Sloped walking surfaces provide a unique environment for examining the bio-mechanics and neural control of locomotion. While sloped surfaces have been used in a variety of studies in recent years, the current literature provides little if any discussion of the integrity, i.e., validity, of the systems used to collect data. The goal of this study was to develop and characterize a testing system capable of evaluating the kinetics of human locomotion on sloped surfaces. A ramped walkway system with an embedded force plate was constructed and stabilized. Center of pressure and reaction force data from the force plate were evaluated at 6 ramp grades (0, 5, 15, 25, 35, and 39%). Ground reaction force data at 0% grade were effectively the same as data from the same force plate when mounted in the ground and were well within the range of intrasubject variability. Collectively, data from all tests demonstrate the fidelity of this ramp system and suggest it can be used to evaluate human locomotion over a range of slope intensities.
Andrea N. Lay, Chris J. Hass, D. Webb Smith and Robert J. Gregor
Kathryn E. Keenan, Saikat Pal, Derek P. Lindsey, Thor F. Besier and Gary S. Beaupre
Cartilage material properties provide important insights into joint health, and cartilage material models are used in whole-joint finite element models. Although the biphasic model representing experimental creep indentation tests is commonly used to characterize cartilage, cartilage short-term response to loading is generally not characterized using the biphasic model. The purpose of this study was to determine the short-term and equilibrium material properties of human patella cartilage using a viscoelastic model representation of creep indentation tests. We performed 24 experimental creep indentation tests from 14 human patellar specimens ranging in age from 20 to 90 years (median age 61 years). We used a finite element model to reproduce the experimental tests and determined cartilage material properties from viscoelastic and biphasic representations of cartilage. The viscoelastic model consistently provided excellent representation of the short-term and equilibrium creep displacements. We determined initial elastic modulus, equilibrium elastic modulus, and equilibrium Poisson’s ratio using the viscoelastic model. The viscoelastic model can represent the short-term and equilibrium response of cartilage and may easily be implemented in whole-joint finite element models.
Andrew R. Kemper, Joel D. Stitzel, Craig McNally, H. Clay Gabler and Stefan M. Duma
The purpose of this study was to determine the influence of loading direction on the structural response of the human clavicle subjected to three-point bending. A total of 20 clavicles were obtained from 10 unembalmed fresh-frozen postmortem human subjects ranging from 45 to 92 years of age. The right and left clavicles from each subject were randomly divided into two test groups. One group was impacted at 0° from the transverse plane, and the second group was impacted at 45° angle from the transverse plane. There was no statistically significant difference in peak force (p = .22), peak moment (p = .30), or peak displacement (p = .44) between specimens impacted at 0° versus 45° from the transverse plane. However, there was a significant difference in the structural stiffness (p = .01) and peak strain (p < .01) between specimens impacted at 0° versus 45° from the transverse plane. The peak strain, however, must be evaluated with caution because of the variation in fracture location relative to the strain gauge. Due to the controlled matched data set, the differences in the structural stiffness with respect to loading direction can be attributed to the complex geometry of the clavicle and not material differences.
Saunders N. Whittlesey, Richard E.A. van Emmerik and Joseph Hamill
Many studies have assumed that the swing phase of human walking at preferred velocity is largely passive and thus highly analogous to the swing of an unforced pendulum. In other words, while swing-phase joint moments are generally nonzero during swing, it was assumed that they were either zero or at least negligibly small compared to gravity. While neglect of joint moments does not invalidate a study by default, it remains that the limitations of such an assumption have not been explored thoroughly. This paper makes five arguments that the swing phase cannot be passive, using both original data and the literature: (1) Computer simulations of the swing phase require muscular control to be accurate. (2) Swing-phase joint moments, while smaller than those during stance, are still greater than those due to gravity. (3) Gravity accounts for a minority of the total kinetics of a swing phase. (4) The kinetics due to gravity do not have the pattern needed to develop a normal swing phase. (5) There is no correlation between pendular swing times and human walking periods in overground walking. The conclusion of this paper is that the swing phase must be an actively controlled process, and should be assumed to be passive only when a study does not require a quantitative result. This conclusion has significant implications for many areas of gait research, including clinical study, control theory, and mechanical modeling.
Robert Chen and Kaviraja Udupa
Several techniques that involve transcranial magnetic stimulation (TMS) can be used to measure brain plasticity noninvasively in humans. These include paired-associative stimulation (PAS), repetitive transcranial magnetic stimulation (rTMS) and theta burst stimulation (TBS). Some of these techniques are based the principle of use dependent plasticity or are designed to mimic protocols used to induce long-term potentiation or depression in animal studies. These studies have been applied to certain neurological and psychiatric disorders to investigate their pathophysiology. For example, PAS induced plasticity is enhanced in dystonia and stroke but is reduced in Huntington’s disease and schizophrenia. Furthermore, TMS may be used to modulate brain plasticity and has therapeutic potential in neurological and psychiatric disorders such as stroke, Parkinson’s disease, dystonia and depression.
Lilian Pichot, Gary Tribou and Norm O’Reilly
Successful sponsorship activities in sport often rely on the integration of relationship marketing, internal marketing, external corporate promotion, and strategic management. Although traditional marketing objectives such as brand integration and consumer targeting remain key components of promotional activities in sport, the use of sport sponsorship in today’s environment increasingly implicates personnel issues in the both the sponsor and the sponsee. In fact, sport sponsorship has become a useful tool for some sponsors and sponsees who seek to motivate and involve their employees more in company activities. Therefore, the focus of this commentary is on the internal-communication and human-resources management functions involved in sport sponsorship decisions. The use of mini-case analyses and a dual-perspective (external and internal objectives) approach allows for informed discussion, and suggestions are made for future research.
Carla Filomena Silva and P. David Howe
This paper is a call to Adapted Physical Activity (APA) professionals to increase the reflexive nature of their practice. Drawing upon Foucault’s concept of governmentality (1977) APA action may work against its own publicized goals of empowerment and self-determination. To highlight these inconsistencies, we will draw upon historical and social factors that explain the implicit dangers of practice not following policy. We propose that APA practitioners work according to ethical guidelines, based upon a capabilities approach (Nussbaum, 2006, 2011; Sen, 2009) to counteract possible adverse effects of APA practitioner action. A capabilities approach is conducive to the development of each individual’s human potential, by holistically considering the consequences of physical activity (i.e., biological, cultural, social, and psychological dimensions). To conclude, this paper will offer suggestions that may lead to an ethical reflection aligned with the best interest of APA’s users.
Alan Hreljac, Alan Arata, Reed Ferber, John A. Mercer and Brandi S. Row
Previous research has demonstrated that the preferred transition speed during human locomotion is the speed at which critical levels of ankle angular velocity and acceleration (in the dorsiflexor direction) are reached, leading to the hypothesis that gait transition occurs to alleviate muscular stress on the dorsiflexors. Furthermore, it has been shown that the metabolic cost of running at the preferred transition speed is greater than that of walking at that speed. This increase in energetic cost at gait transition has been hypothesized to occur due to a greater demand being placed on the larger muscles of the lower extremity when gait changes from a walk to a run. This hypothesis was tested by monitoring electromyographic (EMG) activity of the tibialis anterior, medial gastrocnemius, vastus lateralis, biceps femoris, and gluteus maximus while participants (6 M, 3 F) walked at speeds of 70, 80, 90, and 100% of their preferred transition speed, and ran at their preferred transition speed. The EMG activity of the tibialis anterior increased as walking speed increased, then decreased when gait changed to a run at the preferred transition speed. Concurrently, the EMG activity of all other muscles that were monitored increased with increasing walking speed, and at a greater rate when gait changed to a run at the preferred transition speed. The results of this study supported the hypothesis presented.
Samantha L. Winter and John H. Challis
For a physiologically realistic range of joint motion and therefore range of muscle fiber lengths, only part of the force-length curve can be used in vivo; i.e., the section of the force–length curve that is expressed can vary. The purpose of this study was to determine the expressed section of the force–length relationship of the gastrocnemius for humans. Fourteen male and fourteen female subjects aged 18–27 performed maximal isometric plantar flexions in a Biodex dynamometer. Plantar flexion moments were recorded at five ankle angles: −15°, 0°, 15°, 30°, and 40°, with negative angles defined as dorsiflexion. These measurements were repeated for four randomly ordered knee angles over two testing sessions 4 to 10 days apart. The algorithm of Herzog and ter Keurs (1988a) was used to reconstruct the force–length curves of the biarticular gastrocnemius. Twenty-four subjects operated over the ascending limb, three operated over the descending limb, and one operated over the plateau region. The variation found suggests that large subject groups should be used to determine the extent of normal in vivo variability in this muscle property. The possible source of the variability is discussed in terms of parameters typically used in muscle models.
Kohei Watanabe, Motoki Kouzaki and Toshio Moritani
In some muscles, nonuniform surface electromyography (EMG) responses have been demonstrated within a muscle, meaning that the electrode location could be critical in the results of surface EMG. The current study investigated possible region-specific EMG responses within the human biceps femoris (BF) muscle. Surface EMG was recorded from various regions along the longitudinal axis of the BF muscle with 20 electrodes. Ten healthy men performed maximal isometric contractions of hip extension and knee flexion, which involve the BF muscle. The ratio of the EMG amplitude between hip extension and knee flexion tasks (HE/KF) was calculated and compared among the regions. There were no significant differences in HE/KF among the regions along the BF muscle (P > .05). This suggests that the entire superficial region of the BF muscle is equally regulated in the 2 different tasks. We suggest that the electrode location is not critical in estimating the activation properties and/or functional role of the superficial region, which corresponds with approximately 50% of the muscle length of the BF muscle, using surface EMG during maximal contraction.