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John H. Challis

Segmental moment of inertia values, which are often required to perform mechanical analyses of human movement, are commonly computed using statistical models based on cadaver data. Two sets of equations for estimating human limb moments of inertia were evaluated: linear multivariable equations and nonlinear equations. Equation coefficients for both sets of equations were determined using the cadaver data of Chandler et al. (1975). A cross-validation procedure was used to circumvent the problem of model evaluation when there is limited data with which to develop and evaluate the model. Moment of inertia values for the longitudinal axes were predicted with similar degrees of accuracy with either set of equations, while for the transverse axes the nonlinear equations were superior. An evaluation of the influence of the accuracy of moment of inertia estimates on resultant joint moments for three activities showed that the influence of these errors was generally small.

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John H. Challis

Humans of different sizes move in very similar ways despite the size difference. The principles of geometric scaling provide insight into the reasons for the similar movement patterns observed. In human locomotion, body size influences endurance running performance, with shorter body sizes being an advantage due to better heat exchange compared with their taller counterparts. Scaling can also show the equivalence of child gait with that of adults in terms of stride length and walking velocity. In humans, maximum jump height is independent of standing height, a scaling result which has been validated by examining jumps with mass added to the body. Finally, strength scales in proportion to body mass to the two-thirds power, which explains why shorter people have greater relative body strength compared with taller individuals. Geometric scaling reveals the underlying principles of many human movement forms.

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John H. Challis

Repeat measurements were made by 2 operators on a group of 50 physically active subjects (age, 20.7 years ± 1.8; males: height 1.780 m ± 0.043. mass, 78.09 kg ± 9.30; females: height. 1.680 m ± 0.064. mass. 66.67 kg ± 6.67) to determine the precision with which the subjects' limb segment inertial parameters could be estimated. Segmental inertial parameters were determined using 3 techniques. 2 of which involved modeling segments as geometric solids, and a 3rd which used the equations of Zatsiorsky et al. (1990). Precisions were high for all 3 techniques, with little difference between inter- and intra-operator precisions. The lowest precisions were obtained for the hands and feet. For these segments the use of repeat measures to improve precision is recommended. These results imply that with similarly trained measurers, comparison of inertial parameters determined using the same protocol but obtained by different operators is appropriate, and that it is viable to have 2 measurers taking measurements on the same subject to accelerate data collection.

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John H. Challis

In three-dimensional image-based motion analysis, the direct linear transformation (DLT) is commonly used to measure locations of significant body landmarks. The major drawback of the DLT is that the control points used for calibration must encompass the volume in which the activity occurs. A new procedure is presented where the calibration frame is moved sequentially, permitting calibration of a volume much larger than that encompassed by the calibration frame. A calibration frame with a volume of 0.6 m3 was used to calibrate a volume six times greater, by placing the frame in eight different positions. Reconstruction accuracy was comparable with that for the original frame position. This new multiphase calibration procedure presents the opportunity for calibrating large volumes using a small calibration frame; this may be advantageous, for example, in sporting arenas, where the transportation or manufacture of a sufficiently large calibration frame may be problematic.

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John H. Challis

This study examined the influence of force plate targeting, via stride length adjustments, on the magnitude and consistency of ground reaction force and segment angle profiles of the stance phase of human running. Seven male subjects (height, 1.77 m ± 0.081; mass, 72.4 kg ± 7.52; age range, 23 to 32 years) were asked to run at a mean velocity of 3.2 m · s–1 under three conditions (normal, short, and long strides). Four trials were completed for each condition. For each trial, the ground reaction forces were measured and the orientations of the foot, shank, and thigh computed. There were no statistically significant differences (p > .05) between the coefficients of variation of ground reaction force and segment angle profiles under the three conditions, so these profiles were produced consistently. Peak active vertical ground reaction forces, their timings, and segment angles at foot off were not significantly different across conditions. In contrast, significant differences between conditions were found for peak vertical impact forces and their timings, and for the three lower limb segment angles at the start of force plate contact. These results have implications for human gait studies, which require subjects to target the force plate. Targeting may be acceptable depending on the variables to be analyzed.

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John H. Challis

The results of the 2020 review and ranking of U.S. doctoral programs in kinesiology conducted by the National Academy of Kinesiology (NAK) are presented. These results represent data collected for the  2015, 2016, 2017, 2018, and 2019 calendar years for 43 programs. The rankings reflect data collected on program faculty (productivity, funding, and visibility) and program students (admissions, support, publications, and employment). The data for each assessment index were first transformed into z scores, and then the z scores converted into T-scores. Weights were applied to the T-scores of the indices and then summed to obtain a total T-score. Programs were ranked in two ways: one based on the total T-scores from the data not normalized (unadjusted) and the other with total T-scores from the data normalized with respect to the number of faculty members in each program (adjusted). In addition to program rankings, descriptive data are presented on faculty and student data.

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John H. Challis

This article presents and evaluates a new procedure that automatically determines the cutoff frequency for the low-pass filtering of biomechanical data. The cutoff frequency was estimated by exploiting the properties of the autocorrelation function of white noise. The new procedure systematically varies the cutoff frequency of a Butterworth filter until the signal representing the difference between the filtered and unfiltered data is the best approximation to white noise as assessed using the autocorrelation function. The procedure was evaluated using signals generated from mathematical functions. Noise was added to these signals so mat they approximated signals arising from me analysis of human movement. The optimal cutoff frequency was computed by finding the cutoff frequency that gave me smallest difference between the estimated and true signal values. The new procedure produced similar cutoff frequencies and root mean square differences to me optimal values, for me zeroth, first and second derivatives of the signals. On the data sets investigated, this new procedure performed very similarly to the generalized cross-validated quintic spline.

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Matthew T.G. Pain and John H. Challis

This study had two purposes: to evaluate a new method for measuring segmental dimensions for determining body segment inertial parameters (BSIP), and to evaluate the changes in mass distribution within a limb as a consequence of muscular contraction. BSIP were calculated by obtaining surface data points of the body under investigation using a sonic digitizer, interpolating them into a regular grid, and then using Green’s theorem which relates surface to volume integrals. Four skilled operators measured a test object; the error was approximately 2.5% and repeatability was 1.4% (coefficient of variation) in the determination of BSIP. Six operators took repeat measures on human lower legs; coefficients of variation were typically around 5%, and 3% for the more skilled operators. Location of the center of mass of the lower leg was found to move up 1.7 cm proximally when the triceps surae muscles went from a relaxed state to causing plantar flexion. The force during an impact associated with such motion of the soft tissue of the lower leg was estimated to be up to 300 N. In summary, a new repeatable and accurate method for determining BSIP has been developed, and has been used to evaluate body segment mass redistribution due to muscular contraction.

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Matthew T.G. Pain and John H. Challis

The aims of this study were to quantify intrasegmental motion using an array of 28 surface-mounted markers to examine frequency and amplitude measurements of the intrasegmental motion to calculate forces and energy transfer; and to show that the underlying muscles are a major contributor to the skin marker motion. One participant performed 27 trials under three conditions in which his forearm was struck against a solid object fixed to a force plate while the locations of the markers were recorded at 240 Hz. For impacts with equal peak forces, the muscle tension significantly affected the amount of intrasegmental motion. Tensing the arm reduced the intrasegmental motion by 50%. The quadrilateral sectors defined by the markers changed in area by 11% with approximately equal motion in the vertical and horizontal direction. The maximum linear marker motion was 1.7 cm. The intrasegmental motion had distinct frequency components around 14 and 20 Hz. Soft tissue deformation could account for 70% of the energy lost from the forearm during these impacts. The study has demonstrated the important role that intrasegment soft tissue motion can have on the kinetics of an impact.

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Samantha L. Winter and John H. Challis

The muscle fiber force–length relationship has been explained in terms of the cross-bridge theory at the sarcomere level. In vivo, for a physiologically realistic range of joint motion, and therefore range of muscle fiber lengths, only part of the force–length curve may be used; that is, the section of the force– length curve expressed can vary. The purpose of this study was to assess the accuracy of a method for determining the expressed section of the force– length curve for biarticular muscles. A muscle model was used to simulate the triceps surae muscle group. Three model formulations were used so that the gastrocnemius operated over different portions of the force–length curve: the ascending limb, the plateau region, and the descending limb. Joint moment data were generated for a range of joint configurations and from this simulated data the region of the force– length relationship that the gastrocnemius muscle operated over was successfully reconstructed using the algorithm of Herzog and ter Keurs (1988a). Further simulations showed that the correct region of the force–length curve was accurately reconstructed even in the presence of random and systematic noise generated to reflect the effects of sampling errors, and incomplete muscle activation.