Progenitor Hyperpolarization Regulates the Sequential Generation of Neuronal Subtypes in the Developing Neocortex.

During corticogenesis, ventricular zone progenitors sequentially generate distinct subtypes of neurons, accounting for the diversity of neocortical cells and the circuits they form. While activity-dependent processes are critical for the differentiation and circuit assembly of postmitotic neurons, how bioelectrical processes affect nonexcitable cells, such as progenitors, remains largely unknown. Here, we reveal that, in the developing mouse neocortex, ventricular zone progenitors become more hyperpolarized as they generate successive subtypes of neurons. Experimental in vivo hyperpolarization shifted the transcriptional programs and division modes of these progenitors to a later developmental status, with precocious generation of intermediate progenitors and a forward shift in the laminar, molecular, morphological, and circuit features of their neuronal progeny. These effects occurred through inhibition of the Wnt-beta-catenin signaling pathway by hyperpolarization. Thus, during corticogenesis, bioelectric membrane properties are permissive for specific molecular pathways to coordinate the temporal progression of progenitor developmental programs and thus neocortical neuron diversity.

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.

Dosage-dependent requirements of Magoh for cortical interneuron generation and survival.

Embryonic interneuron development underlies cortical function and its disruption contributes to neurological disease. Yet the mechanisms by which viable interneurons are produced from progenitors remain poorly understood. Here, we demonstrate dosage-dependent requirements of the exon junction complex component Magoh for interneuron genesis in mouse. Conditional Magoh ablation from interneuron progenitors, but not post-mitotic neurons, depletes cortical interneuron number through adulthood, with increased severity in homozygotes. Using live imaging, we discover that Magoh deficiency delays progenitor mitotic progression in a dosage-sensitive fashion, with 40% of homozygous progenitors failing to divide. This shows that Magoh is required in progenitors for both generation and survival of newborn progeny. Transcriptome analysis implicates p53 signaling; moreover, p53 ablation in Magoh haploinsufficient progenitors rescues apoptosis, completely recovering interneuron number. In striking contrast, in Magoh homozygotes, p53 loss fails to rescue interneuron number and mitotic delay, further implicating mitotic defects in interneuron loss. Our results demonstrate that interneuron development is intimately dependent upon progenitor mitosis duration and uncover a crucial post-transcriptional regulator of interneuron fate relevant for neurodevelopmental pathologies.This article has an associated 'The people behind the papers' interview.

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.

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.

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.

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.

Contribution of Eccentric Strength to Cutting Performance in Female Soccer Players.

ABSTRACT: Jones, PA, Dos'Santos, T, McMahon, JJ, and Graham-Smith, P. Contribution of eccentric strength to cutting performance in female soccer players. J Strength Cond Res 36(2): 525-533, 2022-The aim of this study was to examine the contribution of eccentric strength to performance of a 70-90° cutting task (CUT) (time to complete: 5 m approach, 70-90° cut, 3 m exit). Nineteen female soccer players (mean ± SD age, height, and mass; 21.7 ± 4.3 years, 1.67 ± 0.07 m, and 60.5 ± 6.1 kg) from the top 2 tiers of English women's soccer participated in the study. Each player performed 6 trials of the CUT task whereby three-dimensional motion data from 10 Qualisys proreflex cameras (240 Hz) and ground reaction forces from 2 Advanced Mechanical Technology, Inc. force platforms (1,200 Hz) were collected. Relative eccentric knee extensor (ECC-KE) and flexor peak moments (ECC-KF) were collected from both limbs at 60°·s-1 using a Kin-Com isokinetic dynamometer. Hierarchical multiple regression revealed that minimum center of mass (CM) and approach velocities (CM velocity at touchdown of penultimate foot contact) could explain 82% (79% adjusted) of the variation in CUT completion time (F(1,16) = 36.086, p < 0.0001). ECC-KE was significantly (p < 0.05) moderately associated (R ≥ 0.610) with velocities at key instances during the CUT. High (upper 50th percentile) ECC-KE individuals (n = 9) had significantly (p ≤ 0.01; d ≥ 1.34) greater velocities at key instances during the CUT. The findings suggest that individuals with higher ECC-KE produce faster CUT performance, by approaching with greater velocity and maintaining a higher velocity during penultimate and final contact, as they are better able to tolerate the larger loads associated with a faster approach.

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.

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.

Unilateral vs. bilateral hamstring strength assessments: comparing reliability and inter-limb asymmetries in female soccer players.

The aims in the present study were to assess reliability for two unilateral and two bilateral field-based hamstring assessments and compare magnitude, direction and agreement of inter-limb asymmetry between tests and sessions. Twenty-nine female soccer players (age: 21.1 ± 4.5 years; height: 169.7 ± 5.8 cm; body mass: 66.2 ± 6.4 kg) performed three repetitions per leg of unilateral isometric 30° and 90° knee flexion (KF) tasks, and three repetitions total for a bilateral 90° isometric KF and Nordic hamstring exercise. Absolute reliability of most methods were acceptable (<10%). Relative reliability within-session was fair to excellent (ICC≥0.784; lower bound 95%CI ≥0.623). Greater variability in between-session relative reliability was observed during the unilateral tests, demonstrating poor to good (ICC = 0.698-0.798; lower bound 95%CI = 0.274-0.638). Bilateral assessments demonstrated similar ranges of poor to excellent (ICC = 0.679-0.963; lower bound 95%CI = 0.231-0.790). Agreement between-session for inter-limb asymmetry identification was slight and fair in the unilateral tests, with moderate to substantial agreement demonstrated in the bilateral. Being the most reliable within- and between-sessions, demonstrating substantial agreement in asymmetry between-sessions, the NHE would be most appropriate to identify inter-limb asymmetry and assess chronic changes in hamstring strength.

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.

Electromyographical Differences Between the Hyperextension and Reverse-Hyperextension.

ABSTRACT: Cuthbert, M, Ripley, NJ, Suchomel, TJ, Alejo, R, McMahon, JJ, and Comfort, P. Electromyographical differences between the hyperextension and reverse-hyperextension. J Strength Cond Res 35(6): 1477-1483, 2021-The aims of this study were to compare muscle activation of the erector spinae (ES), gluteus maximus (GMax), and biceps femoris (BF) during the hyperextension (HE) and reverse-HE (RHE) exercises. Ten subjects (age, 23 ± 4 years; height, 175.9 ± 6.9 cm; mass, 75.2 ± 9.7 kg) had electromyography (EMG) electrodes placed on the ES, GMax, and BF muscles in accordance with SENIAM (Surface EMG for Non-Invasive Assessment of Muscles) guidelines. Subjects performed 3 maximum voluntary isometric contraction trials of lumbar extension and hip extension using a handheld and isokinetic dynamometer, respectively, to normalize the EMG during the HE and RHE exercises. Three repetitions of each exercise were executed in a randomized order. High reliability (intraclass correlation coefficient ≥0.925) was observed with low variability (coefficient of variation [CV] < 10%) in all but the GMax during the extension phase of the HE (CV = 10.64%). During the extension and flexion phases, the RHE exhibited significantly greater (p ≤ 0.024; 34.1-70.7% difference) peak EMG compared with the HE in all muscles tested. Similarly, the RHE resulted in significantly greater mean EMG compared with the HE (p ≤ 0.036; 28.2-65.0% difference) in all muscles except the BF during the flexion phase (p = 9.960). Therefore, the RHE could be considered as a higher-intensity exercise for the posterior chain muscles compared with the HE, potentially eliciting greater increases in strength of the posterior chain muscles.

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.

Assessment of Loaded Squat Jump Height With a Free-Weight Barbell and Smith Machine: Comparison of the Takeoff Velocity and Flight Time Procedures.

Pérez-Castilla, A, McMahon, JJ, Comfort, P, and García-Ramos, A. Assessment of loaded squat jump height with a free-weight barbell and Smith machine: comparison of the takeoff velocity and flight time procedures. J Strength Cond Res 34(3): 671-677, 2020-The aims of this study were to compare the reliability and magnitude of jump height between the 2 standard procedures of analyzing force platform data to estimate jump height (takeoff velocity [TOV] and flight time [FT]) in the loaded squat jump (SJ) exercise performed with a free-weight barbell and in a Smith machine. Twenty-three collegiate men (age, 23.1 ± 3.2 years; body mass, 74.7 ± 7.3 kg; height, 177.1 ± 7.0 cm) were tested twice for each SJ type (free-weight barbell and Smith machine) with 17-, 30-, 45-, 60-, and 75-kg loads. No substantial differences in reliability were observed between the TOV (coefficient of variation [CV], 9.88%; intraclass correlation coefficient [ICC], 0.82) and FT (CV, 8.68%; ICC, 0.88) procedures (CV ratio, 1.14), whereas the Smith SJ (CV, 7.74%; ICC, 0.87) revealed a higher reliability than the free-weight SJ (CV, 9.88%; ICC, 0.81; CV ratio, 1.28). The TOV procedure provided higher magnitudes of jump height than the FT procedure for the loaded Smith machine SJ (systematic bias, 2.64 cm; p ≤ 0.05), whereas no significant differences between the TOV and FT procedures were observed in the free-weight SJ exercise (systematic bias, 0.26 cm; p > 0.05). Heteroscedasticity of the errors was observed for the Smith machine SJ (r = 0.177) with increasing differences in favor of the TOV procedure for the trials with lower jump height (i.e., higher external loads). Based on these results, the use of a Smith machine in conjunction with the FT more accurately determine jump height during the loaded SJ.

A Comparison of Kinetic and Kinematic Variables During the Pull From the Knee and Hang Pull, Across Loads.

Meechan, D, McMahon, JJ, Suchomel, TJ, and Comfort, P. A comparison of kinetic and kinematic variables during the pull from the knee and hang pull, across loads. J Strength Cond Res 34(7): 1819-1829, 2020-Kinetic and kinematic variables during the pull from the knee (PFK) and hang pull (HP) were compared in this study. Eighteen men (age = 29.43 ± 3.95 years; height 1.77 ± 0.08 m; body mass 84.65 ± 18.79 kg) performed the PFK and HP with 40, 60, 80, 100, 120, and 140% of 1-repetition maximum (1RM) power clean, in a progressive manner. Peak force (PF), mean force (MF), peak system velocity (PSV), mean system velocity (MSV), peak power (PP), mean power (MP), and net impulse were calculated from force-time data during the propulsion phase. During the HP, small-to-moderate yet significantly greater MF was observed compared with the PFK, across all loads (p ≤ 0.001; Hedges g = 0.47-0.73). Hang pull PSV was moderately and significantly greater at 100-140% 1RM (p = 0.001; g = 0.64-0.94), whereas MSV was significantly greater and of a large-to-very large magnitude compared with PFK, across all loads (p < 0.001; g = 1.36-2.18). Hang pull exhibited small to moderate and significantly greater (p ≤ 0.011, g = 0.44-0.78) PP at 100-140%, with moderately and significantly greater (p ≤ 0.001, g = 0.64-0.98) MP across all loads, compared with the PFK. Hang pull resulted in a small to moderate and significantly greater net impulse between 100 and 140% 1RM (p = 0.001, g = 0.36-0.66), compared with PFK. The results of this study demonstrate that compared with the PFK, the HP may be a more beneficial exercise to enhance force-time characteristics, especially at loads of ≥1RM.

A Comparison of Kinetic and Kinematic Variables During the Midthigh Pull and Countermovement Shrug, Across Loads.

Meechan, D, Suchomel, TJ, McMahon, JJ, and Comfort, P. A comparison of kinetic and kinematic variables during the midthigh pull and countermovement shrug, across loads. J Strength Cond Res 34(7): 1830-1841, 2020-This study compared kinetic and kinematic variables during the midthigh pull (MTP) and countermovement shrug (CMS). Eighteen men (age: 29.43 ± 3.95 years, height: 1.77 ± 0.08 m, body mass: 84.65 ± 18.79 kg, and 1 repetition maximum [1RM] power clean: 1.02 ± 0.18 kg·kg) performed the MTP and CMS at intensities of 40, 60, 80, 100, 120, and 140% 1RM, in a progressive manner. Peak force (PF), mean force (MF), peak velocity, peak barbell velocity (BV), peak power, (PP), mean power (MP), and net impulse were calculated from force-time data during the propulsion phase. During the CMS, PF and MF were maximized at 140% 1RM and was significantly greater than the MTP at all loads (p ≤ 0.001, Hedges g = 0.66-0.90); p < 0.001, g = 0.74-0.99, respectively). Peak velocity and BV were significantly and meaningfully greater during the CMS compared with the MTP across all loads (p < 0.001, g = 1.83-2.85; p < 0.001, g = 1.73-2.30, respectively). Similarly, there was a significantly and meaningfully greater PP and MP during the CMS, across all loads, compared with the MTP (p < 0.001, g = 1.45-2.22; p < 0.001, g = 1.52-1.92). Impulse during the CMS was also significantly greater across all loads (p < 0.001, g = 1.20-1.66) compared with the MTP. Results of this study demonstrate that the CMS may be a more advantageous exercise to perform to enhance force-time characteristics when compared with the MTP, due to the greater kinetics and kinematic values observed.

Comparison of the Force-, Velocity-, and Power-Time Curves Between the Concentric-Only and Eccentric-Concentric Bench Press Exercises.

Pérez-Castilla, A, Comfort, P, McMahon, JJ, Pestaña-Melero, FL, and García-Ramos, A. Comparison of the force-, velocity-, and power-time curves between the concentric-only and eccentric-concentric bench press exercises. J Strength Cond Res 34(6): 1618-1624, 2020-The aim of this study was to compare the temporal and mechanical variables between the concentric-only and eccentric-concentric bench press (BP) variants. Twenty-one men (age: 22.0 ± 4.2 years, body mass: 73.4 ± 7.7 kg, height: 177.2 ± 8.0 cm; 1 repetition maximum [1RM]: 1.12 ± 0.12 kg·kg) were evaluated during the concentric-only and eccentric-concentric BP variants using 80% 1RM. Temporal (concentric phase duration, propulsive phase duration, and time to reach the maximum values of force, velocity, and power) and mechanical variables (force, velocity, and power), determined using a linear velocity transducer, were compared between both BP variants. All temporal variables were significantly lower during the eccentric-concentric BP compared with the concentric-only BP (p ≤ 0.05; effect size [ES] range: 0.80-2.52). Maximum force as well as the mean values of velocity and power were significantly higher for the eccentric-concentric BP compared with the concentric-only BP (all p < 0.001; ES range: 2.87-3.58). However, trivial to small differences between both BP variants were observed for mean force (ES: 0.00-0.36) as well as for maximum velocity (ES: 0.40) and power (ES: 0.41). The stretch-shortening cycle (i.e., eccentric-concentric BP) mainly enhanced force production at the early portion of the concentric phase, but this potentiation effect gradually reduced over the latter part of the movement. Finally, force was higher for the concentric-only BP during 49% of the concentric phase duration. These results suggest that both BP variants should be included during resistance training programs to optimize force output at different points of the concentric phase.

Effect of Onset Threshold on Kinetic and Kinematic Variables of a Weightlifting Derivative Containing a First and Second Pull.

James, LP, Suchomel, TJ, McMahon, JJ, Chavda, S, and Comfort, P. Effect of onset threshold on kinetic and kinematic variables of a weightlifting derivative containing a first and second pull. J Strength Cond Res 34(2): 298-307, 2020-This study sought to determine the effect of different movement onset thresholds on both the reliability and absolute values of performance variables during a weightlifting derivative containing both a first and second pull. Fourteen men (age: 25.21 ± 4.14 years; body mass: 81.1 ± 11.4 kg; and 1 repetition maximum [1RM] power clean: 1.0 ± 0.2 kg·kg) participated in this study. Subjects performed the snatch-grip pull with 70% of their power clean 1RM, commencing from the mid-shank, while isolated on a force platform. Two trials were performed enabling within-session reliability of dependent variables to be determined. Three onset methods were used to identify the initiation of the lift (5% above system weight [SW], the first sample above SW, or 10 N above SW), from which a series of variables were extracted. The first peak phase peak force and all second peak phase kinetic variables were unaffected by the method of determining movement onset; however, several remaining second peak phase variables were significantly different between methods. First peak phase peak force and average force achieved excellent reliability regardless of the onset method used (coefficient of variation [CV] < 5%; intraclass correlation coefficient [ICC] > 0.90). Similarly, during the second peak phase, peak force, average force, and peak velocity achieved either excellent or acceptable reliability (CV < 10%; ICC > 0.80) in all 3 onset conditions. The reliability was generally reduced to unacceptable levels at the first sample and 10 N method across all first peak measures except peak force. When analyzing a weightlifting derivative containing both a first and second pull, the 5% method is recommended as the preferred option of those investigated.