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Cameron T. Gibbons, Polemnia G. Amazeen and Aaron D. Likens

posture. In the postural control literature, typical methods either control the participant’s foot placement (e.g.,  Albertsen, Ghédira, Gracies, & Hutin, 2017 ; Kirby, Price, & MacLeod, 1987 ) or allow the participant to self-select their position (e.g.,  Doyle, Dugan, Humphries, & Newton, 2004 ). The

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Scott C. Wearing, James E. Smeathers and Stephen R. Urry

Studies investigating the effect of targeting on gait have focused on the analysis of ground reaction force (GRF) within the time domain. Analysis within the frequency domain may be a more sensitive method for evaluating variations in GRF. The aim of the present study was to investigate the effect of visual targeting on GRF analyzed within the frequency domain. A within-subject repeated-measures design was used to measure the mediolateral, vertical, and antero-posterior components of the GRF of 11 healthy volunteers while walking at their own pace over a paper-covered walkway. A 30 × 24-cm target area was superimposed over a hidden Kistler force plate mounted at the midpoint of the walkway. GRF were recorded with and without the target and were analyzed within the frequency domain. Although visually guided foot placement has previously been undetected by traditional time-domain measures, targeting was found to significantly increase the frequency content of both the mediolateral (t10 = -4.07, p < 0.05) and antero-posterior (t10 = -2.52, p < 0.05) components of GRF. Consequently, it appears that frequency analysis is a more sensitive analytic technique for evaluating GRF. These findings have methodological implications for research in which GRF is used to characterize and assess anomalies in gait patterns.

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Chanel T. LoJacono, Ryan P. MacPherson, Nikita A. Kuznetsov, Louisa D. Raisbeck, Scott E. Ross and Christopher K. Rhea

following metrics for both leading and trailing limbs: (1) foot placement before and after obstacle crossing (Figure  3 ), (2) toe and heel clearance during crossing (Figure  4 ), and (3) toe and heel peak elevation during crossing. Foot distance to the obstacle was calculated as distance from a point to a

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Hendrik Reimann, Tyler Fettrow and John J. Jeka

the CoP and the CoM state, indicating whether the CoM is right or left of the CoP and moving toward or away from it. Foot Placement To avoid falling over and hitting the ground, the CoM has to be kept within the base of support on average over time. The most straightforward way to modify the CoP is to

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Azahara Fort-Vanmeerhaeghe, Ariadna Benet, Sergi Mirada, Alicia M. Montalvo and Gregory D. Myer

and reflexive muscle activity mechanisms. 33 The evaluation of TJA includes 10 item criteria: (1) knee valgus at landing, (2) thighs do not parallel, (3) thighs not equal side to side, (4) foot placement not shoulder width apart, (5) foot placement not parallel, (6) foot contact timing not equal, (7

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Randy Schmitz and Brent Arnold

Evaluating balance can be an important part of the rehabilitation protocol of an athletic injury. One purpose of this study was to determine the intertester and intratester reliability scores of single-leg stability on a platform of gradually decreasing stability using the Biodex Stability System (BSS). The second purpose was to determine intertester and intratester reliability scores of subject foot placement on the BSS. Subjects (N = 19) underwent a familiarization session on Day 1 that included five 30-s balance tests on the BSS. In each of the five tests, platform stability gradually decreased over the 30 s. Subjects were tested without footwear at all times. On the second day, each subject was tested twice by the same investigator and once by a second investigator using the same 30-s test. Investigator tests were counterbalanced to eliminate order effects. Intertester intraclass correlations (ICCs) ranged from .70 to .42 for stability index and from .93 to .54 for foot placement. Intratester ICCs ranged from .82 to .43 for stability index and from .81 to .55 for foot placement. The overall stability index scores were the most reliable stability scores (.82 for intratester and .70 for intertester). A 30-s, single-leg, gradually decreasing platform stability test appears to be highly reliable when performed on the BSS.

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Catherine A. Stevermer and Jason C. Gillette

Variation in the timing indicators separating sit-to-stand (STS) into movement phases complicates both research comparisons and clinical applications. The purpose of this study was to use kinetic reference standards to identify accurate kinematic and kinetic indicators for STS movement analysis such that consistent indicators might be used for STS from varied initial postures. Healthy adults performed STS using 4 foot placements: foot-neutral, foot-back, right-staggered, and left-staggered. Kinetic and kinematic data were collected from force platforms and an 8-camera video system. Initiation, seat-off, vertical posture, and termination were detected with 5% start and 7.5% end thresholds for changes in kinetic and kinematic STS indicators. Timing differences between kinetic and kinematic indicator time points and the reference vertical seated reaction force end point (seatoff) were determined. Kinematic indicators were compared with selected kinetic indicators using timing differences, statistical similarity, and internal consistency measures. Our results suggest that a single force platform system measuring vertical GRF or a simple camera system to evaluate the shoulder marker position and velocity can accurately and consistently detect STS initiation, seat-off, and vertical posture. In addition, these suggested STS indicators for initiation, seat-off, and vertical posture were not dependent upon foot placement.

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Noah J. Rosenblatt, Christopher P. Hurt and Mark D. Grabiner

Recent experimental findings support theoretical predictions that across walking conditions the motor system chooses foot placement to achieve a constant minimum “margin of stability” (MOSmin)—distance between the extrapolated center of mass and base of support. For example, while step width varies, similar average MOSmin exists between overground and treadmill walking and between overground and compliant/irregular surface walking. However, predictions regarding the invariance of MOSmin to step-by-step changes in foot placement cannot be verified by average values. The purpose of this study was to determine average changes in, and the sensitivity of MOSmin to varying step widths during two walking tasks. Eight young subjects walked on a dual-belt treadmill before and after receiving information that stepping on the physical gap between the belts causes no adverse effects. Information decreased step width by 17% (p = .01), whereas MOSmin was unaffected (p = .12). Regardless of information, subject-specific regressions between step-by-step values of step width and MOSmin explained, on average, only 5% of the shared variance (β = 0.11 ± 0.05). Thus, MOSmin appears to be insensitive to changing step width. Accordingly, during treadmill walking, step width is chosen to maintain MOSmin. If MOSmin remains insensitive to step width across other dynamic tasks, then assessing an individual’s stability while performing theses tasks could help describe the health of the motor system.

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Jana Fleischmann, Guillaume Mornieux, Dominic Gehring and Albert Gollhofer

Sideward movements are associated with high incidences of lateral ankle sprains. Special shoe constructions might be able to reduce these injuries during lateral movements. The purpose of this study was to investigate whether medial compressible forefoot sole elements can reduce ankle inversion in a reactive lateral movement, and to evaluate those elements’ influence on neuromuscular and mechanical adjustments in lower extremities. Foot placement and frontal plane ankle joint kinematics and kinetics were analyzed by 3-dimensional motion analysis. Electromyographic data of triceps surae, peroneus longus, and tibialis anterior were collected. This modified shoe reduced ankle inversion in comparison with a shoe with a standard sole construction. No differences in ankle inversion moments were found. With the modified shoe, foot placement occurred more internally rotated, and muscle activity of the lateral shank muscles was reduced. Hence, lateral ankle joint stability during reactive sideward movements can be improved by these compressible elements, and therefore lower lateral shank muscle activity is required. As those elements limit inversion, the strategy to control inversion angles via a high external foot rotation does not need to be used.

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Andrea Biscarini, Fabio M. Botti and Vito E. Pettorossi

We developed a biomechanical model to determine the joint torques and loadings during squatting with a backward/forward-inclined Smith machine. The Smith squat allows a large variety of body positioning (trunk tilt, foot placement, combinations of joint angles) and easy control of weight distribution between forefoot and heel. These distinctive aspects of the exercise can be managed concurrently with the equipment inclination selected to unload specific joint structures while activating specific muscle groups. A backward (forward) equipment inclination decreases (increases) knee torque, and compressive tibiofemoral and patellofemoral forces, while enhances (depresses) hip and lumbosacral torques. For small knee flexion angles, the strain-force on the posterior cruciate ligament increases (decreases) with a backward (forward) equipment inclination, whereas for large knee flexion angles, this behavior is reversed. In the 0 to 60 degree range of knee flexion angles, loads on both cruciate ligaments may be simultaneously suppressed by a 30 degree backward equipment inclination and selecting, for each value of the knee angle, specific pairs of ankle and hip angles. The anterior cruciate ligament is safely maintained unloaded by squatting with backward equipment inclination and uniform/forward foot weight distribution. The conditions for the development of anterior cruciate ligament strain forces are clearly explained.