Search Results (72)

Researchers comparing countermovement (CMJ) and assisted countermovement (ACMJ) jumps reported conflicting findings on the landing impact force (LIF). This was likely due to differences in the landing strategies used. As the magnitude of LIF may have implications on neuromuscular adaptations, the purpose of this study was to compare the LIF between CMJ and ACMJ while adopting soft and stiff landing strategies. Thirteen resistance-trained athletes (sex: female = 5, male = 8, 26.4 ± 3.7 years, 68.4 ± 13.6 kg, 167 ± 5.1 cm) performed three CMJ and ACMJ each at 60%, 70%, 80% and 90% of bodyweight with instructions to either land soft or stiff on a force plate. Repetitions were separated by 30 s and conditions by 3 min. Resistance bands were used to induce the required weight during ACMJ. Data obtained regarding the average of the two closest trials based on jump height was analysed. Jump height significantly increased with increasing assistance during ACMJ for both landing conditions (p < 0.001). Propulsion duration (PD) was significantly shorter with increasing assistance during ACMJ for both landing conditions (p < 0.001). Peak and mean propulsion force significantly decreased with increasing assistance during ACMJ for both landing conditions (p < 0.001 and p < 0.001, respectively). The LIF was significantly greater with increasing assistance during ACMJ in the stiff-landing condition only (p < 0.001). Greater assistance allowed participants to jump higher while reducing PD. The higher LIF observed during stiff landing with greater assistance during ACMJ could be attributed to greater jump height and downward velocity during landing. Full article

Background. In taekwondo (TKD), high-intensity actions—particularly kicks and rapid changes of direction—are key determinants of sport-specific performance. Kinetic vari-ables derived from unloaded countermovement jumps (CMJs) are employed as proxies of neuromuscular efficiency. However, most studies have examined the link between CMJ outputs and TKD using jump height alone in sport-specific tasks. Objective. To determine the associations between unloaded CMJ-derived kinetic variables and sport-specific performance, identifying key determinants of repeated high-intensity kicking capacity and change-of-direction ability. Methods. Fifteen national-team athletes (nine men, six women; 18–27 years) completed unloaded CMJ testing (Day 1) and, after 48 h, the Taekwondo-Specific Agility Test (TSAT) and the Multiple Frequency Speed of Kick Test (FSKTMULT) (Day 2). Results. For FSKTMULT, jump height (r = 0.545–0.746), take-off velocity (r = 0.548–0.799), and mean power (r = 0.602–0.799) were positively correlated with the number of kicks across all sets (p = 0.001–0.044). Stepwise regression identified mean power as the sole significant predictor, explaining 32–46% of the variance across sets. For TSAT, time correlated negatively with mean power (r = −0.678, p = 0.008), mean force (r = −0.536, p = 0.048), and RFD (0–30%) (r = −0.655, p = 0.011). Mean power and mid-propulsion impulse (30–60%) jointly explained 72.8% of the variance in TSAT time (R² = 0.728, p < 0.001). Conclusions. Unloaded CMJ mean power and mid-propulsion impulse (30–60%) emerge as proxies of neuromuscular efficiency linked to sport-specific perfor-mance, supporting their use for athlete monitoring and targeted training. Full article

Background: This study compared the acute effect of performing quarter (QS) and parallel (PS) squat with variable resistance (VR) on countermovement jump (CMJ) performance. Methods: Fifteen resistance trained athletes (age: 27.0 ± 3.7 years, bodyweight: 68.4 ± 7.7 kg, height: 169.7 ± 6.9 cm) performed either the QS or PS to induce post-activation performance enhancement on two separate occasions. During each session, participants performed three repetitions of baseline CMJ prior to performing three repetitions of either QS or PS at their three-repetition maximum load. Participants then performed the post-test CMJ after a five-minute recovery period. Results: Both conditions resulted in increased jump height (QS: p < 0.001, g = 0.19, PS: p < 0.001, g = 0.35). Countermovement depth and time to take-off were significantly decreased in QS (p < 0.001, g = 0.63 and p = 0.005, g = 0.30, respectively) but significantly increased in PS (p = 0.027, g = 0.39 and p < 0.001, g = 0.36, respectively). Mean propulsion force was significantly increased in QS (p < 0.001, g = 0.23) but significantly decreased in PS (p = 0.083, g = 0.13). PS resulted in greater change in jump height (p < 0.001, g = 1.34) and time to take-off (p = 0.005, g = 1.25), while QS resulted in greater change in countermovement depth (p < 0.001, g = 2.33) and mean propulsion force (p < 0.001, g = 1.67). Conclusions: The results showed that performing PS and QS with VR was effective in enhancing CMJ height. However, the two conditions resulted in participants adopting different jump strategies when performing the post-test CMJ. Full article

Background: Cluster sets (CSs) maintain velocity and power in compound movements by employing similar propulsion strategies or maintaining impulse through different mechanisms. This study aimed to explore the effect of four CS conditions on back squat (BS) propulsion and provide models for estimating changes in propulsion based on repetition and set number. Methods: Twenty male participants (age = 28.3 ± 3.1 years, stature = 1.74 ± 8.21 m, body mass = 84.80 ± 7.80 kg, BS 1RM = 140.90 ± 24.20 kg) completed four data collection sessions. Each session consisted of three sets of five repetitions at 80% 1RM BS with three minutes of unloaded inter-set rest, using varying intra-set rest intervals. Experimental conditions included 0 s (TRAD), 10 s (CS10), 20 s (CS20), and 30 s (CS30) inter-repetition rest, randomly assigned to sessions in a counterbalanced order. Ground reaction force data were collected on dual force platforms sampling at 1000 Hz, from which net propulsive impulse (J_PROP), mean force (MF), and propulsion time (t_PROP) were calculated. Conditions and sets were analysed using a 4 × 3 (CONDITION*SET) repeated-measures ANOVA to assess differences between conditions and sets, and linear mixed models (LMMs) were used to provide regression equations for each dependent variable in each condition. Results: The ANOVA revealed no significant interactions for any dependent variable. No main effects of CONDITION or SET were observed for J_PROP. The main effects of CONDITION showed that MF was significantly lower in TRAD than CS20 (g = 0.757) and CS30 (g = 0.749). t_PROP was significantly higher in TRAD than CS20 (g = 0.437) and CS30 (g = 0.569). The main effects of SET showed that MF was significantly lower in S2 (g = 0.691) and S3 (g = 1.087) compared to S1. t_PROP was significantly higher in S2 (g = 0.866) and S3 (g = 1.179) compared to S1. LMMs for CS20 and CS30 revealed no significant effect (p > 0.05) between repetition or set number and dependent variables. Conclusions: The results suggest that CS20 and CS30 maintain J_PROP by limiting MF and t_PROP attenuation. This is less rest than that suggested by the previous literature, which may influence programming decisions during strength and power mesocycles to maximise training time and training density. LMMs provide accurate estimates of BS propulsive force attenuation when separating repetitions by up to 30 s, which may help practitioners optimise training load for long-term adaptations. Full article

Background: Movement symmetry in the lower limbs is critical for biomechanical efficiency, injury prevention, and athletic performance. Lateral (sideways) jumping challenges force production and control in the frontal plane and provide a unique assessment of neuromuscular coordination that may not be detected through sagittal-plane tasks such as running or vertical jumping. This study aimed to evaluate limb asymmetries in isometric knee muscle torque and ground reaction forces (GRFs) during lateral jumps in healthy young women, using the Symmetry Index (SI) to quantify differences between limbs. Methods: Twenty right-limb dominant females (mean age: 20.65 ± 4.51 years) participated in the study. Isometric torque of the knee flexors and extensors was measured using a dynamometric testing station. Lateral jumps were performed onto dual force platforms, with GRF components (vertical (PD), anterior–posterior (AP), mediolateral (ML)) recorded separately for rightward and leftward jumps. SI was calculated for all parameters to determine side-to-side asymmetries, and paired Student’s t-tests were used for statistical comparisons. Results: Right-limb dominance was evident in both knee flexor and extensor torque. Significant asymmetries were observed across all GRF components, varying with jump direction. The trailing limb in each jump direction typically generated greater propulsion forces. In lateral jumps, the trailing limb is generally the leg positioned opposite to the direction of travel, playing a primary role in generating propulsion and absorbing forces during take-off. SI values revealed both inter-individual variability and consistent direction-dependent asymmetry patterns. Conclusions: The or-posterior and vertical components, with greater loading on the dominant leg. Muscle torque measurements also revealed imbalances, with flexors showing more symmetry than extensors. These findings underline the importance of assessing load symmetry to prevent injury and guide rehabilitation. Full article

Rowing is a cyclic sport that consists of repetitive biomechanical actions, with performance being influenced by the balance between propulsive and resistive forces. The current study aimed to assess the relationships between intracycle velocity variation (IVV) and key biomechanical and performance variables in male and female single scullers. Twenty-three experienced rowers (10 females) completed a 2000 m rowing competition, during which boat position and velocity were measured using a 15 Hz GPS, while cycle rate was derived from the integrated triaxial accelerometer sampling at 100 Hz. From these data, it was possible to calculate distance per cycle, IVV, the coefficient of velocity variation (CVV), and technical index values. Males presented higher mean, maximum and minimum velocity, distance per cycle, CVV, and technical index values than females (15.40 ± 0.81 vs. 13.36 ± 0.88 km/h, d = 0.84; 21.39 ± 1.68 vs. 18.77 ± 1.52 km/h, d = 1.61; 11.15 ± 1.81 vs. 9.03 ± 0.85 km/h, d = 1.45; 7.68 ± 0.32 vs. 6.89 ± 0.97 m, d = 0.69; 14.13 ± 2.02 vs. 11.64 ± 1.93%, d = 2.06; and 34.25 ± 4.82 vs. 26.30 ± 4.23 (m²/s·cycle), d = 4.56, respectively). An association between mean velocity and intracycle IVV, CVV, and cycle rate (r = 0.68, 0.74 and 0.65, respectively) was observed in males but not in female single scullers (which may be attributed to anthropometric specificities). In female single scullers, mean velocity was related with distance per cycle and was associated with technical index in both males and females (r = 0.76 and 0.66, respectively). Despite these differences, male and female single scullers adopted similar pacing strategies and CVV remained constant throughout the 2000 m race (indicating that this variable might not be affected by fatigue). Differences were also observed in the velocity–time profile, with men reaching peak velocity first and having a faster propulsive phase. Data provided new information on how IVV and CVV relate to commonly used biomechanical variables in rowing. Technical index (r = 0.87): distance per cycle was associated with technical index in both males and females (r = 0.76 and 0.66, respectively). Future studies should include other boat classes and other performance variables such as the power output and arc length. Full article

Background: Resistance training (RT) promotes muscle hypertrophy and strength gains in both men and women. However, sex differences in neuromuscular performance, muscle fiber composition, and the hormonal environment influence strength and power adaptations. While men generally exhibit greater absolute and relative strength, it remains unclear to what extent these differences persist across various load intensities. A better understanding of sex-specific strength and power profiles may help optimize training strategies. The aim of this study was to compare strength and power performance during the bench press exercise in physically active males and females, relative to body mass and fat-free mass (FFM). Methods: Twenty-nine physically active individuals (16 men: 21.3 ± 4.1 years, 13 women: 22.6 ± 4.9 years) performed a one-repetition maximum (1RM) test and an incremental velocity-based assessment at 45%, 55%, 65%, 75%, and 85% of the 1RM using a Smith machine. The barbell velocity was measured via a linear transducer, with the mean propulsive velocity (MPV) recorded for each load. Power-related variables (e.g., peak force [F0], maximal velocity [V0], and maximal power [Pmax]) were analyzed. To account for differences in body composition, data were adjusted for body mass and FFM. Results: Men exhibited significantly greater strength and power than women across most loads when adjusted for both body mass and fat-free mass (FFM) (p < 0.05). These differences were particularly pronounced when normalized to FFM (45–75%1RM; p = 0.001–0.031), with large effect sizes observed (ηp² = 0.185–0.383). Notably, sex differences in mean propulsive velocity (MPV) disappeared at 85%1RM (p = 0.208; ηp² = 0.06), suggesting that maximal neuromuscular recruitment may minimize sex-related disparities at higher intensities. Furthermore, men demonstrated significantly higher values in six of the seven power-related variables, with no significant differences in the %1RM required to achieve an optimal power output. Conclusions: These findings confirm that men exhibit greater strength and power than women, even after adjusting for body composition. However, at high relative loads (≥85%1RM), sex differences in movement velocity appear to diminish, likely due to similar recruitment patterns of high-threshold motor units. These results highlight the importance of sex-specific resistance training programs, particularly in relation to load prescription and the application of velocity-based training methods. Full article

Objectives: The objective of this study was to examine the neuromuscular fatigue response to playing in a singles pickleball tournament, as measured by performance on a countermovement jump test (CMJ). We hypothesized that players would exhibit neuromuscular fatigue after the tournament. Methods: Six adult pickleball players (five male and one female, M ± SD: 40.2 ± 10.1 years old, height = 178.7 ± 12.3 cm, body mass = 85.4 ± 16.7 kg) participated in a 15 game singles pickleball tournament. Prior to the tournament, everyone completed the CMJ to assess lower body strength and power on paired Hawkin Dynamics force plates. After the tournament, players repeated the CMJ. Mixed-effects regression modeling was used to examine changes in key outcomes measured from the CMJ. Results: All nine outcomes from the CMJ significantly changed from pre to post-tournament (e.g., means for net impulse increased from 2.32 ± 0.22 to 2.40 ± 0.18 N·s, p = 0.0006; RSImod increased from 0.28 ± 0.07 to 0.33 ± 0.05, p = 0.0001, and propulsive peak power increased from 41.79 ± 6.14 to 44.34 ± 4.70 W/kg, p < 0.0001). All the changes demonstrated improved performance in the CMJ test. Seven out of the nine outcomes demonstrated a large effect size by the partial-eta square statistic, with η²-partial of 0.153–0.487, and three key outcomes (RSImod, propulsive peak power, and propulsive mean power) also demonstrated large effect sizes by the F² statistic (F² of 0.4603–0.9495). Conclusions: Contrary to our hypothesis, participants did not demonstrate significant neuromuscular fatigue. In contrast, they showed significant improvements in CMJ performance. It is possible that adequate rest between games prevented neuromuscular fatigue; alternately, singles pickleball may not provide enough stimulus in the lower body musculature to induce neuromuscular fatigue. Full article

Erosion detection in materials exposed to plasma-generated species, such as those used for space propulsion systems, is critical for ensuring their reliability and longevity. This study introduces an efficient image processing technique to monitor the evolution of the erosion depth in boron nitride (BN) subjected to multiple cycles of iodine plasma exposure. Utilising atomic force microscopy (AFM) images from both untreated and treated BN samples, the technique uses a modified semi-automated image registration method that accurately aligns surface profiles—even after substantial erosion—and overcomes challenges related to changes in the eroded surface features. The registered images are then processed through frequency-domain subtraction to visualise and quantify erosion depth. Our technique tracks changes across the BN surface at multiple spatial locations and generates erosion maps at exposure durations of 24, 48, 72 and 84 min using both one-stage and multi-stage registration methods. These maps not only reveal localised material loss (up to 5.5 μm after 84 min) and assess its uniformity but also indicate potential re-deposition of etched material and redistribution across the surface through mechanisms such as diffusion. By analysing areas with higher elevations and observing plasma-treated samples over time, we notice that these elevated regions—initially the most affected—gradually decrease in size and height, while overall erosion depth increases. Progressive surface smoothing is observed with increasing iodine plasma exposure, as quantified by AFM-based erosion mapping. Notably, up to 89.3% of surface heights were concentrated near the mean after 72–84 min of plasma treatment, indicating a more even distribution of surface features compared to the untreated surface. Iodine plasma was compared to argon plasma to distinguish material loss during degradation between these two mechanisms. Iodine plasma causes more aggressive and spatially selective erosion, strongly influenced by initial surface morphology, whereas argon plasma results in milder and more uniform surface changes. Additional scale-dependent slope and curvature analyses confirm that iodine rapidly smooths fine features, whereas argon better preserves surface sharpness over time. Tracking such sharpness is critical for maintaining the fine structures essential to the fabrication of modern semiconductor components. Overall, this image processing tool offers a powerful and adaptable method for accurately assessing surface degradation and morphological changes in materials used in plasma-facing and space propulsion environments. Full article

The objective of this study was to compare the 1 Repetition Maximum (RM) performance in the parallel squat exercise with a low-bar vs. a high-bar technique and to analyze the gender differences. A secondary objective was to analyze the differences in the force–velocity profile between the low- and high-bar squat technique. Nineteen recreational strength-trained participants, 9 men (22 ± 1.9 years, 79.4 ± 13.9 kg, 1.77 ± 0.11 m) and 10 women (27.6 ± 3.12 years, 60.4 ± 5.0 kg, 1.67 ± 0.5 m), participated in this study. All participants performed two evaluations of the 1RM and the force–velocity curve in parallel squat exercises, separated by a week, one with a high bar and the other with a low bar technique. The level of significance set for this study was p < 0.05. The technical × gender interaction was not significant in any of the three variables analyzed: lifted load, mean propulsive velocity, and force. A difference (p < 0.001) in the lifted load and the mean force is observed between the techniques at 1RM, being in both cases (men and women) better in the low-bar performance. A difference (p < 0.001) was observed in relation to the technique × participation interaction when comparing the mean velocity and force obtained with the same absolute submaximal loads in each of the techniques. These data may guide a better and more precise organization of training when performing the squat exercise and differentiating the techniques to be used, using the low bar when the main objective is strength or power training. Full article

Measuring the propulsion performance of sport wheelchairs in ecological conditions remains complex due to variations inherent in real-world practice. This study aims to develop a validation protocol for an instrumented wheel designed to measure propulsion power under ecological conditions. The wheel’s precision was compared to that of the Lode Esseda roller ergometer, the gold standard for measuring the force exerted on both the left and right hands. Tests were conducted at three speeds (1, 2, and 3 m/s) on a multisport wheelchair. Results show a strong correlation between the two systems, confirmed by a repeated measures ANOVA test (p > 0.05) and a root mean square error (RMSE < 5%). Bland–Altman plots reveal good agreement despite discrepancies observed at high speeds, potentially due to mechanical limits. The proposed protocol validates the instrumented wheel and highlights the importance of multi-speed evaluation to ensure valid measurements in ecological conditions. Full article

Countermovement bipodal jumps (CMJs), are widely used for health and performance assessment, but the software required for such analyses is often costly. The study aim was to examine the validity of an Excel/VBA spreadsheet for comprehensive CMJ kinetic analysis. The outcomes have been informed from scientific literature, and the spreadsheet includes modules for data filtering and photogrammetric analysis. To evaluate its validity, 21 participants performed CMJs on a dual force platform system, and the primary outcomes were compared with those derived from prestigious software (MARS 4.0). When jump height was calculated based on take-off speed and flight time the Mean Absolute Errors were 1.79 and 0.69 cm and the minimal detectable changes (MCD) were 1.28 and 0.16 cm. For the propulsive impulse, the error was 5.5 N · s and the MCD was 5.41 N · s. The intraclass correlations were 0.932 (0.902–0.953), 0.984 (0.977–0.989), and 0.940 (0.914–0.959), respectively, demonstrating a strong relationship, and residuals exhibited homoscedasticity. Considering the variability reported in previous studies for intra- and inter-subject comparisons, these errors are minimal, highlighting the spreadsheet’s sensitivity. With its exhaustive analytical capabilities and customizable features, this template serves as a valuable tool for trainers, physiotherapists, and academic teaching settings. Full article

This study evaluated the concurrent validity of the Vitruve linear encoder compared to the T-Force device for measuring mean propulsive velocity (MPV) and peak velocity (PV) during the free-weight bench press exercise. Thirteen resistance-trained men participated in three sessions, during which MPV and PV were recorded simultaneously by both devices. The data were analysed using one-way ANOVA, Pearson’s correlation, Bland–Altman analysis, and effect size calculations, with statistical significance set at p ≤ 0.05. The results showed discrepancies between the Vitruve and T-Force devices across different intensity levels. Specifically, the Vitruve device generally reported higher MPV and lower PV values, particularly at moderate and low intensities. Vitruve was deemed useful for MPV measurements, especially at velocities below 0.65 m/s during free-weight bench press exercises. In conclusion, the Vitruve device overestimated MPV and underestimated PV at moderate and low loads (>0.65 m·s⁻¹), with the discrepancies increasing as velocity rose. It can provide valuable data for monitoring and assessing resistance training programs focused on MPV at heavier loads (<0.65 m·s⁻¹). Researchers and practitioners should take these findings into account when incorporating the Vitruve into velocity-based strength training protocols. Full article

The aim of this study was to compare the braking and propulsion force–time and barbell velocity characteristics between back squat sets performed using traditional (TRAD) or accentuated eccentric loading (AEL) in resistance-trained women. In total, 14 participants completed four separate testing sessions that included a one repetition maximum (1RM) back squat and three squat testing sessions that used either TRAD or AEL. During the squat testing sessions, participants performed sets of three back squat repetitions using TRAD loads with 50, 60, 70, and 80% 1RM or performed the same loads with the addition of weight releasers that equated the total load to 100% (AEL-MAX) or 110% (AEL-SUPRA) 1RM during the eccentric phase of the first repetition of each set. Braking and propulsion mean force, duration, and impulse as well as mean and peak barbell velocity were examined across each back squat set. Significantly greater braking impulses were produced during the AEL conditions across all loads (p < 0.02), while greater braking mean force during AEL-SUPRA was produced compared to TRAD during with 50 and 60% 1RM (p < 0.02). There were no other significant differences in braking, propulsion, or barbell velocity that existed between different conditions (p > 0.05). AEL-MAX and AEL-SUPRA provide a greater braking stimulus compared to TRAD squats, while the propulsion phase may not be significantly impacted. Rapid and maximal force production may be favored by larger and smaller load spreads, respectively. Full article

Background: The tempo of resistance exercises is known to influence performance outcomes, yet its specific effects on post-activation performance enhancement (PAPE) remain unclear. This study aimed to investigate the effects of fast versus slow repetitions at a load of 70% of one-repetition maximum (1-RM) in the bench press exercise, focusing on velocity, surface electromyographic (sEMG) activity, and applied force while equating time under tension on bench press throw performance. Methods: Eleven men (age: 23.5 ± 5.4 years, height: 1.79 ± 0.04 m, body mass: 79.1 ± 6.4 kg, maximum strength 1-RM: 91.0 ± 12.0 kg) participated. Two experimental conditions (FAST and SLOW) and one control (CTRL) were randomly assigned. Participants performed two sets of six repetitions as fast as possible (FAST condition) and two sets of three repetitions at a controlled tempo (SLOW condition) at half the concentric velocity of FAST, as determined in a preliminary session. Before and after the bench press participants performed bench press throws tests (Pre, 45 s, 4, 8, and 12 min after). Results: sEMG activity and peak force during the bench press were higher in FAST vs. SLOW conditioning activity (p < 0.001), with time under tension showing no significant differences between conditions (p > 0.05). Mean propulsive velocity (MPV) during the bench press throw improved equally in both FAST and SLOW conditions compared with baseline from the 4th to the 12th min of recovery (FAST: +6.8 ± 2.9% to +7.2 ± 3.3%, p < 0.01, SLOW: +4.0 ± 3.0% to +3.6 ± 4.5%, p < 0.01, respectively). Compared to the CTRL, both conditions exhibited improved MPV values from the 4th to 12th min (p < 0.01). Peak velocity improvements were observed only after the FAST condition compared to the baseline (p < 0.01) with no differences from SLOW. For all muscles involved and time points, sEMG activity during bench press throws was higher than CTRL in both experimental conditions (p < 0.01), with no differences between FAST and SLOW. Peak force increased in both FAST and SLOW conditions at all time points (p < 0.05), compared to CTRL. Conclusions: These findings suggest that post-activation performance enhancement is independent of movement tempo, provided that the resistive load and total time under tension of the conditioning activity are similar. This study provides valuable insights into the complex training method for athletes by demonstrating that varying tempo does not significantly affect post-activation performance enhancement when load and TUT are equated. Full article