Gender Differences In Frontal Plane Lower Extremity Kinetic Variability During Landing

Investigations of human movement variability have been used as ameans of exploring neuromotor functioning, where performance variability isthought to provide the system with flexibility and a mechanism for adaptation tomovement repetition [1,2,4,6]. Operationally, variability has been considered tofall within optimal limits (Figure 1), while excessively high or low variability hasbeen implicated in injury susceptibility [1,2,4,6]. Landing has been exploreddue to a high incidence of injury in athletic performance, as well as the abilityto easily control task demands through increases in landing height [3,4].The purpose of this investigation was to evaluate changes in lowerextremity kinetic variability in the frontal plane, exploring gender comparisonsduring landing. Peak frontal plane joint moments were used to accessvariability across landing heights at the hip, knee, and ankle joints. Landingheight was increased as a proportion of maximum vertical jump height (MVJH),which characterized lower extremity functioning across a range of taskdemands

Examining Lower Extremity Range of Motion And Movement Variability Chages Due To Focus of Attention During Landing

Attentional focus (AF) has been explored among a variety of motor skills providing evidence that external AF promotes automaticity and enhanced performance [6]. External focus of attention is distinguished from internal focus such that external focus is directed toward movement effect rather than body movements [6]. Movement variability provides a means of assessing functional characteristics of the neuromotor system, where normal functioning is suggested to occur within optimal limits, while excessively high or low movement variability is indicative of system dysfunction [2,4,5]. Additionally, the ability of the motor system to vary, or broadly distribute, internal loads is thought to reduce the risk of injury, and increase adaptation to a wider array of stimuli [2,4,5]. Viewing movement variability as an inherent and functional element of the neuromotor system provides an avenue for investigating injury susceptibility [2,4,5]. Landing has been explored due to a high incidence of injury in athletic performance, and the ability to experimentally control task demands [3,4]. Examinations of lower extremity functioning during landing have demonstrated equivocal findings among variables, with the influence of AF instructions on injury risk remaining unexplored [3,4,5,6]. The purpose of this research was to examine the effects of AF instructions on landing kinematics, exploring strategies for reducing injury risk. Movement variability was used to assess neuromotor functioning and the ability of the motor system to vary internal loads

EVALUATING THE INFLUENCE OF KNEE JOINT ANGLE ON MAXIMUM ISOMETRIC BELT SQUAT PERFORMANCE

Belt squat testing measures maximum upward isometric force from the lower extremities using a ground-tethered belt around the waist. A lack of standardized body positioning during isometric belt squat testing can lead to inconsistent test results. We aimed to evaluate the influence of sagittal knee joint angles on maximum isometric belt squat performance. Thirty-three healthy volunteers (24 female) performed one maximal effort belt squat at five randomly ordered sagittal knee joint angle ranges: (1) 80-100°, (2) 100-120°, (3) 120-140°, (4) 140-160°, and (5) 160-180°. Sagittal knee joint angles between 120-140° and 140-160° led to greater maximum vertical ground reaction forces compared to each other condition (p £ 0.017). Our results provide a starting point to establish best-practices for assessing lower limb strength during maximum isometric belt squat testing

Comparing vertical jump height measurement methods

Vertical jump height is a method of assessing muscle strength and power in the lower body, and is used to assess athletic ability. The gold standard in measuring vertical jump height is the measurement of the vertical centre of mass (COM) displacement from three-dimensional (3D) video analysis. Vertical jump height is ultimately affected by takeoff COM velocity, as greater takeoff velocity results in greater jump height. The current study explored the use of takeoff versus maximum COM velocity by examining the relationships and differences between 3D video analysis and 3D force platform analysis when predicting vertical COM displacement. Use of the Vertec, and correction of takeoff COM velocity using takeoff posiion, was explored through methods proposed by Aragon-Vargas (2000) and Moir (2008)

Kinematic Effects of Stride Length Perturbations on System COM Horizontal Velocity During Locomotion

PURPOSE: To investigate the kinematic effect on the systems’ center of mass horizontal velocity in response to stride length perturbations. METHODS: Twelve healthy adults (23.1±7.71 yrs; 1.69±0.1 m; 66.82±12.6 kg; leg length 894.7±66.1 mm) performed 5 trials of preferred speed walking (PW) and running (PR)followed by 5 stride length perturbations based on percentages of leg length (60%, 80%, 100%, 120% and 140%). 3D kinematic analysis was completed using a 12-camera infrared motion capture system (Vicon, 200hz). Dependent variables computer for each condition included: center of mass horizontal velocity at the highest vertical position (COMHVhi) and at the lowest vertical position (COMHVlo). Statistical analysis included correlation matrices across levels of perturbation for each dependent variable (α=.05). RESULTS: COMHVhi demonstrated significant correlations with greater than 50% shared variance for PR vs 100% (r=.742), 60% vs 80% (r=.824), 60% vs 100% (r=.748), 60% vs 120% (r=.709), 80% vs 100% (r=.896), 100% vs 120% (r=.887), and 100% vs 140% (r=.728), and 120% vs 140% (r=.895). COMHVlo demonstrated significant correlations with greater than 50% shared variance for PR vs 100% (r=.753), PW vs 80% (r=.794), 60% vs 80% (r=.814), 60% vs 100% (r=.735), 60% vs 120% (r=.748), 80% vs 100% (r=.902), 80% vs 120% (r=.751), 100% vs 120% (r=.892), and 120% vs 140% (r=.710). DISCUSSION: Results suggest PR and PW have a greater relationship to stride length less than or equal to leg length, and thus extending stride length begins to diminish mechanical efficiency. It is a well-established mechanical relationship that horizontal velocity is a product of stride length and stride rate. Study results suggest that increases in stride length beyond 100% of leg length may be less than optimal mechanically. CONCLUSION: Stride lengths greater than 100% leg length during walking may be inefficient, perhaps owing to changes in lower extremity stiffness

Step Length Perturbations Alter Variations in Center of Mass Horizontal Velocity

PURPOSE: The purpose of the study was to investigate the effects of SL perturbations on system COM forward velocity (vx) during walking gait. METHODS: Eight healthy adults (23.5±3.6 yrs; 1.72±0.18 m; 73.11±15.29 kg) performed 5 trials of preferred speed walking (PW) and running (PR) followed by 5 stride length perturbations based on percentages of leg length (LL: 60%, 80%, 100%, 120% and 140%). 3D kinematic analysis was completed using a 12-camera infrared motion capture system (Vicon MX T40-S, 200Hz). Data filtering and interpolation included a low pass, 4th order Butterworth filter (cutoff frequency 15Hz) and cubic (3rd order spline). Maximum and minimum system COMvx comparisons were made independently among stride conditions using one-way repeated measures ANOVA and Bonferroni post-hoc contrasts. Change in system COMvx across gait stride were evaluated using one-way repeated measures ANOVA and Bonferroni post-hoc contrasts (α=0.05). RESULTS: Differences in maximum COMvx were detected among stride conditions (F[1.847,59.105]=339.458, pdetected among stride conditions (F[2.118,65.666] =130.951, pdetected significantly greater ΔCOMvx at 140% LL, and significantly less ΔCOMvx at 60% LL (p≤.005). DISCUSSION: Differences in maximum COMvx were detected among stride conditions (F[1.847,59.105]=339.458,

COMPARISON OF METHODS FOR ASSESSING VERTICAL JUMP HEIGHT PERFORMANCE

Relationships, explained variance, measurement error, and limits of agreement were examined among field and laboratory countermovement vertical jump tests, including Vertec, 3D video, and force platform data. Data were simultaneously collected on a single countermovement jump trial for 13 female varsity volleyball players. Vertical jump height computed using maximum centre of mass (COM) velocity from force platform data demonstrated the greatest precision, as well as the strongest correlation (r=0.90), greatest explained variance (R2=0.81), and lowest standard error of the estimate (0.02m) in vertical 3D video COM displacement. Jump height calculation using maximum COM velocity may highlight relevant performance measures, providing jump height estimations more quickly and easily, and with greater precision via force platform analysis

Investigating single-leg landing strategies and movement control across changes in task demands

Variability is an intrinsic characteristic of human movement, with hypothesized connections to neuromotor functioning and mechanisms of injury. The purpose of this study was to evaluate changes in movement variability among kinematic, kinetic, and electromyographic (EMG) variables following mechanical task demand manipulations during single-leg drop landings. Biomechanical outcome variables included 3 kinematic (sagittal, hip, knee, and ankle angles), 4 kinetic (sagittal hip, knee, ankle moments and vertical ground reaction force; GRFz), and 5 EMG variables (gluteus maximus, vastus medialis, biceps femoris, medial gastrocnemius, and tibialis anterior muscles). Mechanical task demands were altered using load and landing height manipulations, computed as percentages of participant anthropometrics (bodyweight: BW, BW+12.5%, BW+25%, and height: H12.5% and H25%, respectively). Fewer emergent strategies were identified under greater mechanical task demands, defined using the load accommodation strategies model, alongside decreased movement variability, assessed using principal component analysis (PCA). Joint-specific biomechanical adjustments were identified, highlighting mechanisms for the observed load accommodation strategies and changes in movement variability. An increasingly upright landing posture was observed under greater mechanical task demands, decreasing effective landing height and reducing landing impulse. Alterations in movement variability were interpreted in the context of the available functional degrees of freedom at each lower extremity joint, aligning with physiological predictions and theories from motor control. The holistic approach taken in this investigation provided a more complete understanding of mechanisms contributing to changes in movement variability and factors that may underlie landing injuries

Making too much of a weak case

LetterB E Christopher Nordin, Robin M Daly, John Horowitz, Andrew V Metcalf

Predictive Modeling for Buying and Selling Bitcoin

Investable assets are frequently targeted by the general public in an attempt to turn some money into more money. One of the most volatile investable assets is Bitcoin. In September 2017, the value of one Bitcoin reached $20,000 before crashing to around$6,000 in December 2017. Many investors are attracted to Bitcoin due to this volatility. In this project, we will be attempting to use numerical modeling methods to analyze the price of Bitcoin over time. The goal of modeling the price of Bitcoin will be to form a system of predicting when it will rise and fall. This will allow us to write software that automates the buying and selling of Bitcoin to maximize the value of our trades