Reactive Strength Index Modified Is a Valid Measure of Explosiveness in Collegiate Female Volleyball Players

Kipp, K, Kiely, MT, and Geiser, CF. Reactive strength index modified is a valid measure of explosiveness in collegiate female volleyball players. J Strength Cond Res 30(5): 1341–1347, 2016—The purpose of this study was to investigate the validity of the reactive strength index modified (RSImod) as a measure of lower body explosiveness. Fifteen female, National Collegiate Athletic Association Division I volleyball players performed vertical countermovement jumps (CMJs) while standing on a force plate. Each player performed 3 CMJs. The vertical ground reaction forces collected during each jump were used to calculate jump height, time to take-off, time to peak force, peak force, peak rate of force development, and peak power; the latter 3 variables were all normalized to body mass. Reactive strength index modified was calculated as the ratio between jump height and time to take-off. All variables, except for jump height, were then entered a factor analysis, which reduced the input data into 2 factors: a force factor and a speed factor. Although RSImod loaded more strongly onto the force factor, further analysis showed that RSImod loaded positively onto both force and speed factors. Visual analysis of the Cartesian coordinates also showed that RSImod loaded into the quadrant of greater force and speed abilities. These results indicate that the construct of RSImod, as derived from CMJ force-time data, captures a combination of speed-force factors that can be interpreted as lower body explosiveness during the CMJ. Reactive strength index modified therefore seems to be a valid measure to study lower body explosiveness

Biomechanical Determinants of the Reactive Strength Index During Drop Jumps

The Reactive Strength Index (RSI) is often used to quantify drop-jump (DJ) performance; however, not much is known about its biomechanical determinants. The purpose of this study was to investigate the correlations between the RSI and several biomechanical variables calculated from DJ performed with different initial drop heights. Twelve male NCAA Division I basketball players performed DJs from drop heights of 30, 45, and 60 cm. Force plates were used to calculate DJ performance parameters (ie, DJ height, contact time, and RSI) and DJ biomechanical variables (ie, vertical stiffness and eccentric/concentric energetics). Regression analyses were used to assess the correlations between variables at each drop height, and ANOVAs were used to assess the differences of all variables across drop heights. Follow-up analyses used 2 neural networks to determine if DJ performance and biomechanical data could accurately classify DJ trials by drop-height condition. Vertical-stiffness values were significantly correlated with RSI at each height but did not change across drop heights. Surprisingly, the RSI and other DJ parameters also did not vary across drop height, which resulted in the inability of these variables to accurately classify DJ trials. Given that vertical stiffness did not change across drop height and was highly correlated with RSI at each height, the RSI appears to reflect biomechanical behavior related to vertical stiffness during DJ. However, the inability of the RSI to accurately classify drop-height condition questions the use of RSI profiles established from DJs from different heights

Multidimensional analysis of the microbial and genetic links in inflammatory bowel disease

Over 200 genes have been associated with IBD. Most of these are responsible for bacterial sensing and immune processing. Little is known about the dynamics of the gut microbiome over time, in the early Crohn's lesion and in mesenteric lymph nodes. Aims of the studies To detect differences in the IBD microbiome over time (longitudinal study), space (lymph node study) and in the early lesion (aphthous ulcers versus normal tissue). To use whole genome sequencing (WGS) to find a rare gene in a subset of IBD patients with PSC-IBD. Study 1: The role of inflammation in temporal shifts in the IBD mucosal microbiome. We studied the mucosal microbiome of patients who underwent multiple procedures over time (average 2.4 years between each procedure). We found significantly lower alpha diversity (within sample variation) in patients who had undergone previous abdominal surgery. There were no significant associations with antibiotics, smoking, IBD subtype, inflammation or medication class. Significantly, we found great changes in beta diversity (between-sample variation) in patients with active inflammation at both time-points. This suggests that inflammation is closely associated with shifts in the microbiome over time. Study 2: The microbiome of translocated bacterial populations in patients with and without IBD. We interrogated the mesenteric lymph nodes of patients (and controls) who had undergone intestinal resection, using the presence of bacterial RNA as a surrogate for viability. We found large numbers of viable bacteria present in patients with IBD and surgical controls. The bacterial populations were similar to those at the mucosal surface, however Escherichia/Shigella were significantly more abundant in lymph nodes compared with mucosal sites, which gives further evidence of involvement of these bacteria in IBD pathogenesis. Study 3: The microbiome of Crohn's disease aphthous ulcers. In this study, we compared the microbiome of the early Crohn's lesion with that of adjacent mucosa, and healthy controls. We found that the microbiome did not significantly differ, and that changes that had previously been associated with IBD were not present in the early Crohn's lesion. This was also true for the three patients with new-onset disease. This provides further evidence to the hypothesis that inflammation causes dysbiosis. A separate study demonstrated that the transcriptome of aphthous ulcers is very different to that of healthy mucosa and Peyers patches. Study 4: Whole genome sequencing in primary sclerosing cholangitis (PSC) and IBD. Genome-wide association studies (GWAS) have previously identified 22 genes associated with PSC. WGS has been performed before in PSC. This allows the discovery of rare mutations. We performed WGS on 10 patients with PSC/IBD and 16 of their parents, to identify rare alleles or novel mutations. We also analysed the 22 previously identified loci from GWAS. While we did not find any novel loci, we did find that our patient population had a higher-than-expected frequency of a PTPN2 mutation compared with the broader population (63% versus 38%, p=0.015), further implicating this gene. Overall summary of findings The dramatic shifts that have been consistently observed in the IBD microbiome correlate with the presence of ongoing inflammation. We have demonstrated that these changes do not appear to be present in the early Crohn's lesion. This implicates inflammation itself as the cause of these changes. The altered microbiome therefore may not be relevant in the causation of ongoing immune activation. Moreover, bacteria that are able to evade the initial immune defences appear to be very important in IBD. These findings may help to explain the tepid clinical response that treatments directed at altering the microbiome in IBD have had in obtaining and maintaining remission (antibiotics and faecal microbial transplant)

Competition Volume and Changes in Countermovement Jump Biomechanics and Motor Signatures in Female Collegiate Volleyball Players

Kipp, K, Kiely, M, and Geiser, C. Competition volume and changes in countermovement jump biomechanics and motor signatures in female collegiate volleyball players. J Strength Cond Res 35(4): 970–975, 2021—The purpose of this study was to investigate the relationship between competition volume and preseason to postseason changes in countermovement jump (CMJ) biomechanics and motor signatures in female collegiate volleyball players. Ten National Collegiate Athletic Association Division I female volleyball players performed CMJs on force plates before (PRE) and after (POST) their season. Countermovement jump height was calculated, and 4 discrete biomechanical variables (peak body-mass normalized force [PeakF], peak body-mass normalized rate of force development [PeakRFD], movement time [TIME], and the ratio between eccentric and total movement time [EccT:TIME]) were calculated. A factor analysis of the 4 biomechanical variables was used to identify CMJ motor signatures. The total number of sets played by each player was used to define total competition volume for the season. Correlation coefficients were used to investigate the associations between competition volume and changes in CMJ height, discrete biomechanical variables, and the components of the CMJ motor signature. The statistical analysis indicated that team-average jump height did not change over the course of the season. However, competition volume was negatively associated with changes in CMJ height, such that decreases in CMJ height over the course of the season occurred in players who played large numbers of sets. Although CMJ during POST testing was characterized by longer TIME and greater PeakRFD, CMJ motor signatures did not change and suggest that the female volleyball players in this study retained their preferred jumping strategy across the season. Given that decreases in CMJ height were most pronounced in players who played the most sets, and scored the most points during the season, future research may need to focus on player- or position-specific interventions that help players retain CMJ performance in the face of the competitive demands of a collegiate volleyball season

CHANGES IN PRINCIPAL COMPONENT STRUCTURE OF COUNTERMOVEMENT JUMPS AFTER A VOLLEYBALL SEASON

The purpose of this study was to investigate changes in the principal component structure of countermovement jumps (CMJ) in female volleyball players over the course of a competitive season. Eleven NCAA Division I female volleyball players performed CMJs on a force plate before and after a competitive season. Discrete biomechanical variables were extracted from the force-time records of all CMJs and entered into a factor analysis. The analysis yielded two factors that could account for the biomechanical structure of the CMJs: a temporal and a force factor. Although no differences in factor scores were identified between pre- and post-season testing sessions, sub-group analysis highlighted large individual changes in temporal and force factor scores

Mechanical Demands of the Hang Power Clean and Jump Shrug: A Joint-level Perspective

The purpose of this study was to investigate the joint- and load-dependent changes in the mechanical demands of the lower extremity joints during the hang power clean (HPC) and the jump shrug (JS). Fifteen male lacrosse players were recruited from an NCAA DI team, and completed three sets of the HPC and JS at 30%, 50%, and 70% of their HPC 1-Repetition Maximum (1-RM HPC) in a counterbalanced and randomized order. Motion analysis and force plate technology were used to calculate the positive work, propulsive phase duration, and peak concentric power at the hip, knee, and ankle joints. Separate three-way analysis of variances were used to determine the interaction and main effects of joint, load, and lift type on the three dependent variables. The results indicated that the mechanics during the HPC and JS exhibit joint-, load-, and lift-dependent behavior. When averaged across joints, the positive work during both lifts increased progressively with external load, but was greater during the JS at 30% and 50% of 1-RM HPC than during the HPC. The JS was also characterized by greater hip and knee work when averaged across loads. The joint-averaged propulsive phase duration was lower at 30% than at 50% and 70% of 1-RM HPC for both lifts. Furthermore, the load-averaged propulsive phase duration was greater for the hip than the knee and ankle joint. The jointaveraged peak concentric power was the greatest at 70% of 1-RM for the HPC and at 30% to 50% of 1-RM for the JS. In addition, the joint-averaged peak concentric power of the JS was greater than that of the HPC. Furthermore, the load-averaged peak knee and ankle concentric joint powers were greater during the execution of the JS than the HPC. However, the loadaveraged power of all joints differed only during the HPC, but was similar between the hip and knee joints for the JS. Collectively, these results indicate that compared to the HPC the JS is characterized by greater hip and knee positive joint work, and greater knee and ankle peak concentric joint power, especially if performed at 30 and 50% of 1-RM HPC. This study provides important novel information about the mechanical demands of two commonly used exercises and should be considered in the design of resistance training programs that aim to improve the explosiveness of the lower extremity joints

On Autonomous Agents in a Cyber Defence Environment

Autonomous Cyber Defence is required to respond to high-tempo cyber-attacks. To facilitate the research in this challenging area, we explore the utility of the autonomous cyber operation environments presented as part of the Cyber Autonomy Gym for Experimentation (CAGE) Challenges, with a specific focus on CAGE Challenge 2. CAGE Challenge 2 required a defensive Blue agent to defend a network from an attacking Red agent. We provide a detailed description of the this challenge and describe the approaches taken by challenge participants. From the submitted agents, we identify four classes of algorithms, namely, Single- Agent Deep Reinforcement Learning (DRL), Hierarchical DRL, Ensembles, and Non-DRL approaches. Of these classes, we found that the hierarchical DRL approach was the most capable of learning an effective cyber defensive strategy. Our analysis of the agent policies identified that different algorithms within the same class produced diverse strategies and that the strategy used by the defensive Blue agent varied depending on the strategy used by the offensive Red agent. We conclude that DRL algorithms are a suitable candidate for autonomous cyber defence applications.Comment: Presented at the 2nd Internation Workshop on Adaptive Cyber Defence, 202

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

SUBJECT- AND JOINT-SPECIFIC STRATEGIES USED BY MALE BASKETBALL PLAYERS TO MAXIMIZE COUNTERMOVEMENT JUMP HEIGHT

The purpose of this project was to study the subject- and joint-specific strategies that male basketball players use to increase countermovement jump (CMJ) height. Lower extremity joint kinematics and kinetics were recorded as 11 male, NCAA Division I basketball players performed 8-10 CMJ with increasing effort. Correlations between maximal potential energy of players’ centre-of-mass (surrogate for CMJ height) and the amount of eccentric and concentric work done at the hip, knee, and ankle joint Singlesubject and group-average analyses were used to study. The group-average analysis showed that all joint work variables predicted potential energy, whereas the singlesubject analysis revealed varying levels of subject-specific correlations (i.e., joint-specific CMJ strategies) that did not necessarily reflect the group-average data