Search Results

You are looking at 71 - 80 of 3,828 items for :

Clear All
Restricted access

Jeffrey Graham and Sylvia Trendafilova

This case challenges future sport managers to consider the importance of organizational structure and the impact structure has on job performance and motivation. In the case, students are presented with a university ticket sales department with a traditionally tall bureaucratic organizational structure. In 2014, the department struggled with poor performance, high turnover, and low levels of employee morale. However, the department took drastic steps and adopted an organizational structure that is based on the idea of self-managed teams. Now in 2016 the department is undergoing a thorough evaluation to see whether the organizational change made two years ago has had a positive impact. Even though the case uses a fictional university (i.e., Western Field University), the issues and challenges involved in changing an organizational structure, motivating employees, and leading change stem from real-world situations. The case contains ticket sales data, employee turnover information, and sample quotes from employees that aid in the analysis. This case is intended for use in human resource management classes, but it also has implications for organizational behavior or leadership courses.

Restricted access

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.

Restricted access

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.

Restricted access

Timothy R. Derrick, Graham E. Caldwell and Joseph Hamill

A modified mass-spring-damper model was used to simulate the vertical ground reaction forces of a human runner as stride length was altered. Spring stiffness values were selected by an optimizing routine that altered model parameters to match the model ground reaction force curve to a runner’s actual ground reaction force curve. A mass in series with a spring was used to simulate the behavior of body structures that produce the active portion of the ground reaction force. A second mass in series with a spring-damper system was used to simulate the behavior of those components that cause the impact portion of the ground reaction force. The stiffness of the active spring showed a 51% decrease as subjects increased their stride length. The stiffness value of the impact spring showed a trend opposite that of the active spring, increasing by 20% as strides lengthened. It appears that the impact stiffness plays a role in preventing the support leg from collapsing in response to the increased contact velocities seen in the longer strides.

Restricted access

Hyeonki Choi and Ray Vanderby Jr.

This study developed a three-dimensional biomechanical model to investigate the internal loads on the human neck that result from isometrically generated loads resisted by a force on the head. The first goal was to apply the double-optimization (DOPT) method, the EMG-based method, and the EMG assisted optimization (EMGAO) method to the neck model, calculating muscle forces and C4/5 cervical joint loads for each method. The second goal was to compare the results of the different methods, and the third was to determine maximum exertion forces in the cervical spine for isometric contractions. To formulate the EMG-based model, electromyographic signals were collected from 10 male subjects. EMG signals were obtained from 8 sites around the C4/5 level of the neck by surface electrodes, while the subject performed near maximum, isometric exertions. The mean maximum values (±SD) calculated for C4/5 joint compressive forces during peak exertions were 1654 (±308) N in flexion by the EMG method, 1674 (±319) N in flexion by the EMGAO method, and 1208 (±123) N in extension by the DOPT method. In contrast to the DOPT method, the EMG and EMGAO methods showed activation of all the muscles, including the antagonists, and accommodated various load distribution patterns among the agonist muscles during generation of the same magnitude of moments, especially in lateral bending. The EMG and EMGAO methods predicted higher cervical spinal loads than previously published results by the DOPT method. These results may be helpful to engineers and surgeons who are designing and using cervical spine implants and instrumentation.

Restricted access

David Preen, Brian Dawson, Carmel Goodman, John Beilby and Simon Ching

The purposes of this investigation were first to determine the impact of 3 different creatine (Cr) loading procedures on skeletal muscle total Cr (TCr) accumulation and, second, to evaluate the effectiveness of 2 maintenance regimes on retaining intramuscular TCr stores, in the 6 weeks following a 5-day Cr loading program (20 g · day−1). Eighteen physically active male subjects were divided into 3 equal groups and administered either: (a) Cr (4 X 5 g · day−1 X 5 days), (b) Glucose+Cr (1 g · kg−1 of body mass twice per day), or (c) Cr in conjunction with 60 min of daily muscular (repeated-sprint) exercise. Following the 5-day loading period, subjects were reassigned to 3 maintenance groups and ingested either 0 g · day−1, 2 g · day−1 or 5 g · day−1 of Cr for a period of 6 weeks. Muscle biopsy samples (vastus lateralis) were taken pre- and post-loading as well as post-maintenance and analyzed for skeletal muscle ATP, phosphocreatine (PCr), Cr, and TCr concentrations. Twenty-four hour urine samples were collected for each of the loading days and last 2 maintenance days, and used to determine whole body Cr retention. Post-loading TCr stores were significantly (p < .05) increased in all treatment conditions. The Glucose+Cr condition produced a greater elevation (p < .05) in TCr concentrations (25%) than the Cr Only (16%) or Exercise+Cr (18%) groups. Following the maintenance period, muscle TCr stores were still similar to post-loading values for both the 2 g · day−1 and 5 g · day−1 conditions. Intramuscular TCr values for the 0 g · day−1 condition were significantly lower than the other conditions after the 6-week period. Although not significantly different from pre-loading concentrations, muscle TCr for the 0 g · day−1 group had not fully returned to baseline levels at 6 weeks post-loading. The data suggests that Glucose+Cr (but with a much smaller glucose intake than currently accepted) is potentially the most effective means of elevating TCr accumulation in human skeletal muscle. Furthermore, after 5 days of Cr loading, elevated muscle TCr concentrations can be maintained by the ingestion of small daily Cr doses (2-5 g) for a period of 6 weeks and that TCr concentrations may take longer than currently accepted to return to baseline values after such a Cr loading regime.

Restricted access

Xiaocai Shi and Dennis H. Passe

The purpose of this study is to summarize water, carbohydrate (CHO), and electrolyte absorption from carbohydrate- electrolyte (CHO-E) solutions based on all of the triple-lumen-perfusion studies in humans since the early 1960s. The current statistical analysis included 30 reports from which were obtained information on water absorption, CHO absorption, total solute absorption, CHO concentration, CHO type, osmolality, sodium concentration, and sodium absorption in the different gut segments during exercise and at rest. Mean differences were assessed using independent-samples t tests. Exploratory multiple-regression analyses were conducted to create prediction models for intestinal water absorption. The factors influencing water and solute absorption are carefully evaluated and extensively discussed. The authors suggest that in the human proximal small intestine, water absorption is related to both total solute and CHO absorption; osmolality exerts various impacts on water absorption in the different segments; the multiple types of CHO in the ingested CHO-E solutions play a critical role in stimulating CHO, sodium, total solute, and water absorption; CHO concentration is negatively related to water absorption; and exercise may result in greater water absorption than rest. A potential regression model for predicting water absorption is also proposed for future research and practical application. In conclusion, water absorption in the human small intestine is influenced by osmolality, solute absorption, and the anatomical structures of gut segments. Multiple types of CHO in a CHO-E solution facilitate water absorption by stimulating CHO and solute absorption and lowering osmolality in the intestinal lumen.

Restricted access

Guest Editor: Bradley D. Hatfield INTRODUCTION Optimization of Human Performance Bradley D. Hatfield * Calvin M. Lu * Jo B. Zimmerman * 1 02 2020 9 1 1 3 10.1123/kr.2019-0065 kr.2019-0065 SCHOLARLY ARTICLES Optimizing Human Performance—A Brief History of Macro and Micro Perspectives Mark S

Open access

Manuel Trinidad-Fernández, Manuel González-Sánchez and Antonio I. Cuesta-Vargas

the first use of this methodology in humans. This study aimed to evaluate a new, minimally invasive method of tracking internal and external rotation of the scapula using ultrasound imaging combined with the signal provided by a 3-dimensional electromagnetic sensor and to assess the reliability of

Restricted access

Kevin Deschamps, Giovanni Matricali, Maarten Eerdekens, Sander Wuite, Alberto Leardini and Filip Staes

, Alexander RM . The spring in the arch of the human foot . Nature . 1987 ; 325 ( 6100 ): 147 – 149 . doi:10.1038/325147a0 10.1038/325147a0 3808070 9. Farley CT , Glasheen J , McMahon TA . Running springs: speed and animal size . J Exp Biol . 1993 ; 185 : 71 – 86 . PubMed ID: 8294853 8294853