Neural mechanisms determining temporal muscle activity patterns during postural control are not well understood. We hypothesize that a feedback control mechanism can predict both temporal extensor muscle EMG and CoM kinematics (acceleration, velocity, and displacement) during postural perturbations before and following peripheral neuropathy to group I afferents induced by pyridoxine intoxication. We introduce a feedback model for analyzing temporal EMG patterns that decomposes recorded electromyogram (EMG) signals into the sum of three center of mass (CoM) feedback components. EMG and CoM kinematics during postural responses due to support surface translations were measured before and 14 days after somatosensory loss in cats. We successfully predicted EMG before and after peripheral neuropathy by modeling a standing cat as an inverted pendulum and decomposing temporal EMG patterns using a simulation with time delayed feedback loop of CoM kinematics. This model accounts for over 60% of the total temporal variability of recorded extensor EMG patterns. Feedback gains for acceleration, velocity and position necessary to predict EMGs before and after sensory loss were different. For intact animals, more that 90% of the initial burst of EMG were due to CoM acceleration feedback, while later portions were due entirely to velocity and position feedback. After peripheral neuropathy, the initial burst was absent and the acceleration gain was significantly reduced when compared to the acceleration gain of intact animals for extensor muscles (p lt 0.05). By successfully decomposing EMG into three kinematic gains, a quantitative comparison of temporal EMG patterns before and after peripheral neuropathy is possible. The reduction of acceleration gain in sensory loss cats suggests that group I afferents provide necessary information that is used as acceleration feedback.

We studied the effects of varying perturbation magnitude and direction on the postural control process of the central nervous system (CNS) caused by perturbation, before and after sensory loss. The electromyogram (EMG) response to a postural perturbation can be composed by a weighted sum of the center of mass (CoM) kinematics. We extended an existing CoM feedback model which predicted EMG of one muscle for unidirectional perturbations; we used recorded data of bidirectional perturbations, which caused muscle activity in anterior as well as posterior muscles. Modeling the CNS as two delayed feedback controllers, we reconstructed the EMGs of two antagonistic muscles simultaneously that were recorded during postural perturbation experiments on cats. Minimizing the error between predicted and recorded EMG and CoM kinematics, we were able to identify controller gains that would result in the best prediction of the recorded EMGs. We hypothesized that the weights on the CoM kinematics remained constant independent of variations in perturbation magnitude or reversed perturbation direction. We applied our model to data from bidirectional perturbations with varying magnitude, with which the cats were perturbed for a short time in one direction and a longer time in the opposite direction. The gains showed small variation for EMG predictions following long perturbations; however, the prediction of EMG following the initial displacement resulted in large gain variations. We showed that these variations were caused by our optimization methods, which was not able to consistently identify controller gains for short initial movements. Using the weights identified for unidirectional perturbations, we were able to predict muscle activity for both directions with the same gains. This suggests that the weights of the CoM kinematics for each muscle did not change for varying perturbation magnitude. We conclude that varying EMG shapes were induced solely by the variation of the CoM kinematics. We repeated the investigations on data that was recorded from cats suffering from sensory loss and found reduced CoM acceleration feedback.

Introduction: Several authors have demonstrated that, while cycling at a constant power output, EMG activity from the gastrocnemius increases systematically with increases in pedaling cadence, but that soleus EMG remains unchanged (Marsh & Martin 1995; Sanderson et al. 2006). The reason for this differential effect of cadence on the muscles of the triceps surae is unclear. Whatever factor(s) are responsible, it is assumed that, as they vary, the differential electromyographic response will vary accordingly. Decreasing the seat height has been shown to alter the kinematic characteristics of cycling (Too, 1990). The first objective of this study was to examine the effect of a decrease in seat height on the kinematics and muscle activation of the lower limb. The second objective was to investigate the effect of seat height on the relationship between cadence and triceps surae activation and, in doing so, to reveal possible factors mediating the response to changes in cadence. Methods: Participants pedaled a cycle ergometer at 200 Watts for five minutes at each of five cadences (50, 65, 80, 95, 110 rpm) and at each of two seat heights (100% and 90% trochanteric height). Kinematics of the lower limb were calculated from digitized video records of reflective markers placed on the skin over seven bony landmarks. EMG data were collected from eight lower-limb muscles. Results: The most notable findings were 1) that activation of the gastrocnemii was less in the low-seat condition and, contrary to what the findings of past research would suggest, was not associated with changes in muscle length; 2) that the medial and lateral gastrocnemii responded differently to changes in cadence at each seat height, suggesting that the functional roles of these muscles in cycling differ; 3) that several factors, including muscle length, muscle velocity, ankle angle and the direction of muscle action, were not responsible for the differential effect of cadence on activation of the soleus and gastrocnemius. Future research should investigate afferent feedback from proprioceptors in the knee joint and knee extensor muscles as possible factors mediating the effect.

Impaired performance while executing a motor task is attributed to a disruption of normal automatic processes when an internal focus of attention is used (Wulf, McNevin, & Shea, 2001). When an external focus of attention is adopted, automaticity is not constrained and improved performance is noted. What remains unclear is whether the specificity of internally focused task instructions may impact task performance. In the present study, behavioural, kinematic and neurophysiological outcome measures assessed the implications of changing attentional focus for novice and skilled performers in a golf putting task. Findings provided evidence that when novice participants used an internal focus of attention related to task execution, accuracy, kinematics of the putter, and variability of EMG activity in the upper extremity were all adversely affected as task difficulty increased. Instructions which were internal but anatomically distal to the primary movement during the task appeared to have an effect similar to an external focus of attention and did not adversely affect outcomes.

Introduction: Several authors have demonstrated that, while cycling at a constant power output, EMG activity from the gastrocnemius increases systematically with increases in pedaling cadence, but that soleus EMG remains unchanged (Marsh & Martin 1995; Sanderson et al. 2006). The reason for this differential effect of cadence on the muscles of the triceps surae is unclear. Whatever factor(s) are responsible, it is assumed that, as they vary, the differential electromyographic response will vary accordingly. Decreasing the seat height has been shown to alter the kinematic characteristics of cycling (Too, 1990). The first objective of this study was to examine the effect of a decrease in seat height on the kinematics and muscle activation of the lower limb. The second objective was to investigate the effect of seat height on the relationship between cadence and triceps surae activation and, in doing so, to reveal possible factors mediating the response to changes in cadence. Methods: Participants pedaled a cycle ergometer at 200 Watts for five minutes at each of five cadences (50, 65, 80, 95, 110 rpm) and at each of two seat heights (100% and 90% trochanteric height). Kinematics of the lower limb were calculated from digitized video records of reflective markers placed on the skin over seven bony landmarks. EMG data were collected from eight lower-limb muscles. Results: The most notable findings were 1) that activation of the gastrocnemii was less in the low-seat condition and, contrary to what the findings of past research would suggest, was not associated with changes in muscle length; 2) that the medial and lateral gastrocnemii responded differently to changes in cadence at each seat height, suggesting that the functional roles of these muscles in cycling differ; 3) that several factors, including muscle length, muscle velocity, ankle angle and the direction of muscle action, were not responsible for the differential effect of cadence on activation of the soleus and gastrocnemius. Future research should investigate afferent feedback from proprioceptors in the knee joint and knee extensor muscles as possible factors mediating the effect.

Introduktion/bakgrund:Situp är troligtvis den övning de flesta generellt relaterar till vid träning av magen och det är en övning som de flesta provat på. Forskningen visar olika resultat vad gäller muskelaktivitet i bålen vid övningen situp beroende på övningens utförande och om man fixerar fötterna eller inte.  Syfte:Syftet med studien var att undersöka muskelaktiveringen i bålen vid olika former av situps.  Metod:Fyra personer rekryteras till studien där de fick genomföra 3 stycken olika former av situps. Den första formen av situps genomfördes med ett motståndsband runt fötterna och där en kontraktion i hamstringsmuskulaturen genomfördes. I övning nummer tvåfixerades fötterna mot golvet och i tredjeövningen fick deltagarna genomföra situpsen på valfritt sätt men med samma knävinkel som de två tidigare.  Resultat:Samtliga deltagare följde ett mönster där muskelaktiviteten i rectus femoris var lägst i den övning där kontraktion i hamstrings utfördes och högst under övningen med fixerade fötter. Tre av 4 deltagare fick högst muskelaktivitet i rectus abdominis vid övningen där fötterna fixerades mot underlaget men 3 av 4 deltagare uppnådde lägst muskelaktivitet i obliquus externus under samma övning.  När deltagarna fick genomföra situps på valfritt sätt så blev resultaten väldigt varierande. En deltagare fick högst muskelaktivering i både rectus abdominis och obliquus externus medans 2 deltagare fick lägst aktivitet i rectus abdominis. Konklusion: Kontraktion i hamstrings innebär lägst aktivitet i rectus femoris. Fixerade fötter skapar störst muskelaktivitet i rectus abdominis. Fria fötter är att föredra för störst muskelaktivitet i obliquus externus.

abstract: Perceived heaviness of lifted objects has been shown to scale to a ratio of muscle activity and movement during elbow lifts. This scaling reflects the importance of the forces applied to an object and the resulting kinematics for this perception. The current study determined whether these perceived heaviness dynamics are similar in other lifting conditions. Anatomically sourced context-conditioned variability has implications for motor control. The current study investigated whether these implications also hold for heaviness perception. In two experiments participants lifted objects with knee extension lifts and with several arm lifts and reported perceived heaviness. The resulting psychophysiological functions revealed the hypothesized muscle activity and movement ratio in both leg and arms lifts. Further, principal component regressions showed that the forearm flexors and corresponding joint angular accelerations were most relevant for perceived heaviness during arm lifts. Perceived heaviness dynamics are similar in the arms and legs. / Dissertation/Thesis / Masters Thesis Psychology 2016

Submitted by Isaac Francisco de Souza Dias (isaac.souzadias@ufpe.br) on 2015-05-21T18:58:22Z No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Dissertação Versão 13.pdf: 3038068 bytes, checksum: d35211f8ce524e4409508e0a61f42c38 (MD5) / Made available in DSpace on 2015-05-21T18:58:22Z (GMT). No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Dissertação Versão 13.pdf: 3038068 bytes, checksum: d35211f8ce524e4409508e0a61f42c38 (MD5) Previous issue date: 2015-01-30 / Este trabalho fala sobre o desenvolvimento de um protótipo de um sistema de aquisição de sinais de ECG e EMG, de baixo custo de fabricação, baixo consumo de energia e que se comunica via wireless, utilizando protocolo de comunicação Bluetooth, com dispositivos AndroidTM. O desenvolvimento desse protótipo teve como finalidade a monitorização, em tempo real, dos sinais de ECG e EMG de um indivíduo, durante a realização de atividades físicas. Neste equipamento procurou-se realizar o projeto dos amplificadores para sinais biológicos (ECG e EMG), que combinasse baixo consumo e portabilidade, ou seja, os componentes escolhidos para este trabalho objetivaram reduzir o tamanho do circuito. Além disso, a transmissão de dados via Bluetooth foi adequada para que esses dados fossem utilizados em um dispositivo AndroidTM (smartphone), gerando a oportunidade para uma nova gama de produtos, os quais possam integrar a tecnologia existente nos celulares modernos à tecnologia de instrumentação biomédica aplicada ao monitoramento remoto de sinais biológicos. Com o intuito de atingir esse objetivo, foram desenvolvidos os sistemas de controle e processamento, baseados na arquitetura RISC, amplificação e filtragem, fonte de alimentação e comunicação Bluetooth, integrados em duas placas de circuito impresso, ambas com dimensão de 3x5cm. O firmware do sistema de aquisição e o software de visualização, controle e armazenamento de sinal foram desenvolvidos com a finalidade de tornar compatível o sistema com a maioria dos dispositivos baseados no sistema operacional AndroidTM. O sistema foi testado, apresentando bom desempenho na transmissão de dados e boa estabilidade em relação ao armazenamento e controle do consumo de energia. Atualmente, este sistema vem sendo utilizado em projetos de pesquisa e dissertações de mestrado com a finalidade de identificar possíveis problemas ou adequações a serem realizadas, tanto ao nível de hardware como de software. Com o sistema validado muitas pessoas podem ser beneficiadas, pois esse equipamento une a praticidade e multifuncionalidade dos telefones AndroidTM com a tecnologia de aquisição e processamento de sinais biológicos.

Introduction: Several authors have demonstrated that, while cycling at a constant power output, EMG activity from the gastrocnemius increases systematically with increases in pedaling cadence, but that soleus EMG remains unchanged (Marsh & Martin 1995; Sanderson et al. 2006). The reason for this differential effect of cadence on the muscles of the triceps surae is unclear. Whatever factor(s) are responsible, it is assumed that, as they vary, the differential electromyographic response will vary accordingly. Decreasing the seat height has been shown to alter the kinematic characteristics of cycling (Too, 1990). The first objective of this study was to examine the effect of a decrease in seat height on the kinematics and muscle activation of the lower limb. The second objective was to investigate the effect of seat height on the relationship between cadence and triceps surae activation and, in doing so, to reveal possible factors mediating the response to changes in cadence. Methods: Participants pedaled a cycle ergometer at 200 Watts for five minutes at each of five cadences (50, 65, 80, 95, 110 rpm) and at each of two seat heights (100% and 90% trochanteric height). Kinematics of the lower limb were calculated from digitized video records of reflective markers placed on the skin over seven bony landmarks. EMG data were collected from eight lower-limb muscles. Results: The most notable findings were 1) that activation of the gastrocnemii was less in the low-seat condition and, contrary to what the findings of past research would suggest, was not associated with changes in muscle length; 2) that the medial and lateral gastrocnemii responded differently to changes in cadence at each seat height, suggesting that the functional roles of these muscles in cycling differ; 3) that several factors, including muscle length, muscle velocity, ankle angle and the direction of muscle action, were not responsible for the differential effect of cadence on activation of the soleus and gastrocnemius. Future research should investigate afferent feedback from proprioceptors in the knee joint and knee extensor muscles as possible factors mediating the effect. / Education, Faculty of / Kinesiology, School of / Graduate

Terränglöpning sker på varierande underlag med stora höjdskillnader, utmanande miljöer och ställer höga krav på utövaren. Ökat excentriskt arbetet i nedre extremitet vid utförslöpning har kopplats till mer skador och värk. Få tidigare studier har gjorts på utförslöpning brantare än -12º lutning. Syftet med studien var att jämföra muskelaktiviteten i nedre extremitet och bål vid brantare utförslöpning och användning av olika skor. Syftet var också att undersöka deltagarnas upplevelser under testet. Metod: Fyra kvinnor deltog, tillfrågade med bakgrund av erfarenhet inom terränglöpning (ålder 36 ±3,6 år, vikt 63 ±3,7 kg, längd 170 ±1,7 cm). Studien utfördes på en ramp där deltagarna sprang två gånger per lutning och skomodell. Muskelaktivitet mättes med elektromyografi (EMG) för nedre extremitet och bål. EMG-amplituden beräknades med root mean square (RMS) och medelvärde och standardavvikelse presentades för respektive lutning och sko. Ett frågeformulär skapades för att undersöka deltagarnas upplevelser av testen. Resultat: Framsida lår och ryggsträckarmuskulaturen visade ökad aktivitet från 0º till - 20º och - 26º samt ännu högre vid - 32º lutning. Magmuskulaturen visade ökad aktivitet från 0º till övriga lutningar. Ingen skillnad mellan skor noterades, utom ökad aktivitet i magmuskulaturen vid löpning med Inov8 jämfört med Salomon, vilket var den sko som deltagarna upplevde hade bäst grepp mot underlaget. Konklusion: Brant utförslöpning visade ökad muskelaktivitet i främst framsida lår och bålmuskulatur. På grund av få mätningar gjordes ingen signifikansanalys. Resultaten från denna pilotstudie är endast preliminära indikationer, större studier med fler deltagare och testförsök behövs. De subjektiva upplevelserna från deltagarna var generellt positiva och utgör viktig information vid framtida studier.