Search Results

You are looking at 61 - 70 of 3,828 items for :

Clear All
Restricted access

Alan Hreljac, Rodney T. Imamura, Rafael F. Escamilla, W. Brent Edwards and Toran MacLeod

The primary purpose of this project was to examine whether lower extremity joint kinetic factors are related to the walk–run gait transition during human locomotion. Following determination of the preferred transition speed (PTS), each of the 16 subjects walked down a 25-m runway, and over a floor-mounted force platform at five speeds (70, 80, 90, 100, and 110% of the PTS), and ran over the force platform at three speeds (80, 100, and 120% of the PTS) while being videotaped (240 Hz) from the right sagittal plane. Two-dimensional kinematic data were synchronized with ground reaction force data (960 Hz). After smoothing, ankle and knee joint moments and powers were calculated using standard inverse dynamics calculations. The maximum dorsiflexor moment was the only variable tested that increased as walking speed increased and then decreased when gait changed to a run at the PTS, meeting the criteria set to indicate that this variable influences the walk–run gait transition during human locomotion. This supports previous research suggesting that an important factor in changing gaits at the PTS is the prevention of undue stress in the dorsiflexor muscles.

Restricted access

Scott O. Cloyd, Mont Hubbard and LeRoy W. Alaways

Feedback control of a human-powered single-track bicycle is investigated through the use of a linearized dynamical model in order to develop feedback gains that can be implemented by a human pilot in an actual vehicle. The object of the control scheme is to satisfy two goals: balance and tracking. The pilot should be able not only to keep the vehicle upright but also to direct the forward motion as desired. The two control inputs, steering angle and rider lean angle, are assumed to be determined by the rider as a product of feedback gains and “measured” values of the state variables: vehicle lean, lateral deviation from the desired trajectory, and their derivatives. Feedback gains are determined through linear quadratic regulator theory. This results in two control schemes, a “full” optimal feedback control and a less complicated technique that is more likely to be usable by an inexperienced pilot. Theoretical optimally controlled trajectories are compared with experimental trajectories in a lane change maneuver.

Restricted access

Jeffrey J. Brault, Theodore F. Towse, Jill M. Slade and Ronald A. Meyer

Short-term creatine supplementation is reported to result in a decreased ratio of phosphocreatine (PCr) to total creatine (TCr) in human skeletal muscle at rest. Assuming equilibrium of the creatine kinase reaction, this decrease in PCr:TCr implies increased cytoplasmic ADP and decreased Gibbs free energy of ATP hydrolysis in muscle, which seems contrary to the reported ergogenic benefits of creatine supplementation. This study measured changes in PCr and TCr in vastus lateralis muscle of adult men (N = 6, 21–35 y old) during and 1 day after 5 d of creatine monohydrate supplementation (0.43 g·kg body weight−1·d−1) using noninvasive 31P and 1H magnetic-resonance spectroscopy (MRS). Plasma and red-blood-cell creatine increased by 10-fold and 2-fold, respectively, by the third day of supplementation. MRS-measured skeletal muscle PCr and TCr increased linearly and in parallel throughout the 5 d, and there was no significant difference in the percentage increase in muscle PCr (11.7% ± 2.3% after 5 d) vs. TCr (14.9% ± 4.1%) at any time point. The results indicate that creatine supplementation does not alter the PCr:TCr ratio, and hence the cytoplasmic Gibbs free energy of ATP hydrolysis, in human skeletal muscle at rest.

Restricted access

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.

Restricted access

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.

Restricted access

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.

Restricted access

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.

Restricted access

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.

Restricted access

Anneliese Goslin

South African society is a complex mix of first- and third-world components. Urgent socio-economic and political problems must be addressed to avoid chaos. Sport may be a key factor in bringing about change. Sport training strategies should form an integral part of affirmative action and sport development programs in South Africa. The overall aim of this research was to develop a structured scientific approach to the training and development of human resources in South African sport. The research was conducted in four phases over a 2-year period. The aims of the respective phases were to determine the current standard and scope of sport management in black developing townships, to compile a profile of competencies and training needs of sport managers, to develop an in-service training model for the aforementioned sport managers, and to design a comprehensive sport development strategy for South African sport. Research methodologies included questionnaires on general and functional managerial variables and training needs, content analysis of job descriptions, and personal interviews. Results revealed an insufficient standard of sport management in developing townships. A competency-based training and development model was proposed and positioned in an overall strategy for sport development in South Africa.

Restricted access

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.