PREDICTING ACTIVE FOOT CONTACT IN THE ACCELERATION PHASE OF ATHLETIC SPRINTING THROUGH ACCELEROMETER MEASUREMENTS

Active foot contact (absence of a braking impulse) during the acceleration phase of athletic sprinting is associated with the motion of the foot before touchdown (TD). Since the identification of braking impulses through force plate measurements is cost-expensive, the aim of this study was to develop a machine learning algorithm to predict active foot contact occurrences based on ankle-mounted accelerometer measurements. Ten recreationally active athletes (three females, seven males) performed 30 sprint-block-starts each, which were used as input to the machine learning model. Model performance was assessed by the AUC for both validation (AUC = 0.96) and testing (AUC = 0.94). It is therefore possible to predict active foot contact occurrence by a machine learning algorithm solely based on ankle-mounted accelerometer measurement data

rac-2-Methyl-3,4,5,6-tetra­hydro-2H-2,6-methano-1,3-benzoxazocin-4-one

The title compound, C12H13NO2, represents a conformationally restricted 2-pyridone analogue of 1,4-dihydro­pyridine-type calcium antagonists and was selected for a crystal structure determination in order to explore some aspects of drug-receptor inter­action. In the mol­ecule, two stereogenic centres are of opposite chirality, whereas a racemate occurs in the crystal. It was found that the formally aminic N atom of the heterocycle is essentially sp 2-hybridized with the lone-pair electrons partially delocalized through conjugation with the adjacent carbonyl bond. As a result, the central pyridone ring assumes an unsymmetrical half-chair conformation. The critical 4-phenyl ring is fixed in a pseudo-axial and perpendicular orientation [dihedral angle 85.8 (1)°] with respect to the pyridone ring via an oxygen bridge. In the crystal a pair of centrosymmetric N—H⋯O hydrogen bonds connect mol­ecules of opposite chirality into a dimer. The dimers are packed by hydrophobic van der Waals inter­actions

ASSESSMENT OF ANALYZING BLOCK START PERFORMANCE WITHOUT ARM GROUND REACTION FORCES

The purpose of this study was to assess the analysing reaction time (RT) and normalized power when calculated using two different methods: a method using ground reaction forces (GRFs) of only the legs (legs F-based method) and a method using GRFs of arms and legs (whole F-based method). In total, 127 block start motions from fourteen male sprinters were analysed from all participants. The RT of the legs F-based method was not similar to that of the whole F-based method: the mean difference was 7.4 ms and the 95% CI was –45.1–59.8 ms. In contrast, the normalized power of the legs F-based method was similar to that of the whole F-based method. This information will help reconsider the golden standard methods currently used to analyse RT and encourage the use of analysis methods to analyse the performance in block starts

JOINT SPECIFIC MECHANICAL POWER DURING VERTICAL JUMPS OF ELITE BOBSLEIGH ATHLETES

The purpose of the study was to quantify jumping mechanics of elite male bobsleigh athletes (N=10; 28?3 yrs; 193?5 cm; 99?8 kg) performing two different kinds of vertical jumps (squat and countermovement). Kinetics and kinematics were measured with two force platforms (one per leg, 1080 Hz) and eight high-speed infrared cameras sampled at 120 Hz. Detection of the joint specific mechanical power generation pattern between legs and across athletes was realized via inverse-dynamic calculation. The results show an average jumping height of about 50 cm, which is associated with average body mass of almost 100 kg. An average joint specific contribution of mechanical power generation during squad and countermovement jumps could be determined close to one third per joint (hip, knee, ankle)

DETERMINANTS OF ACCELERATION PERFORMANCE IN ELITE FEMALE SPRINTERS

The purpose of this study was to explore the determinants of performance in the early acceleration phase (first four meters) in nine elite female sprinters. Acceleration performance was quantified using a modified version of the normalized average horizontal block power. Ground reaction forces were collected using an instrumented starting block and three force plates. In addition, full body kinematics were captured using an optoelectronic motion capture system. The results indicate that a starting technique facilitating a horizontal push-off direction and force application with short contact times is beneficial for starting performance. This might be achieved through a greater forward lean of the body. Previously proposed beneficial effects of an active touchdown of the foot could not be confirmed in the present study

DIFFERENCES BETWEEN TAKE-OFF BEHAVIOR DURING VERTICAL JUMPS AND TWO ARTISTIC ELEMENTS

The present study analysed the possible application of vertical jumps as a diagnostic tool for the acrobatic elements backward somersault (6s) and Menichelli (MEN). Therefore, 14 female gymnasts of the German national squad performed dassical vertical jumps (CMJ, SJ, DJ), backward somersaults and Menichellis during a diagnostic camp at the German Research Centre of Elite Sport (momentum). Kinematic and kinetic parameters were captured by a 30-motion capture system and two force plates. Take off velocities of the CMJ and backward somersault showed significant correlations (r=0.86). Besides possible predictions for take4ff velocity of BS performing CMJ, findings did not address execution of MEN. Concerning training purposes, vertical jumping does not affect performance characteristics of acrobatic elements

JOINT SPECIFIC CONTRIBUTION OF MECHANICAL POWER AND WORK DURING ACCELERATION AND TOP SPEED IN ELITE SPRINTERS

The purpose of the study was to quantify and compare sprint mechanics of elite female sprinters (N=9; PB 11.4?0.2s) during acceleration (1st, 2nd, 3rd step) and top speed (‘flying 30m) running. Three dimensional kinetics and kinematics were measured on an IAAF indoor track armed with four force plates and 16 cameras. The comparison between the 1st, 2nd and 3rd step and the ‘flying 30m’ (vave= 9.0?0.2 ms-1) shows a progressive change in absorption and generation of mechanical power. Whilst the knee extensors where able to minimize energy absorption during acceleration, the ankle extensors showed a stretch-shortening cycle and a small absorption from the first step. This energy loss at the ankle joint does not necessarily leads to a decrease in sprint performance, it also offers the plantar flexors to work in an stretch-shortening cycle instead of concentric only mode

JOINT WORK OF THE TAKE-OFF LEG DURING ELITE HIGH JUMP

The purpose of the study was to evaluate kinematics and kinetics in elite high jumpers and to estimate joint work of the lower extremity with a custom-modified full-body model. Motions of seven male athletes (personal best 2.24 ± 0.06 m) during jumping were filmed with 19 Infrared-Highspeed-Cameras and ground reaction forces were captured with a force plate. The results show that knee joint energy absorption is twice as much as at the ankle joint (p 0.05) in energy generation between the knee and ankle joint, but the ankle joint generates more energy than it absorbs (p < 0.05). The problem-solving approach to raise the center of mass to 2.10 m was different between the jumpers

Unraveling the spontaneous zwitterionic copolymerization mechanism of cyclic imino ethers and acrylic acid

We report a high-resolution electrospray ionization mass spectrometric (HR ESI MS) access route leading to in-depths insight into the spontaneous zwitterionic copolymerization mechanism between cyclic imino ethers (i.e. 2-methyl-2-oxazoline (MeOx), 2-ethyl-2-oxazoline (EtOx) or 2-ethyl-2-oxazine (EtOz)) with acrylic acid (AA), exploiting the characteristic species accumulating during the copolymerization as well as tandem mass spectrometry (MS/MS). We demonstrate preferences in α,ω-end group formation by screening various feed ratios of cyclic imino ethers and acrylic acid (e.g. MeOx:AA = 1:1; MeOx:AA = 2:1; MeOx:AA = 1:2). Critically, a calibration curve – based on AA-MeOx-AA dimer – was established allowing for semi-quantitative determination of the end group ratios with different feed ratios of acrylic acid. The formation of, previously suggested, alternating copolymers was confirmed by MS/MS experiments. Deviations from an ideal alternating composition were found to decrease from MeOx to EtOx to EtOz. The results of (semi-quantitative) HR ESI MS and MS/MS measurements suggest, for the first time presented in such precision, a polymerization mechanism for the spontaneous zwitterionic (alternating) copolymerization indicating optimal monomer ratios and pairings

Polyether-tethered imidazole-2-thiones, imidazole-2-selenones and imidazolium salts as collectors for the flotation of lithium aluminate and spodumene

Imidazolium salts were prepared which possess 2-ethoxyethyl pivalate or 2-(2-ethoxyethoxy)ethyl pivalate groups as amphiphilic side chains with oxygen donors as well as n-butyl substituents as hydrophobic groups. The N-heterocyclic carbenes of the salts, characterized by 7 Li and 13 C NMR spectroscopy as well as by Rh and Ir complex formation, were used as starting materials for the preparation of the corresponding imidazole-2-thiones and imidazole-2-selenones. Flotation experiments in Hallimond tubes under variation of the air flow, pH, concentration and flotation time were performed. The title compounds proved to be suitable collectors for the flotation of lithium aluminate and spodumene for lithium recovery. Recovery rates up to 88.9% were obtained when the imidazole-2-thione was used as collector