1,720,989 research outputs found
Effects of altered sensory information during posture and gait: A developmental perspective.
No full textIn young adults, the role of Ia primary muscle spindles from the gastroc-soleus have been investigated extensively during quiet standing and are considered important contributors to the maintenance of quiet stance. The Ia primary muscle spindles may play a limited influence on the modulation of muscle activity during the stance phase of gait for young adults. An investigation into the contribution of Ia primary muscle spindles to the control of postural stability and gait in children between the ages of 5--7 and 9--11 years of age was completed. During the postural task afferent information was manipulated via unilateral tendon vibration with and without visual information. In general, the perturbation of the proprioceptive information during the postural control task was more destabilizing to the children compared to the young adults, particularly when vision was occluded. Based on the current findings it was not definitive that peripheral factors contributed significantly to postural differences observed between children and adults. However, several centrally mediated factors, such as difficulty reweighing sensory inputs, delayed muscle onsets and inefficient muscle activity, were considered attractive and plausible explanations contributing to the differences observed between children and adults. During the walking task, vision was always available and vibration was briefly applied during the swing and stance phases or continuously throughout the gait cycle. The principal findings related to the walking study involved the modulation of plantarflexor muscle activity during the stance phase for the children and not the young adults, and a greater number of alterations to the walking characteristics during the continuous vibration condition for the children when compared to the young adults. The modulation of muscle activity during the stance phase for the children suggests peripheral factors specific to the phasic gating of sensory information appears to be different for children than young adults during walking. While the differences observed between the children and young adults during the continuous vibration condition are suggestive of difficulties with centrally mediated processes potentially related to the ability to flexibility manage, extract, and process afferent inputs.PhDBiological SciencesHealth and Environmental SciencesKinesiologyPhysiologyUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/125829/2/3224696.pd
Arm movement analysis before and after birth: A comparison of non-diabetic and diabetic pregnancies.
No full textDiabetes during pregnancy may affect the motor development of fetuses before and after birth potentially causing changes to their movement patterns. This study explored arm movement variables before and after birth in fetuses and infants of non-diabetic and diabetic mothers. We used a unique measurement method to analyze arm movements looking at the count, range, velocities and duration. In study one we observed fetuses at 28, 32, and 36 weeks of gestation using ultrasound observations. Before birth fetuses of diabetic mothers had larger estimated fetal weight (EFW), larger amniotic fluid index especially at 32 weeks of gestation, and similar 'uterine space' as compared to fetuses of non-diabetic mothers. We observed a recurring group by age interaction pattern where fetuses of diabetic mothers increased the range and average velocity of their arm movements between 32 and 36 weeks of gestation while fetuses of non-diabetic mothers decreased. We would like to suggest a possible connection between the increased amniotic fluid index at 32 weeks of gestation and movement variables (range and average velocity) that requires future exploration. In study two we observed infants at 1, 4, and 8 weeks of age using two infant seat positions (30° & 70° from horizontal) that provided a gravitational manipulation for performing arm movements. After birth infants of diabetic mothers had lower count and smaller range of their arm movements as compared to infants of non-diabetic mothers. The 30° seat position seemed to be a 'higher demand' position for infants to move their arms as compared to the 70° seat position while the 70° seat position was a more sensitive seat position to detect group differences. These results indicate that before birth there were no quantitative differences while after birth there were quantitative and qualitative differences of arm movements. We would like to suggest the lingering effects of the diabetic environment as well as the increased gravitational demands to the system in the form of seat position. These results and our method require further exploration including multiple glucose measurements and long term follow up during the first years of life.PhDDevelopmental biologyHealth and Environmental SciencesKinesiologyUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/125676/2/3208479.pd
The relationship between musculoskeletal system capacity and task requirements in simulated crouch standing.
No full textThis dissertation provides insights into the complex interrelationships between crouch severity, musculoskeletal system capacity, task requirements, musculoskeletal system costs, and crouch endurance stand (ES) time for simulated crouch standing in able-bodied adults (19- to 45-years-old). The primary goal of this dissertation was to determine the best musculoskeletal predictors of crouch ES time by comparing the predictive validity of: (1) maximum voluntary torque-generating capacity (MAXT), which is a measure of musculoskeletal system capacity, (2) net muscle torque required (REQT) at each lower extremity (LE) joint to maintain standing, which is a measure of task requirements, and (3) percent maximum torque (PMAXT) required to maintain a given posture, which is a relative musculoskeletal system cost factor. Specifically, the percentage of the variance explained by MAXT, REQT, and PMAXT were compared to determine the best predictor of standing endurance. Secondary purposes were to determine the: (1) effect of crouch severity on system capacity and task requirements, (2) best methods of assessing MAXT and calculating PMAXT by comparing five strength assessment methods (unilateral single joint or multi-joint varying, prediction, and bilateral, multi-joint varying strength methods), and (3) additional percent variances in standing endurance explained by: (a) personal traits (e.g. age, gender, physical activity level, and self-efficacy), (b) psychophysical ratings (e.g. perceived exertion, pain, and fatigue), and (c) crouch ES performance variability. Our results demonstrate that crouch standing altered the musculoskeletal system capacity (MAXT) and increased the task requirements (REQT), with the net result being increased costs to the musculoskeletal system (PMAXT). Crouch ES time was inversely proportional to crouch severity (CS). The bilateral, multi-joint varying strength assessment method was a better predictor of crouch ES time than the unilateral single-joint or multi-joint varying methods, predicting 8.7% of the variance compared to 1% to 2.6% for the other methods. PMAXT was the best musculoskeletal predictor of crouch ES time across all LE joints and CS conditions, predicting 25% to 40.5% of the variance compared to 8.7% for MAXT and 8.6% for REQT. Self-efficacy and perceived muscle fatigue, combined with PMAXT predicted 61.2% of the variance in crouch ES time for all subjects. Predictions held best for subjects who required 10% or greater PMAXT to maintain crouch standing, where self-efficacy, physical activity level, and COPy variability combined with PMAXT predicted 80.5% of the variance in crouch ES time. Subjects reported high levels of perceived muscle fatigue and discomfort while standing in the crouch posture, thus indicating the importance of establishing guidelines and safety limits for clinical management using a task-specific cost factor, such as PMAXT.PhDHealth and Environmental SciencesKinesiologyPhysical therapyUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/123857/2/3106077.pd
Balance control in reaching tasks: Effects of development and somatosensory feedback.
No full textBalance control is a fundamental component in the success of reaching tasks. A proposed model suggests that movement experience enhances the prediction of sensory feedback encountered during reaching. This enhanced prediction improves balance control through a two-phase process where a phase of rapid acquisition of balance control precedes a phase of fine-tuning. In the model, this process is not age locked but rather experience and task difficulty dependent. To examine this model, younger children, older children, and adults performed reach holds and reach reversals to arm's length and maximum target distances. Somatosensory feedback was altered by having subjects stand on hard, knobby, and foam surfaces. Balance control was assessed through measures of center of pressure (COP), center of mass (COM), and the relationship between the COP and COM in the anterior-posterior (AP) and medial-lateral (ML) directions. Compared to adults, gross indicators of AP balance control, such as COP excursion (COPE), demonstrated less effective balance control in younger children [p < 0.001]. As a result of increased task difficulty, only those indicators of finely tuned AP balance control, such as COP amplitude, revealed less effective balance control in older children compared to adults [p < 0.001]. ML balance control, indicated by ML COPE, was less effective in the youngest children compared to adults even for easier tasks [p < 0.001]. ML COPE was also decreased in older children but only as a result of the combined effect of reaching task and somatosensory manipulations [p < 0.001]. These results suggest that gross balance control in the direction of reaching (AP direction) develops rapidly in children because differences between the older children and adults existed only for measures of fine-tuning. Differences in ML balance control between older children and adults indicated by ML COPE suggested that balance control developed more slowly in the direction perpendicular to reaching. It is argued that movement experience contributes to the building of an internal representation of the body. Through the construction of this internal representation, gross balance control is first achieved and balance control is refined as the planning of balance control and prediction of sensory feedback improves.PhDDevelopmental biologyHealth and Environmental SciencesKinesiologyUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/123961/2/3106170.pd
Acute effects of time of day on physical and cortical performance after a resistance training session in recreationally trained men
Get PDF[ABSTRACT ONLY; NO FULL TEXT] Mechanisms exist within individual human cells which rhythmically dictate the timing of activity for the cell and coordinate the function of many hormones, organs, and systems throughout the body. Exercise is also found to have profound effects on both physical and cortical responses in humans. Therefore, the time of day in which physical activity occurs may play a substantial role in determining the magnitude of these responses and may acutely impact training and sports performance outcomes. The primary purpose of this project was to examine the scientific literature about the acute effects of time of day on physical and cortical performance, both during and immediately after a resistance training session in recreationally trained men. Anticipated results are provided within the context of a randomized, counterbalanced clinical trial in which theoretical subjects participated in a resistance training protocol at two different times of the day (between 8 and 10 am or between 6 and 8 pm). The subjects were to be fitted with an EEG headcap to record brain waves and a surface EMG apparatus to record muscle activation immediately before, during, immediately after, and 15 minutes after performing 3 sets of 10RM standing biceps curls exercise. It is expected that different times of the day do not affect physical performance, muscle activity, and cortical activity after a resistance training session, regardless of the subject's preference to morning or evening. Specifically, it is expected that all participants show similar peak force, muscle activation, and cortical activity in both the morning and evening time. In addition, it can be expected that a similar number of repetitions per set, total number of repetitions, time under tension, and ratings of perceived exertion for both resistance training sessions is observed regardless of the time of day. Considering these anticipated results, it is assumed that there may be a psychosocial effect on physical performance output at different times of day. Additionally, the timing of resistance training should be selected to fall between family, work, or other training obligations in order to prioritize convenience and facilitate long term exercise adherence
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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