such that the y-axis represented the horizontal direction from the kicking tee to the target, the z-axis was vertical, and the x-axis was the cross-product of the two. Following a self-selected warm-up, including submaximal and maximal familiarisation kicks, participants were asked to kick as if from their maximum range until five or six trials were collected. Participants were allowed sufficient self-selected rest between kicks. Marker position data were reconstructed using Vicon© Nexus (v. 1.8, UK).
Kicking foot take-off (KFO) from its last ground contact before ball contact (BC) was identified as the frame when the marker on the fifth metatarsal-phalangeal joint was greater than 0.1 m above the ground. Support foot contact (SFC) was identified as the frame in which the vertical GRF first increased, and subsequently remained, above 10 N. Ball contact was identified as the frame in which the resultant displacement of the centre of the ball was first greater than, and subsequently remained above, the determined measurement precision (0.9 mm). The marker trajectories and raw GRF data prior to BC were exported to Visual3D (v. 5.0, C-Motion©, USA). Gaps in the marker trajectory data (n ≤ 10 samples) were interpolated with a cubic spline using three data points either side of the gap. All marker and GRF data were padded by reflection (n = 20 points) at both ends and filtered using a fourth order zero-lag Butterworth filter with the same cut-off frequency (18 Hz) to prevent potential artefacts in the subsequently determined joint kinetics (Bezodis et al., 2013).
The 14-segment model was reconstructed from the marker data using a global optimisation approach (Lu & O’Connor, 1999) which permitted 3-D rotations at all joints but no relative segmental translation. Inertia parameters were obtained from de Leva (1996) to define the properties of the body segments. Hip, knee and ankle joint angular displacements were calculated relative to the proximal segment at each joint using an XYZ Cardan rotation sequence and joint angular velocities were calculated with the proximal segment of the joint used as the both the reference segment and resolution coordinate system. Full hip and knee extension were defined as 0°, and the ankle angle from each participant’s static trial was defined as 0°. Resultant joint moments and powers were resolved into the joint coordinate system through an inverse dynamics analysis. All joint mechanics were time-normalised to 101 points across the kicking phase (from SFC to BC) and data prior to SFC (termed the late approach phase) were normalised using the same scale factor. Initial ball velocity was calculated in each direction by fitting a polynomial to the first four frames of recorded ball flight (first order for the horizontal displacements and second order for vertical displacement) and resultant ball velocity was determined. Kick accuracy was quantified as the angle between the resultant ball velocity vector and the y-axis when projected onto the x-y plane. To allow comparison with previous studies, discrete values were normalised using the recommendations of Hof (1996) and the data for left-footed kickers was adjusted to correspond with the convention defined for right-footed kickers. For all continuous and discrete variables, mean values were calculated from all trials for each participant, and the mean ± s across all participants was subsequently determined.
เช่นที่แกน y แสดงทิศทางแนวนอนจากทีเตะเพื่อเป้าหมาย z-axis การคือแนวตั้ง และแกนถูกคูณ ไขว้สอง ต่ออุ่นเครื่องที่เลือกด้วยตนเอง เตะ submaximal และสูงสุด familiarisation รวมทั้งผู้เข้าร่วมได้ต้องเตะว่าช่วงสูงสุดจนถึงห้า หรือหกทดลองถูกรวบรวม ผู้เรียนได้รับอนุญาตเหลือตัวเลือกเพียงพอระหว่างเตะ เครื่องหมายตำแหน่งข้อมูลถูกเชิดใช้ Vicon © Nexus (v. 1.8 สหราชอาณาจักร)เตะเท้าตัด (KFO) จากการติดต่อของเราสุดท้ายก่อนที่ลูกบอลติดต่อ (BC) ระบุเป็นเฟรมเมื่อเครื่องหมายบนร่วม metatarsal phalangeal ห้ามากกว่า 0.1 m เหนือพื้นดิน ระบุเหลือเท้า (SFC) เป็นเฟรมที่ GRF แนวตั้งแรก เพิ่มขึ้น และในเวลาต่อมา ยังคง เหนือ 10 N. ลูกติดต่อระบุเป็นเฟรมที่แทนผลแก่ของศูนย์กลางของลูกบอลเป็นครั้งแรกมากกว่า และมาอยู่ข้างบน ความแม่นยำของวัดกำหนด (0.9 mm) เครื่องหมาย trajectories และโปรแกรมเมอร์ GRF ก่อน BC ถูกส่งออกไปยัง Visual3D (v. 5.0, C เคลื่อนไหว ©, สหรัฐอเมริกา) ช่องว่างในข้อมูลเครื่องหมายวิถี (n ≤ 10 ตัวอย่าง) มีการส ด้วยเหมือนลูกบาศก์ที่ใช้จุดข้อมูลแต่ละด้านของช่องว่าง เครื่องหมายและ GRF ข้อมูลทั้งหมดถูกเบาะ โดยสะท้อน (n = 20 คะแนน) ที่ปลายทั้งสอง และใช้กรองสี่สั่งกรองบัตเตอร์เวิร์ทศูนย์ความล่าช้า ด้วยความถี่ตัดเดียวกัน (Hz 18) เพื่อป้องกันสิ่งที่อาจเกิดขึ้นในจลนพลศาสตร์ร่วมมากำหนด (Bezodis et al., 2013)The 14-segment model was reconstructed from the marker data using a global optimisation approach (Lu & O’Connor, 1999) which permitted 3-D rotations at all joints but no relative segmental translation. Inertia parameters were obtained from de Leva (1996) to define the properties of the body segments. Hip, knee and ankle joint angular displacements were calculated relative to the proximal segment at each joint using an XYZ Cardan rotation sequence and joint angular velocities were calculated with the proximal segment of the joint used as the both the reference segment and resolution coordinate system. Full hip and knee extension were defined as 0°, and the ankle angle from each participant’s static trial was defined as 0°. Resultant joint moments and powers were resolved into the joint coordinate system through an inverse dynamics analysis. All joint mechanics were time-normalised to 101 points across the kicking phase (from SFC to BC) and data prior to SFC (termed the late approach phase) were normalised using the same scale factor. Initial ball velocity was calculated in each direction by fitting a polynomial to the first four frames of recorded ball flight (first order for the horizontal displacements and second order for vertical displacement) and resultant ball velocity was determined. Kick accuracy was quantified as the angle between the resultant ball velocity vector and the y-axis when projected onto the x-y plane. To allow comparison with previous studies, discrete values were normalised using the recommendations of Hof (1996) and the data for left-footed kickers was adjusted to correspond with the convention defined for right-footed kickers. For all continuous and discrete variables, mean values were calculated from all trials for each participant, and the mean ± s across all participants was subsequently determined.
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