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Kim Bennell, Kay Crossley, Tim Wrigley and Julie Nitschke

The aim of our study was to assess the interday test-retest reliability (focussing on the separate contribution of systematic and random error) of selected 10-trial mean ground reaction force (GRF) parameters and GRF symmetry indices measured during running. Ten competitive male heel-strike runners (aged, 26.2 ± 5.7 years) performed 10 successful running trials across the force platform at a constant velocity of 4.0 m · s-1 ±10% wearing their customary running footwear. The testing procedure was repeated under similar conditions 1 week later. The results showed no statistically significant differences between the means of Test 1 and Test 2 for most GRF parameters and symmetry indices, indicating non-significant systematic error. Correlation coefficients ranged from 0.73 to 0.99 for GRF parameters. Random error was small with SEmeas less than 10% of the Test 1 mean value for almost all GRF parameters. Symmetry indices displayed correlation coefficients ranging from −0.44 to 0.91. Based on these and the size of the SEmeas, the symmetry indices displayed variable reliability, with the most reliable being those associated with peak vertical active force and peak horizontal propulsive force.

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Erik A. Wikstrom, Kyeongtak Song, Kimmery Migel and Chris J. Hass

potentially reduce PTOA prevalence. While the underlying etiology of ankle joint degeneration has not yet been elucidated, a growing body of evidence is emerging regarding possible biomechanical 6 – 8 influences on cartilage health. Vertical ground reaction force (vGRF) and vGRF loading rate, defined as the

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Caroline Lisee, Tom Birchmeier, Arthur Yan, Brent Geers, Kaitlin O’Hagan, Callum Davis and Christopher Kuenze

ACL injury associated with common sport-related tasks. Kinetic variables, such as peak vertical ground reaction force (vGRF), and linear loading rates provide key insights into the characteristics of forces acting on the body as well as an individual’s response to these forces during functional tasks

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Ewald M. Hennig and Mario A. Lafortune

Using data from six male subjects, this study compared ground reaction force and tibial acceleration parameters for running. A bone-mounted triaxial accelerometer and a force platform were employed for data collection. Low peak values were found for the axial acceleration, and a time shift toward the occurrence of the first peak in the vertical force data was present. The time to peak axial acceleration differed significantly from the time to the first force peak, and the peak values of force and acceleration demonstrated only a moderate correlation. However, a high negative correlation was found for the comparison of the peak axial acceleration with the time to peak vertical force. Employing a multiple regression analysis, the peak tibial acceleration could be well estimated using vertical force loading rate and peak horizontal ground reaction force as predictors.

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AmirAli Jafarnezhadgero, Morteza Madadi-Shad, Christopher McCrum and Kiros Karamanidis

.01 ± 0.01 −0.01 ± 0.01 0.02 ± 0.01 0.01 ± 0.02 −0.01 ± 0.02 Negative peak −0.07 ± 0.02 −0.06 ± 0.02 −0.01 ± 0.03 −0.07 ± 0.03 −0.06 ± 0.03 −0.01 ± 0.03 GRF = ground reaction force; TTP = time to peak; FM = free moment. *Significant within group difference. **Significant difference between control and

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Ali Jalalvand and Mehrdad Anbarian

Helsinki, approved all the procedures before the beginning of the investigation. Instrumentation Ground reaction force data were collected using a Kistler force plate (type 9281; Kistler Instrument AG, Winterthur, Switzerland) at a frequency of 1000 Hz. Studies have shown that the Kistler force plate is a

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Gaspare Pavei, Elena Seminati, Jorge L.L. Storniolo and Leonardo A. Peyré-Tartaruga

We compared running mechanics parameters determined from ground reaction force (GRF) measurements with estimated forces obtained from double differentiation of kinematic (K) data from motion analysis in a broad spectrum of running speeds (1.94–5.56 m⋅s–1). Data were collected through a force-instrumented treadmill and compared at different sampling frequencies (900 and 300 Hz for GRF, 300 and 100 Hz for K). Vertical force peak, shape, and impulse were similar between K methods and GRF. Contact time, flight time, and vertical stiffness (kvert) obtained from K showed the same trend as GRF with differences < 5%, whereas leg stiffness (kleg) was not correctly computed by kinematics. The results revealed that the main vertical GRF parameters can be computed by the double differentiation of the body center of mass properly calculated by motion analysis. The present model provides an alternative accessible method for determining temporal and kinetic parameters of running without an instrumented treadmill.

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Brian J. O'Connor, H. John Yack and Scott C. White

A strategy is presented for temporally aligning ground reaction force and kinematic data. Alignment of these data requires marking both the force and video records at a common event. The strategy uses the information content of the video signal, which is A/D converted along with the ground reaction force analog signals, to accomplish this alignment in time. The vertical blanking pulses in the video signal, which define the start of each video field, can be readily identified, provided the correct A/D sampling rate is selected. Knowledge of the position of these vertical blanking pulses relative to the synchronization pulse makes it possible to precisely align the video and analog data in time. Choosing an A/D sampling rate of 598 Hz would enable video and analog data to be synchronized to within 1/1,196 s. Minimizing temporal alignment error results in greater accuracy and .reliability in calculations used to determine joint kinetics.

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Ewald M. Hennig, Thomas L. Milani and Mario A. Lafortune

Ground reaction force data and tibial accelerations from a skin-mounted transducer were collected during rearfoot running at 3.3 m/s across a force platform. Five repetitive trials from 27 subjects in each of 19 different footwear conditions were evaluated. Ground reaction force as well as tibial acceleration parameters were found to be useful for the evaluation of the cushioning properties of different athletic footwear. The good prediction of tibial accelerations by the maximum vertical force rate toward the initial force peak (r 2 = .95) suggests that the use of a force platform is sufficient for the estimation of shock-absorbing properties of sport shoes. If an even higher prediction accuracy is required a regression equation with two variables (maximum force rate, median power frequency) may be used (r 2 = .97). To evaluate the influence of footwear on the shock traveling through the body, a good prediction of peak tibial accelerations can be achieved from force platform measurements.

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Klaus Peikenkamp, Martin Fritz and Klaus Nicol

The surface-athlete interaction is discussed as one possible factor in overuse injuries, as the ground reaction force does not depend only on the athlete’s movement during surface contact but also on the mechanical properties of the playing surface. Since it is extremely difficult to measure the ground reaction force on an area-elastic surface, two damped linear-spring models were combined to calculate both the vertical ground reaction force on area-elastic surfaces and their deformations during the athlete’s landing from a jump height of 0.45 m. The athlete model consists of 4 segments (feet, shanks, thighs, and rest of the body) and the surface model consists of 5 segments each connected (a) to the concrete and (b) to each other via an additional imaginary segment. While the connections to the concrete were kept constant, the surface mass and the connections between the segments were varied in order to consider different degrees of area-elasticity of the simulated surfaces. With this approach it was shown that both the passive and active maximum of the vertical ground reaction force depend only on the maximum deformation of the surface, whereas the force rates vary greatly for identical maximum deformations. It appears that these differences increase with increasing maximum deformation. Therefore, in constructing area-elastic sport surfaces, the maximum deformation allowed should be as large as would coincide with other functions the surface must fulfill. Subsequently, the surface mass interacting with the athlete during landing should be large and the damping properties between these mass-segments should be very small.