Developing the elastomer materials with high mechanical robustness through simple and environmentally friendly methods poses significant challenges. In this research, a simple solvent‐free ...polymerization method is reported to synthesize a transparent polyurea‐urethane elastomer using polycaprolactone (PCL) as soft segment and adjusting various hard segments. The target elastomer successfully combine acceptable mechanical performance and exceptional crack tolerance, whereby the notched samples can readily lift 25000 times (a rarely reported value) its weight. Moreover, the superhigh elastic restorability allow target elastomer recover to its original dimension from elongation over 5 times or to fracture. These results are attained due to the presence of densely and uniformly distributed hard microdomains within the elastomer, leading to effective energy dissipation. Furthermore, owing to the linear structure of the molecular chains and the reversible hydrogen‐bonding interactions between the chains, target elastomer can be conveniently healed and recycled under heating conditions. This research can provide a general and feasible strategy for the construction of elastomer materials with exceptional comprehensive properties, and the elastomers are expected to be applied in emerging fields such as protective elements and flexible electronics.
As shown, IPDI‐PCL‐DMTDA was obtained through an extremely simple and controllable solvent‐free polymerization method. The outstanding comprehensive performance of the target elastomer was mainly attributed to the unique hard domain structure formed by multiple hydrogen bonds in its polymer network, while its mechanical properties were at the forefront among the elastomers reported in the literature.
PURPOSEThe 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.
METHODSThree-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.
RESULTSDuring 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.
CONCLUSIONSDuring 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.
The development and innovation of biomechanical measurement methods provide a solution to the problems in ski jumping research. At present, research on ski jumping mostly focuses on the local ...technical characteristics of different phases, but studies on the technology transition process are less.
This study aims to evaluate a measurement system (i.e. the merging of 2D video recording, inertial measurement unit and wireless pressure insole) that can capture a wide range of sport performance and focus on the key transition technical characteristics.
The application validity of the Xsens motion capture system in ski jumping was verified under field conditions by comparing the lower limb joint angles of eight professional ski jumpers during the takeoff phase collected by different motion capture systems (Xsens and Simi high-speed camera). Subsequently, the key transition technical characteristics of eight ski jumpers were captured on the basis of the aforementioned measurement system.
Validation results indicated that the joint angle point-by-point curve during the takeoff phase was highly correlated and had excellent agreement (0.966 ≤ r ≤ 0.998, P < 0.001). Joint root-mean-square error (RMSE) differences between model calculations were 5.967° for hip, 6.856° for knee and 4.009° for ankle.
Compared with 2D video recording, the Xsens system shows excellent agreement to ski jumping. Furthermore, the established measurement system can effectively capture the key transition technical characteristics of athletes, particularly in the dynamic changes of straight turn into arc in inrun, the adjustment of body posture and ski movement during early flight and landing preparation.
This study endeavors to explore the intricate interplay between the fundamental skills of basketball—defensive slide, crossover dribbling, and full approach jump—and the shoe outsole friction ...coefficient, with the overarching goal of advancing our comprehension regarding the pivotal role of footwear in athlete performance. Employing a comprehensive methodology that integrates 3D motion capture, force platform dynamometry, and biomechanical modeling, the study seeks to quantify the inherent motor control intricacies associated with these fundamental skills. Data collection involved 12 varsity players, and the research systematically assesses the influence of the shoe friction coefficient on both skill quality and injury risk, utilizing a set of 13 parameters for evaluation. The findings unveil that, with an increased friction coefficient, the following changes occur: for the defensive slide, we observed decreased contact time (p < 0.05), boosted medio–lateral impulse (p < 0.05), and lowered ankle torque (p < 0.01); for crossover dribbling, we observed increased anterior–posterior impulse (p < 0.05) and ankle torque (p < 0.05); for the full approach jump, we observed decreased contact time (p < 0.05) and increased jump height (p < 0.05). Generally, the equal increment in the shoe outsole friction coefficient did not result in equal changes in the selected parameters of motor skill control, indicating a non-linear relationship between the performance quality of essential basketball skills and the shoe friction coefficient. The results suggest the potential existence of an optimal value for skill execution. Notably, the study identifies that, while an augmentation in the friction coefficient enhances specific skill aspects, there is a discernible saturation point, signifying diminishing returns. This investigation makes a substantial contribution to our understanding of the precise impacts of shoe friction coefficients on basketball skills, thereby prompting considerations for the judicious selection of optimal friction coefficients and advocating for possible personalized footwear recommendations based on individual biomechanical profiles.
Since the summer of 2022, the whole world has suffered the abnormal weather phenomena of high ambient temperature. Equipment for refrigeration, particularly portable refrigeration equipment, is ...crucial for personal protection in high-temperature environments, but cooling performance and miniaturization have been challenging issues. A portable air conditioner based on a semiconductor refrigeration device for human body cooling was developed. The total weight of the device is 450 g. The overall power consumption of the device is 82 W and the energy consumption ratio of semiconductor cooling plate is 0.85. The semiconductor refrigeration technology is based on the Peltier effect, supplemented by a DC fan to send the cooling air out to a specified position or zone. The structural parts are manufactured by 3D printing technology to make the overall size of the device more compact. The air volume and cooling performance of the device were analyzed by computational fluid dynamics simulation and the temperature distribution was measured by an infrared thermal imager and other instruments, and the measured results agreed with the CFD simulation results. The test ambient temperature was 20 °C. The measurement results showed that the wind speed of the hot air outlet was 6.92 m/s and that of the cold air outlet was 8.24 m/s. The cold air surface temperature reached a stable state of 13.9 °C in about 4 min, while the hot air surface temperature reached a stable state of 47.2 °C.
As artificial synapse devices, memristors have attracted widespread attention in the field of neuromorphic computing. In this paper, Al/polymethyl methacrylate (PMMA)/egg albumen (EA)-graphene ...quantum dots (GQDs)/PMMA/indium tin oxide (ITO) electrically/optically tunable biomemristors were fabricated using the egg protein as a dielectric layer. The electrons in the GQDs were injected from the quantum dots into the dielectric layer or into the adjacent quantum dots under the excitation of light, and the EA-GQDs dielectric layer formed a pathway composed of GQDs for electronic transmission. The device successfully performed nine brain synaptic functions: excitatory postsynaptic current (EPSC), paired-pulse facilitation (PPF), short-term potentiation (STP), short-term depression (STD), the transition from short-term plasticity to long-term plasticity, spike-timing-dependent plasticity (STDP), spike-rate-dependent plasticity (SRDP), the process of learning, forgetting, and relearning, and Pavlov associative memory under UV light stimulation. The successful simulation of the synaptic behavior of this device provides the possibility for biomaterials to realize neuromorphic computing.
Purpose This study aimed to examine the effects of shoelace tightness on shoelace tension, lower limb kinematics and kinetics, and subjective perception in basketball players. Methods Sixteen male ...college basketball players performed lateral shuffle movements with their dominant foot landing on a force plate under three shoelace tightness conditions (loose, comfortable, and tight). A motion capture system and a force plate were used to measure lower limb kinematics and kinetics, respectively. A customized wireless shoelace tension system was used to measure shoelace tension at three locations on the dorsum of the foot. Visual analogue scales were used to assess perceived comfort, foot pressure, and in-shoe displacement. Results Shoelace tension increased with shoelace tightness (loose: 13.56 ± 6.21 N, comfortable: 16.14 ± 5.35 N, tight: 21.25 ± 6.19 N) and varied with shoelace position (front: 20.19 ± 5.99 N, middle: 13.71 ± 5.59 N, rear: 17.04 ± 6.95 N). Shoelace tightness also affected some of the knee joint kinematics and kinetics, as well as the subjective ratings of foot pressure and in-shoe displacement (p < 0.05). the loose shoelace reduced the knee inversion angle, while the comfortable shoelace decreased the knee negative power and work. The tight shoelace increased the perceived foot pressure and reduced the in-shoe movement (p < 0.05). Conclusions Shoelace tightness could significantly affect lower limb biomechanics and subjective perception during lateral shuffle in basketball. Basketball footwear designer should consider the incorporation of multiple shoelaces or zonal lacing systems to allow athletes to fine-tune the tension across different areas of the foot.
Abstract The purpose of this study was to investigate the effect of elastic compression on muscle strength, electromyographic (EMG), and mechanomyographic (MMG) responses of quadriceps femoris during ...isometric and isokinetic contractions. Twelve participants performed 5 s isometric maximal voluntary contractions (MVC) and 25 consecutive and maximal isokinetic knee extensions at 60 and 300 °/s with no (control, CC), medium (MC), and high (HC) compression applied to the muscle. The EMG and MMG signals were collected simultaneously with muscle isometric and isokinetic strength data. The results showed that the elevated compression did not improve peak torque, peak power, average power, total work, and regression of torque in the isometric and isokinetic contractions. However, the root mean squared value of EMG in both HC and MC significantly decreased compared with CC at 60 and 300 °/s ( p < 0.01). Furthermore, the EMG mean power frequency in HC was significantly higher than that in CC at 60 °/s ( p < 0.05) whereas no significant compression effect was found in the MMG mean power frequency. These findings provide preliminary evidence suggesting that the increase in local compression pressure may effectively increase muscle efficiency and this might be beneficial in reducing muscle fatigue during concentric isokinetic muscle contractions.
Abstract The aims of this study were to investigate the functions of muscle torque and its relation to other torque components during sprinting stance and swing phases. Three-dimensional kinematics ...and ground reaction force data were collected from eight elite male sprinters performing maximal-effort sprinting on a synthetic track. Intersegmental dynamics approach (ISD) was used to quantify lower extremity joint torque and their components during one gait cycle of the maximal speed phase during sprinting. Specifically, a modified version of the ISD was used to determine the relationship among the active muscle torque (MST), passive motion-dependent torque (MDT), ground reaction torque (EXT), gravitational torque (GTT), and net joint torque (NET) during stance and swing phases. The contribution of each torque component to lower extremity joint motion was quantified. Our results revealed that the active MST functioned to counteract EXT during stance phase. EXT acted to accelerate knee extension and hip flexion, meanwhile the muscles across these joints produced flexion torque at the knee and extension torque at the hip. During swing phase, MDT at the knee and hip joints was mainly produced by leg angular acceleration which was very significant at the moment when leg swing from forward to backward, active MST counterbalanced the effect of MDT. In summary, muscle torque functions mainly to push the ground to counter ground reaction force for controlling the movement during stance phase. However, the role of muscle torque changes during swing phase to mainly counteract the effect of MDT to control the movement direction of the lower extremity at both the hip and knee joints.
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.
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