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1

Effect of foot strike patterns and cutting angles on knee kinematics and kinetics during side-cutting maneuvers

Zhou Wenxing, Qi Yujie, Liu Mengjun, Hsiao Chengpang, Wang Lin

Acta of Bioengineering and Biomechanics

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2023

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Vol. 25, no. 1

27--34

EN

Cutting maneuvers are important actions in multidirectional sports but associated with noncontact anterior cruciate ligament (ACL) injuries. This study aimed to investigate the effect of different foot strike patterns and cutting angles on knee kinematics and kinetics. Methods: Twenty healthy male team sports athletes performed cuts with maximum speed at three angles (45, 90 and 135°) with different foot strike patterns (rearfoot strike [RFS] and forefoot strike [FFS]). A three-dimensional motion capture system combined with a force plate was used to collect makers trajectory and ground reaction force (GRF). Vertical GRF, and knee joint angles and moments were compared among these cutting tasks. Results: Regardless of foot strike patterns, increased knee flexion angle, knee valgus moment, and knee internal rotation moment were observed during cutting to sharper angles ( p < 0.001). At 90 and 135°, the FFS condition remained in a varus position and showed lower knee flexion moment than the RFS condition ( p ≤ 0.004). However, no significant differences in knee kinematic and kinetic variables were found between foot strike patterns during cutting to 45°. Conclusions: These findings suggest that sharper cutting angles potentially increase the risk of ACL injury. Compared with the RFS pattern, the FFS pattern induces a slight knee varus angle and a lower knee flexion moment at sharper angles, which might further reduce the load placed on the knee.

2

Flexural characteristics of artificial ice in winter sports rinks: experimental study and nondestructive prediction based on surface hardness method

Zhang Wenyuan, Li Junxing, Wang Lin, Yuan Baojiang, Yang Qiyong

Archives of Civil and Mechanical Engineering

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2022

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Vol. 22, no. 2

art. no. e67, 1--19

EN

Interest in the construction of prefabricated ice rink for international competition has increased in recent years, where the ice sheet is directly supported by soft thermal insulation materials. However, bending failure in the ice sheets for these rinks is highly possible because of different compression and tension behaviors. Moreover, the mechanical behaviors of the artificial ice produced layer-by-layer in rinks remain unclear. Therefore, microstructure observations, hardness tests, and three-point bending tests were conducted in this study to better understand artificial ice. First, the crystal structures were obtained through observations in both the vertical and horizontal directions. Then, the hardness of the ice surface at different temperatures, water qualities, ice-making methods, and surrounding environmental conditions was measured using the Shore hardness apparatus. Finally, systematic three-point bending tests on 80 effective ice specimens under a wide range of loading and ice-making parameters were performed. The results show that artificial ice is a typical kind of columnar ice with smaller grain sizes at lower surfaces. The ice surface hardness, roughly normally distributed, was mainly affected by temperature and ice-making mode. Moreover, it was found that all the test ice beam exhibited brittle fracture, and the flexural strength ranged from 0.84 to 2.47 MPa, with the maximum average at a strain rate of 1× 10-4 s-1 . Based on these test results, empirical functions for the effects of the investigated parameters on the flexural strength and effective modulus were developed. Also, the relationships between flexural and tensile strength for artificial ice were established using Weibull law and the coupled criterion. In addition, the linear regression model was established and verified using different prediction methods to predict the ice flexural behavior in practical rinks based on the measured hardness in a simple, reliable, and nondestructive way. The current experiment and analysis are beneficial for the design, operation and maintenance of prefabricated ice rinks.

3

Lower extremity stiffness in habitual forefoot strikers during running on different overground surfaces

Zeng Ziwei, Yin Lulu, Zhou Wenxiong, Zhang Yy, Jiang Jiayi, Wang Lin

Acta of Bioengineering and Biomechanics

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2021

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Vol. 23, no. 2

73--80

EN

Purpose: Sports surface is one of the known external factors affecting running performance and injury. To date, we have found no study that examined the lower extremity stiffness in habitual forefoot strikers running on different overground surfaces. Therefore, the objective of this study was to investigate lower extremity stiffness and relevant kinematic adjustments in habitual forefoot strikers while running on different surfaces. Methods: Thirty-one male habitual forefoot strikers were recruited in this study. Runners were instructed to run at a speed of 3.3 m/s (±5%) on three surfaces, named synthetic rubber, concrete, and artificial grass. Results: No significant differences were found in leg stiffness, vertical stiffness, and joint stiffness in the sagittal plane during running on the three surfaces ( p > 0.05). Running on artificial grass exerted a greater displacement in knee joint angle than running on synthetic rubber ( p = 0.002, 95% CI = 1.52–7.35 degrees) and concrete ( p = 0.006, 95% CI = 1.04–7.25 degrees). In the sagittal plane, peak knee moment was lower on concrete than on artificial grass ( p = 0.003, 95% CI = 0.11–0.58 Nm/kg), whereas peak ankle moment was lower on synthetic rubber than on concrete (p < 0.001, 95% CI = 0.03–0.07 Nm/kg) and on artificial grass (p < 0.001, 95% CI = 0.02–0.06 Nm/kg). Among the three surfaces, the maximal ground reaction forces on concrete were the lowest (p < 0.05). Conclusions: This study indicated that running surfaces cannot influence lower extremity stiffness in habitual forefoot strikers at current running speed. Kinematic adjustments of knee and ankle, as well as ground reaction forces, may contribute to maintaining similar lower extremity stiffness.

4

Thermal performances and optical property of poly(L-lactic acid) under the influence of N,N’-dodecanedioic bis(3-phenylpropionic acid) dihydrazide as a crystallization promoter

Yang Xiao-Yu, Zhao Li-Sha, Cai Yan-Hua, Zhao Jie, Wang Lin, Ma Xiao-Li

Polimery

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2020

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T. 65, nr 7-8

523--532

EN

Poly(L-lactic acid) (PLLA) as an important biodegradable polymer suffers from slow crystallization rate and poor heat resistance. An organic compound N,N’-dodecanedioic bis(3-phenylpropionic acid) dihydrazide (BHADD) was synthesized to evaluate its general influences on the physical properties of PLLA. The melt-crystallization process indicated that BHADD could serve as a heterogeneous nucleating agent for improving the crystallization of PLLA, and PLLA/1%BHADD exhibited the sharpest melt-crystallization peak located at the highest temperature, as well as an increase of cooling rate weakened the crystallization ability of BHADD-nucleated PLLA. And the final melting temperature also displayed the significant effect on the crystallization process of PLLA. For the cold-crystallization process, both BHADD concentration and heating rate affected the cold-crystallization behavior of PLLA/BHADD, the increasing of BHADD concentration caused the cold-crystallization peak to shift to the lower temperature; in contrast, a higher heating rate during heating leaded to the peak’s shift toward the higher temperature because of the thermal inertia. The melting behavior of PLLA/BHADD depended on the crystallization temperatures and heating rates, and the double melting peaks were attributed to the melting-recrystallization. Thermal decomposition experiment showed all PLLA/BHADD samples as the pure PLLA only exhibited one thermal decomposition stage, but PLLA/BHADD had a lower thermal stability than the pure PLLA. Additionally, the addition of BHADD seriously decreased the light transmittance of PLLA.

PL

Poli(kwas L-mlekowy) (PLLA) to ważny biodegradowalny polimer charakteryzujący się małą szybkością krystalizacji i słabą odpornością na ciepło. Dihydrazyd kwasu bis(3-fenylopropiono) N,N'-dodekanodiowego (BHADD) zsyntetyzowano w celu oceny jego wpływu na właściwości fizyczne PLLA. Przebieg procesu krystalizacji ze stopu świadczy o tym, że BHADD może służyć jako heterogeniczny środek zarodkujący zwiększający szybkość krystalizacji PLLA. Mieszanina PLLA/1% mas. BHADD wykazywała najostrzejszy pik krystalizacji ze stopu zlokalizowany w zakresie najwyższej temperatury, a jednocześnie większą szybkość chłodzenia osłabiającą zdolność krystalizacji PLLA zarodkowanej BHADD. Również końcowa temperatura topnienia w istotnym stopniu wpływała na proces krystalizacji PLLA. W procesie krystalizacji na zimno zarówno stężenie BHADD, jak i szybkość ogrzewania oddziaływały na zachowanie PLLA/BHADD podczas krystalizacji, zwiększenie stężenia BHADD powodowało przesunięcie piku krystalizacji na zimno w kierunku niższej temperatury, natomiast większa szybkość ogrzewania prowadziła do, spowodowanego bezwładnością cieplną, przesunięcia piku krystalizacji na zimno w kierunku wyższej temperatury. Zachowanie PLLA/BHADD podczas topnienia zależało od temperatury krystalizacji i szybkości ogrzewania, a drugi pik topnienia przypisano procesowi rekrystalizacji. Badany przebieg rozkładu termicznego świadczy, że wszystkie próbki PLLA/BHADD, tak jak czysty PLLA, wykazywały tylko jeden etap rozkładu termicznego, mieszanina PLLA/BHADD charakteryzowała się jednak mniejszą stabilnością termiczną niż czysty PLLA. Dodatek BHADD w znacznym stopniu zmniejszył przepuszczalność światła PLLA.