Braking Rate Research Articles

Relationship between Countermovement Jump and Sprint Performance in Professional Football Players.

Objectives: The aim of this study was to assess the relationship between the countermovement jump (CMJ) and sprint performance of professional football players, and to determine which strength and speed elements assessed by the CMJ translate into effective running. Methods: The research sample comprised 87 male professional football players (age 23.7 ± 4.20 years; body mass 82.33 ± 6.56 kg; body height 1.86 ± 0.05 m) who performed the CMJ on a dual-force platform, as well as the 30 m sprint test. The time and velocity of the run were recorded by photocells at 0, 5, 10, and 30 m of the distance. Results: No significant differences were noted in the time or velocity of the sprint over the initial 5 m between the groups of football players with a higher and lower braking rate of force development (RFD) in the CMJ (p > 0.05). However, at subsequent intervals (5-10 m and 10-30 m), players with a higher braking RFD achieved significantly better time and velocity than those with a lower RFD. Significant correlations in the group with a lower braking RFD between the CMJ and sprint variables occurred in the propulsion phase of the CMJ and most of them were in the first interval (0-5 m). In the group with a higher braking RFD, significant relationships were visible in both the propulsion (concentric) and braking (eccentric) phases of the CMJ, mainly during the second and third intervals of the sprint test. Conclusions: The noted observations may suggest that the relationship between strength and running performance is more complex than previously indicated, and that higher strength in the CMJ does not fully correlate with better sprinting. Therefore, it has been hypothesized that training aimed at generally increasing strength may not always be fully beneficial for running performance in football players and hence specific training guidelines are suggested for targeted strengthening of the required muscle performance characteristics. This may possibly contribute to reducing the unnecessary muscle overload during both training and matches, thereby preventing sports-related injuries.

Influence of different verbal cue types on countermovement jump performance in youth female athletes

Although external (EXT) verbal cues have been shown to improve jump performance, limited research has been conducted in youth athletes. Therefore, the purpose of this study was to investigate how different EXT verbal cue types influenced countermovement jump (CMJ) performance in youth athletes. Ten young trained female athletes (16.80 ± 0.60 years) performed the CMJ using four different EXT verbal cues including external-distal (DIST), external-proximal (PROX), analogy (ANA) and holistic (HOL) as well as a neutral cue (CON). Jump height, reactive strength index modified (RSIMOD), countermovement depth, jump time and force-time measures from eccentric and concentric CMJ subphases were measured. No significant differences between cue types were found for RSIMOD. ANA resulted in significantly higher jump height compared to CON ( g = 0.37). PROX significantly increased jump time ( g = 0.60), concentric time ( g = 0.47) and braking time ( g = 0.52), as well as significantly decreasing eccentric braking mean force ( g = 0.43) and eccentric braking rate of force development ( g = 0.59) compared to CON. Countermovement depth significantly increased when using PROX ( g = 0.60), HOL ( g = 0.46) and ANA ( g = 0.51) compared to CON. These results suggest that compared to a neutral cue, EXT verbal cues result in similar CMJ performance in trained youth athletes. However, PROX verbal cues appear to result in reduced performance in many CMJ force-time measures.

Index of braking behaviour in two dimensions within risk perception

Time To Collision (TTC) and other physical indices are widely used to predict drivers' braking behaviour. However, these indices often overlook the psychological aspects of how drivers perceive risk. Moreover, such indices are predominantly one-dimensional and do not account for the shared space, where vehicles can move in two dimensions. In this study, we introduce an index designed to predict drivers' braking behaviour in the shared space, taking into account the drivers' risk perception. In Experiment 1, a functional equation was derived to estimate the probability that drivers would brake in a given situation. The results confirmed that the index provides an adequate reflection of drivers' risk perception. In Experiment 2, the braking rate estimated with the index provided a better fit to a third-person risk evaluation when compared to other physical indices.

Effects of a Strength and Conditioning Offseason Program on Countermovement Jump Ground Reaction Forces in Division I American Football Players.

Gillen, ZM, Burch, RF, Saucier, DN, Strawderman, L, Luczak, T, Piroli, A, Petway, AJ, and Rath, T. Effects of a strength and conditioning offseason program on countermovement jump ground reaction forces in Division I American football players. J Strength Cond Res 38(3): e86-e95, 2024-The purpose of this study was to examine the effects of a 10-week strength and conditioning offseason program on the ground reaction forces (GRFs) of American football players during single-leg and double-leg countermovement jumps (SLJ and CMJ, respectively). Each subject visited the laboratory twice, once for preoffseason and once for postoffseason testing. During each visit, subjects performed CMJs and SLJs for each leg. Ground reaction forces were collected by force plates to quantify unweighting, braking, propulsive, and performance metrics for each jump. In addition, an efficiency index was calculated for each jump to examine changes in vertical jump efficiency. Dependent samples t tests compared all CMJ metrics. Two-way repeated measures analyses of variance (leg × time) compared all SLJ metrics. An alpha level of p ≤ 0.05 was considered statistically significant. For the CMJ, propulsive phase duration decreased due to the program ( p = 0.007), whereas peak braking power, peak propulsive power, mean propulsive force, and jump height increased ( p ≤ 0.012). For the SLJ, peak braking power, force at the low position, braking rate of force development, eccentric force, peak propulsive power, mean propulsive force, and jump height increased in both legs ( p ≤ 0.044). The efficiency index increased for the CMJ and the SLJ for both legs ( p ≤ 0.016). This study demonstrated that SLJ and CMJ vertical jump performance significantly increases in as few as 10 weeks of offseason strength and conditioning. Strength and conditioning programming may effectively increase vertical jump performance, as assessed by GRFs, which can be used as a simple indicator regarding changes in athletic performance.

Vertical Jump Neuromuscular Performance Characteristics Determining On-Court Contribution in Male and Female NCAA Division 1 Basketball Players.

While various quantifiable physical attributes have been found to contribute to athletes' performance, there is a lack of scientific literature focused on examining how they relate to success during competition performance. The aim of this study was to investigate different countermovement jump (CMJ)-derived force-time characteristics and their utility in distinguishing high from low performers within a measure of on-court contribution (i.e., minutes per game played). Twenty-nine collegiate athletes (n = 15 males and n = 14 females) volunteered to participate in this investigation and performed CMJs on dual force plates sampling at 1000 Hz, weekly over the course of their basketball season. The athletes' average of their three best test-days across the season was used for further analysis. To identify their on-court contribution, athletes were divided into groups with high and low minutes per game, based on a median-split analysis. The findings suggest that at the overall group level (i.e., both genders), the modified reactive strength index (mRSI) and braking rate of force development (RFD) revealed the greatest between-group magnitudes of difference, with athletes playing more minutes per game showing greater performance. At the team-specific level, the braking RFD, average braking velocity, and mRSI were shown to be the greatest differentiators between groups for the men's team. The women's high-minutes group displayed greater magnitudes of mRSI and jump height. By identifying the neuromuscular qualities seen in top performers within their respective populations, the attributed physical performance underpinning these qualities may be identified, providing practitioners with insights into physical performance qualities and training methodologies that have the potential to influence basketball performance.

Comparison of Force-Time Metrics Between Countermovement Vertical Jump With and Without an Arm Swing in Professional Male Basketball Players

With technological developments over the last decade, a wide range of countermovement vertical jump (CMJ) force-time metrics can be derived from commercially available portable force plate systems. However, it should be noted that how the test is performed can have a substantial impact on the outcome of the assessment. Thus, the purpose of the present study was to determine differences in biomechanical variables between CMJ with and without an arm swing in a cohort of elite athletes. Ten professional male basketball players volunteered to participate in the present study. Following a standardized warm-up procedure, athletes stepped on a uni-axial force plate sampling at 1000 Hz and performed three CMJ without arm swing (i.e., hands on the hips) followed by three CMJ with an arm swing (i.e., arms positioned slightly in the front of the body with elbows flexed at a 90-degree angle). To minimize the possible influence of fatigue, each jump was separated by a 15-30 s rest interval. The findings of the present study indicate phase- specific differences in multiple force-time metrics between the two CMJ testing modalities. While having greater eccentric duration, CMJ with an arm swing had lower eccentric braking and deceleration rate of force development and lower eccentric peak force when compared to CMJ without an arm swing. During the concentric phase of the jump, concentric duration, impulse, peak velocity, and peak power were significantly greater in favor of CMJ with an arm swing. Also, despite longer contraction time, incorporating an arm swing resulted in greater vertical jump heights. Overall, these data describe the CMJ performance of professional male basketball players and provide helpful information for practitioners when designing assessment protocols to monitor athletes’ neuromuscular performance.

Analyzing the Impact of C-ITS Services on Driving Behavior: A Case Study of the Daejeon–Sejong C-ITS Pilot Project in South Korea

This paper analyzes the impact of C-ITS service on driving behavior, focusing on a pilot project in Daejeon–Sejong, South Korea. C-ITS, an advanced technology, enables bidirectional wireless communication between vehicles or infrastructure, allowing for real-time traffic data collection and dissemination. The study uses a unique analytical method, employing parallel processing techniques for variable extraction and a paired t-test to examine the short-term effects of C-ITS on driving behavior. Findings indicate a significant change in drivers’ behavior, particularly in average speed, hard braking rate, severe deceleration rate, speeding rate, and excessive speeding rate, towards safer trends after receiving C-ITS warning services. Reductions in hard braking and severe deceleration were immediate after C-ITS service initiation, while a decrease in excessive speeding was observed after four months. Further research is needed to identify other potential influencing variables and provide an unbiased evaluation of C-ITS effectiveness. The study’s implications highlight its role in promoting public acceptance of C-ITS-service-based cooperative autonomous driving strategies.

Force-plate derived predictors of lateral jump performance in NCAA Division-I men's basketball players.

A lateral jump assessment may provide unique benefits in sports such as basketball that require multidirectional performance optimization. This study aimed to examine selected force-plate derived metrics as predictors of lateral jump task distance in men's basketball players. Twenty-two NCAA Division-I men's basketball players (19.4 ± 1.3 years, 95.0 ± 12.5 kg, 196.5 ± 8.1 cm) each performed six single leg lateral jumps while standing on a force plate (1200 Hz, Kistler Instrument Corp). The lateral jump task involved the subject beginning by standing on the force plate and jumping sideways off one foot and then landing on the floor with the opposite foot. Three-dimensional ground reaction force curves were used to identify the eccentric and concentric phases of the jump and variables were computed each from the lateral (y), vertical (z), and resultant (r) force traces. Peak ground reaction force (pGRF), ground reaction force angle (θr), eccentric braking rate of force development (ECC-RFD), average concentric force (CON-AVG), total jump duration, eccentric phase duration, and eccentric to total time ratio were evaluated for predictive ability. Three regression models were able to significantly (p<0.05) predict jump distance: (1) pGRFy, pGRFz, and θr (p<0.001, R2 = 0.273), (2) Relative pGRFy, Relative pGRFz, and θr ((p<0.001, R2 = 0.214), and (3) Relative CON-AVGy and Relative pGRFr (p<0.001, R2 = 0.552). While several force plate-derived metrics were identified as significant predictors, a model with Relative CON-AVGy and Relative pGRFr explained a greater variability in performance (R2 = 0.55) compared to the other variables which were low, yet also significant. These results suggest that lateral ground reaction forces can be used to evaluate lateral jump performance with the use of three-dimensional force plates. The identified predictors can be used as a starting point for performance monitoring, as basketball training interventions can be directed at specific improvements in the identified metrics.

Countermovement Jump Performance and Team Membership of Youth Female and Male Ice Hockey Players

This study compared the CMJ performance of two teams of young male ice hockey players and two teams of female ice hockey players of different levels of competition and examined whether a specific CMJ variable could predict Prep or Varsity team membership and thus be used as part of the talent identification process for ice hockey. A retrospective analysis of six CMJ variables collected via force platforms was conducted. Independent samples t-tests were used to compare the means of the six CMJ variables between the male teams and female teams and a logistic regression analysis was performed to compare team membership to Prep or Varsity teams with the specific CMJ variables. Significant differences (p &lt; 0.05) were found between Prep and Varsity male players in four CMJ variables, all in favor of the Varsity group: mRSI (p = 0.016, ES = -0.860), peak propulsive power (p = 0.022, ES = -0.811), time to take-off (p = 0.005, ES = 1.008), and braking rate of force development (p = 0.005, ES = -1.025). For the female players, only countermovement depth was significantly different (p = 0.030, ES = 0.841) between Prep and Varsity teams, in favor of the Varsity group. Following the logistic regression analysis, only countermovement depth (Wald's p-value = 0.011) could predict team membership to the Prep or Varsity group for the girls while no CMJ variables could significantly predict team membership to the Prep or Varsity teams for the boys. Results from this study suggest that other CMJ kinetic variables should be used when comparing CMJ performance between athletes rather than only using jump height. In addition, countermovement depth can be used by coaches of female ice hockey players to predict team membership.

A Study on the Entire Take-Over Process-Based Emergency Obstacle Avoidance Behavior.

Nowadays, conditional automated driving vehicles still need drivers to take-over in the scenarios such as emergency hazard events or driving environments beyond the system's control. This study aimed to explore the changing trend of the drivers' takeover behavior under the influence of traffic density and take-over budget time for the entire take-over process in emergency obstacle avoidance scenarios. In the driving simulator, a 2 × 2 factorial design was adopted, including two traffic densities (high density and low density) and two kinds of take-over budget time (3 s and 5 s). A total of 40 drivers were recruited, and each driver was required to complete four simulation experiments. The driver's take-over process was divided into three phases, including the reaction phase, control phase, and recovery phase. Time parameters, dynamics parameters, and operation parameters were collected for each take-over phase in different obstacle avoidance scenarios. This study analyzed the variability of traffic density and take-over budget time with take-over time, lateral behavior, and longitudinal behavior. The results showed that in the reaction phase, the driver's reaction time became shorter as the scenario urgency increased. In the control phase, the steering wheel reversal rate, lateral deviation rate, braking rate, average speed, and takeover time were significantly different at different urgency levels. In the recovery phase, the average speed, accelerating rate, and take-over time differed significantly at different urgency levels. For the entire take-over process, the entire take-over time increased with the increase in urgency. The lateral take-over behavior tended to be aggressive first and then became defensive, and the longitudinal take-over behavior was defensive with the increase in urgency. The findings will provide theoretical and methodological support for the improvement of take-over behavior assistance in emergency take-over scenarios. It will also be helpful to optimize the human-machine interaction system.

Driver behavior indices from large-scale fleet telematics data as surrogate safety measures

Large-scale telematics data enable a high-resolution inference of road network’s safety conditions and driver behavior. Although many researchers have investigated how to define meaningful safety surrogates and crash predictors from telematics, no comprehensive study analyzes the driver behavior derived from large-scale telematics data and relates them to crash data and the road networks in metropolitan cities. This study extracts driver behavior indices (e.g., speed, speed variation, hard braking rate, and hard acceleration rate) from large-scale telematics data, collected from 4000 vehicles in New York City five boroughs. These indices are compared to collision frequencies and collision rates at the street level. Moderate correlations were found between the safety surrogate measures and collision rates, summarized as follows: (i) When normalizing crash frequencies with traffic volume, using a traffic AADT model, safety-critical regions almost remain the same. (ii) The correlation magnitude of hard braking and hard acceleration varies by road types: hard braking clusters are more indicative of higher collision rates on highways, whereas hard acceleration is a stronger hazard indicator on non-highway urban roads. (iii) Locations with higher travel times coincide with locations of high crash incidence on non-highway roads. (iv) However, speeding on highways is indicative of collision risks. After establishing the spatial correlation between the driver behavior indices and crash data, two prototype safety metrics are proposed: speed corridor maps and hard braking and hard acceleration hot-spots. Overall, this paper shows that data-driven network screening enabled by telematics has great potential to advance our understanding of road safety assessment.

Unsupervised Clustering Techniques Identify Movement Strategies in the Countermovement Jump Associated With Musculoskeletal Injury Risk During US Marine Corps Officer Candidates School.

Musculoskeletal injuries (MSKI) are a significant burden on the military healthcare system. Movement strategies, genetics, and fitness level have been identified as potential contributors to MSKI risk. Screening measures associated with MSKI risk are emerging, including novel technologies, such as markerless motion capture (mMoCap) and force plates (FP) and allow for field expedient measures in dynamic military settings. The aim of the current study was to evaluate movement strategies (i.e., describe variables) of the countermovement jump (CMJ) in Marine officer candidates (MOCs) via mMoCap and FP technology by clustering variables to create distinct movement strategies associated with MSKI sustained during Officer Candidates School (OCS). 728 MOCs were tested and 668 MOCs (Male MOCs = 547, Female MOCs = 121) were used for analysis. MOCs performed 3 maximal CMJs in a mMoCap space with FP embedded into the system. De-identified MSKI data was acquired from internal OCS reports for those who presented to the OCS Physical Therapy department for MSKI treatment during the 10 weeks of OCS training. Three distinct clusters were formed with variables relating to CMJ kinetics and kinematics from the mMoCap and FPs. Proportions of MOCs with a lower extremity and torso MSKI across clusters were significantly different (p < 0.001), with the high-risk cluster having the highest proportions (30.5%), followed by moderate-risk cluster (22.5%) and low-risk cluster (13.8%). Kinetics, including braking rate of force development (BRFD), braking net impulse and propulsive net impulse, were higher in low-risk cluster compared to the high-risk cluster (p < 0.001). Lesser degrees of flexion and shorter CMJ phase durations (braking phase and propulsive phase) were observed in low-risk cluster compared to both moderate-risk and high-risk clusters. Male MOCs were distributed equally across clusters while female MOCs were primarily distributed in the high-risk cluster. Movement strategies (i.e., clusters), as quantified by mMoCap and FPs, were successfully described with MOCs MSKI risk proportions between clusters. These results provide actionable thresholds of key performance indicators for practitioners to use for screening measures in classifying greater MSKI risk. These tools may add value in creating modifiable strength and conditioning training programs before or during military training.

Volleyball Competition on Consecutive Days Modifies Jump Kinetics but Not Height.

In volleyball, jump execution is critical for the match outcome. Game-play-related neuromuscular impairments may manifest as decreased jump height (JH) or increased jump total duration, both of which are pivotal for performance. To investigate changes in JH and kinetics with game play, the authors conducted a prospective exploratory analysis using minimal-effect testing (MET) and equivalence testing with the 2 one-sided tests procedure, univariate, and bivariate functional principal component analysis, respectively. Twelve male varsity athletes completed 3-set matches on 2 consecutive days. Countermovement jumps were performed on a force platform immediately prematch and postmatch on days 1 and 2 and once on days 3 and 4. Across sessions, JH was equivalent (P < .022, equivalence test), while total duration reported inconclusive changes (P > .227). After match 2, MET indicated that relative force at zero velocity (P = .036) decreased, while braking duration (P = .040) and time to peak force (P = .048) increased compared with baseline. With the first and second functional principal components, these alterations, together with decreased relative braking rate of force development (P = .092), were already evident after match 1. On day 4, MET indicated that relative peak force (P = .049), relative force at zero velocity (P = .023), and relative braking rate of force development (P = .021) decreased, whereas braking duration (P = .025) increased from baseline. Impairments in jump kinetics were evident from variables related to the countermovement-jump braking phase, while JH was equivalent. In addition to these experimental findings, the present research provides information for the choice of sample size and smallest effect size of interest when using MET and 1- and 2-dimensional analyses for countermovement-jump height and kinetics.

About Braking of Wheeled Vehicle Equipped with Automated Brake Control System

The paper proposes a method for determining a vehicle stopping distance based on a braking rate and a coefficient of using an adhesion force by an automated control system for regulating a braking force on the example of a multi-axle vehicle. The aim of the study is to calculate parameters of the braking efficiency of a multi-axle wheeled vehicle equipped with an automated braking force control system based on the adhesion between a tire and a supporting surface. A peculiarity of the considered method is the use of the calculated braking coefficient of the vehicle and the coefficient of use of adhesion forces during the operation of automated system for regulating the braking force. The presence of new mathematical relationships between the position of the coordinate of the vehicle’s gravity center, realized by the clutches of its wheels, and the braking coefficient of the vehicle makes it possible to simulate the change in the deceleration of a wheeled vehicle in various braking modes of its motion. The terms describing the interaction of an elastic tire with a supporting surface in the braking mode of a wheeled vehicle have been substantiated. Equations are written that permit to calculate: a position of the coordinate of gravity center of a multi-axle wheeled vehicle relative to its front and rear axles; a braking coefficient value of a multi-axle wheeled vehicle based on the coordinates of the position of its gravity center, clutches that are realized between its tires and a supporting surface; load distribution between the respective front and rear axles of the vehicle. To calculate the stopping distance of a wheeled vehicle, it is proposed to take a coefficient value of use of the adhesion force equal to 0.83, regardless of the change in weather and climatic conditions in which the vehicle is operated (a calculation error under an accepted assumption is not more than 5 %). In a graphical form, a design diagram of the coordinate position of a gravity center of a multi-axle wheeled vehicle is presented, which gives a general idea about the redistribution of masses between front and rear axles of the vehicle. Scientific publications on the change in the value of the realized adhesion between the tire and the supporting surface in the braking mode of the automobile wheel under various factors have been analyzed in the paper. The proposed concept for determining parameters of the braking efficiency of a multi-axle wheeled vehicle clarifies some provisions in the theory of vehicle motion, in particular, it allows to apply the calculated method for determining the deceleration of a vehicle in the problem of increasing vertical loads on the axles of a multi-axle wheeled vehicle in the braking mode. The given method for calculating coefficients of weight distribution between adjacent front or rear axles of a multi-axle wheeled vehicle increases an accuracy of determining the amount of deceleration of the vehicle by the calculation method.

Evaluation of the PCC slabs of the bus corridors of Anapolis according to its extension

The Brazilian law N° 12.587/12 on urban mobility, currently in effect, aims to ensure the improvement of accessibility, and the trafficability of people and cargo in cities, as well as integrate transport modes, and study mechanisms for infrastructure management. Cities with a population of more than 20,000 had to create their urban mobility plans, according to the requirements of the Ministry of the City. The objective of the plan is to conceive projects that aim to mitigate operational and functional problems in the transportation network within the municipalities. One of these cities that is creating a mobility plan is Anápolis-GO, where its plan includes the implementation of bus lanes on the main avenues of the municipality. In these corridors, there was the substitution of the flexible pavement by slabs of PCC (Portland cement concrete), at the boarding and alighting points, due to the sudden braking events and occasional acceleration. Given this scenario, the study aimed to analyze the stopping distance at these locations, as a function of road speed and braking rate, to assess whether the length of these slabs would be sufficient to what was proposed. In addition, it was sought to monitor the pavement against the performance of the PCC slabs, given the incident loads of braking and acceleration, as well as the performance of the flexible pavement, predicting the possible consequences and/or pathologies that may occur due to the operation, since the existing traffic in the corridors should be compatible with that of a high-speed road.

Energy-efficient train control using nonlinear bounded regenerative braking

Energy-efficient train control (EETC) has been studied a lot over the last decades, because it contributes to cost savings and reduction of CO2 emissions. The aim of EETC is to minimize total traction energy consumption of a train run given the running time in the timetable. Most research is focused to apply mechanical braking on this problem. However, current trains are able to use regenerative braking, which leads to another optimal driving strategy compared to mechanical braking. Research on EETC with a realistic nonlinear bounded model for regenerative braking or a combination between regenerative and mechanical braking is limited. The aim of this paper is to compare the difference between the EETC with regenerative and/or mechanical braking. First, we derive the optimal control structure for the problems with different braking combinations. Second, we apply the pseudospectral method on different scenarios where we investigate the effect of varying speed limits and gradients on the different driving strategies. Results indicate that compared to pure mechanical braking, combined regenerative and mechanical braking leads to a driving strategy with higher energy savings, a lower optimal cruising speed, a shorter coasting phase and a higher speed at the beginning of the braking phase. In addition, a nonlinear bounded regenerative braking curve leads to a different driving strategy compared to a constant braking rate that is commonly used in literature. We show that regenerative braking at a constant braking rate overestimates the total energy savings.

Modification in Braking Technology of Ships

This paper aims to draw people’s attention towards one of the major cause of accidents at sea, its impact and the methods we can adopt to reduce the chances of accidents considerably. The paper finds slow braking rate as the key cause of maximum accidents and suggests two systems designed to increase the deceleration rate of the ships. A detailed explanation about the working and the setting up of our proposed systems ECDS (Emergency Cargo Drop Stop) and EBP (Emergency Braking Propellers) has been provided in the course of the paper. It also draws a comparison between the pros and the cons of these systems. The study’s conclusion indicates the significance of these two systems and how it paves the way for further study on the application and benefits of these systems.

Three-dimensional, Isotonic Comparison Of Dominant And Non-dominant Upper Limb Force Production

Athletes and coaches have traditionally relied on isokinetic devices to compare dominant and non-dominant strength ratios; the information provided is limited in its application. Recent technology permits strength and power comparisons in an isotonic, three-dimensional environment that is more compatible with the load profiles experienced during sport performance. PURPOSE: To determine the difference in power between dominant and non-dominant arms across various loads, motions, and planes. METHODS: 206 subjects performed 3,727 unilateral sets of 10 repetitions in upper-extremity movements on Proteus (Proteus Motion, USA). Loads were applied through magnetic resistance and ranged from 5-25 lbs; they were divided between dominant (n=1,975) and non-dominant (n=1,747) arms. The performance variables were explosiveness (peak force development rate), peak power, and braking (rate of deceleration). Descriptive statistics characterized mean performances. Linear regression models predicted the effect of arm dominance on performance parameters, holding the load and exercise constant. RESULTS: Across all sets, explosiveness was 852.61 ± 629.46 watts/sec, peak power was 206.40 ± 112.42 watts, and braking was 1059.90 ± 766.63 watts/sec. Dominant and non-dominant arms were different in explosiveness (p=0.005), peak power (p=0.041), and braking (p=0.035). With confounding variables held constant, linear regression found use of the non-dominant arm to predict a 10-watt decrease in peak power (R2=0.691; p<0.001), a 46-watt/sec decrease in mean explosiveness (R2=0.553; p=0.001), and a 65-watt/sec decrease in braking (R2=0.668; p<0.001). CONCLUSIONS: In an athletic population, the independent use of dominant and non-dominant limbs is often critical to success. It is important to know the non-dominant performance deficit in a setting applicable to sport performance. This information can contribute to optimal training protocols and return-to-play testing batteries.

Alfvén-wave-driven Magnetic Rotator Winds from Low-mass Stars. I. Rotation Dependences of Magnetic Braking and Mass-loss Rate

Abstract Observations of stellar rotation show that low-mass stars lose angular momentum during the main sequence. We simulate the winds of sunlike stars with a range of rotation rates, covering the fast and slow magneto-rotator regimes, including the transition between the two. We generalize an Alfvén-wave-driven solar wind model that builds on previous works by including the magneto-centrifugal force explicitly. In this model, the surface-averaged open magnetic flux is assumed to scale as , where and Ro are the surface open-flux filling factor and Rossby number, respectively. We find that, (1) the angular-momentum loss rate (torque) of the wind is described as , yielding a spin-down law . (2) The mass-loss rate saturates at , due to the strong reflection and dissipation of Alfvén waves in the chromosphere. This indicates that the chromosphere has a strong impact in connecting the stellar surface and stellar wind. Meanwhile, the wind ram pressure scales as , which is able to explain the lower envelope of the observed stellar winds by Wood et al. (3) The location of the Alfvén radius is shown to scale in a way that is consistent with one-dimensional analytic theory. Additionally, the precise scaling of the Alfvén radius matches previous works, which used thermally driven winds. Our results suggest that the Alfvén-wave-driven magnetic rotator wind plays a dominant role in the stellar spin-down during the main sequence.

Comparison of Calf Only External Pneumatic Compression and Compression Socks on Performance Characteristics in Counter Movement Jump

PURPOSETo identify the recovery effect of calf only external pneumatic compression (EPC) compared to a commercially available compression sock (CS) on markers of jump performance following a muscle damaging protocol.METHODS19 healthy active male participants (23.5 ± 3.2 yr, 181.3 ± 9.1 cm, 88.1 ± 10.1 kg) completed four testing sessions (pre, post, 24 hr, 48 hr) consisting of: visual analog scales (VAS) to assess perceived soreness and fatigue, three counter movement jumps (CMJ) and three squat jumps (SJ) via force plates (Hawkin Dynamics). After participants finished pre assessments they completed 100 drop jumps (0.6 m) followed by a randomized 30 min single treatment session of either EPC (110 mmHg) n=9 or CS (20–30 mmHg) n=10.RESULTSNo differences were found between groups for body composition (18.7 ± 2.8 % Body Fat, 61.8 ± 8.8 kg Fat Free Mass, 14.7 ± 2.8 kg Fat Mass). VAS soreness linearly increased regardless of group (p&lt;0.001). Within EPC and CS 24 hr soreness was higher than pre, post, 30 min post (p&lt;0.05); 48 hr was higher than pre and 30 min post (p&lt;0.05); and post was higher than pre (p&lt;0.05). Additionally, CS soreness at 48 hr was higher than post (p&lt;0.05). VAS fatigue changed over time regardless of group (p&lt;0.001). Within EPC post fatigue was higher than pre, 30 min post, 24 hr, and 48 hr (p&lt;0.05); 24 hr was higher than pre, post, and 48 hr (p&lt;0.05); 30 min post and 48 hr was higher than pre and post (p&lt;0.05). CS post fatigue was higher than pre and 30 min post (p&lt;0.05); 30 min post was higher than pre (p&lt;0.05); and 24 and 48 hr were higher than pre (p&lt;0.05). VAS fatigue was trending (p=0.055) towards being higher in CS compared to EPC regardless of time. For CMJ, CS peak braking force and relative peak braking force linearly declined over time (p&lt;0.001), and peak braking force was highest at pre compared to post, 24 hr and 48 hr (p&lt;0.05). For CMJ, CS relative peak braking force was highest at pre compared to post, 24 hr, 48 hr (p&lt;0.01) and post was higher than 48 hr (p=0.025). For CMJ, CS braking phase linearly increased over time (p&lt;0.001), and was higher at 24 hr and 48 hr compared to pre and post (p&lt;0.05). For CMJ, CS braking rate of force development (RFD) linearly declined over time (p&lt;0.001), and was highest at pre compared to 24 hr and 48 hr (p&lt;0.01). No differences in performance variables were found for SJ.CONCLUSIONIt appears that the drop jump protocol was successful at eliciting muscle soreness and fatigue in our participants. Additionally, these aforementioned variables seemed to effect participants in the CS group because they were unable to maintain braking force and peak braking RFD, and took longer to complete the braking phase. These results were not seen in the EPC group as they were able to maintain consistent performance in these measures. Therefore, it appears a single 30 min calf only EPC treatment may help maintain consistent breaking force and braking RFD within a CMJ when following strenuous or damaging exercise bouts.Support or Funding InformationFunding was provided to P.W.M by MAS Holdings (Colombo, Sri Lanka).