Induced Post-activation Potentiation and its Relationship to Performance Variables in the Block Start

Post-activation potentiation (PAP) is an induced physical state commonly utilized in training and competition environments. There are a wide variety of methods used to induce PAP but the mechanisms and most effective means specific to the different speed/power events need to be investigated further for the potential of maximizing performance. Therefore, the purpose of this study is to investigate the effect of drop jumps on maximum vertical ground reaction force on the push-off phase after the first touchdown step and its relationship to block start performance. Participants included 3 male and 3 female, Division I collegiate track and field athletes (mean ± SD, age = 20.7 ± 0.47 yrs., height = 168.5 ± 5 cm, mass = 60.9 ± 6.7 kg) who were currently in-season having at least two years of experience with block starts, strength training and plyometrics. Each participant performed two sets of 5 blocks starts under 3 conditions (control, bike and drop jump). Results of a univariate ANOVA indicated no significant difference in mean force between subjects per condition (F 2, 179 =(2.179), p \u3e 0.05). And a post-hoc analysis showed no significant difference in maximum force between the pre and post trials of each condition (F (1, 179) = 1.726, p \u3e 0.05). Although the result of this study did not show any significant difference in maximum vertical force output, further analysis of the data can be done looking into other neuromuscular and kinematic and time variables that may yield different results

Biomechanical Response of the Leg to Single leg drop Landings Before and After Prolonged Plantar flexor Stretch.

The plantar flexor muscles have become important in activities such as gait analysis in healthy and patient populations. The duration of stretch is reported to influence their ability to generate force and if mechanical laxity is present after stretching, it is unclear how this laxity will influence the movement patterns of the lower extremities. PURPOSE: The study aimed to investigate influence of prolonged stretch to plantar flexor muscles on landing biomechanics during a single-leg drop landings. METHODS: Sixteen active participants (24.6 ± 3.1 yrs, 75.4 ± 15.6 kg mass, 1.75 ± 0.9m height) were recruited and randomly assigned to either the experimental group (n=8) or control group (n=8). The experimental group (EG) performed six single leg drop-landings from a 65 cm height onto a force platform before and after a 10 minute continuous stretch to the ankle plantar flexor muscles of their dominant leg. Once landed they maintained their position for 5 s. An isokinetic dynamometer was used to provide a continuous stretch to the ankle plantar flexor muscles by fixing the ankle in a maximal tolerated dorsiflexed position. Simultaneously muscle torque was recorded during 10min stretch. Additionally, participants performed maximal voluntary contractions (MVIC) in plantar flexed (+15⁰) and dorsiflexed (-15⁰) position before and after the stretch (-30⁰). The control group (CG) performed all landing and MVIC measures and did not perform the stretching procedure. Force platform measurements included peak value of vertical ground reaction force (vGRF), rate of force development (RFD), and center of pressure (COP) and COP velocity. The Statistical Package for Social Sciences was used to assess differences present between groups and the pre and post stretch landing conditions with an analysis of variance (ANOVA). Alpha level was set at p \u3c 0.05. RESULTS: There was a significant reduction in the torque output during the 10 min stretch (p \u3c 0.01, T0 to T10: -5.26 ± 4.1 Nm) There was no significant difference in vGRF, RFD, range COPx and MVIC pre and post stretch. However, there were group (EG 0.115 ± 0.02 vs CG 0.123 ± 0.02 m, p=0.021) and pre/post (Pre 0.123 ± 0.02 vs Post 0.115 ± 0.02 m, p=0.0017) in COPy range as well as COPy velocity (EG -0.01 ± 0.01 vs -0.014 ± 0.004 m/s, p=0.001). CONCLUSION: This study concludes that there is a significant effect of stretching on landing biomechanics and balance in the anterioposterior direction. A stress-relaxation of the passive tissues during prolonged stretch of the plantar flexor muscles was observed

Determination of Biomechanical Differences Between Elite and Novice San Shou Female Athletes

Determining the key factors in athletic performance is important for developing the technique and strength of athletes. Many martial arts forms have been studied, but a relatively new form of martial arts competition, San Shou, has not been analyzed. The purpose of this study was to determine key attributes necessary in the development of the San Shou athlete, particularly in female participants. Six elite and six novice competitors performed 30 continuous repetitions of cyclic extension and flexion of the trunk segment, knee joints, and elbows joints at two velocities, 60°/second and 180°/second, using an isokinetic dynamometer. Variables of interest were maximum torque production, normalized torque (Nm/kg), fatigue indexes (average of three maximal forces in the first three cycles/average of maximal forces in the last three cycles), and rate of torque development (Nm/s). Results indicate significant differences between groups only during trunk flexion for maximum torque, normalized torque, and rate of force development, whereas differences between movement velocities were apparent for multiple variables at each anatomic region. These analyses assist in providing further information regarding the possible key factors in developing the San Shou female athlete. Further work is required to identify additional parameters in developing the San Shou athlete

Understanding High Recession Rates of Carbon Ablators Seen in Shear Tests in an Arc Jet

High rates of recession in arc jet shear tests of Phenolic Impregnated Carbon Ablator (PICA) inspired a series of tests and analysis on FiberForm (a carbon preform used in the fabrication of PICA). Arc jet tests were performed on FiberForm in both air and pure nitrogen for stagnation and shear configurations. The nitrogen tests showed little or no recession, while the air tests of FiberForm showed recession rates similar to that of PICA (when adjusted for the difference in density). While mechanical erosion can not be ruled out, this is the first step in doing so. Analysis using a carbon oxidation boundary condition within DPLR was used to predict the recession rate of FiberForm. The analysis indicates that much of the anomalous recession behavior seen in shear tests may simply be an artifact of the non-flight like test configuration (copper upstream of the test article) a result of dissimilar enthalpy and oxygen concentration profiles on the copper. Shape change effects were also investigated and shown to be relatively small

Magnitude of behavioral deficits varies with job-related chlorpyrifos exposure levels among Egyptian pesticide workers.

Chronic occupational exposure to organophosphorus pesticides (OPs) is consistently associated with deficits on behavioral tests when compared to unexposed comparison groups. However, a dose-response relationship has yet to be established, leading some to doubt an association between occupational OP exposure and behavioral deficits. Pesticide application teams in Egypt who are primarily exposed to one OP, chlorpyrifos (CPF), were recruited into a field assessment. Trail Making A and the more challenging Trail Making B tests were administered to 54 engineers (who supervise the pesticide application process, usually from the side of the field), 59 technicians (who guide the pesticide applicators in the field), 31 applicators (who mix and apply pesticides using knapsack sprayers), and 150 controls (who did not work in the fields) at two different times during the OP application season as well as immediately after applications had ended and 1.5 months later. All participants were males since only males work on pesticide application teams in Egypt. Urinary levels of 3,5,6-trichloro-2-pyridinol (TCPy), a specific metabolite of CPF, confirmed the pattern of lower to higher CPF exposures from engineers to technicians to applicators, and these were all greater than urinary metabolite levels in controls. A consistent relationship between job title and performance speed on the behavioral task was observed: Controls had the best (fastest) performance on Trail Making A and B tests throughout the application season, and applicators had significantly slower performance than engineers on Trail Making A (p = 0.015) and B (p = 0.003). However, individual urinary TCPy, blood acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) levels did not predict individual performance. This study identifies a dose-related effect based on job title, which serves as a surrogate for chronic exposure in that differing job titles exhibit varying group exposure levels. The results establish that chronic occupational exposure to chlorpyrifos is neurotoxic and suggest that the classic biomarkers of recent CPF exposure are not predictive of chronic exposure effects

The Effects of Body Composition on Resting Metabolic Rate among College Aged Students

Resting metabolic rate (RMR) is the measure of daily energy expenditure while the body is at rest. RMR is becoming more useful in order to measure the energy demands in both athletes and non-athletes. PURPOSE: The purpose of this study is to analyze the RMR among college aged students, along with their body compositions in order to determine if there is a correlation between body fat percentage and RMR. METHODS: Participants in this study included 19 students at Midwestern State University between the ages of 19-25. (n = 19; female = 12; male = 7). Participants were asked prior to their initial measurements about their fitness status and were placed into either a physically active (PA) group or a sedentary group (S). Each participant was assigned a date and time in the morning for resting measurements, including: height (cm), weight (kg), resting heart rate (RHR), body fate percentage (%) and RMR (kcal). A Pearson Product R Correlation Coefficient was run to determine association between RMR, body fat percentage and other variables. Results are represented as means and standard deviations (+SD). Statistical significance was set a priori at p ≤ 0.05. RESULTS: A total of 19 participants were tested in this study (PA=15, S=4). Because there were only four (4) participants determined to be sedentary, statistical analysis was run as one sample size of 19 rather than two separate groups. The mean RMR of the participants was 1858.95 ± 337.55 kcal*day-1. There were no significant correlations between RMR and body fat percentage (r = -0.4, p \u3e 0.05). There were significant correlations in height and weight when related to RMR (r = 0.75; r = 0.68, respectively). A post hoc analysis with BMI was then conducted. Mean (SD) BMI of the participants was 25.11 (2.89) kg*m-2. There was no significant association between BMI and RMR (r = 0.30, p \u3e 0.05). Lean body mass (LBM) was observed to have a significant correlation with RMR (r = 0.83, p \u3c 0.05). A post hoc analysis was conducted in order to determine gender differences between the subjects. BMI was not significantly different between males and females (p = 0.79, p \u3e 0.05). CONCLUSION: Body fat percentage is not significantly correlated with RMR. However, body composition does affect RMR, specifically through LBM

Community Seismic Network

The article describes the design of the Community Seismic Network, which is a dense open seismic network based on low cost sensors. The inputs are from sensors hosted by volunteers from the community by direct connection to their personal computers, or through sensors built into mobile devices. The server is cloud-based for robustness and to dynamically handle the load of impulsive earthquake events. The main product of the network is a map of peak acceleration, delivered within seconds of the ground shaking. The lateral variations in the level of shaking will be valuable to first responders, and the waveform information from a dense network will allow detailed mapping of the rupture process. Sensors in buildings may be useful for monitoring the state-of-health of the structure after major shaking

The Effect of Covid-19 on Cardiac Health Investigated by Electrocardiogram in Collegiate Athletes

Covid-19 has emerged as a global pandemic and affected almost every organ of the body. There is limited data on cardiovascular involvement in athletes with covid-19 infection. PURPOSE: The purpose of the study is to determine the effect of covid-19 on cardiac health in collegiate athletes by electrocardiogram. METHODS: Prior to testing, all subjects signed an Informed Consent approved by the university Institutional Review Board (IRB). Screening electrocardiograms were performed in 45 Covid-19 infected basketball, football and soccer playing athletes (39 males and 6 females) of 18-25 years of age and have since shown to be negative following two successive tests. The data were then compared to ECG values in non-infected basketball, football, and soccer athletes, obtained by conducting meta-analyses with having same age and sport criteria. Descriptive statistics were means and standard deviation (SD). Additional statistical analyses utilized a Factorial ANOVA with main effect, post hoc Tukey and effect size calculations. Statistical significance is set a priori at P \u3c 0.05. RESULTS: The total number of subjects in experimental group were 12 male basketball players, 23 male football players, 4 male soccer players and 6 female Soccer players. The total number of subjects in control group obtained through meta-analyses were 591 male basketball athletes, 176 male footballers, 588 male soccer athletes and 154 female soccer athletes. The baseline characteristics of mean (SD) BMI (kg/m2) for experimental group was as follows: male basketball: 23.4 (1.77), male football: 31.5 (6.53), male soccer: 23.9 (1.55), and female soccer: 24.5 (4.52). For control groups, BMI were as follows: male basketball: 25, male football: 22.6 (7), male soccer: 23.1 (0.8), and female soccer: 21.8 (0.3). The factorial ANOVA shows that there is a significant difference in ECG parameters between male and females (p=0.001) and between sports (p= 0.000034) but not between experimental and control group (p=0.18). The post hoc Tukey analysis indicated the following: PR interval and QRS duration were significantly (p=0.006, p=0.017) higher in males compared to females, respectively; PR interval was significantly (p=0.04) lower in Soccer players compared to other sports. The resting heart rate (RHR) was significantly (p=0.01) higher in the experimental group compared to controls, yet was within normal range of heart rate. While there was not a significant difference between the two groups in the ECG parameters, there was a small to huge effect size in ECG parameters in male and female soccer players. In male soccer players between the groups, the value of Cohen D for RHR was 0.16 (very small effect size), 0.92 (large effect size) for QRS duration and 0.72 (medium effect size) for QTc interval. For the female soccer players, the value of Cohen D for RHR was 1.70 (very large effect size), and 0.67 (medium effect size) for QRS duration. There is a huge effect size in RHR in male football athletes with a Cohen D value of 2.1. CONCLUSION: The effect of Covid-19 on ECG parameters is more profound in male athletes compared to female counterparts, primarily in RHR, PR interval and QRS duration. In terms of sports, the male and female soccer players have changes in ECG parameters when compared to male football and basketball athletes