (PJ), and split jerk (SJ). Eighteen resistance-trained men performed the 1 repetition maximum (1RM) tests (visit 1)3-7 days before an incremental loading protocol (60, 75, and 90% 1RM) of the 3 exercises (visit 2). Kinetics and kinematics were derived from force-time data and compared using a repeated-measures analysis of variance with load and exercise as within-subject factors. Dependent variables for the biomechanics assessment were categorized as output (power and impulse), driver (force and work), and strategy (displacement and duration) metrics. The interrepetition reliability was assessed using the intraclass correlation coefficient and coefficient of variation. The PP, PJ, and SJ 1RM performance were 89.7 ± 15.4, 95.6 ± 14.4, and 103.0 ± 16.9 kg, respectively. Driver, strategy, and outcome metrics displayed moderate-to-excellent (intraclass correlation coefficient: 0.58-0.98) reliability with acceptable variability (% co-efficient of variation: 2.02-10.00). Increased load resulted in significantly large increases in force, work, displacement, duration, power, and impulse (p < 0.001, ηp² = 0.534-0.903). Exercise selection had a significant and large effect on power, impulse, work, and force (p < 0.016, ηp² = 0.387-0.534). There was a significant and large effect of load x exercise interaction on work, displacement, and duration (p < 0.019, ηp² = 0.158-0.220). Practitioners are encouraged to use heavier loads (90 > 75 > 60% 1RM) during the SJ exercise to maximize output, driver, and strategy kinetics and kinematics. [ABSTRACT FROM AUTHOR]

This study investigated the stability of three repetition maximum (3RM) strength during the deadlift. Eleven participants performed four testing sessions comprising a one repetition maximum test and 3RM tests separated by 48 h. Preparedness was assessed before each testing session using countermovement jumps and by measuring barbell velocity during each set of deadlifts. Trivial statistically significant differences were determined for the 3RM between T1 and both T2 (p = 0.012; ES [95% CI] = −0.1 [−0.58, 0.41]) and T3 (p = 0.027; ES [95% CI] = −0.09 [−0.57, −0.43]). No significant differences were noted between T2 and T3 (p = 0.595; ES [95% CI] = 0.01 [−0.49, 0.50]). No significant differences in jump height (p = 0.071), time-to-take-off (p = 0.862), eccentric displacement (p = 0.209), or mean force during any countermovement jump sub-phase were found between each session (p = 0.529–0.913). Small differences in barbell mean velocity were found between both T1–T2 (effect size statistics (ES) = −0.21–0.27) and T2–T3 (ES = 0.31–0.48), while trivial differences were found at others. Therefore, 3RM deadlift strength appears stable enough over a microcycle to continue using traditionally recommended heavy/light programming strategies. [ABSTRACT FROM AUTHOR]

The primary aim of this study was to investigate the stability of the six-repetition maximum (6RM) deadlift over the length of a five-day microcycle and whether the fatigue induced by maximal effort testing detrimentally impacted preparedness. Twelve participants performed four testing sessions, comprising a one-repetition maximum test and three 6RM tests separated by 48 hours. Countermovement jumps were performed before each testing session, and barbell velocity was measured during each warm-up set to assess changes in preparedness. The 6RM deadlift was not statistically different between any of the testing sessions (p =.056; ηp2 = 0.251). Similarly, there were no significant differences in jump height or other CMJ variables between sessions (p >.05). There were small to moderate differences in mean barbell velocity between the first and second 6RM test (g = 0.24–0.88), while there were only small differences in mean velocity (MV) between the second and third 6RM test at some of the warm-up loads (40% 6RM: g = 0.20; 80% 6RM: g = −0.47). Taken collectively, these data indicate that 6RM deadlift strength is stable over five days and does not appear to induce sufficient fatigue to impact vertical jump performance or rating of perceived exertion despite some changes in barbell velocity. [ABSTRACT FROM AUTHOR]

The purpose of this study was to determine the usefulness of calculating jump take-off momentum in rugby league (RL) by exploring its relationship with sprint momentum, due to the latter being an important attribute of this sport. Twenty-five male RL players performed 3 maximal-effort countermovement jumps on a force platform and 3 maximal effort 20-m sprints (with split times recorded). Jump take-off momentum and sprint momentum (between 0 and 5, 5 and 10, and 10 and 20 m) were calculated (mass multiplied by velocity) and their relationship determined. There was a very large positive relationship between both jump take-off and 0- to 5-m sprint momentum (r =.781, P <.001) and jump take-off and 5- to 10-m sprint momentum (r =.878, P <.001). There was a nearly perfect positive relationship between jump take-off and 10- to 20-m sprint momentum (r =.920, P <.001). Jump take-off and sprint momentum demonstrated good–excellent reliability and very large–nearly perfect associations (61%–85% common variance) in an RL cohort, enabling prediction equations to be created. Thus, it may be practically useful to calculate jump take-off momentum as part of routine countermovement jump testing of RL players and other collision-sport athletes to enable the indirect monitoring of sprint momentum. [ABSTRACT FROM AUTHOR]

The assessment of the mechanical power production is of great importance for researchers and practitioners. The purpose of this review was to compare the differences in ground reaction force (GRF), kinematic, and combined (bar velocity x GRF) methods to assess mechanical power production during weightlifting exercises. A search of electronic databases was conducted to identify all publications up to 31 May 2019. The peak power output (PPO) was selected as the key variable. The exercises included in this review were clean variations, which includes the hang power clean (HPC), power clean (PC) and clean. A total of 26 articles met the inclusion criteria with 53.9% using the GRF, 38.5% combined, and 30.8% the kinematic method. Articles were evaluated and descriptively analysed to enable comparison between methods. The three methods have inherent methodological differences in the data analysis and measurement systems, which suggests that these methods should not be used interchangeably to assess PPO in Watts during weightlifting exercises. In addition, this review provides evidence and rationale for the use of the GRF to assess power production applied to the system mass while the kinematic method may be more appropriate when looking to assess only the power applied to the barbell. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The aim of this study was to examine whether ground reaction force (GRF) side differences were transmitted and related to bar end power output asymmetries during hang power clean (HPC) performance and whether progressive loading would intensify this effect. Differences between the dominant (D) and nondominant (ND) side average GRFs (AGRFs) of both feet and average bar end power outputs were recorded simultaneously from 15 recreationally trained male volunteers at 30, 60, and 90% 1 RM using 2 force platforms and 3 high-speed digital cameras, quantifying side dominance from perceived handedness (left- or right-side dominance [LRSD]), GRF side dominance (force side dominance [FSD]), and bar end power output side dominance (barbell side dominance [BSD]). With the exception of the LRSD condition, differences between the D and ND side AGRFs were significant (FSD: 1.8-4.3%; BSD: 5.1-6.4%, p < 0.05). Bar end power output side differences were significant for all conditions (LRSD: 1.5-5.4%; FSD: 0.5-3.4%; BSD: 3.9-5.6%, p < 0.05). Progressive loading did not significantly affect GRF side differences or the FSD average bar power side differences. However, during the LRSD and BSD conditions, the 60 and 90% side average bar power side differences were >the 30% equivalents. Average GRF side differences were not related to bar end power output side differences. Because of the consistent side difference of 4-6% investigators and strength and conditioning practitioners should exercise caution when interpreting changes in bar end power output. KEY WORDS asymmetry, strength imbalance, weightlifting, ground reaction force

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. [ABSTRACT FROM AUTHOR]

Biomechanical characteristics of the one-handed dumbbell power snatch (DBPS) were examined to determine whether significant differences existed between unilateral and bilateral weightlifting movements. Kinetic and kinematic movement data were recorded from 10 male weightlifters (mean [+ or -] SD: age: 30.2 [+ or -] 10.2 years; height: 174.2 [+ or -] 4.4 cm; body mass: 81.5 [+ or -] 14.6 kg) during one-handed dumbbell (DB) and traditional barbell (BBPS) power snatch performance with loads of ~800% of respective lift one repetition maximums (1RM) with the use of 2 synchronized Kistler force plates and high-speed 3-dimensional video. Results highlighted asymmetry in the ground reaction force and kinematic profile of the DBPS, which deviated from the observed patterns of the bilateral movement. This study found that the nonlifting side (the side corresponding with the hand that did not hold the DB) tended to generate a greater pull phase peak vertical ground reaction forces significantly faster (p = 0.001) than the lifting side (the side corresponding with the hand that held the DB) during the DBPS. In addition, the DBPS nonlifting side catch phase loading rate was approximately double that of the lifting side loading rate (p < 0.05). These results quantify symmetrical deviations in the movement patterns of the unilateral power snatch movement both during the concentric muscular contraction of load vertical displacement, and the loading implications of unilateral landing. This asymmetry supports the contention that unilateral variations of weightlifting movements may provide a different training stimulus to athletes. KEY WORDS force-time curve, rate of force development, ground reaction force, kinematics, resistance training.