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Keitaro Kubo, Takanori Teshima, Norikazu Hirose and Naoya Tsunoda

The purpose of this study was to compare the morphological and mechanical properties of the human patellar tendon among elementary school children (prepubertal), junior high school students (pubertal), and adults. Twenty-one elementary school children, 18 junior high school students, and 22 adults participated in this study. The maximal strain, stiffness, Young’s modulus, hysteresis, and cross-sectional area of the patellar tendon were measured using ultrasonography. No significant difference was observed in the relative length (to thigh length) or cross-sectional area (to body mass2/3) of the patellar tendon among the three groups. Stiffness and Young’s modulus were significantly lower in elementary school children than in the other groups, while no significant differences were observed between junior high school students and adults. No significant differences were observed in maximal strain or hysteresis among the three groups. These results suggest that the material property (Young’s modulus) of the patellar tendons of elementary school children was lower than that of the other groups, whereas that of junior high school students was already similar to that of adults. In addition, no significant differences were observed in the extensibility (maximal strain) or viscosity (hysteresis) of the patellar tendon among the three groups.

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Laurence Houghton, Brian Dawson and Jonas Rubenson

Effects of prolonged running on Achilles tendon properties were assessed after a 60 min treadmill run and 140 min intermittent shuttle running (simulated cricket batting innings). Before and after exercise, 11 participants performed ramp-up plantar flexions to maximum-voluntary-contraction before gradual relaxation. Muscle-tendon-junction displacement was measured with ultrasonography. Tendon force was estimated using dynamometry and a musculoskeletal model. Gradients of the ramp-up force-displacement curves fitted between 0–40% and 50–90% of the preexercise maximal force determined stiffness in the low- and high-force-range, respectively. Hysteresis was determined using the ramp-up and relaxation force-displacement curves and elastic energy storage from the area under the ramp-up curve. In simulated batting, correlations between tendon properties and shuttle times were also assessed. After both protocols, Achilles tendon force decreased (4% to 5%, P < .050), but there were no changes in stiffness, hysteresis, or elastic energy. In simulated batting, Achilles tendon force and stiffness were both correlated to mean turn and mean sprint times (r = −0.719 to −0.830, P < .050). Neither protocol resulted in fatigue-related changes in tendon properties, but higher tendon stiffness and plantar flexion force were related to faster turn and sprint times, possibly by improving force transmission and control of movement when decelerating and accelerating.

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Lee N. Burkett, Jack Chisum, Ralph Cook, Bob Norton, Bob Taylor, Keith Ruppert and Chris Wells

Numerous studies in the past 30 years have researched physiological adaptation to stress by wheelchair-bound subjects. Instrumentation necessary to produce this effect had to be designed and tested prior to obtaining valid data. This study had two main purposes: to design a wheelchair ergometer for physiological testing of spinal cord-injured subjects, and to demonstrate the validity of the maximal stress test when using the wheelchair ergometer. To test the validity of the wheelchair ergometer, 10 disabled subjects (9 paraplegic and 1 quadriplegic) participated in both a maximal field test (FT) and a maximal wheelchair ergometer test (WERG), with each subject serving as his or her own control. A randomly assigned counterbalanced design (5 subjects assigned to complete the FT first, with the second group of 5 subjects completing the WERG first) was used to reduce the learning effect in the study. The results of the t-tests indicated there was no significant difference between V̇O2 and V̇E, (STPD) averages for the WERG and FT for maximal effort with two-tailed significant levels of t = .9016 and t = .7294, respectively. The Pearson product moment correlation level was statistically significant at p < .0001, when the WERG V̇O2 was compared to the FT V̇O2 (r = .94), and was significant at p < .005 when the WERG V̇E was compared to the FT V̇E (r = .82).

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Ching-Chao Chan, Chou-Ching K. Lin and Ming-Shaung Ju

The steady-state passive joint moment was considered as a nonlinear elasticity in the past. However, we found that it was path dependent and the estimation error could be large if the commonly used path-independent functions were adopted. The aim of this study was to develop a model to describe the movement history-dependent passive moment in the steady state. The steady-state passive ankle moments of the rabbit were measured by a series of ramp-and-hold angle changes (stairway angle trajectory). A customized discrete Preisach model was constructed and a commonly adopted double-exponential function was also implemented. Two sets of data with different angle paths (major loop and inward loop trajectories) were acquired for model validation. The performance of the two models was compared. The results showed that the proposed model could accurately estimate the steady-state passive moment for both sets of validation data. The estimated error of the proposed model was approximately 50% smaller than that of the double-exponential function approach. It is expected that this new approach, by reducing the error of estimating passive joint moment, may contribute to the active control of joint moments.

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Stacy M. Lopresti-Goodman, Michael J. Richardson, Reuben M. Baron, Claudia Carello and Kerry L. Marsh

The actualization of a simple affordance task—grasping and moving wooden planks of different sizes using either one or two hands—was assessed in the context of taskrelevant (plank sequence, plank presentation speed) and task-irrelevant (cognitive load) manipulations. In Experiment 1, fast (3 s/plank) and self-paced (≈5 s/plank) presentation speeds revealed hysteresis; the transition point for ascending series was greater than the transition point for descending series. Hysteresis was eliminated in the slowest presentation speed (10 s/plank). In Experiment 2, hysteresis was exaggerated by a cognitive load (counting backward by seven) for both fast and slow presentation speeds. These results suggest that behavioral responses to the attractor dynamics of perceived affordances are processes that require minimal cognitive resources.

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Christoph Schütz, Matthias Weigelt, Dennis Odekerken, Timo Klein-Soetebier and Thomas Schack

Previous studies on sequential effects of human grasping behavior were restricted to binary grasp type selection. We asked whether two established motor control strategies, the end-state comfort effect and the hysteresis effect, would hold for sequential motor tasks with continuous solutions. To this end, participants were tested in a sequential (predictable) and a randomized (nonpredictable) perceptual-motor task, which offered a continuous range of posture solutions for each movement trial. Both the end-state comfort effect and the hysteresis effect were reproduced under predictable, continuous conditions, but only the end-state comfort effect was present under nonpredictable conditions. Experimental results further revealed a work range restriction effect, which was reproduced for the dominant and the nondominant hand.

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Brian L. Davis, Julie E. Perry, Donald C. Neth and Kevin C. Waters

A device has been designed to simultaneously measure the vertical pressure and the anterior-posterior and medial-lateral distributed shearing forces under the plantar surface of the foot. The device uses strain gauge technology and consists of 16 individual transducers (each with a surface area measuring 2.5 × 2.5 cm) arranged in a 4 × 4 array. The sampling frequency is 37 Hz and data may be collected for 2 s. The device was calibrated under both static and dynamic conditions and revealed excellent linearity (±5%), minimal hysteresis (±7.5%), and very good agreement between applied and measured loads (±5%). Vector addition of the distributed loads gave resultant forces that were qualitatively very similar to those obtained from a standard force plate. Data are presented for measurements from the forefoot of 4 diabetic subjects during the initiation of gait, demonstrating that distributed shear and pressure on the sole of the foot can be measured simultaneously.

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Louise M. Cahill, Bruce E. Murdoch, Deborah G. Theodoros, Edward J. Triggs, Bruce G. Charles and Amy A. Yao

To quantify lip function in 16 subjects with Parkinson's disease, a computerized semiconductor lip pressure transducer system was used prior to subjects being administered oral levodopa and at approximately 0.5 hr, 1.5 hr, and 3.0 hr postmedication. Two blood samples were taken from each subject at varying times during the levodopa dosage interval, and the exact time and dosage of levodopa were noted. Lip function measurements were expressed as percentage changes from baseline and were plotted for each subject against time and levodopa concentrations to determine the effects of levodopa therapy on articulatory function. The results supported the effectiveness of levodopa therapy in improving lip function. In particular, lip pressures recorded during both speech and nonspeech tasks tended to improve after levodopa administration, the lip measures improving somewhat in parallel with the rise and fall of blood plasma levodopa concentrations. Evidence of a hysteresis effect was noted.

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Christophe Gernigon, Walid Briki and Katie Eykens

Borrowing the dynamical systems perspective, two studies aimed to examine the potential properties of nonlinearity and history dependence of psychological momentum. Male regional-level table tennis players were asked to empathize with players in a very important contest by watching two video scenarios of a table tennis game in two separate sessions. The videos presented two inverted scenarios in which score gaps gradually increased or decreased. Competitive anxiety, self-confidence (Study 1), and goal involvement states (Study 2) were measured before each point. Cognitive and somatic anxieties decreased linearly during the increasing scenario, but increased nonlinearly in the decreasing scenario. Mastery-avoidance goals decreased nonlinearly in the increasing scenario, increased nonlinearly in the decreasing scenario, and displayed a negative hysteresis pattern. These findings offer new insights into the dynamics of psychological momentum and suggest new avenues of research.

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Li Li

Variability has long been used as an indication of stability in the application of a dynamical systems approach to human motion (i.e., greater variability has been related to a less stable system and vise versa). This paper incorporates the probability of gait transition during walking and running at a certain speed to represent the stability of human locomotion. The mathematical representation concerning the probability of gait transition change with locomotory speed was derived for increasing walking speed and decreasing running speed. Additionally, the influence of acceleration and deceleration on the stability landscapes of walking and running was discussed based on experimental data. The influence of acceleration was also used to explain the different trends of hysteresis observed by various researchers. Walk-to-run transition speed was greater than run-to-walk transition speed, with a greater magnitude of acceleration, while the trend was reversed with a lesser acceleration magnitude. The quantitative measure of the relationship between variability and stability needs to be explored in the future.