Isometric Postures Research Articles

Passive Stiffness Reduction in Human Ankle Joint Mechanical Impedance When Exposed to Externally Imposed Movement.

Exoskeleton design is based on achieving representative torques for both active and passive joint mechanics for a given task. The latter has been typically estimated for static postures during relaxed muscle activity. However, some studies have shown that differences in the estimates during voluntary motion versus isometric postures have resulted in lower impedance estimates during active muscle activity. The objective of this study was to determine if the estimates for the passive joint impedance of the human ankle exhibited the same reduction during relaxed muscle states with an externally imposed movement over static posture estimates. System identification techniques were used to analyze the passive joint impedance as a second-order model with inertia, damping, and stiffness. The experimental results showed little differences for the inertia and damping coefficients; however, a 10 to 34% reduction in the passive stiffness estimate was observed during movement when compared to static posture estimates. It is postulated that the 22% increase in angular velocity of the perturbations due to the superimposed externally imposed motion may be a contributing factor to these statistically different estimates. This reduced passive stiffness yields possibly new insights into muscle mechanics and applications to exoskeleton design. With lower torque and power estimates for passive resistance during imposed movement, reductions in motor sizing and inertial effects could lead to improved overall performance.

Dynamic balance ability in young elite soccer players: implication of isometric strength.

Soccer requires maintaining unilateral balance when executing movement with the contralateral leg. Despite the fact that balance requires standing with maintaining isometric posture with the support leg, currently there is a lack of studies regarding the implication of isometric strength on dynamic balance's performance among young soccer players. Therefore, the aim of this study was to examine the relationship between the Y-Balance Test and 12 lower limbs isometric strength tests. Twenty-six right footed soccer players (mean±SD, age=16.2±1.6 years, height=175±4.2 cm, body mass=68.8±6.1 kg) performed a dynamic balance test (star excursion balance-test with dominant- (DL) and nondominant-legs (NDL). Furthermore, maximal isometric contraction tests of 12 lower limb muscle groups were assessed in DL and NDL. Correlations analysis reported a significant positive relationship between some of isometric strength tests (with DL and NDL) and the Y-Balance Test. Furthermore, stepwise multiple regression analysis showed that maximal isometric strength explained between 21.9% and 49.4% of the variance of the Y-Balance Test. Moreover, maximal isometric strength was dependent upon the reaching angle of the Y-Balance Test and the leg used to support body weight. This study showed a significant implication of maximal isometric strength of the lower limb and the Y-Balance Test. Moreover, the present investigation suggests the implementation of specific lower limb strengthening exercises depending on players' deficit in each reaching direction and leg. This result suggests that further studies should experiment if increasing lower limbs isometric strength could improve dynamic balance ability among young soccer players.

Anatomia descritiva aplicada à cinesiologia e biomecânica básica dos músculos da cintura peitoral, estilopódio e zeugopódio do jacaré do papo amarelo

Objetivou-se identificar os parâmetros de origem e inserção musculares da cintura peitoral e membro torácico de Caiman latirostris, mediante abordagem anatômica, cinesiológica e biomecânica básica. Foram utilizados dois exemplares de C. latirostris, machos, medindo, em média, 1,50cm de comprimento, adultos, pertencentes ao acervo do Laboratório de Ensino e Pesquisa em Animais Silvestres, Universidade Federal de Uberlândia/MG, Brasil. Foi notada postura isométrica entremeando movimentos rotativos, além de grande área de secção transversa, na maioria dos músculos extensores e estabilizadores, conferindo-lhes, maior força, denotando inferências funcionais e organizacionais. Foi possível reconhecer e predefinir o comportamento da espécie investigada, relacionando duração, direção e dimensão dos níveis de ação.

Análise eletromiográfica dos músculos reto femoral e reto abdominal durante a execução dos exercícios hundred e teaser do método pilates

A literatura tem mostrado que pequenas modificações em um exercício do método Pilates podem alterar o padrão de ativação muscular. Além disto, são poucos os estudos que avaliaram exercícios desse método do ponto de vista cinesiológico. Nesta perspectiva, o objetivo deste trabalho foi comparar dois exercícios realizados no solo e em aparelho no que diz respeito à ativação elétrica de grupos musculares atuantes. Participaram do estudo 11 mulheres saudáveis praticantes do método Pilates. Foram coletados dados eletromiográficos dos músculos reto femoral e reto abdominal, porções direita e esquerda, enquanto os exercícios hundred no solo, hundred no Reformer, teaser no solo e teaser no Cadillac eram mantidos na postura isométrica. Foram analisados os cinco segundos centrais de cada execução, normalizados por contração voluntária máxima. A análise estatística apresentou diferença entre a ativação dos grupos musculares, sendo maior no reto femoral, e interação entre músculos e exercício, onde no exercício hundred no solo e no Reformer o reto femoral teve maior ativação, enquanto no exercício teaser o reto abdominal foi mais ativo quando executado no Cadillac. Com base nos resultados do estudo pode-se afirmar que: i) quando comparados os exercícios hundred (no solo e no Reformer) e teaser (no solo e no Cadillac), não houve diferença entre os exercícios no que se refere à ativação dos músculos reto abdominal e reto femoral; ii) quando comparados os grupamentos musculares, o reto femoral apresentou maiores níveis de ativação nos exercícios hundred executado no solo e no Reformer, enquanto o reto abdominal apresentou maior ativação durante o exercício teaser executado no Cadillac.

A new approach to assess movements and isometric postures of spine and trunk at the workplace

Low back pain is regarded as the primary cause of occupational disability in many countries worldwide. However, there is a lack of valid assessment of kinematic spine and trunk parameters to provide further insight into occupational spine loads. A new 3-dimensional mobile measurement system (3D-SpineMoveGuard) was developed and evaluated by means of repeated dynamic and isometric trunk positions by 10 male and 10 female volunteers. The interclass correlation coefficient indicates high test-retest reliability (r=0.975-0.999) of the 3D-SpineMoveGuard. Moreover, analysis of validity revealed almost identical results for the new measurement system. The evaluation study indicates a good scientific quality for the use in occupational task analyses. The objective assessment of indirectly measured spine and trunk kinematics will give further insight to predict and prevent job-related spine loads.

Studies of spinal shrinkage to evaluate low-back loading in the workplace.

Measurement of spinal shrinkage (stadiometry) has been suggested to be a convenient measure of low-back load in workplace settings. This report documents three separate experiments that collectively form a central theme: Is the measurement of spinal shrinkage a suitable assessment technique to quantify the cumulative effect of loading on the low back given the many sources for variability in the signal? A stadiometer was fabricated to measure both sitting and standing height. The first experiment was to compare sitting with standing stature changes over time in an attempt to locate the major site of shrinkage. There were no statistically significant differences in stature change found between either the sitting or standing posture for any condition suggesting that nearly all height changes occur in the spine. The second experiment compared the cumulative effects from static load holding to dynamic load lifting. Some subjects experienced more shrinkage in the static task while others experienced more in the dynamic task. In the third experiment, subjects performed work-rest cycles consisting of periods of sitting and lifting, and repeated over two days, to examine the recovery phenomenon. No specific pattern emerged owing to unpredictable subject variability. The first general observation obtained from the results of all three experiments is that the response of subjects to a wide array of activities appears to be variable both within each subject and over repeated exposures to identical conditions on different days. While subject variability (and perhaps biological variability) is a liability, it may be feasible to develop load time integrals for load exposure in the future, since the asset of the spinal shrinkage approach appears to be that it is one of the few available techniques to assess cumulative loading for both isometric postures, prolonged sitting, repeated tasks and responds to the positive adaptive changes that occur from periods of rest. However, it would appear that more quantification of the relationships that modulate spinal shrinkage are required to account for the variance in stature measurements.

Fine force instability: a quantitative measure of neuroleptic-induced dyskinesia in the hand

The results of a new procedure for the quantification of tardive dyskinesia (TD) in the hand are reported. Fourier analyses were made of steady-state isometric force control in 41 neuroleptic-treated patients with and without hand TD. Results indicated that spectral analysis of isometric posture represents a reliable, sensitive, and valid measure of neuroleptic-induced dyskinesia.