Can Countermovement Jump Neuromuscular Performance Qualities Differentiate Maximal Horizontal Deceleration Ability in Team Sport Athletes?

This investigation aimed to determine the countermovement jump (CMJ) neuromuscular performance (NMP) qualities that differentiate between athletes with high or low horizontal deceleration ability. Twenty-seven male university team sport athletes performed a CMJ on vertical axis force plates and a maximal horizontal deceleration following a 20 m maximal horizontal sprint acceleration. The instantaneous velocity throughout the maximal horizontal deceleration test was measured using a radar device. The deceleration ability was evaluated using the average deceleration (HDEC, m·s−2) and change in momentum—referred to as the horizontal braking impulse (HBI, N·s·kg−1). Participants were dichotomised into high and low HDEC and HBI according to a median-split analysis, and CMJ variables calculated for the overall eccentric, eccentric-deceleration and concentric phases. When horizontal deceleration ability was defined by HDEC, the CMJ concentric (effect size (ES) = 0.95) and eccentric (ES = 0.72) peak forces were the variables with the largest difference between groups. However, when defined using HBI, the largest difference was the concentric (ES = 1.15) and eccentric (ES = −1.00) peak velocities. Only the concentric mean power was significantly different between the high and low groups for both HDEC (ES = 0.85) and HBI (ES = 0.96). These findings show that specific eccentric and concentric NMP qualities may underpin the horizontal deceleration abilities characterised by HDEC and HBI. Specific NMP training interventions may be beneficial to target improvements in either of these measures of horizontal deceleration abilities

A low-volume Nordic hamstring curl programme improves change of direction ability, despite no architectural, strength or speed adaptations in elite youth soccer players:A low-volume Nordic hamstring curl programme improves change of direction ability, despite no architectural, strength or speed adaptations in elite youth soccer players

Nordic hamstring curls (NHC) are a commonly used injury intervention method in amateur team sports. Seventeen elite male academy soccer players performed an 8-week low volume NHC programme. Pre-post intervention measures of isokinetic eccentric knee flexor (KF) strength, linear speed, COD performance, hamstring muscle thickness, pennation angle and fascicle length were recorded. No significant main effects were observed for measures of isokinetic KF strength (P ≥ 0.19), linear sprint speed (P ≥ 0.47) or hamstring muscle architecture (P ≥ 0.30). However, significance was noted for improved COD performance (P < 0.01; mean difference, -0.06, p = 0.001, 95% CI = 0.03 to 0.09; d = 0.80), exceeding the minimal detectable difference (MDD = 0.05 s). A low-volume NHC intervention may contribute to significant improvements in COD ability, independent of no significant changes in eccentric KF strength, linear sprint speed or muscle architectural properties in elite youth soccer players

Towards GPU Utilization Prediction for Cloud Deep Learning

Understanding the GPU utilization of Deep Learning (DL) workloads is important for enhancing resource-efficiency and cost-benefit decision making for DL frameworks in the cloud. Current approaches to determine DL workload GPU utilization rely on online profiling within isolated GPU devices, and must be performed for every unique DL workload submission resulting in resource under-utilization and reduced service availability. In this paper, we propose a prediction engine to proactively determine the GPU utilization of heterogeneous DL workloads without the need for in-depth or isolated online profiling. We demonstrate that it is possible to predict DL workload GPU utilization via extracting information from its model computation graph. Our experiments show that the prediction engine achieves an RMSLE of 0.154, and can be exploited by DL schedulers to achieve up to 61.5% improvement to GPU cluster utilization

Harper, D.J., Hobbs, S.J. & Moore, J. (2011). The ten to five repeated jump test: A new test for evaluation of lower body reactive strength. BASES 2011 Annual Student Conference. Integrations and Innovations: An Interdisciplinary Approach to Sport and Exercise Science. 2011 April 12-13; Chester, United Kingdom. Chester,: The University of Chester; 2011.

Reactive strength is generating sharp interest with research and applied practitioners as a measure to monitor an individual’s ability to change quickly (<0.25s) from an eccentric to a concentric contraction (Young, 1995: New Stud Athletics, 10, 88-96). In order to further replicate the rebound qualities exhibited in many sporting activities Lloyd et al. (2009: Journal of Sports Sciences, 27, 1565-1573) used a maximal bi-lateral hopping test performed over five repeated repetitions. However, the ability of this test to detect training induced changes in performance was poor. Analysis of covariance (CV) for the average height obtained was 15%. The authors acknowledged that this greater variability was likely due to difficulties in postural control. The purpose of this study therefore was to refine and develop a methodology for assessment of lower body reactive strength, examine it for test-retest reliability, determine the internal consistency of the test across five trials and, in addition, validate measures using contact mat against those acquired from ground-fixed force plate measures. Sixteen male Super League rugby league players (age, 19.7 + 0.8 years; body mass 88.5 + 12.0 kg; height 177.3 + 6.1m; mean + s) volunteered to participate in the reliability study. An additional group of seven male college academy level rugby league players (age 17.4 + 0.6 years; body mass 81.6 + 16.3 kg) participated in the internal consistency and validity study. All jumps were performed on a mobile contact mat (Smart-jump, Fusion Sport, Australia) with instantaneous feedback on contact time (CT), flight time (FT), peak power output (PPO), impulse (IMP) and the reactive strength index (RSI) collected and displayed via a hand-held PDA (iPAQ, Hewlett Packard, USA). For the validity and internal consistency study the mobile contact mat was positioned directly over a 400 x 600 mm ground-fixed force plate sampling at 500 Hz (Kistler Instruments Ltd., Alton, Hampshire, UK; Model 9281CA). The ten to five repeated jump test (RJT) involved participants performing optimal vertical rebounds (i.e. maximal elevation at each jump) with minimal ground contact (<0.25s) performed for a series of eleven jumps. Participants were instructed to keep their hands on the hips to ensure no contribution from the arms. Further instructions were given to (a) “minimize ground contact time”, (b) “maximize jump height”, (c) “imagine the ground as a hot surface”, and (d) “legs like a stiff spring” (Flanaghan & Comyns, 2008, Strength and Conditioning Journal, 30, 32-38). From the eleven jumps that were recorded the first jump was discarded from the analysis since this did not involve a fast stretch-shortening cycle. From the remaining ten jumps the five jumps with greatest height exhibiting ground contact of less than 0.25s were used for further analysed. The height of these five jumps was then added together to provide a repeated reactive strength score. For the validity study participants performed five trials and for the reliability study two trials were performed on each testing session which were separated by one week. All participants in both studies were given a minimum of one minutes rest between successive trials. Pearson’s correlation coefficient revealed a significant (r=0.897; P=<0.01) level of agreement between the mobile contact mat and force plate for ground contact time. There was a 14.25% change in the mean height from trial 1 to trial 5, however after an 11.55% change between trial 1 and 2 the change between trial 2 to 5 varied from only 0.33 to 1.25%. The average CV across all seven participants in the validity study was 9%. The test-retest reliability results displayed a significant (r=0.782; P=<0.01) relationship between trial 1 and 2. The main finding of the present study was that the CV of the ten to five RJT was found to be 9%. The higher levels of sensitivity in the present protocol compared to Lloyd et al. (2009) can be attributed to the elimination of the lowest 5 jump heights that are likely to have been a result of deficiencies in postural control. Another important finding was that the ten to five RJT was found to gain consistent scores after just 2 trials. Furthermore, the mobile contact mat used in the present study was shown to have a high level of criterion validity in agreement with Lloyd et al. (2009). Consequently, for coaches working with large groups of athletes the ten to five RJT can provide a quick and reliable means of monitoring individual progress and evaluating the success of interventions aimed at developing the reactive strength capabilities of their athletes

Harper, D.J., Hobbs, S.J. & Moore, J. (2011). Reactive strength vs power: The best predictor of speed in elite U’20 Super League Rugby Players. 16th Annual Congress of European College of Sports Science. 2011 July 6-9; Liverpool, United Kingdom.

Introduction. There is a paucity of research that as investigated what strength characteristics best transfer to the high intensity sprint movements performed by elite rugby-league players (Baker & Nance, 1999; Cronin & Hansen, 2005; Harris et al., 2008). Therefore, the aim of this study was to identify relationships between reactive strength and power and measures of speed, change of direction (COD) ability and reactive agility in elite rugby-league players. Method Sixteen Super League rugby-league players (age, 19.7 + 0.8 years, weight 88.5 + 12.0 kg, height 177.3 + 6.1m) participated in the study. Tests included: sprint time (5-m, 10-m, 20-m and 30-m); COD ability (L-run); reactive agility (cut test); loaded (25 and 50% body weight) and unloaded vertical jump (VJ); squat jump (SJ) and reactive strength via a vertical rebound jump (10 to 5 repeated jump test) performed over a series of 10 repetitions with ground contact time of less than 0.25s. All tests were measured using Smart-speed/jump (Fusion Sport, Australia). Results The 5-m, 10-m, 20-m and 30-m sprint times were all significantly correlated (r=0.80 to 0.95). Significant relationships (r=-0.54) were found with 5-m speed and unloaded VJ height. In addition a significant relationship (r=-0.54) was found between 30-m speed and loaded VJ (50%BW). The reactive agility (cut test) time had a significant relationship with SJ height (r= 0.58). The single best predictor of change of direction speed was SJ height (r=-0.75). Squat jump height had significant relationships with all VJ heights (r= 0.69 to 0.87). Reactive strength had moderate to large relationships (r=-0.34 to -0.51) with all sprint measures and a large relationship with COD speed (r=-0.49). Discussion Reactive strength had moderate to large relationships with all sprint distances, accounting for up to 26% of sprint performance. The lack of relationship between reactive strength and sprint performance however is not surprising. The running mechanics of rugby league players is characterised by a more slouched upper body posture with significant forward lean. Interestingly, it was the measures of concentric only (SJ) performance that resulted in the highest correlations with all speed measures. References Baker, D. G. & Nance, S. (1999). The relation between running speed and measures of strength and power in professional rugby league players. Journal of Strength & Cond. Res. 13, (3), 187-304. Cronin, J. B. & Hansen, K. R. (2005). Strength and power predictors of sports speed. Journal of Strength Cond

Validity of Velocity Measurements of a Motorized Resistance Device During Change of Direction

The aim of this study was to determine validity of velocity measurements of a motorized resistance device (MRD) during change of direction (CoD). Eight male (age: 22.1 ± 4.2 yrs; weight: 83.3 ± 17.1 kg; height: 181.6 ± 12.6 cm) and three female participants (age: 21.7 ± 1.5 yrs; mass: 69.7 ± 2.4 kg; height: 167.0 ± 3.6 cm) completed the modified 505 CoD test (m505) with turning off the left and right foot while exposed to external loads (3, 6, and 9 kg) provided by the MRD. Three-dimensional kinematic data were measured (200 Hz) for all tests using a full-body marker set with an additional marker placed on the pulley used to attach the carabiner (CAR) at the end of the line from the MRD to the participant. Average velocity of overall center of mass (COMvel), pelvis (COMpelvis_vel), and pulley (CARvel) was then calculated and compared to the velocity measured by MRD (MRDvel) in 0.5 s intervals 1.5 s before and after CoD. Average velocities from these intervals were then compared using correlational, Bland–Altman analysis, coefficient of variation (CV), and statistical parametric mapping (SPM). Mostly, excellent correlations were observed and ranged from 0.93 to 1.00, 0.53 to 1.00 and 0.93 to 1.00 for the 3, 6, and 9 kg load conditions, respectively. CV values ranged from 0.3 to 3.2%, 0.8 to 4.3%, and 1.5 to 7.7% for the CARvel, COMpelvis_vel, and COMvel comparisons, respectively. The biases for CARvel comparisons ranged from −0.027 to 0.05 m/s, −0.246 to 0.128 m/s and −0.486 to 0.082 m/s across all load conditions and time intervals for the CARvel, COMpelvis_vel, and COMvel comparisons, respectively. SPM analysis indicated significant differences between MRDvel and COMvel and COMpelvis_vel over short time periods during the CoD, but no difference between MRDvel and CARvel. The velocity measurements obtained by a MRD during a m505 test are valid as low biases, low CV’s, and high correlations are observed for the MRDvel to CARvel comparison. As single points of measurement (i.e., laser) has been proven useful to assess other athletic tasks (i.e., sprint running), the single point CARvel comparison is an appropriate comparison for validating MRDvel measurements during the m505 test

Brain Cells in the Avian ‘Prefrontal Cortex’ Code for Features of Slot-Machine-Like Gambling

Slot machines are the most common and addictive form of gambling. In the current study, we recorded from single neurons in the ‘prefrontal cortex’ of pigeons while they played a slot-machine-like task. We identified four categories of neurons that coded for different aspects of our slot-machine-like task. Reward-Proximity neurons showed a linear increase in activity as the opportunity for a reward drew near. I-Won neurons fired only when the fourth stimulus of a winning (four-of-a-kind) combination was displayed. I-Lost neurons changed their firing rate at the presentation of the first nonidentical stimulus, that is, when it was apparent that no reward was forthcoming. Finally, Near-Miss neurons also changed their activity the moment it was recognized that a reward was no longer available, but more importantly, the activity level was related to whether the trial contained one, two, or three identical stimuli prior to the display of the nonidentical stimulus. These findings not only add to recent neurophysiological research employing simulated gambling paradigms, but also add to research addressing the functional correspondence between the avian NCL and primate PFC

Reliability of phase-specific outcome measurements in change-of-direction tests using a motorized resistance device

This study aims to determine test-retest reliability of phase-specific information during initial acceleration, deceleration, and re-acceleration phases of different change-of-direction (CoD) tests using a motorized resistance device (MRD). A total of 21 participants (16 males and five females, with mean age of 22.3 ± 3.9 years, body mass of 75.2 ± 6.9 kg, height of 177.9 ± 6.8 cm) completed the modified 505 (m505), 10-0-5, and 15-0-5 CoD tests on four different test sessions while exposed to an external load (3 kg) provided by the MRD. Outcome variables included overall and phase-specific kinetic (force, power, and impulse) and kinematic (time, distance, velocity, and acceleration/deceleration) data during the initial acceleration, deceleration, and re-acceleration phases. The deceleration and re-acceleration phases were further divided into two subphases, namely, early and late subphases, using 50% of maximum velocity. Reliability was assessed using an intraclass correlation coefficient (ICC), coefficient of variation (CV), typical error (TE), and minimal detectable change (MDC). Good to excellent ICC values (>0.75) and acceptable (<10%) to good (<5%) CV values were observed for most outcome measurements. Specifically, 80.1% (822 out of 1,026) of all variables showed good or better relative reliability (i.e., ICC ≥ 0.75), while 97.0% (995 out of 1,026) of all variables showed acceptable or better absolute reliability (i.e., CV < 10%). In conclusion, the present study demonstrates that the MRD can obtain reliable phase-specific outcome measurements across different CoD tests, providing coaches and researchers with new opportunities to advance our understanding of CoD ability and inform more advanced CoD training prescriptions

Agility in Invasion Sports: Position Stand of the IUSCA

Agility is a complex skill that is influenced by several physical, technical and cognitive factors. In this position stand, we discuss agility as it relates to invasion sports such as the many football codes. An important concept when conceptualising agility is understanding how it is applied on the field or court. Agility is particularly important in contests between attackers and defenders. For example, an attacker needs to create space or separation from defenders, in order to evade or to maintain possession of the ball. Conversely, defenders may require agility to reduce time and space in relation to the attacker, thereby applying pressure with the intention of achieving a turnover of possession. The movements performed in an agility scenario are diverse, and may involve an isolated deceleration, or a range of actions to produce a lateral displacement of the body at various angles and speeds. To create novel insights into agility, the interactions between predators and prey are explored in the animal world and reveal that successful pursuit (like a defender) or escape (like an attacker) is influenced by the ability to accelerate and attain high speeds, decelerate, and manoeuvre with control at optimum speeds, as well as expressing perceptual and cognitive skills. A plethora of sports literature claiming to discuss agility actually refers to pre-planned change-of-direction (COD) movements, known as COD ability. There are several differences between agility and COD ability, which should be considered when testing and prescribing agility activities. The characteristics of different agility techniques are presented and discussed with consideration to performance and the risk of injury such as anterior cruciate ligament (ACL) rupture, with the aim of creating multiple movement solutions for the athlete. Due to the diversity of agility actions performed in invasion sports, physical development should include tissue strengthening as well as fast and slow stretch-shortening cycle exercises to cater for different speeds and angles of agility movements. The speed and accuracy of decision-making in agility contests (cognitive component) are determined by the athlete’s ability to anticipate opponent’s actions, visually scan the environment, recognise patterns of play, and predict movement strategies based on knowledge of situations. One versus one contests, small-sided games, and video perceptual training can enhance the cognitive component of agility. Finally, there is no single coaching strategy or method that should be used to develop agility. Instead, the appropriate methodology must fit the individual needs of athletes, and therefore a mixed multicomponent approach is needed as part of an agility framework. Training examples to develop agility are presented throughout this position statement