THE DYNAMIC LOAD ON HAMSTRING MUSCLES DURING SPRINTING

The purpose of this study was to analyze the load condition on hamstring muscles during stance and swing phase of sprinting. Three-dimensional videographic and ground reaction force data were collected and the intersegmental dynamics of lower limb was quantified while eight elite male sprint runners performed sprint running with maximum effort. During initial stance phase, the ground reaction torque (EXT) was the main passive torque at knee and hip. During late swing phase, it was motion-dependent torque (MDT) as well. The muscle torques counteracted the large effect of EXT and MDT. This result revealed that the hamstring muscles would suffer from tremendous loads in both initial stance phase and late swing phase. Thus it can be speculated that hamstring muscles were exposed to a higher risk of injury during these two phases in sprinting

How Joint Torques Affect Hamstring Injury Risk in Sprinting Swing-Stance Transition

Purpose: The potential mechanisms of hamstring strain injuries in athletes are not well understood. The study, therefore, was aimed at understanding hamstring mechanics by studying loading conditions during maximum-effort overground sprinting. Methods: Three-dimensional kinematics and ground reaction force data were collected from eight elite male sprinters sprinting at their maximum effort. Maximal isometric torques of the hip and knee were also collected. Data from the sprinting gait cycle were analyzed via an intersegmental dynamics approach, and the different joint torque components were calculated. Results: During the initial stance phase, the ground reaction force passed anteriorly to the knee and hip, producing an extension torque at the knee and a flexion torque at the hip joint. Thus, the active muscle torque functioned to produce flexion torque at the knee and extension torque at the hip. The maximal muscle torque at the knee joint was 1.4 times the maximal isometric knee flexion torque. During the late swing phase, the muscle torque counterbalanced the motion-dependent torque and acted to flex the knee joint and extend the hip joint. The loading conditions on the hamstring muscles were similar to those of the initial stance phase. Conclusions: During both the initial stance and late swing phases, the large passive torques at both the knee and hip joints acted to lengthen the hamstring muscles. The active muscle torques generated mainly by the hamstrings functioned to counteract those passive effects. As a result, during sprinting or high-speed locomotion, the hamstring muscles may be more susceptible to high risk of strain injury during these two phases

Effect of Football Shoe Collar Type on Ankle Biomechanics and Dynamic Stability During Anterior and Lateral Single-Leg Jump Landings

In this study, we investigated the effects of football shoes with different collar heights on ankle biomechanics and dynamic postural stability. Fifteen healthy college football players performed anterior and lateral single-leg jump landings when wearing high collar, elastic collar, or low collar football shoes. The kinematics of lower limbs and ground reaction forces were collected by simultaneously using a stereo-photogrammetric system with markers (Vicon) and a force plate (Kistler). During the anterior single-leg jump landing, a high collar shoe resulted in a significantly smaller ankle dorsiflexion range of motion (ROM), compared to both elastic (p = 0.031, dz = 0.511) and low collar (p = 0.043, dz = 0.446) types, while also presenting lower total ankle sagittal ROM, compared to the low collar type (p = 0.023, dz = 0.756). Ankle joint stiffness was significantly greater for the high collar, compared to the elastic collar (p = 0.003, dz = 0.629) and low collar (p = 0.030, dz = 1.040). Medial-lateral stability was significantly improved with the high collar, compared to the low collar (p = 0.001, dz = 1.232). During the lateral single-leg jump landing, ankle inversion ROM (p = 0.028, dz = 0.615) and total ankle frontal ROM (p = 0.019, dz = 0.873) were significantly smaller for the high collar, compared to the elastic collar. The high collar also resulted in a significantly smaller total ankle sagittal ROM, compared to the low collar (p = 0.001, dz = 0.634). Therefore, the high collar shoe should be effective in decreasing the amount of ROM and increasing the dynamic stability, leading to high ankle joint stiffness due to differences in design and material characteristics of the collar types

PolyMetformin combines carrier and anticancer activities for in vivo siRNA delivery

Metformin, a widely implemented anti-diabetic drug, exhibits potent anticancer efficacies. Herein a polymeric construction of Metformin, PolyMetformin (PolyMet) is successfully synthesized through conjugation of linear polyethylenimine (PEI) with dicyandiamide. The delocalization of cationic charges in the biguanide groups of PolyMet reduces the toxicity of PEI both in vitro and in vivo. Furthermore, the polycationic properties of PolyMet permits capture of siRNA into a core-membrane structured lipid-polycation-hyaluronic acid (LPH) nanoparticle for systemic gene delivery. Advances herein permit LPH-PolyMet nanoparticles to facilitate VEGF siRNA delivery for VEGF knockdown in a human lung cancer xenograft, leading to enhanced tumour suppressive efficacy. Even in the absence of RNAi, LPH-PolyMet nanoparticles act similarly to Metformin and induce antitumour efficacy through activation of the AMPK and inhibition of the mTOR. In essence, PolyMet successfully combines the intrinsic anticancer efficacy of Metformin with the capacity to carry siRNA to enhance the therapeutic activity of an anticancer gene therapy

Plasma noise in TianQin time delay interferometry

TianQin is a proposed geocentric space-based gravitational wave observatory mission, which requires time-delay interferometry (TDI) to cancel laser frequency noise. With high demands for precision, solar-wind plasma environment at $\sim 10^5$ km above the Earth may constitute a non-negligible noise source to laser interferometric measurements between satellites, as charged particles perturb the refractivity along light paths. In this paper, we first assess the plasma noises along single links from space-weather models and numerical orbits, and analyze the time and frequency domain characteristics. Particularly, to capture the plasma noise in the entire measurement band of $10^{-4} - 1$ Hz, we have performed additional space-weather magnetohydrodynamic simulations in finer spatial and temporal resolutions and utilized Kolmogorov spectra in high-frequency data generation. Then we evaluate the residual plasma noises of the first- and second-generation TDI combinations. Both analytical and numerical estimations have shown that under normal solar conditions the plasma noise after TDI is less than the secondary noise requirement. Moreover, TDI is shown to exhibit moderate suppression on the plasma noise below $\sim 10^{-2}$ Hz due to noise correlation between different arms, when compared with the secondary noise before and after TDI.Comment: 12 pages, 15 figures, accepted by Phys. Rev.

Alternating-electric-field-enhanced reversible switching of DNA nanocontainers with pH

Macroscopically realizable applications of DNA-based molecular devices require individual molecules to cooperate with each other. However, molecular crowding usually introduces disorder to the system, thus jeopardizing the molecular cooperation and slowing down their functional performance dramatically. A challenge remaining in this field is to obtain both smarter response and better cooperation simultaneously. Here, we report a swift-switching DNA nanodevice that is enhanced by an alternating electric field. The device, self-assembled from folded four-stranded DNA motifs, can robustly switch between closed and open states in smart response to pH stimulus, of which the closed state forms a nanometer-height container that is impermeable to small molecules. This character was used to directly and non-specifically catch and release small molecules emulating mechanical hand in a controllable way. The alternating electric field was used to accelerate molecular cooperative motion during the device switching, which in turn shortened the closing time remarkably to thirty seconds

Fast decomposed gradient projection algorithm for sparse representation

Finding the sparse representation of a signal on an over-complete dictionary plays a very important role in many problems, such as pattern recognition and compressive sensing. In this paper we propose a novel technique called fast decomposed gradient projection algorithm (FDGP) to solve the sparse representation problem by minimizing a bound-constrained quadratic problem (BCQP) containing a quadratic error term and a regularization term. Different from the original gradient projection method, FDGP iterates from an all-zero vector and only updates the positions that are most likely nonzero in each iteration. In view of that the sparse solution usually contains a very small number of nonzero elements, the proposed method can efficiently improve convergence rate of the gradient projection method for sparse representation especially on large scale problems. As we will show, the complexity of the proposed method can be little influenced by the size of the dictionary and only depends on the sparsity of a given signal. Experimental results show the proposed methods can achieve effective and efficient decomposition performance under the over-complete dictionary

Graph embedding based feature selection

Usually many real datasets in pattern recognition applications contain a large quantity of noisy and redundant features that are irrelevant to the intrinsic characteristics of the dataset. The irrelevant features may seriously deteriorate the learning performance. Hence feature selection which aims to select the most informative features from the original dataset plays an important role in data mining, image recognition and microarray data analysis. In this paper, we developed a new feature selection technique based on the recently developed graph embedding framework for manifold learning. We first show that the recently developed feature scores such as Linear Discriminant Analysis score and Marginal Fisher Analysis score can be seen as a direct application of the graph preserving criterion. And then, we investigate the negative influence brought by the large noise features and propose two recursive feature elimination (RFE) methods based on feature score and subset level score, respectively, for identifying the optimal feature subset. The experimental results both on toy dataset and real-world dataset verify the effectiveness and efficiency of the proposed methods