Relationships Between Modifiable Risk Factors of Hamstring Strain Injury.

ABSTRACT: Ripley, NJ, Comfort, P, and McMahon, JJ. Relationships between modifiable risk factors of hamstring strain injury. J Strength Cond Res 38(3): 510-516, 2024-The aims of this study were to determine whether any relationship exists between eccentric hamstring strength and isokinetic strength imbalances and bicep femoris long head (BF LH ) architecture. Eighteen physically active men (age 24.7 ± 4.3 years, height 181.9 ± 7.2 cm, mass 84.9 ± 12.9 kg) had resting BF LH muscle architecture assessed using ultrasound, with images taken at the midmuscle belly. Measures of isokinetic strength of the knee extensors and flexors involved subjects performing 3 maximal effort repetitions of concentric knee extension and eccentric knee flexion at 60°·s -1 . Good-excellent relative reliability (intraclass correlation coefficient ≥0.86) and low variability (coefficient of variation <10%) were observed for all variables. Relative BF LH fascicle length (FL) demonstrated significant moderate-to-nearly-perfect associations with isokinetic measures identified as hamstring strain injury risk factors ( p < 0.05, r = 0.38-0.92), whereas absolute BF LH FL was not significantly or meaningfully associated with isokinetic measures ( p = 0.07-0.961, r = 0.01-0.30). Relative BF LH FL should be considered when assessing resting BF LH muscle architecture because it is potentially a more appropriate measure of injury risk because of its greater association with strength measures. However, absolute BF LH FL may have a greater usefulness during growth, maturation, and individual proportions.

Can the Velocity of a 1RM Hang Power Clean Be Used to Estimate a 1RM Hang High Pull?

ABSTRACT: Suchomel, TJ, Techmanski, BS, Kissick, CR, and Comfort, P. Can the velocity of a 1RM hang power clean be used to estimate a 1RM hang high pull? J Strength Cond Res 38(7): 1321-1325, 2024-The purpose of this study was to estimate the 1-repetition maximum hang high pull (1RM HHP) using the peak barbell velocity of a 1RM hang power clean (HPC). Fifteen resistance-trained men (age = 25.5 ± 4.5 years, body mass = 88.3 ± 15.4 kg, height = 176.1 ± 8.5 cm, relative 1RM HPC = 1.3 ± 0.2 kg·kg-1) with previous HPC experience participated in 2 testing sessions that included performing a 1RM HPC and HHP repetitions with 20, 40, 60, and 80% of their 1RM HPC. Peak barbell velocity was measured using a linear position transducer during the 1RM HPC and HHP repetitions performed at each load. The peak barbell velocity achieved during the 1RM HPC was determined as the criterion value for a 1RM performance. Subject-specific linear regression analyses were completed using slope-intercept equations created from the peak velocity of the 1RM HPC and the peak barbell velocities produced at each load during the HHP repetitions. The peak barbell velocity during the 1RM HPC was 1.74 ± 0.30 m·s-1. The average load-velocity profile showed that the estimated 1RM HHP of the subjects was 98.0 ± 19.3% of the 1RM HPC. Although a 1RM HHP value may be estimated using the peak barbell velocity during the HPC, strength and conditioning practitioners should avoid this method because of the considerable variation within the measurement. Additional research examining different methods of load prescription for weightlifting pulling derivatives is needed.

Early Versus Late Rapid Force Production During Single-Joint Isometric Hamstring Assessment Using Force Plates.

ABSTRACT: Ripley, NJ, Barber, R, Fahey, JT, and Comfort, P. Early versus late rapid force production during single-joint isometric hamstring assessment using force plates. J Strength Cond Res XX(X): 000-000, 2024-The aim of this study was to assess differences in time-matched early versus late rapid force (RF) development in female soccer players in the 90-90 isometric hamstring assessment. Twenty-one elite female soccer players (age: 20.7 ± 4.7 years; height: 168.2 ± 5.5 cm; body mass: 62.8 ± 7.0 kg), with no recent (>6 months) history of hamstring strain injury, volunteered to participate in the study. Following a standardized warm-up, each subject performed 3 maximal isometric unilateral hamstring contractions, with their heel resting on a force plate, elevated on a box, to ensure that their hips and knees were at 90°. Data were analyzed to determine peak force, early RF (ERF) 0-100 milliseconds and late RF (LRF) 100-200 milliseconds. Significant and large differences were observed in the percentage of peak force achieved between ERF (52.85 ± 11.53%; 54.99 ± 9.80%) and LRF (15.82 ± 5.58%; 15.25 ± 3.91%) for the left and right limbs, respectively (p < 0.001, g = 2.13-3.06). The large differences between ERF and LRF can be used by practitioners to streamline performance assessment, which in turn will allow practitioners to act upon data collected more effectively. Additionally, regular monitoring ERF production could inform practitioners of any interventions that maybe required, such as reduction of load or introduction of specific recovery modalities and during return to play protocols.

Velocity-Based Training With Weightlifting Derivatives: Barbell and System Velocity Comparisons.

ABSTRACT: Suchomel, TJ, Kissick, CR, Techmanski, BS, Mann, JB, and Comfort, P. Velocity-based training with weightlifting derivatives: Barbell and system velocity comparisons. J Strength Cond Res XX(X): 000-000, 2024-The aim of this study was to examine the differences in barbell and system (i.e., subject + load) velocity during weightlifting derivatives performed across a spectrum of relative loads. 14 resistance-trained men participated in 6 testing sessions, which included 1 repetition maximum hang power clean (HPC) testing and individual jump shrug (JS), hang high pull (HHP), HPC, hang clean pull (HCP), and countermovement shrug (CMS) sessions. The order of the exercise testing sessions was randomized and required the subjects to perform either JS, HHP, HPC, HCP, or CMS repetitions while standing on a force platform with a linear position transducer attached to the barbell. The JS and HHP were performed with 20, 40, 60, 80, and 100% of their 1 repetition maximum HPC, HPC with 20, 40, 60, and 80% 1RM, and the HCP and CMS performed with 20, 40, 60, 80, 100, 120, and 140% 1RM. Mean and peak barbell and system velocities were determined across all exercises and loads using either 2 × 5, 2 × 4, or 2 × 7 repeated measures ANOVA depending on the number of loads performed. Significantly ( p < 0.001) and meaningfully ( g ≥ 1.49) greater mean and peak barbell velocities existed at every exercise and load combination compared with the mean and peak system velocities produced. Barbell and system velocity are distinct characteristics that should not be substituted for one another. Owing to the characteristics of the transition phase, mean barbell and system velocity may not provide strength and conditioning practitioners with meaningful information related to load prescription.

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.

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.

The Effect of Rest Redistribution on Kinetic and Kinematic Variables During the Countermovement Shrug.

ABSTRACT: Meechan, D, McMahon, JJ, Suchomel, TJ, and Comfort, P. The effect of rest redistribution on kinetic and kinematic variables during the countermovement shrug. J Strength Cond Res 37(7): 1358-1366, 2023-This study compared the effects of rest redistribution (RR) on kinetic and kinematic variables during the countermovement shrug (CMS). Twenty-one male subjects (age 27.2 ± 3.3. years, height 1.78 ± 0.07 m, body mass 77.2 ± 10.6 kg, relative 1 repetition maximum (1RM) power clean [PC] 1.22 ± 0.16 kg·kg-1) performed the CMS using 140% of 1RM PC with 3 traditional sets of 6 repetitions (TS), 9 sets of 2 repetitions with RR [45 s rest after 2 repetitions] (RR45), and 6 sets of 3 repetitions with RR [72 s rest after 3 repetitions] (RR72). There were no significant or meaningful differences (p > 0.05, g = 0.00-0.15) between set configurations for any variables for the average of the 18 repetitions. There were no significant (p > 0.05) or meaningful (g = 0.00-0.14) differences for configuration and configuration × set for peak (PF) and mean force (MF), peak velocity (PV), impulse, phase duration, peak velocity decline, peak velocity maintenance, and rating of perceived exertion. There was significantly greater (p = 0.034) albeit small (g = 0.15) difference for mean velocity (MV) during TS compared with RR72. There were no significant or meaningful differences (p > 0.05, g = 0.00-0.09) between sets for PF, MF, PV, MV, impulse, and duration across TS, RR45, and RR72. Rest redistribution protocols did not result in greater kinetics or kinematics during the CMS compared with TS, when total rest time was equated. Thus, shorter more frequent rest periods during the CMS may not be required to maintain force-time characteristics.

National Strength and Conditioning Association Position Statement on Weightlifting for Sports Performance.

ABSTRACT: Comfort, P, Haff, GG, Suchomel, TJ, Soriano, MA, Pierce, KC, Hornsby, WG, Haff, EE, Sommerfield, LM, Chavda, S, Morris, SJ, Fry, AC, and Stone, MH. National Strength and Conditioning Association position statement on weightlifting for sports performance. J Strength Cond Res 37(6): 1163-1190, 2023-The origins of weightlifting and feats of strength span back to ancient Egypt, China, and Greece, with the introduction of weightlifting into the Olympic Games in 1896. However, it was not until the 1950s that training based on weightlifting was adopted by strength coaches working with team sports and athletics, with weightlifting research in peer-reviewed journals becoming prominent since the 1970s. Over the past few decades, researchers have focused on the use of weightlifting-based training to enhance performance in nonweightlifters because of the biomechanical similarities (e.g., rapid forceful extension of the hips, knees, and ankles) associated with the second pull phase of the clean and snatch, the drive/thrust phase of the jerk and athletic tasks such as jumping and sprinting. The highest force, rate of force development, and power outputs have been reported during such movements, highlighting the potential for such tasks to enhance these key physical qualities in athletes. In addition, the ability to manipulate barbell load across the extensive range of weightlifting exercises and their derivatives permits the strength and conditioning coach the opportunity to emphasize the development of strength-speed and speed-strength, as required for the individual athlete. As such, the results of numerous longitudinal studies and subsequent meta-analyses demonstrate the inclusion of weightlifting exercises into strength and conditioning programs results in greater improvements in force-production characteristics and performance in athletic tasks than general resistance training or plyometric training alone. However, it is essential that such exercises are appropriately programmed adopting a sequential approach across training blocks (including exercise variation, loads, and volumes) to ensure the desired adaptations, whereas strength and conditioning coaches emphasize appropriate technique and skill development of athletes performing such exercises.

Comparing biomechanical time series data across countermovement shrug loads.

The effect of load on time-series data has yet to be investigated during weightlifting derivatives. This study compared the effect of load on the force-time and velocity-time curves during the countermovement shrug (CMS). Twenty-nine males performed the CMS at relative loads of 40%, 60%, 80%, 100%, 120%, and 140% one repetition maximum (1RM) power clean (PC). A force plate measured the vertical ground reaction force (VGRF), which was used to calculate the barbell-lifter system velocity. Time-series data were normalized to 100% of the movement duration and assessed via statistical parametric mapping (SPM). SPM analysis showed greater negative velocity at heavier loads early in the unweighting phase (12-38% of the movement), and greater positive velocity at lower loads during the last 16% of the movement. Relative loads of 40% 1RM PC maximised propulsion velocity, whilst 140% 1RM maximized force. At higher loads, the braking and propulsive phases commence at an earlier percentage of the time-normalized movement, and the total absolute durations increase with load. It may be more appropriate to prescribe the CMS during a maximal strength mesocycle given the ability to use supramaximal loads. Future research should assess training at different loads on the effects of performance.

Force Plate-Derived Countermovement Jump Normative Data and Benchmarks for Professional Rugby League Players.

The countermovement jump (CMJ) is an important test in rugby league (RL), and the force plate is the recommended assessment device, as it permits the calculation of several variables that explain jump strategy, alongside jump height. The purpose of this study was to produce normative CMJ data and objective benchmarks for professional RL forwards and backs. Normative data for jump height, modified reactive strength index, and jump momentum are provided for 121 professional RL players (66 forwards and 55 backs) who completed CMJ testing on a portable force plate during preseason training. Standardized T-scores (scaled from 0 to 100) were calculated from the respective positional group mean and standard deviation to create CMJ performance bands that were combined with a qualitative description (ranging from extremely poor to excellent) and a traffic light system to facilitate data interpretation and objective benchmark setting by RL practitioners. The jump height and modified reactive strength index benchmarks were larger for the lighter backs, whereas the jump momentum benchmarks were larger for the heavier forwards. The presented novel approach to compiling and presenting normative data and objective benchmarks may also be applied to other data (i.e., from other tests or devices) and populations.

Relationship Between Physical Fitness and the Physical Demands of 50-Over Cricket in Fast Bowlers.

ABSTRACT: Webster, TM, Comfort, P, and Jones, PA. Relationship between physical fitness and the physical demands of 50-over cricket in fast bowlers. J Strength Cond Res 36(3): e66-e72, 2022-Professional cricket is constantly evolving and resulting in increased physiological demand placed on players. Fast bowlers experience the greatest physical demand during match-play; despite this, research has overlooked the importance of specific physical attributes to optimizing physical match performance. The aim of this study was to investigate the relationships between 50-Over physical match performance and tests of physical qualities in fast bowlers. Fifteen professional male fast bowlers (age = 23.8 ± 4.0 years; height = 183.4 ± 6.7 cm; body mass = 82.9 ± 9.2 kg) participated in the study. Subjects completed the following physical fitness tests; sum of skinfolds, countermovement jump (CMJ), 20-m sprint, and the Yo-Yo intermittent recovery test level 1. Global positioning system data were collected during 6 professional 50-Over fixtures. Moderate correlations were established between CMJ height to total distance covered (r = 0.585; p = 0.022), sprinting distance (ρ = 0.554; p = 0.032), and maximal velocity (r = 0.567; p = 0.027); 20-m sprint time to total distance covered (ρ = -0.519; p = 0.047) and PlayerLoad (ρ = -0.561; p = 0.03); and Yo-Yo distance to total match distance (r = 0.520; p = 0.047) and sprinting distance (ρ = 0.524; p = 0.045). These findings demonstrate the predictive importance of prolonged intermittent running ability, jump, and sprint performance to match running performance of elite fast bowlers in 1-day cricket. Strength and conditioning coaches should use such information to design training to ensure fast bowlers are adequately conditioned to meet the demands of match running performance.

Comparison of Countermovement Jump-Derived Reactive Strength Index Modified and Underpinning Force-Time Variables Between Super League and Championship Rugby League Players.

ABSTRACT: McMahon, JJ, Jones, PA, and Comfort, P. Comparison of countermovement jump-derived reactive strength index modified and underpinning force-time variables between super league and championship rugby league players. J Strength Cond Res 36(1): 226-231, 2022-The countermovement jump (CMJ) is regularly tested in rugby league (RL), with recent work reporting reactive strength index modified (RSImod) to distinguish between levels of play. Differences in CMJ-derived RSImod and underpinning force-time variables between English Super League (SL) and RL Championship (RLC) players are, however, unknown. As SL and RLC teams compete against each other, this study addressed this knowledge gap. Sixty RL players from the English SL (n = 30) and RLC (n = 30) performed 3 CMJs on a force platform at the start of the preseason training. The RSImod was calculated by dividing jump height (JH) by time to take-off (TTT), and several other variables were also extracted from the force-time record. The SL players achieved a significantly higher (large effect) RSImod by performing the CMJ with a significantly shorter (large effect) TTT but a similar (small effect) JH. The SL players achieved the shorter TTT through a significantly reduced (large effects) relative displacement during both the countermovement (combined unweighting and braking displacement) and propulsion phases but a significantly higher (moderate effects) propulsion peak force and power. The relationships between TTT and relative countermovement (r = 0.719, p < 0.001) and propulsion (r = 0.771, p < 0.001) displacement for combined group data were very large. Practitioners working in RL should, therefore, consider reporting RSImod and TTT, alongside JH, after CMJ force-time testing. We also suggest that RL players who produce lower RSImod scores would benefit from being trained to produce larger CMJ propulsion forces over a shallower range of hip, knee, and ankle extension.

Biomechanical Effects of a 6-Week Change of Direction Speed and Technique Modification Intervention: Implications for Change of Direction Side step Performance.

ABSTRACT: Dos'Santos, T, Thomas, C, Comfort, P, and Jones, PA. Biomechanical effects of a 6-week change of direction speed and technique modification intervention: implications for change of direction side step performance. J Strength Cond Res 36(10): 2780-2791, 2022-The aim of this study was to evaluate the biomechanical effects of change of direction (COD) speed and technique modification training on COD performance (completion time, ground contact time [GCT], and exit velocity) during 45° (CUT45) and 90° (CUT90) side step cutting. A nonrandomized, controlled 6-week intervention study was administrated. Fifteen male, multidirectional, sport athletes (age, 23.5 ± 5.2 years; height, 1.80 ± 0.05 m; mass, 81.6 ± 11.4 kg) formed the intervention group (IG) who participated in two 30-minute COD speed and technique modification sessions per week, whereas 12 male, multidirectional, sport athletes (age, 22.2 ± 5.0 years; height, 1.76 ± 0.08 m; mass, 72.7 ± 12.4 kg) formed the control group (CG) and continued their normal training. All subjects performed 6 trials of the CUT45 and CUT90 task whereby pre-to-post intervention changes in lower-limb and trunk kinetics and kinematics were evaluated using 3-dimensional motion and ground reaction force analyses. Two-way mixed analysis of variances revealed significant main effects for time (pre-to-post changes) for CUT45 completion time, exit velocity, and CUT90 completion time ( p ≤ 0.045; η 2 = 0.152-0.539), and significant interaction effects of time and group were observed for CUT45 completion time, GCT, exit velocity, and CUT90 completion time ( p ≤ 0.010; η 2 = 0.239-0.483), with the IG displaying superior performance postintervention compared with the CG ( p ≤ 0.109; g = 0.83-1.35). Improvements in cutting performance were moderately to very largely associated ( p ≤ 0.078; r or ρ = 0.469-0.846) with increased velocity profiles, increased propulsive forces over shorter GCTs, and decreased knee flexion. Change of direction speed and technique modification is a simple, effective training method requiring minimal equipment that can enhance COD performance, which practitioners should consider incorporating into their pitch- or court-based training programs.

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.

How Does Lower-Body and Upper-Body Strength Relate to Maximum Split Jerk Performance?

ABSTRACT: Soriano, MA, Jiménez-Ormeño, E, Amaro-Gahete, FJ, Haff, GG, and Comfort, P. How does lower-body and upper-body strength relate to maximum split jerk performance? J Strength Cond Res 36(8): 2102-2107, 2022-The aims of this study were to (I) determine the relationships between the maximum dynamic strength of the upper and lower body, measured by overhead press and back squat 1 repetition maximum (1RM) performances, and the split jerk (SJ) performance in trained weightlifters and (II) explore the magnitude of these relationships for men and women to establish sex-specific prediction equations. Twenty men (age: 28.9 ± 6.6 years; height: 1.8 ± 0.1 m; body mass [BM]: 82.5 ± 10.2 kg; weightlifting training experience: 4.2 ± 2.4 years) and 13 women (age: 27.7 ± 4.4 years; height: 1.7 ± 0.1 m; BM: 61.8 ± 5.2 kg; weightlifting training experience: 2.7 ± 1.7 years) competitive weightlifters participated. The 1RM performances of the overhead press, back squat, and SJ were assessed for all subjects. A very strong correlation exists between the back squat and overhead press, with maximum SJ performance for all subjects (r = 0.97; p < 0.001). Similarly, very strong correlations were found for men (r = 0.90, p < 0.001) and women (r = 0.90, p = 0.0002), separately. The coefficient of determination indicates that the prediction equation for the maximum SJ performance is quite accurate (R2 = 0.94) for all subjects and men (R2 = 0.83) and women (R2 = 0.81), separately. These results provide evidence that the maximum strength of the upper and lower body are major contributors to SJ performance. In addition, SJ performance can accurately be predicted from the back squat and overhead press performances.

Rate of Force Development Adaptations After Weightlifting-Style Training: The Influence of Power Clean Ability.

ABSTRACT: James, LP, Suchomel, TJ, Comfort, P, Haff, GG, and Connick, M. Rate of force development adaptations after weightlifting-style training: the influence of power clean ability. J Strength Cond Res 36(6): 1560-1567, 2022-This experiment examined changes to the rate of force development (RFD) expressed under loaded jump conditions between individuals with a higher (stronger) and lower (weaker) weightlifting performance (as assessed by the 1 repetition maximum [RM] power clean) after training with the weightlifting derivatives. Two groups of markedly different weightlifting ability undertook 10 weeks of training with the power clean variants, snatch pulls, and jump squats across heavy and light conditions. Testing was performed at baseline, after 5 weeks of training (mid-test) and after training (post-test). During testing, RFD was assessed under a series of loads (20-80% squat 1RM) through the jump squat. Furthermore, the force-velocity relationship, and unloaded jump strategy (through the force-time curve waveform), were also examined. Very large change (Hedge's g, 95% confidence interval [g] = 2.10, 1.24 to 4.16) in RFD at 20% 1RM at mid-test occurred within the stronger group. Conversely, a small increase (g = 0.27, 0.53-1.91) among the weaker subjects existed in this measure at mid-test, reaching a moderate increase at post-test (g = 0.71, -0.18 to 2.15). Limited improvements were seen by the stronger subjects in RFD at 60 and 80% 1RM at either mid-test (60%: g = 0.27, -0.75 to 1.33; 80% = 0.02, -1.01 to 1.00) or post-test (60%: g = 0.52, -0.38 to 1.80; 80% = -0.26, -1.23 to 0.77). The stronger group experienced a shift throughout the force-velocity relationship while a more force-dominant adaptation occurred in weaker subjects. Differences in jump strategy between groups were also noted. Such training will elicit practically different adaptations in rapid force production depending on the individual's baseline weightlifting ability.

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.

The Reliability and Magnitude of Time-Dependent Force-Time Characteristics During the Isometric Midthigh Pull Are Affected by Both Testing Protocol and Analysis Choices.

ABSTRACT: Guppy, SN, Kotani, Y, Brady, CJ, Connolly, S, Comfort, P, and Haff, GG. Title: The reliability and magnitude of time-dependent force-time characteristics during the isometric mid-thigh pull are impacted by both testing protocol and analysis choices. J Strength Cond Res 36(5): 1191-1199, 2022-This study aimed to investigate whether the use of short-duration (SHORT) isometric midthigh pull (IMTP) trials resulted in greater reliability and magnitude of time-dependent force-time characteristics than traditionally performed IMTP trials (TRAD). Fourteen subjects with >6 months' training experience with the power clean volunteered to take part in the study. Subjects performed five ∼1-second IMTP trials (SHORT) and five 5-second IMTP trials (TRAD). SHORT resulted in substantially more reliable rate of force development (RFD) measures (intraclass correlation coefficient [ICC] = 0.97-0.99; coefficient of variation [CV] = 2.6-7.0%), particularly during time bands from force-onset to 150 ms, compared with TRAD when trials were selected for analysis based on peak force (ICC = 0.66-0.83; CV = 14.1-38.5%). Selecting TRAD trials based on RFD0-200 resulted in similar reliability compared with SHORT of those same epochs (ICC = 0.97-0.99; CV = 2.5-7.8%). Furthermore, SHORT resulted in significantly greater force at specific time points, RFD, and impulse compared with TRAD trials (p = 0.001-0.033; g = -0.16 to -0.66). Based on these results, strength and conditioning professionals should use specific testing protocols (i.e., TRAD and SHORT) depending on the component of an athlete's force-generating capacity that they wish to assess and remain aware of the effect analysis choices they have on the reliability of IMTP force-time characteristics.

Changes in Early and Maximal Isometric Force Production in Response to Moderate- and High-Load Strength and Power Training.

ABSTRACT: Comfort, P, Jones, PA, Thomas, C, Dos'Santos, T, McMahon, JJ, and Suchomel, TJ. Changes in early and maximal isometric force production in response to moderate- and high-load strength and power training. J Strength Cond Res 36(3): 593-599, 2022-The aims of this study were to determine the changes in early (50-, 100-, 150-, 200-, 250 ms) and maximal isometric force production, in response to a 4-week period of moderate-load resistance training (60-82.5% 1 repetition maximum [1RM]), followed by a 4-week period of high-load (80-90% 1RM) resistance training. Thirty-four subjects (age 19.5 ± 2.8 years; height 1.72 ± 0.08 m; body mass 69.9 ± 11.4 kg; maximal power clean 0.92 ± 0.03 kg·kg-1) participated in this study. Only trivial-to-moderate (0.2-2.7%, d = 0.00-0.88) and nonsignificant (p > 0.05) changes in early isometric force production were observed in response to the moderate-load training period, whereas very large (9.2-14.6%, d = 2.71-4.16), significant (p ≤ 0.001) increases in early isometric force production were observed in response to high-load training. In contrast, there was a very large, significant increase in peak force (PF) across the moderate-load phase (7.7 ± 11.8%, d = 2.02, p = 0.003), but only a moderate significant increase in PF (3.8 ± 10.6%, d = 1.16, p = 0.001) across the high-load phase. The results of this study indicate that high-load multijoint resistance training, that follows moderate-load training, results in superior increases in early multi-joint force production, compared with the changes observed after moderate-load resistance training.

Does Sex Impact the Differences and Relationships in the One Repetition Maximum Performance Across Weightlifting Overhead Pressing Exercises?

ABSTRACT: Soriano, MA, García-Ramos, A, Calderbank, J, Marín, PJ, Sainz de Baranda, P, and Comfort, P. Does sex impact the differences and relationships in the one repetition maximum performance across weightlifting overhead pressing exercises? J Strength Cond 36(7): 1930-1935, 2022-This study aimed to determine the impact of sex on the differences and relationships of the one repetition maximum (1RM) performance between 3 overhead pressing exercises (push press [PP], push jerk [PJ] and split jerk [SJ]). 15 men (body mass [BM]: 82.3 ± 9.9 kg; weightlifting training experience: 2.6 ± 1.6 years) and 15 women (BM: 64.4 ± 7.0 kg; weightlifting training experience: 2.2 ± 1.4 years) participated in this study. A ratio-scaled (1RM·BM-1) was used for the comparison between them. The 1RM of the 3 exercises were evaluated within the same testing session using a combined 1RM assessment method. The interaction effect of exercise and sex did not reach statistical significance (p = 0.671; η2 = 0.001). In contrast, there were significant main effects of exercise (p ≤ 0.01) and sex (p < 0.001) with medium (η2 = 0.096) and large effect sizes (η2 = 0.306), respectively. A similar main effect of exercise was reported for both men (PP [1.0 ± 0.1 kg·kg-1] < PJ [1.1 ± 0.2 kg·kg-1] ∼ SJ [1.2 ± 0.2 kg·kg-1]) and women (PP [0.8 ± 0.1 kg·kg-1] < PJ [0.9 ± 0.2 kg·kg-1] ∼ SJ [0.9 ± 0.2 kg·kg-1]). The 1RM performance of the 3 exercises was significantly correlated for men (r [range] = 0.856-0.963) and women (r [range] = 0.636-0.925). Sex does not affect the differences in the 1RM performance across weightlifting overhead pressing exercises. However, stronger correlations and lower variation in the 1RM performance during the PP, PJ, and SJ are expected for men compared with women.