Comparing biomechanical time series data across countermovement shrug loads

The effect of load on time-series data has yet to be investigated during weightlifting derivatives. This study compared the effect of load on the force–time and velocity–time curves during the countermovement shrug (CMS). Twenty-nine males performed the CMS at relative loads of 40 %, 60 %, 80 %, 100 %, 120 %, and 140 % one repetition maximum (1RM) power clean (PC). A force plate measured the vertical ground reaction force (VGRF), which was used to calculate the barbell-lifter system velocity. Time-series data were normalized to 100 % of the movement duration and assessed via statistical parametric mapping (SPM). SPM analysis showed greater negative velocity at heavier loads early in the unweighting phase (12–38 % of the movement), and greater positive velocity at lower loads during the last 16 % of the movement. Relative loads of 40 % 1RM PC maximised propulsion velocity, whilst 140 % 1RM maximized force. At higher loads, the braking and propulsive phases commence at an earlier percentage of the time-normalized movement, and the total absolute durations increase with load. It may be more appropriate to prescribe the CMS during a maximal strength mesocycle given the ability to use supramaximal loads. Future research should assess training at different loads on the effects of performance

The effect of load placement on the power production characteristics of three lower extremity jumping exercises

The purpose of this study was to compare the power production characteristics of the jump squat (JS), hexagonal barbell jump (HEXJ), and jump shrug (JShrug) across a spectrum of relative loads. Fifteen resistance-trained men completed three testing sessions where they performed repetitions of either the JS, HEXJ, or JShrug at body mass (BM) or with 20, 40, 60, 80, or 100% of their BM. Relative peak power (PPRel), relative force at PP (FPP), and velocity at PP (VPP) were compared between exercises and loads. In addition, power-time curves at each load were compared between exercises. Load-averaged HEXJ and JShrug PPRel were statistically greater than the JS (both p < 0.01), while no difference existed between the HEXJ and the JShrug (p = 1.000). Load-averaged JShrug FPP was statistically greater than both the JS and the HEXJ (both p < 0.001), while no statistical difference existed between the JS and the HEXJ (p = 0.111). Load averaged JS and HEXJ VPP were statistically greater than the JShrug (both p < 0.01). In addition, HEXJ VPP was statistically greater than the JS (p = 0.009). PPRel was maximized at 40, 40, and 20% BM for the JS, HEXJ, and JShrug, respectively. The JShrug possessed statistically different power-time characteristics compared to both the JS and the HEXJ during the countermovement and propulsion phases. The HEXJ and the JShrug appear to be superior exercises for PPRel compared to the JS. The HEXJ may be considered a more velocity-dominant exercise, while the JShrug may be a more force-dominant one

Control and efficiency analysis for a Lundell-alternator/active-rectifier system in automotive applications

This paper presents a control strategy for a conventional Lundell alternator and an active-rectifier. The control scheme focuses on the minimisation of the stator copper losses of the alternator in an effort to maximise its efficiency. The modulation scheme of the active-rectifier is being investigated with the introduction of three different modulation techniques in order to quantify the effect they have on the alternator’s efficiency. Steady-state results from experimental measurements of the alternator rectifier system are compared against a standard passive rectifier. The comparison indicates that the modulation scheme of the active-rectifier is significant to the alternator’s efficiency as well as to the overall system efficiency

Efficiency improvement and power loss breakdown for a Lundell-alternator/active-rectifier system in automotive applications

A control strategy for a conventional Lundell alternator and an active-rectifier using different modulation schemes was proposed in previous work. The modulation techniques examined indicated that the system could operate more efficiently than a passive rectifier over a certain speed and power range. This paper extends the modulation scheme analysis using a SVM scheme with six commutations per switching cycle, giving better electrical and overall efficiency. Furthermore, a power loss breakdown is performed for the active-rectifier with the assistance of experimental and simulation results of double pulse tests. Switching loss estimation curves are produced allowing the loss examination of the active-rectifier. Switching losses account only for a minor portion of the total rectifier losses in comparison to conduction losses. Finally, a higher dc-link voltage of 14.5 V was introduced using SVM scheme, giving better efficiency, in order to exploit further the rectifier loss distribution

Relationship between reactive strength index variants in rugby league players

Two reactive strength index (RSI) variants exist, the RSI and RSI modified (RSImod) which are typically calculated during the drop jump (DJ) and countermovement jump (CMJ), respectively. Both RSI variants have been used to monitor athletes' ability to complete stretch-shortening cycle actions quickly, but they have never been compared. The purpose of this study was to determine if they yield relatable information about reactive strength characteristics. Male professional rugby league players (n = 21, age = 20.8±2.3 years, height = 1.82±0.06 m and body mass = 94.3±8.4 kg) performed three DJs (30 cm) and CMJs on a force plate. RSI and RSImod were subsequently calculated by dividing jump height by ground contact time (GCT) and time to take-off (TTT), respectively. All variables were highly reliable (intraclass correlation coefficient ≥0.78) with acceptable levels of variability (coefficient of variation ≤8.2%), albeit larger variability was noted for DJ variables. Moreover, there was a large relationship between RSI and RSImod (r=0.524, P=0.007), whereas very large relationships were noted between jump heights (r=0.762, P<0.001) and between GCT and TTT (ρ=0.705, P<0.001). Additionally, RSI (0.90±0.22) was largely and significantly (d=2.57, P<0.001) greater than RSImod (0.47±0.08). The DJ-derived RSI yields much larger values than the CMJ-derived RSImod and although a large relationship was noted between them, it equated to just 22% shared variance. These results suggest that the two RSI variants do not explain each other well, indicating that they do not assess entirely the same reactive strength qualities and should not be used interchangeably

The effect of rest redistribution on kinetic and kinematic variables during the hang pull

The aim of this study was to compare the effects of rest redistribution (RR) on kinetics and kinematics during the hang pull (HP). Twenty-one male athletes (age 29.5 ± 4.3 years, height 1.78 ± 0.07 m, body mass 75.17 ± 11.11 kg, relative one repetition maximum [1RM] power clean [PC] 1.17 ± 0.14 kg.kg-1) performed the HP using 140% of 1RM PC with 3 traditional sets of 6 repetitions (TS), 9 sets of 2 repetitions with RR [45s rest after 2 repetitions] (RR45) and 6 sets of 3 repetitions with RR [72s rest after 3 repetitions] (RR72). Peak velocity (PV) was higher during RR72 (1.18 ± 0.11 m.s-1) compared to RR45 (1.14 ± 0.11 m.s-1) for the average of 18 repetitions (p = 0.025, g = 0.36). There was a main effect for set configuration with greater peak force (PF) (p 0.05, g = 0.00–0.59) between configurations for any other variables. Rest redistribution protocols did not result in significantly or meaningfully greater kinetics or kinematics during the HP when compared to a TS protocol; although performing RR72 resulted in higher PF, PV, and impulse, with improved PVM compared to RR45

Effect of onset threshold on kinetic and kinematic variables of a weightlifting derivative containing a first and second pull

This study sought to determine the effect of different movement onset thresholds on both the reliability and absolute values of performance variables during a weightlifting derivative containing both a first and second pull. Fourteen men (age: 25.21 ± 4.14 years; body mass: 81.1 ± 11.4 kg; and 1 repetition maximum [1RM] power clean: 1.0 ± 0.2 kg·kg) participated in this study. Subjects performed the snatch-grip pull with 70% of their power clean 1RM, commencing from the mid-shank, while isolated on a force platform. Two trials were performed enabling within-session reliability of dependent variables to be determined. Three onset methods were used to identify the initiation of the lift (5% above system weight [SW], the first sample above SW, or 10 N above SW), from which a series of variables were extracted. The first peak phase peak force and all second peak phase kinetic variables were unaffected by the method of determining movement onset; however, several remaining second peak phase variables were significantly different between methods. First peak phase peak force and average force achieved excellent reliability regardless of the onset method used (coefficient of variation [CV] 0.90). Similarly, during the second peak phase, peak force, average force, and peak velocity achieved either excellent or acceptable reliability (CV 0.80) in all 3 onset conditions. The reliability was generally reduced to unacceptable levels at the first sample and 10 N method across all first peak measures except peak force. When analyzing a weightlifting derivative containing both a first and second pull, the 5% method is recommended as the preferred option of those investigated

Simulating Descent and Landing of a Spacecraft

The Dynamics Simulator for Entry, Descent, and Surface landing (DSENDS) software performs high-fidelity simulation of the Entry, Descent, and Landing (EDL) of a spacecraft into the atmosphere and onto the surface of a planet or a smaller body. DSENDS is an extension of the DShell and DARTS programs, which afford capabilities for mathematical modeling of the dynamics of a spacecraft as a whole and of its instruments, actuators, and other subsystems. DSENDS enables the modeling (including real-time simulation) of flight-train elements and all spacecraft responses during various phases of EDL. DSENDS provides high-fidelity models of the aerodynamics of entry bodies and parachutes plus supporting models of atmospheres. Terrain and real-time responses of terrain-imaging radar and lidar instruments can also be modeled. The program includes modules for simulation of guidance, navigation, hypersonic steering, and powered descent. Automated state-machine-driven model switching is used to represent spacecraft separations and reconfigurations. Models for computing landing contact and impact forces are expected to be added. DSENDS can be used as a stand-alone program or incorporated into a larger program that simulates operations in real time

The Primordial Inflation Polarization Explorer (PIPER)

The Primordial Inflation Polarization Explorer (PIPER) is a balloon-borne cosmic microwave background (CMB) polarimeter designed to search for evidence of inflation by measuring the large-angular scale CMB polarization signal. BICEP2 recently reported a detection of B-mode power corresponding to the tensor-to-scalar ratio r = 0.2 on ~2 degree scales. If the BICEP2 signal is caused by inflationary gravitational waves (IGWs), then there should be a corresponding increase in B-mode power on angular scales larger than 18 degrees. PIPER is currently the only suborbital instrument capable of fully testing and extending the BICEP2 results by measuring the B-mode power spectrum on angular scales $\theta$ = ~0.6 deg to 90 deg, covering both the reionization bump and recombination peak, with sensitivity to measure the tensor-to-scalar ratio down to r = 0.007, and four frequency bands to distinguish foregrounds. PIPER will accomplish this by mapping 85% of the sky in four frequency bands (200, 270, 350, 600 GHz) over a series of 8 conventional balloon flights from the northern and southern hemispheres. The instrument has background-limited sensitivity provided by fully cryogenic (1.5 K) optics focusing the sky signal onto four 32x40-pixel arrays of time-domain multiplexed Transition-Edge Sensor (TES) bolometers held at 140 mK. Polarization sensitivity and systematic control are provided by front-end Variable-delay Polarization Modulators (VPMs), which rapidly modulate only the polarized sky signal at 3 Hz and allow PIPER to instantaneously measure the full Stokes vector (I, Q, U, V) for each pointing. We describe the PIPER instrument and progress towards its first flight.Comment: 11 pages, 7 figures. To be published in Proceedings of SPIE Volume 9153. Presented at SPIE Astronomical Telescopes + Instrumentation 2014, conference 915

Reliability of Automated Biochemical Identification of Burkholderia pseudomallei Is Regionally Dependent

Misidentifications of Burkholderia pseudomallei as Burkholderia cepacia by Vitek 2 have occurred. Multidimensional scaling ordination of biochemical profiles of 217 Malaysian and Australian B. pseudomallei isolates found clustering of misidentified B. pseudomallei isolates from Malaysian Borneo. Specificity of B. pseudomallei identification in Vitek 2 and potentially other automated identification systems is regionally dependent