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OBJECTIVE:Knee adduction moment and knee adduction angular impulse enlargement is the main biomechanical risk factor of knee osteoarthritis.According to the survey,a change in the foot progression angle could effectively change the motion mode of patients with knee osteoarthritis.However,the impact of toe-in and toe-out on knee adduction moment and knee adduction angular impulse in young and elderly patients did not reach a consensus.Therefore,this study comprehensively discussed the effect of foot progression angle on knee adduction moment and knee adduction angular impulse in different populations through meta-analysis and provided a reference for the treatment of knee osteoarthritis. METHODS:By June 2022,searches were conducted on Web of Science,EBSCO,PubMed and CNKI databases using"foot progression angle,knee adduction moment,knee adduction angular impulse,gait"as Chinese and English search terms.Self-controlled randomized controlled studies analyzing the effects of toe-in and toe-out on knee adduction moment bimodality and knee adduction angular impulse were included.The cochrane bias risk assessment tool was utilized to make a quality evaluation of the literature.Stata 15.1 software was used for subgroup analysis to determine the effect of foot progression angle on knee adduction moment and knee adduction angular impulse.Meta-regression analysis was used to further determine characteristics of outcome indicators(knee adduction moment,knee adduction angular impulse)changing with foot progression angle. RESULTS:(1)A total of 15 self-control trials and 2 randomized controlled trials(455 subjects)were included in the meta-analysis.All of the included articles were of medium to high quality.(2)The meta-analysis results showed that the toe-in gait could reduce the first peak of knee adduction moment(SMD=-0.380,95%CI:-0.710 to-0.060,P=0.022)and knee adduction angular impulse(SMD=-1.470,95%CI:-2.160 to-0.770,P<0.001)in young patients.The toe-out gait reduced the second peak of knee adduction moment(SMD=-0.720,95%CI:-1.010 to-1.440,P<0.001)in young patients.In addition,toe-in gait could reduce the first peak of knee adduction moment in elder patients(SMD=-0.550,95%CI:-0.800 to-0.300,P<0.001),but increase the second peak knee adduction moment of elderly(SMD=0.280,95%CI:-0.010 to 0.560,P=0.047).The toe-out gait could decrease the second peak knee adduction moment in this population(SMD=-0.510,95%CI:-0.830 to-0.190,P=0.002).(3)Meta-regression showed that the greater the toe-out in elderly patients,the lower the second peak knee adduction moment. CONCLUSION:(1)Toe-in reduced the first peak knee adduction moment and knee adduction angular impulse in young knee osteoarthritis patients aged 18 to 34 years.Since knee adduction moment and knee adduction angular impulse were associated with medial knee loading and knee osteoarthritis incidence,toe-in gait intervention may be a suitable rehabilitation strategy for young patients.(2)Toe-in increased the second peak of knee adduction moment in older knee osteoarthritis patients over 60 years of age,which may exacerbate knee osteoarthritis in this population.However,the second peak of knee adduction moment during walking in this population decreases as the toe-out increases,contributing to a reduction in medial knee loading,suggesting that older patients may consider using toe-out gait during walking.

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Generation of angular impulse during foot contact is regulated by controlling the relative orientation between the total body center of mass (CoM) and the reaction force (RF) applied to the feet. Between-task differences in initial CoM horizontal momentum were hypothesized to alter how forward angular impulse was generated during two forward translating tasks. Five skilled athletes performed standing (SFS) and running (RFS) forward somersaulting dives. Sagittal plane kinematics and RFs were obtained during the take-off phase of both tasks. The initial CoM momentum differences resulted in significant differences in control of the CoM relative to the RF, RF generation mechanisms, and knee and hip net joint moments (NJMs). During the RFS, angular impulse was generated by positioning the feet anterior to the CoM at initial contact so that the RF passed posterior to the CoM throughout the take-off phase. During the SFS, angular impulse was generated by positioning the CoM anterior to the feet prior to the push interval so that the RF passed posterior to the CoM. Task-specific differences in segment kinematics and RF direction contributed to the redistribution of knee and hip NJMs. These results suggest that initial conditions influence strategies the nervous system uses to satisfy task objectives.

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Soft landing after jumping is associated with the prevention of lower extremity injuries during sports activities in terms of the energy absorption mechanisms. In this study, the contribution of lower extremity joints during soft landing was investigated. Subjects comprised 20 healthy females. Kinetics and kinematics data were obtained during drop vertical jumps using a three-dimensional motion analysis system. Negative mechanical work values in the lower extremity joints were calculated during landing. A multiple regression analysis was performed to determine which lower extremity joints contributed more in achieving soft landing. The means of mechanical work of the hip, knee, and ankle in the sagittal plane were -0.30 ± 0.17, -0.62 ± 0.31, and -1.03 ± 0.22 J/kg, respectively. Results showed that negative mechanical work in the hip and knee is effective in achieving soft landing. These findings indicate that energy absorption in the hip and knee joints might be an important factor in achieving soft landing, whereas that in the ankle has a negative effect. Therefore, when improving soft landing techniques, we should consider energy absorption in the hip and knee via eccentric activation of the hip and knee extensors during landing.

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BACKGROUND: Walking and mobility are essential for a satisfactory quality of life. However, individuals with transfemoral amputations have difficulties in preventing falls due to prosthetic knee buckling, defined as the sudden loss of postural support during weight-bearing activities. The risk of prosthetic knee buckling can be evaluated by determining the prosthetic knee angular impulse (PKAI) during the early stance phase. However, little is known about the factors associated with PKAI in individuals with unilateral transfemoral amputations. RESEARCH QUESTION: What are the demographic factors that can be associated with the risk of prosthetic knee buckling, quantified by PKAI, during walking in individuals with unilateral transfemoral amputations? METHODS: Thirteen individuals with unilateral transfemoral amputations were instructed to perform level walking at a comfortable, self-selected speed on a straight, 10-m walkway. PKAI was calculated as the time integral of the prosthetic knee external flexion-extension moment during the initial 40 % of the prosthetic gait cycle. We used Pearson's correlation coefficients to examine the relationship of PKAI with the following variables: the subject's body height, body mass, and age; the time since amputation; and the current prosthesis use history. Furthermore, an independentt-test was used to compare PKAI according to the sex (male vs. female) and etiology (trauma vs. nontrauma). RESULTS: PKAI exhibited a significant negative linear relationship with the subject's body height and body mass. However, it showed no significant correlation with age, the time since amputation, and the current prosthesis use history. It was also significantly greater in women than in men and was not significantly influenced by the etiology. SIGNIFICANCE: Awareness about demographic factors associated with PKAI during walking can contribute to fall assessments in gait rehabilitation programs for individuals with unilateral transfemoral amputations.

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In this study, the kinetic characteristics of lower limbs during batting were investigated by comparing batting off a tee with batting a pitched ball. Participants were 10 male collegiate baseball players who performed tee batting (TB) and batting using a pitching machine (MB; approximate ball speed: 33.3 m/s). Three-dimensional coordinate data were acquired using a motion capture system, and ground reaction forces were measured using three force platforms. Lower limb joint torques were obtained by inverse dynamics calculations. The results indicated that the angular velocity of the lower trunk was larger in TB than in MB for rotation. The swing time from stride foot contact with the ground to ball impact was significantly longer in MB than in TB. The angular impulses of bilateral hip adduction, pivot hip external rotation, and stride hip and knee extension torques were significantly larger in MB, suggesting that batters exert these joint torques earlier for pitched balls to handle time constraints by changing the rotation of the lower trunk in response to the unknown ball location and speed in MB. These findings will help to fill a gap in the literature and provide coaching insights for improving batting motion.

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A local minimum for running energetics has been reported for a specific bending stiffness, implying that shoe stiffness assists in running propulsion. However, the determinant of the metabolic optimum remains unknown. Highly stiff shoes significantly increase the moment arm of the ground reaction force (GRF) and reduce the leverage effect of joint torque at ground push-off. Inspired by previous findings, we hypothesized that the restriction of the natural metatarsophalangeal (MTP) flexion caused by stiffened shoes and the corresponding joint torque changes may reduce the benefit of shoe bending stiffness to running energetics. We proposed the critical stiffness, kcr, which is defined as the ratio of the MTP joint (MTPJ) torque to the maximal MTPJ flexion angle, as a possible threshold of the elastic benefit of shoe stiffness. 19 subjects participated in a running test while wearing insoles with five different bending stiffness levels. Joint angles, GRFs, and metabolic costs were measured and analyzed as functions of the shoe stiffness. No significant changes were found in the take-off velocity of the center of mass (CoM), but the horizontal ground push-offs were significantly reduced at different shoe stiffness levels, indicating that complementary changes in the lower-limb joint torques were introduced to maintain steady running. Slight increases in the ankle, knee, and hip joint angular impulses were observed at stiffness levels exceeding the critical stiffness, whereas the angular impulse at the MTPJ was significantly reduced. These results indicate that the shoe bending stiffness is beneficial to running energetics if it does not disturb the natural MTPJ flexion.

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Stepping on coronally-uneven and unpredictable terrain is a common gait disturbance that can lead to injurious falls. This study identified the biomechanical response to a step on coronally-uneven and unpredictable terrain through observation of participants traversing a walkway with a middle step that could be blinded to participants, and positioned either 15° inverted, 15° everted, or flush. The isolated disturbance was intended to simulate stepping on a rock, object, or other transient coronal disturbance and allow for observation of the subsequent balance recovery. Gait balance was affected by the disturbance, and was measured by the range of coronal whole-body angular momentum, which compared to unblinded flush, increased during blinded eversion, and decreased during blinded inversion. Analysis of external coronal moments applied to the body about the center-of-mass by the disturbed and recovery legs suggested the disturbed leg contributed more to differences in the range of coronal angular momentum, and thus more to balance recovery. The stepping strategy for the disturbed and recovery steps was measured by mediolateral foot position, and appeared to have been mostly affected by anticipatory actions taken by participants before stepping on the blinded terrain, and not by the terrain angle. In contrast, on the disturbed step, distinct differences between blinded inversion and eversion in the coronal moments of the hip and ankle suggested the hip and ankle joint moment strategies were important for adapting to the terrain angle. A clinical implication of this result was interventions that augment these moments may improve gait balance control on coronally-uneven and unpredictable terrain.

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During initiation of a piqué turn, a dancer generates impulse to achieve the desired lateral translation and whole-body rotation. The goal of this study was to determine how individuals regulate impulse generation when initiating piqué turns with increased rotational demands. Skilled dancers (n=10) performed single (∼360°) and double (∼720°) piqué turns from a stationary position. Linear and angular impulse generated by the push and turn legs were quantified using ground reaction forces and compared across turn conditions as a group and within a dancer using probability-based statistical methods. The results indicate that as the rotation demands of the piqué turn increased, the net angular impulse generated increased whereas net lateral impulse decreased. Early during turn initiation, the free moment contributed to angular impulse generation. Later during turn initiation, horizontal reaction forces were controlled to generate angular impulse. As rotational demands increased, the moment applied increased primarily from redirection of the horizontal reaction force (RFh) at the push leg and a combination of RFh magnitude and moment arm increases at the turn leg. RFh at each leg were coordinated to limit unwanted net linear impulse. Knowledge of observed subject-specific mechanisms is important to inform the design of turning performance training tools.

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This study determined how dancers regulated angular and linear impulse during the initiation of pirouettes of increased rotation. Skilled dancers (n = 11) performed single and double pirouette turns with each foot supported by a force plate. Linear and angular impulses generated by each leg were quantified and compared between turn types using probability-based statistical methods. As rotational demands increased, dancers increased the net angular impulse generated. The contribution of each leg to net angular impulse in both single and double pirouettes was influenced by stance configuration strategies. Dancers who generated more angular impulse with the push leg than with the turn leg initiated the turn with the center of mass positioned closer to the turn leg than did other dancers. As rotational demands increased, dancers tended to increase the horizontal reaction force magnitude at one or both feet; however, they used subject-specific mechanisms. By coordinating the generation of reaction forces between legs, changes in net horizontal impulse remained minimal, despite impulse regulation at each leg used to achieve more rotations. Knowledge gained regarding how an individual coordinates the generation of linear and angular impulse between both legs as rotational demand increased can help design tools to improve that individual's performance.

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BACKGROUND: The Advanced Throwers Ten Exercise Program incorporates sustained isometric contractions in conjunction with dynamic shoulder movements. It has been suggested that incorporating isometric holds may facilitate greater increases in muscular strength and endurance. However, no objective evidence currently exists to support this claim. HYPOTHESIS/PURPOSE: The purpose of this research was to compare the effects of a sustained muscle contraction resistive training program (Advanced Throwers Ten Program) to a more traditional exercise training protocol to determine if increases in shoulder muscular strength and endurance occur in an otherwise healthy population. It was hypothesized that utilizing a sustained isometric hold during a shoulder scaption exercise from the Advanced Throwers Ten would produce greater increases in shoulder strength and endurance as compared to a traditional training program incorporating a isotonic scapular plane abduction (scaption) exercise. STUDY DESIGN: Randomized Clinical Trial. METHOD: Fifty healthy participants were enrolled in this study, of which 25 were randomized into the traditional training group (age: 26 ± 8, height:172 ± 10 cm, weight: 73 ± 13 kg, Marx Activity Scale: 11 ± 4) and 25 were randomized to the Advanced Throwers Ten group (age: 28 ± 9, height: 169 ± 23 cm, weight: 74 ± 16 kg, Marx Activity Scale: 11 ± 5). No pre-intervention differences existed between the groups (P>0.05). Arm endurance and strength data were collected pre and post intervention using a portable load cell (BTE Evaluator, Hanover, MD). Both within and between group analyses were done in order to investigate average torque (strength) and angular impulse (endurance) changes. RESULTS: The traditional and Advanced Throwers Ten groups both significantly improved torque and angular impulse on both the dominant and non-dominant arms by 10-14%. There were no differences in strength or endurance following the interventions between the two training groups (p>0.75). CONCLUSIONS: Both training approaches increased strength and endurance as the muscle loads were consistent between protocols indicating that either approach will have positive effects. LEVEL OF EVIDENCE: Level 2.