Eccentric Force Research Articles

Mechanical performance and analytical model of BC joint with assembly error and load-carrying capacity of its single-layer dome based on numerical analysis

The mechanical performance of prefabricated single-layer dome is significantly affected by assembly errors of BC joint, which are inevitable in practical engineering due to manufacture and installation, etc. In this study, mechanical performance of BC joint with assembly error is comprehensively investigated. Finite element model of bolt-column (BC) joint is firstly established and validated based on previous research. Then bending behaviors about the strong axis and mechanical performance of BC joint with assembly error under eccentric force are comprehensively investigated. Moment-rotation curves, load-displacement curves and failure modes of the joint under other static loading conditions are also obtained. Subsequently, an analytical model for the strong axis moment-rotation curves of BC joints with assembly error is proposed. Ultimately, load-carrying capacity and failure mode of the imperfect semi-rigid single-layer dome are determined. A comprehensive investigation is conducted on the mechanical behaviors of dome that incorporates assembly error of BC joints. The research demonstrates that (I) there are two stages, slip stage and contact stage, appearing in the strong axis bending moment-rotation curves; (II) under eccentric force, joint with assembly error demonstrates two different mechanical behaviors as eccentric distance increasing, that is small eccentric behavior and large eccentric behavior; (III) the static force performance of BC joint shows significant sensibility to assembly error, except for axial tension performance; (IV) the proposed analytical model can accurately capture the characteristics of strong axis moment-rotation curve; (V) assembly error has a non-negligible effect on the mechanical performance of single-layer dome; (VI) single kind of joint stiffness affects the limit load of dome little. However, the coupling effect of all kinds of stiffness can not be neglected.

Forces experienced at different levels of the musculoskeletal system during horizontal decelerations

ABSTRACT Horizontal decelerations are frequently performed during team sports and are closely linked to sports performance and injury. This study aims to provide a comprehensive description of the kinetic demands of decelerations at the whole-body, structural, and tissue-specific levels of the musculoskeletal system. Team-sports athletes performed maximal-effort horizontal decelerations whilst full-body kinematics and ground reaction forces (GRFs) were recorded. A musculoskeletal model was used to determine whole-body (GRFs), structural (ankle, knee, and hip joint moments and contact forces), and tissue (twelve lower-limb muscle forces) loads. External GRFs in this study, especially in the horizontal direction, were up to six times those experienced during accelerated or constant-speed running reported in the literature. To cope with these high external forces, large joint moments (hip immediately after touchdown; ankle and knee during mid and late stance) and contact forces (ankle, knee, hip immediately after touchdown) were observed. Furthermore, eccentric force requirements of the tibialis anterior, soleus, quadriceps, and gluteal muscles were particularly high. The presented loading patterns provide the first empirical explanations for why decelerating movements are amongst the most challenging in team sports and can help inform deceleration-specific training prescription to target horizontal deceleration performance, or fatigue and injury resistance in team-sports athletes.

The effects of horizontal deceleration training on sprint and countermovement jump neuromuscular performance qualities

ABSTRACT This study examined the effect of 6-week training to improve horizontal deceleration ability on sprint acceleration and countermovement jump (CMJ) neuromuscular performance (NMP) parameters. Twenty male soccer players were divided into the training (TRA), and the control (CON) group. Pre-and post-training players performed an acceleration-deceleration ability test (ADA) and a jump on a vertical axis dual force plate. ADA deceleration parameters were analysed using Kinovea Software. Distance-to-stop (DTS), time-to-stop (TTS), 20 m sprint time (t 20 m), CMJ parameters were measured at pre-post-training. The largest improvement was determined in the TRA in the t 20 m (effect size = 0.88). Despite the increase in the weight of the TRA, t 20 m was shortened by 5.62% in TRA and 1.91% in CON. Deceleration ability was evaluated with CMJ eccentric parameters. While the percentage change of eccentric peak force differed between the groups, eccentric peak power (11.84 vs. 14.57 W·kg–1, ds: 0.72) and velocity (0.91 vs. 1.05 m.s–1, ds: 0.70) increased. Accordingly, it was determined that the improvement in CMJ eccentric and concentric peak velocity was due to speed-based power output. The training improved the maximum horizontal deceleration ability and confirmed that concentric peak velocity, as well as CMJ eccentric parameters, is an important NMP determinant of horizontal deceleration ability.

Peak torque and eccentric rate of torque development of the hamstrings might not be reflected by contractile properties measured by tensiomyography.

Eccentric maximum strength and explosive force production of the hamstrings are crucial for performance in many sports. Tensiomyography (TMG has been shown to be a valuable tool to assess muscle contractility and function. For eccentric force production, neural activation has been proposed to be the predominant influencing factor. Nevertheless, high muscle fiber tension has to be generated. Therefore, this study aims to test the hypothesis that eccentric force production does not correlate with muscle contractility measured by TMG. Twenty-three physical active males (26.09±3.25 years) performed maximal eccentric hamstring contractions at 210 °/s on an isokinetic dynamometer. Additionally, TMG measurements were conducted on the biceps femoris. Contraction time, delay time, maximal deformation and contraction velocity were derived and investigated. Spearman correlations between the TMG parameters and maximum torque, rate of torque development (RTD) and time to peak torque were calculated. Furthermore, Kruskal Wallis test was calculated for the TMG parameters between the top and bottom participants according to RTD. The correlation analysis showed no significant relationships between the TMG parameters and eccentric force production (P>0.05 for all comparisons). For the comparison between the high RTD group and the low RTD group, no significant differences in muscle contractility could be observed. The results of the present study suggest that muscle contractile properties play a minor role in eccentric force production. Therefore, TMG measures seem not to be suitable to investigate eccentric behavior.

Neuromuscular Performance and the Intensity of External Training Load During the Preseason in National Collegiate Athletic Association Division I Men's Collegiate Basketball Players.

Curtis, M, Kupperman, N, Westbrook, J, Weltman, AL, Hart, J, and Hertel, J. Neuromuscular performance and the intensity of external training load during the preseason in National Collegiate Athletic Association Division I men's collegiate basketball players. J Strength Cond Res XX(X): 000-000, 2024-The aim of the study was to determine whether acute changes in neuromuscular performance can be detected through countermovement jumps (CMJs) conducted pre- and postpractice sessions in conditions of high or low intensity measured by microsensors technology. Using an observational repeated measures design, data were collected from 10 male collegiate basketball players. Countermovement jump data were collected before and after practice exposures over 4 weeks of preseason. Select CMJ kinetics were compared in conditions of high and low training load intensity to detect neuromuscular performance changes in displacement of the center of mass and kinetics. Kinetic measures were categorized as output, underpinning, and strategy-related variables. We investigated "output" defined as displacement (jump height [JH]), "underpinning" defined as force-related (mean eccentric force, mean concentric force, force at zero velocity), and "strategy" defined as time-related (countermovement depth [CMD], eccentric duration (EccDur), concentric duration [ConcDur]) variables. There were significant condition × time interactions in CMJ variables namely eccentric mean force (EccForce), force at zero velocity (Force@0), CMDepth, EccDur, and ConcDur. In conditions of high intensity, players had significant, but small decreases in EccForce and Force@0, with small increases in CMD, EccDur, and ConDur, respectively. However, there were no significant decreases in JH. High-intensity practice exposures did not impact neuromuscular performance specific to "output," suggesting that collegiate basketball athletes can maintain JH despite alterations in "underpinning" and "strategy-related" variables. This could have relevance in understanding how fatigue associated with higher-intensity training exposures may potentially alter jump strategy and force production capacities due to external load intensity in collegiate basketball athletes.

A narrative review of velocity-based training best practice: the importance of contraction intent versus movement speed.

Explosive movements requiring high force and power outputs are integral to many sports, posing distinct challenges for the neuromuscular system. Traditional resistance training can improve muscle strength, power, endurance, and range of motion; however, evidence regarding its effects on athletic performance, such as sprint speed, agility, and jump height, remains conflicting. The specificity of resistance training movements, including velocity, contraction type, and joint angles affects performance outcomes, demonstrates advantages when matching training modalities with targeted sports activities. However, independent of movement speed, the intent to contract explosively (ballistic) has also demonstrated high velocity-specific training adaptations. The purpose of this narrative review was to assess the impact of explosive or ballistic contraction intent on velocity-specific training adaptations. Such movement intent may predominantly elicit motor efferent neural adaptations, including motor unit recruitment and rate coding enhancements. Plyometrics, which utilize rapid stretch-shortening cycle movements, may augment high-speed movement efficiency and muscle activation, possibly leading to improved motor control through adaptations like faster eccentric force absorption, reduced amortization periods, and quicker transitions to explosive concentric contractions. An optimal training paradigm for power and performance enhancement might involve a combination of maximal explosive intent training with heavier loads and plyometric exercises with lighter loads at high velocities. This narrative review synthesizes key literature to answer whether contraction intent or movement speed is more critical for athletic performance enhancement, ultimately advocating for an integrative approach to resistance training tailored for sports-specific explosive action.

Relationship between Peak Eccentric Force during the Nordic Hamstring Exercise and One Repetition Maximum Deadlift Performance.

The Nordic hamstring exercise (NHE) is useful for preventing hamstring strain injuries. However, its adoption rates in the sports field are currently low, necessitating a safe and efficient introduction. The purpose was to examine the relationship between the eccentric force during the NHE and the one repetition maximum of deadlift. It was hypothesized that the eccentric force during the NHE would be correlated with the one repetition maximum (1RM) of the deadlift. Cross-sectional study. Healthy student rugby players with no history of hamstring tears were recruited to participate. The peak eccentric forces during the NHE, which is the vertical peak force on the part holding the leg, were measured in both legs, while gradually leaning forward to a prone position over three seconds. The 1RM of deadlift was calculated from the weight that could be raised three times during a deadlift (x kg) using the estimated formula (x kg / 0.93). The correlation between the left and right peak eccentric forces during the NHE, the total left and right forces, and the 1RM of the deadlift was examined using Spearman's rank correlation coefficient, with all values corrected for body mass. During the NHE, the peak eccentric force of the right and left legs and the total peak eccentric force of both legs were 3.8 ± 1.1 N/BM, 3.8 ± 1.2 N/BM, and 7.6 ± 2.1 N/BM, respectively. The 1RM of deadlift was 1.9 ± 0.3 kg/BM. Weak correlations (r = 0.34-0.37) were found between the 1RM of the deadlift and the peak eccentric force in the right and left legs and the total peak eccentric force of both legs. The present study revealed a weak correlation between the peak eccentric force during the NHE and 1RM of deadlift. 2c.

The Effects of the Leg Position on the Nordic Hamstring Exercise Eccentric Force: A Randomized Cross-Over Study

Given the posterior chain configuration, it is anticipated that tibial positioning influences hamstring recruitment; medial hamstrings should be more activated during medial rotation, while lateral hamstrings should be more activated during lateral rotation. However, most studies showing this pattern have focused on concentric or isometric strength, leaving the influence on eccentric strength fairly unknown. Therefore, the aim of this study was to investigate the electromyographic response of the hamstring muscles during Nordic hamstring exercises in three leg positions: internal rotation, external rotation, and neutral. This study encompassed a randomized crossover study and used surface electromyography to analyze the activity of the biceps femoris and semitendinosus muscles during the Nordic hamstring exercise, in the three positions. Results indicated no statistically significant differences in muscle activation between positions or sides (p > 0.05), though small effect sizes were observed for the biceps femoris in different positions (η2 = 0.01–0.03). Furthermore, the internal rotation position generally elicited the highest muscle activations. Notably, biceps femoris muscles exhibited higher activations compared to semitendinosus muscles, with the greatest differences seen in the internal rotation position. This suggests that tibial rotation influences hamstring recruitment patterns; however, it was lower than expected.

Self-powered sensor for online monitoring of eccentricity faults in rotating machinery and its application in spindle eccentricity monitoring of machine tools

With their unique structures and functionalities, rotating machineries are widely employed in various high-end industries. However, eccentric faults of rotors during continuous high-speed operation represent a critical factor in causing safety accidents. Therefore, real-time monitoring of rotor health is crucial for promptly identifying potential safety hazards and fault indications, enabling preventative maintenance, and enhancing safety performance. Nonetheless, traditional monitoring methods rely on sensors installed on rotating components, which are prone to interference in rotational environments, involve complex installation and maintenance procedures, and pose significant challenges to rotor health monitoring. In this study, a self-powered rotor eccentricity monitoring sensor (RE-TENGs) is designed and fabricated, integrating triboelectric nanogenerator technology. This sensor utilizes the rotor as the self-sensing entity, requiring no external power supply and featuring simplified installation, enabling real-time monitoring of rotor health during rotational machinery operation. A linear relationship between the RE-TENG's eccentric response and electrical characteristics was established through dynamic testing. Furthermore, the actual eccentricity orientation of the rotor was successfully determined by employing vector analysis and synthesis methods with multiple RE-TENGs coupled. To further validate the practicality and accuracy of RE-TENGs, a monitoring testbed for eccentric faults of the spindle rotor in a CNC machine tool was constructed, with the spindle rotor's eccentric fault simulated through misaligned installation. Experimental results demonstrate that RE-TENGs can effectively detect rotor faults induced by eccentric forces during the actual operation of machine tools, accurately determining the eccentric direction and displacement. With an actual angle recognition error of less than ±0.824° and an eccentric distance recognition accuracy exceeding 98 %, the exceptional performance of RE-TENGs in monitoring and precise identification of eccentric faults in rotating machinery rotors is unequivocally verified. By integrating triboelectric nanogenerator (TENG) technology, this study realizes real-time monitoring and precise identification of eccentric faults in rotating machinery rotors. It provides a novel solution for health condition monitoring of rotating machinery and offers a reference for overcoming the cumbersome installation and complex wiring of traditional sensors in practical applications.

Impact of lengthening velocity on the generation of eccentric force by slow-twitch muscle fibers in long stretches

After an initial increase, isovelocity elongation of a muscle fiber can lead to diminishing (referred to as Give in the literature) and subsequently increasing force. How the stretch velocity affects this behavior in slow-twitch fibers remains largely unexplored. Here, we stretched fully activated individual rat soleus muscle fibers from 0.85 to 1.3 optimal fiber length at stretch velocities of 0.01, 0.1, and 1 maximum shortening velocity, vmax, and compared the results with those of rat EDL fast-twitch fibers obtained in similar experimental conditions. In soleus muscle fibers, Give was 7%, 18%, and 44% of maximum isometric force for 0.01, 0.1, and 1 vmax, respectively. As in EDL fibers, the force increased nearly linearly in the second half of the stretch, although the number of crossbridges decreased, and its slope increased with stretch velocity. Our findings are consistent with the concept of a forceful detachment and subsequent crossbridge reattachment in the stretch’s first phase and a strong viscoelastic titin contribution to fiber force in the second phase of the stretch. Interestingly, we found interaction effects of stretch velocity and fiber type on force parameters in both stretch phases, hinting at fiber type-specific differences in crossbridge and titin contributions to eccentric force. Whether fiber type-specific combined XB and non-XB models can explain these effects or if they hint at some not fully understood properties of muscle contraction remains to be shown. These results may stimulate new optimization perspectives in sports training and provide a better understanding of structure–function relations of muscle proteins.

Changes in Countermovement Vertical Jump Force-Time Metrics During a Game in Professional Male Basketball Players.

Cabarkapa, D, Johnson, QR, Cabarkapa, DV, Philipp, NM, Eserhaut, DA, and Fry, AC. Changes in countermovement vertical jump force-time metrics during a game in professional male basketball players. J Strength Cond Res 38(7): 1326-1329, 2024-As technology within elite basketball advances and is more available to sporting organizations, novel approaches for assessing and addressing athletic performance during practice or competition are being continuously explored. The aim of this investigation was to examine changes in neuromuscular performance during live basketball play. Eight professional male basketball players volunteered to participate in this study. The testing procedures were conducted during a pre-tournament camp over a span of 2 days. During the first day, the athletes were familiarized with the testing procedures, and baseline measurements were obtained. Using a uni-axial force plate system sampling at 1,000 Hz, each athlete performed 3 countermovement vertical jumps (CVJ) without an arm swing before proceeding with their regular training activities. During the second day of the pre-tournament camp, the athletes repeated identical CVJ testing procedures before the start of the first quarter and post-first, second, third, and fourth quarter of a simulated 5-on-5 basketball game. Repeated-measures testing design was used to examine statistically significant differences in various force-time metrics of interest in comparison to the baseline levels (p < 0.05). Besides a trivial decrease in eccentric mean force, the findings of this study revealed no statistically significant changes in any force-time metrics of interest within both eccentric and concentric phases of the CVJ (i.e., mean and peak force and power, jump height, impulse, velocity, and contraction time). Thus, we can conclude that these variables were not sensitive to acute fatigue, suggesting that the neuromuscular performances of professional male basketball players tend to remain unchanged throughout a 5-on-5 simulated game.

Strength characteristics in faster change of direction basketball players: A comparison across cutting angles.

Change of directions (COD) involves multidirectional and complex actions, with performance influenced by multiple factors. As lower limb strength is one of the most determinant of COD performance, the present study aimed to (a) explore the differences in strength outcomes across different lower limb muscle actions between faster and slower basketball players in COD actions at different angles and (b) analyse the relationship between isometric, concentric and eccentric strength outcomes and COD performance at different cutting angles. Twenty-five basketball players (44% female) completed a battery of tests, encompassing isokinetic and isometric squat strength assessments, along with COD tests at 45°, 90° and 180°. Players were categorised as 'low-performance' and 'high-performance' groups based on execution time in COD, facilitating a comparison between performance groups. Results indicated that concentric strength showed the greatest differences between performance groups at 45° COD (effect size≥0.813; p≤0.034). Isometric and eccentric strength demonstrated a moderate-to-large relationship with 90° COD performance (Rho≥0.394; p≤0.045), and all muscle actions exhibited a large relationship with 180° COD (Rho≥0.445; p≤0.030). Moreover, the fastest players showed higher levels of concentric strength relative to eccentric strength, regardless of the cutting angle. These findings hold practical applications, suggesting that basketball coaches should train a specific kind of muscle action depending on the individual players' COD demands, focusing on improving the rapid eccentric force application while striving to reduce the eccentric/concentric ratio.

Differences in anthropometric and vertical jump force-time characteristics between U16 and U18 female basketball players.

Considering the importance of body composition and lower-body strength and power for basketball players' on-court performance, as well as a lack of sports science research focused on female athletes, the purpose of the present investigation was to record the anthropometric and countermovement vertical jump (CMJ) characteristics of top-tier U16 and U18 female basketball players and examine between-group differences in the aforementioned tests. Thirty-two athletes who were a part of the national basketball academy volunteered to participate in the present investigation. Following the body composition assessment conducted via a segmental multifrequency bioimpedance analyzer, athletes performed three CMJs while standing on a force plate system sampling at 1000 Hz. Independent t-test and Mann-Whitney U-test were used to examine between-group differences. The findings reveal significant differences in body composition and lower-body neuromuscular performance characteristics between female basketball players ages 16 and 18. Although no differences were observed in muscle and body fat percentages, the U18 group had significantly greater height, overall body mass (both muscle and fat mass), as well as greater segmental fat-free mass (trunk, both legs and arms), intracellular and extracellular water, and body mass index when compared to their U16 counterparts. On the other hand, the U18 group demonstrated longer eccentric, concentric, and braking phase duration, as well as overall contraction time when compared to the U16 players. In addition, the U18 athletes exhibited higher eccentric mean force and power, concentric impulse, peak power, and mean and peak force.

Relationship between vertical jump performance and playing time and efficiency in professional male basketball players.

With innovative force plate technology being available to many sports organizations worldwide that allow for time-efficient in-depth neuromuscular performance assessment, the purpose of the present study was to examine the relationship between some of the most commonly analyzed countermovement vertical jump (CVJ) force-time metrics and basketball playing time and efficiency. Twenty-four professional male basketball players volunteered to participate in the present study. The CVJ testing procedures were conducted within the first quarter of the competitive season span. Following a standardized warm-up protocol, each athlete stepped on a dual uni-axial force plate system sampling at 1,000 Hz and performed three maximum-effort CVJs with no arm swing. To minimize the possible influence of fatigue, each jump trial was separated by a 10-15 s rest interval and the average value across three jumps was used for performance analysis purposes. Basketball playing efficiency and average playing time were obtained at the end of the regular season competitive period from the coaching staff records and the official team records. Pearson product-moment correlation coefficients (r) were used to examine the strength of the relationships between force-time metrics and basketball playing time and efficiency, separately for each dependent variable (p < 0.05). A significant positive association was observed between playing efficiency and eccentric mean force and eccentric mean and peak power (r = 0.406-0.552). Similarly, an increase in eccentric mean power was positively correlated with the number of minutes played during the competitive season (r = 0.464). Moreover, the aforementioned relationship remained present even when eccentric mean power was expressed relative to the player's body mass (r = 0.406). Thus, the findings of the present study indicate that, at the professional level of men's basketball competition, CVJ eccentric strength and power have a positive impact on both playing time and efficiency.

Changes in Countermovement Vertical Jump Force-Time Metrics Across Different Competitive Levels in Women’s Volleyball

As one of the most fundamental skills in volleyball, the countermovement vertical jump (CVJ) has been commonly implemented as a non-invasive and time-efficient method for the assessment of lower-body neuromuscular function. The purpose of the present study was to examine differences in CVJ performance between three different competitive levels in female volleyball players (i.e., national team [n=20], professional league [n=16], collegiate [n=16]). While standing on a uni-axial force plate system sampling at 1000 Hz, athletes performed three maximal-effort CVJs with no arm swing (i.e., hands on the hips during the entire movement). Each jump was separated by a 10-15 second rest interval to minimize the possible influence of fatigue. Significantly greater eccentric braking impulse, peak velocity, peak force, mean and peak power, vertical jump height, reactive strength index-modified, countermovement depth, and shorter braking phase, eccentric duration, and contraction times were observed for the national team and professional players when compared to collegiate athletes. Also, national team players demonstrated significantly greater eccentric braking impulse, peak velocity, mean and peak power, reactive strength index-modified, and countermovement depth than professional volleyball players. However, during the concentric phase of the CVJ, the only significant differences observed were between national team players and collegiate athletes, where national team players exhibited significantly greater peak velocity, impulse, and mean and peak power. Thus, it can be concluded that higher-level players may be more capable of effectively utilizing the eccentric phase of the CVJ and executing the stretch-shortening action more rapidly, which contributes to better CVJ height.

SERCA2a overexpression improves muscle function in a canine Duchenne muscular dystrophy model

Excessive cytosolic calcium accumulation contributes to muscle degeneration in Duchenne muscular dystrophy (DMD). Sarco/endoplasmic reticulum calcium ATPase (SERCA) is a sarcoplasmic reticulum (SR) calcium pump that actively transports calcium from the cytosol into the SR. We previously showed that adeno-associated virus (AAV)-mediated SERCA2a therapy reduced cytosolic calcium overload and improved muscle and heart function in the murine DMD model. Here we tested whether AAV SERCA2a therapy could ameliorate muscle disease in the canine DMD model. 7.83 x 1013 viral genome particles of the AAV vector were injected into the extensor carpi ulnaris (ECU) muscles of four juvenile-affected dogs. Contralateral ECU muscles received excipient. Three months later, we observed widespread transgene expression and significantly increased SERCA2a levels in the AAV-injected muscles. Treatment improved SR calcium uptake, significantly reduced calpain activity, significantly improved contractile kinetics, and significantly enhanced resistance to eccentric contraction-induced force loss. Nonetheless, muscle histology was not improved. To evaluate the safety of AAV SERCA2a therapy, we delivered the vector to the ECU muscle of adult normal dogs. We achieved strong transgene expression without altering muscle histology and function. Our results suggest that AAV SERCA2a therapy has the potential to improve muscle performance in a dystrophic large mammal.

Utjecaj ekscentrične porivne sile na odabir statvenog kliznog ležaja

Stern tube slide bearing of the shaft line of the ship's propulsion system causes losses during operation. Friction and material wear of the tribosystem occur. One of the reasons is the different navigating regimes of the ship, which have an influence on the formation of the velocity field on the ship's propeller. The variable velocity field defines the magnitude and the position of the thrust force. The methodology presented in this paper is based on the fact of the existence of the eccentricity of the thrust force, i.e. loads due to the action of the moment of the eccentric thrust force. Due to the changing position of the thrust force, the curvature of the elastic line of the sleeve inside the stern tube bearing, which is mostly spatial, changes. Spatial elastic line of the sleeve has an influence on the working area of the slide bearing. Therefore, the importance of a sufficient thickness of the lubricant layer for lubrication in relation to these changes was highlighted. In this paper, this is the initial criterion for the selection of materials and lubricants of the stern tube bearing. An equally important criterion would be to define the possible harmful impact of lubricant leakage with particles of bearing bush material on the ecosystem. In order to facilitate the whole process, the simplified analytical model is presented, which can be used in the initial stage of stern tube bearing selection. Such a model allows a simpler analysis of the influence of the elastic line on the condition of the stern tube bearing due to the loading by the weight of the ship's propeller and by the moment of the eccentric thrust force. The procedure for the initial selection of the stern tube bearing created by this methodological approach could have its practical application. For this reason, the paper analyzed different navigating regimes and their influence on the working area of the stern tube slide bearing. The obtained results can be useful in the selection of materials and lubricants for the stern tube bearing tribosystem.

Kinetic Comparison between Drop Jumps and Horizontal Drop Jumps in Elite Jumpers and Sprinters

Previous research addressed the spatiotemporal variables of the drop jump (DJ) versus the horizontal drop jump (HDJ). This study compared the kinetic variables of the DJ versus the HDJ in elite jumpers and sprinters. In a single session, sixteen elite jumpers and sprinters performed two DJ attempts with three different fall heights (0.30 m, 0.40 m, and 0.50 m), and after 2 h, performed two HDJ attempts from the same fall heights (0.30 m, 0.40 m, and 0.50 m). Kinetic variables: eccentric ground reaction forces (GRFE) and concentric ground reaction forces; eccentric impulse (PE) and concentric impulse (PC); peak power in the concentric phase; and rate of force decrease (RFDe) were measured using a research-grade force plate. The Wilcoxon test was used to compare the vertical and anteroposterior axes. GRFE was significantly higher (p ≤ 0.05) in the DJ vs the HDJ with large effect sizes. The PE (p ≤ 0.006) and PC (p = 0.002) were significantly lower in the DJ than in the HDJ. The RFDe was also significantly lower in the DJ at 0.30 m vs. the HDJ at 0.30 m (p = 0.002). In summary, elite jumpers and sprinters may benefit from incorporating both the DJ and the HDJ into their training regimens, with the DJ being particularly advantageous for enhancing power metrics and RFDe.

The relationship between agility, linear sprinting, and vertical jumping performance in U-14 and professional senior team sports players.

The aim of this paper is to determine the relationship between the modified agility T-test (change of direction speed ability), 20-meter sprint test (linear speed ability), and countermovement jump test (vertical jumping performance) in U-14 and professional senior team sports players. The sample included 78 (59 female and 19 male) U-14 athletes (age 11.70 ± 1.33 years, height 153.00 ± 12.20 cm and body mass 47.10 ± 11.20 kg) and 43 (18 female and 25 male) senior professional athletes (age 24.80 ± 6.58 years, height 169.00 ± 9.13 cm and body mass 71.20 ± 15.10 kg). Both samples participated in different team sports including basketball, field hockey, and football. Participants underwent a series of tests to assess their speed, change of direction speed, and explosive power. Speed assessments involved 20-meter sprints (sec), while change of direction speed was measured using the modified agility T-test (sec). Explosive power was evaluated through countermovement jumps (CMJ), where concentric mean force (N), concentric peak force (N), concentric peak velocity (m/s), eccentric peak force (N), jump height (cm), peak power (W), peak power/BM (W/kg), RSI (m/s) and vertical velocity (m/s) were determined. Pearsońs product moment-correlation coefficient (r) served to determine correlations and linear regression was conducted to explain the relationship between the dependent variable (CODS) and independent variables (S20 m and CMJ). The level of statistical significance was set at p < 0.05 and the confidence interval was 95%. The Pearson product-moment correlation analysis in the U-14 athletes indicated no correlation (r = 0.11, p = 0.34) between the 20-meter linear sprint speed and the modified change of direction T-test. Additionally, the results revealed that 4 out of 10 CMJ values showed a significant moderate correlation (r = 0.3, p < 0.05) between CMJ and the modified change of direction T-test. In contrast, senior players exhibited statistically significant correlations in all variables. A significant correlation (r = 0.90, p = 0.01) was found between 20-meter linear sprint speed and the modified change of direction T-test, while CMJ values showed a range of correlations from moderate to large. In both competitive categories, according to the linear regression model, only linear sprint speed over 20-meters significantly explained (p < 0.05) the CODS speed ability, while the other CMJ parameters did not reach the significance level (p > 0.05). The study emphasized the influence of explosive power performance (CMJ) and linear speed (S20 m) on agility (CODS) within the sample, particularly among professional senior team sports players. These findings indicate that agility, linear sprinting, and jumping abilities may share common underlying factors.

Female National Collegiate Athletic Association Division-I Athlete Injury Prediction by Vertical Countermovement Jump Force-Time Metrics.

Merrigan, JJ, Stone, JD, Kraemer, WJ, Vatne, EA, Onate, J, and Hagen, JA. Female National Collegiate Athletic Association Division-I athlete injury prediction by vertical countermovement jump force-time metrics. J Strength Cond Res 38(4): 783-786, 2024-Vertical countermovement jump (CMJ) assessments on force plates have been purported to screen for musculoskeletal injury risk (MSKI) but with little scientific support. Thus, this study aimed to identify associations and noncontact lower-body injury predictability with CMJ force-time metrics in female athletes. The study entailed a retrospective analysis of routine injury and performance monitoring from 155 female National Collegiate Athletics Association Division I athletes. Noncontact lower-body injuries included in analysis were confirmed by medical staff, occurred during competition or training, resulted in time loss from training, and occurred within 3 months following CMJ testing (2 maximal effort, no arm swing, jumps on dual force plates). A total of 44 injuries occurred within 3 months following CMJ baseline testing and resulted in an average of 24.5 missed days from training. Those who sustained an injury were more likely to sustain another injury (15 of 44 injuries [33.1%]; odds ratio = 3.05 [95% CI = 1.31-6.99]). For every 1-unit increase from the mean in eccentric mean power and minimum eccentric force, there was a decrease in odds of sustaining a MSKI. Despite high overall model accuracy (85.6%), the receiving operating characteristic area under the curve (65.9%) was unacceptable and the true positive rate (recall) was 0.0%. Thus, no injuries in the testing data set were correctly classified by the logistic regression model with CMJ force-time metrics as predictors. Baseline CMJ assessment may not be useful for noncontact lower-body musculoskeletal injury screening or predictability in National Collegiate Athletics Association female athletes.