Objective:To study the effect of pig interleukin 2(IL 2) eukaryon expression plasmid on cellular immune responses of BALB/c mice immuned with pcDNA PRRSV ORF5 DNA vaccine.Methods:BALB/c mice were immunized with pcDNA PRRSV ORF5 DNA vaccine and pig interleukin 2(IL 2) eukaryon expression plasmid by the routes of co injection and DNA vaccine injection alone respectively, with PBS and pcDNA3 1(+) as controls. Fluoresecence Activated Cell Sorter(FACS),T lymphocyte proliferation test(MTT) were used to detect the number of CD4 +、CD8 + and the T lymphocyte proliferation in peripheral blood of mice vaccinated.Results:ConA response of T lymphocytes in blood was higher in experiment group than the control group ( P

Objectives To explore the effect of fatigue intervention on biomechanics of lower extremity and performance during the stretch-shortening cycle(SSC) movement-drop jumps(DJ).Methods The Vicon motion capture system and 3D Kistler force plates were used to collect sagittal plane kinematics and ground reaction force data synchronously of a total of fifteen trained male athletes under pre-and post-fatigue conditions with shuttle running + vertical jumping fatigue protocol.The joint angle,joint moment,power,work,and leg/joint stiffness were compared before and after fatigue.Results After fatigue,the maximum height of DJ decreased(P＜0.05),while the touchdown angle and the range of motion(△θ) of knee and ankle joints,as well as the occurrence time for the eccentric,concentric and total phase increased(P＜0.05).However,the maximum push-off moment and power of knee reduced(P＜ 0.05).The stiffness of knee and ankle joints during the eccentric phase reduced,resulting in the reduction of the leg stiffness(P＜0.05).Moreover,the energy absorption and net energy of the ankle joint decreased;meanwhile,the energy contribution of the knee joint decreased during the eccentric phase of a DJ task.Conclusion Fatigue changes the movement pattern,decreasing the control ability of the lower extremity especially in the knee and ankle joint,and results in decreased performance.Moreover,the decrease of leg,ankle and knee stiffness and the corresponding energy can be used as sensitive indexes to evaluate the performance of drop jumps in a fatigued condition.

Achilles tendon is the key structure to connect the heel and foot plantar flexors and transmit the force from the leg triceps muscle, which is the key to storing and releasing energy storage during running and jumping. At present, the primary causes of Achilles tendon injury are non-homologous loading during stance phase and deficient recovery after overload. However, the relevant measures to prevent Achilles tendon injury cannot achieve full recovery. This paper reviewed the research progress of Achilles tendon’s motor function and its application in biomechanics domestically and internationally, reconsidering the role of Achilles tendon in human running and jumping which included anatomical structure of the Achilles tendon, the relationship between internal force and external force, and the effective training program. The key for future research on motor function of Achilles tendon is to improve its mechanical properties, keep the increased load in a better range and ultimately improve motion performance and reduce sports injury from the source.

Objective To investigate the effects of different foot strike patterns during running on Achilles tendon(AT)morphology and mechanical loading.Methods Fourteen habitual rearfoot strike runners and 14 habitual forefoot strike runners were recruited.Morphological characteristics(tendon length,cross-sectional area,and thickness)of the AT were collected using ultrasound imaging.The AT loading characteristics(plantar flexion moment,tendon force,load rate,impulse,and stress)of subjects wearing cushioned running shoes while running at a speed of 10 km/h were collected and calculated using a three-dimensional force measurement treadmill.Results Compared to habitual rearfoot strike runners,habitual forefoot strike runners showed a significant increase in peak plantar flexion moment of ankle joint,AT peak force,average loading rate,and peak loading rate(P<0.05).However,the differences in AT length,cross-sectional area,and thickness between the two groups were not statistically significant(P>0.05).Conclusions Long-term forefoot strike patterns can adaptively enhance the mechanical loading characteristics of the AT during repetitive stretch-shortening cycles.

The research progress in fatigue protocols and biomechanics of lower extremity and its relationship with injury induced by exercise-induced fatigue was reviewed in this paper. At present, fatigue protocols can be divided into the traditional fatigue-induced protocol and the functional fatigue-induced protocol under laboratory condition. The former mainly includes power-cycling model, treadmill run model and step-ups model, while the latter is closer to what is experienced during competition, which is usually shown as multidirectional movements. In addition, the biomechanical measures of exercise-induced fatigue mainly include kinematics, ground reaction force, joint mechanics and electromyography. Different fatigue protocols do not uniformly produce alterations in lower limb biomechanical factors. The refinement of fatigue protocols and specific indicators should be considered in future studies, in order to compare the induced effects of fatigue protocols and provide references for the selection of fatigue protocols in laboratory tests. Meanwhile, the relationship between the response of brain-nerve system and the activation of musculoskeletal system for specific athletic task should be focused, so as to understand the difference of biomechanical mechanisms between fatigue protocols and further explore the effect of exercise-induced fatigue on sports injuries.

Objective By establishing the intervention mode of 12-week gait retraining (GR) (with the specific aim of changing the habitual running gait), to determine the changes of vertical ground reaction force (vGRF), kinematics and dynamics of hip, knee, ankle joints, as well as stiffness of lower limbs in running before and after GR, and to explore the influence of running posture transformation on impact force and lower limb biomechanics. Methods Vicon motion capture system and Kistler 3D force measurement platform were used to collect the GRF and marker track of 30 runners (15 in experimental group and 15 in control group) before and after GR with the minimalist shoes at a speed of 12 km/h±5%. Results A total of 17 subjects (9 in experimental group and 8 in control group) completed the GR. After GR, the maximum loading rate of both groups decreased significantly, and the maximum loading rate of experimental group was lower than that of control group. The foot strike angle in experimental group decreased significantly after GR, and the plantarflexion angle and hip joint angular extension velocity increased in both groups. The force moment of ankle joint increased in experimental group, and the stiffness of lower limbs was significantly improved in both groups. Conclusions A 12-week GR exercise intervention model was successfully established, with 78% conversion rate (from rearfoot strike to forefoot strike). GR can effectively avoid the peak of impact force, reduce the maximum loading rate, increase the lower limb stiffness, and thus reduce or even avoid the risk of running injury caused by impact force and may provide a possibility for the improvement of running economy.

Objective To examine the effects of shoe cushioning on impact characteristics, kinematics and dynamics of lower extremities before and after neuromuscular fatigue during drop landing. Methods Fifteen trained male athletes were required to execute three successful trials of drop landing from a 60-cm platform before and after fatigue protocol. The impact force, loading rate, lower extremity kinematics, joint moment, joint stiffness were compared. Results Before fatigue, highly-cushioned shoes reduced the loading rate at heel before fatigue, and the time to peak loading rate of heel was significantly shorter than that of control shoes. After fatigue, highly-cushioned shoes significantly reduced the peak impact force and loading rate at heel, loading rate at forefoot. Meanwhile the time to peak impact force and peak loading rate at heel were significantly longer, and the contact and minimum angle of ankle were significantly greater. No significant changes were found in lower extremity stiffness, peak moment and joint stiffness of ankle. Conclusions In the situation where neuromuscular activity is reduced, highly-cushioned shoes can effectively attenuate the impact, thereby helping to avoid or reduce the potential impact damage after fatigue.

Objective To explore the relationship between shoe comfort and foot loading characteristics in two types of basketball shoe during different basketball footwork. Methods Two Kistler 3D force platforms and Medilogic insole plantar pressure system were used to collect the kinetic data of 12 healthy male basketball players wearing two types of basketball shoe (shoe L and shoe N) during three varieties of basketball footwork (side-step cutting, 90° varied-direction running, lay-up), including peak impact force, peak loading rate, and peak plantar pressure. The perception test scale was used to evaluate comfort for two types of basketball shoe during three kinds of basketball footwork. Results For the two types of basketball shoes, there was no significantly difference in the impact force during the three kinds of basketball footwork, but the plantar pressure of shoe L was significantly greater than that of shoe N during side-step cutting and lay-up. Shoe N was significantly more comfortable than shoe L, with a significant difference in preference (heel stability, heel responsiveness, forefoot cushioning, heel cushioning, and overall liking) and intensity (forefoot and heel cushioning) on a dynamic scale. Conclusions The plantar pressure and comfort show significant differences in the two types of shoes; however, none of the shoes appeared definitively superior in the two evaluations. It is suggested that the biomechanical characteristics of the shoes and the subjective evaluation of the athletes should be considered in the overall design and evaluation of specialized shoes.

Objective To investigate the mechanical properties of Achilles tendon (AT) during running under different shoe conditions (minimalist vs conventional shoes). MethodsSixteen healthy male runners with habitual rearfoot strike patterns were recruited to complete the running trials at the speed of 3.16~3.50 m/s under two shoe conditions. The cross-sectional area of the AT was obtained by ultrasound imaging. Sagittal plane ankle kinematics and ground reaction forces were recorded by motion capture system and three-dimensional force platform simultaneously. Mechanical properties of the ankle and AT were calculated. Paired t test was used to compare the effects of two shoe conditions on various parameters (ankle angle, strike angle, AT force, stress, strain, etc). ResultsCompared with conventional shoes, foot inclination angle was significantly reduced by 39.9% with minimalist shoes. Obvious increase in ankle moment, peak AT force, peak AT loading rate, average loading rate, and obvious decrease in time to peak AT force were observed with minimalist shoes. Peak AT stress, peak AT strain and corresponding stress rate, peak strain rate also increased significantly with minimalist shoes. ConclusionsGreater AT loading was observed when runners with habitual rearfoot strike pattern in conventional shoes begin to wear minimalist shoes. Therefore, a gradual transition to minimalist shoes was recommended for them so as to improve the ability to load adaptively.

Objective To explore the correlation between foot morphology and toe/metatarsophalangeal joint muscle strength. Methods Twenty-six male recreational runners were recruited. Foot length, truncated foot length, foot width, navicular height, dorsum height at 50% of the foot length, metatarsophalangeal joint strength, tensile force of the first and remaining four toes were measured by using digital caliper, metatarsophalangeal joint strength tester and dynameter, respectively. Partial correlations were used to analyze the correlation between foot morphology and foot muscle strength. ResultsWith adjusted age and body mass index (BMI), the foot width in standing position and truncated foot length in sitting and standing position were positively correlated to tensile force of the first toe; the foot length, foot width and truncated foot length were positively correlated to tensile force of the remaining four toes in both positions, and the arch height index in sitting position was negatively associated with tensile force of the remaining four toes; the foot width was positively correlated to metatarsophalangeal joint strength in both positions. Conclusions The longer foot length, foot width, truncated foot length, and the lower arch height in normal range might be related to the larger foot muscle strength. The consideration of the differences in foot morphological characteristics in different positions during the measurement of foot morphology can provide references for predicting foot muscle strength and preventing foot injury.