RESUMEN
Trunk muscles are responsible for maintaining trunk stability during sitting. However, the effects of anticipation of perturbation on trunk muscle responses are not well understood. The objectives of this study were to identify the responses of trunk muscles to sudden support surface translations and quantify the effects of anticipation of direction and time of perturbation on the trunk neuromuscular responses. Twelve able-bodied individuals participated in the study. Participants were seated on a kneeling chair and support surface translations were applied in the forward and backward directions with and without direction and time of perturbation cues. The trunk started moving on average approximately 40ms after the perturbation. During unanticipated perturbations, average latencies of the trunk muscle contractions were in the range between 103.4 and 117.4ms. When participants anticipated the perturbations, trunk muscle latencies were reduced by 16.8±10.0ms and the time it took the trunk to reach maximum velocity was also reduced, suggesting a biomechanical advantage caused by faster muscle responses. These results suggested that trunk muscles have medium latency responses and use reflexive mechanisms. Moreover, anticipation of perturbation decreased trunk muscles latencies, suggesting that the central nervous system modulated readiness of the trunk based on anticipatory information.
Asunto(s)
Anticipación Psicológica/fisiología , Postura/fisiología , Tiempo de Reacción/fisiología , Percepción Espacial/fisiología , Percepción del Tiempo/fisiología , Torso/fisiología , Estimulación Acústica/métodos , Adulto , Electromiografía/métodos , Humanos , Masculino , Contracción Muscular/fisiología , Músculo Esquelético/fisiología , Adulto JovenRESUMEN
BACKGROUND: The purpose of this study was to examine the impact of functional electrical stimulation (FES) induced co-activation of trunk muscles during quiet sitting. We hypothesized that FES applied to the trunk muscles will increase trunk stiffness. The objectives of this study were to: 1) compare the center of pressure (COP) fluctuations during unsupported and FES-assisted quiet sitting - an experimental study and; 2) investigate how FES influences sitting balance - an analytical (simulation) study. METHODS: The experimental study involved 15 able-bodied individuals who were seated on an instrumented chair. During the experiment, COP of the body projected on the seating surface was calculated to compare sitting stability of participants during unsupported and FES-assisted quiet sitting. The analytical (simulation) study examined dynamics of quiet sitting using an inverted pendulum model, representing the body, and a proportional-derivative (PD) controller, representing the central nervous system control. This model was used to analyze the relationship between increased trunk stiffness and COP fluctuations. RESULTS: In the experimental study, the COP fluctuations showed that: i) the mean velocity, mean frequency and the power frequency were higher during FES-assisted sitting; ii) the frequency dispersion for anterior-posterior fluctuations was smaller during FES-assisted sitting; and iii) the mean distance, range and centroidal frequency did not change during FES-assisted sitting. The analytical (simulation) study showed that increased mechanical stiffness of the trunk had the same effect on COP fluctuations as the FES. CONCLUSIONS: The results of this study suggest that FES applied to the key trunk muscles increases the speed of the COP fluctuations by increasing the trunk stiffness during quiet sitting.
Asunto(s)
Estimulación Eléctrica , Músculo Esquelético/fisiología , Femenino , Humanos , Masculino , Equilibrio Postural/fisiología , Postura/fisiología , Torso/fisiologíaRESUMEN
BACKGROUND: Individuals with cervical spinal cord injury usually sustain impairments to the trunk and upper and lower limbs, resulting in compromised sitting balance. The objectives of this study were to: 1) compare postural control of individuals with cervical spinal cord injury and able-bodied individuals; and 2) investigate the effects of foot support and trunk fluctuations on postural control during sitting balance. METHODS: Ten able-bodied individuals and six individuals with cervical spinal cord injury were asked to sit quietly during two 60s trials. The forces exerted on the seat and the foot support surfaces were measured separately using two force plates. The global centre of pressure sway was obtained from the measurements on the two force plates, and the sway for each force plate was calculated individually. FINDINGS: Individuals with spinal cord injury had at least twice as large global and seat sways compared to able-bodied individuals, while foot support sway was not significantly different between the two groups. Comparison between global and seat sways showed that anterior-posterior velocity of global sway was larger compared to the seat sway in both groups. INTERPRETATION: Postural control of individuals with cervical spinal cord injury was worse than that of able-bodied individuals. The trunk swayed more in individuals with spinal cord injury, while the stabilization effect of the feet did not differ between the groups. Foot support affected anterior-posterior fluctuations in both groups equally. Thus, trunk control is the dominant mechanism contributing to sitting balance in both able-bodied and spinal cord injury individuals.
Asunto(s)
Médula Cervical/lesiones , Médula Cervical/fisiopatología , Equilibrio Postural/fisiología , Traumatismos de la Médula Espinal/fisiopatología , Torso/fisiopatología , Adulto , Anciano , Femenino , Pie , Humanos , Masculino , Persona de Mediana Edad , PresiónRESUMEN
INTRODUCTION: Eye movements convey important information about brain function. Neuropsychiatric conditions and medications may produce abnormal eye movements (EMs) in sleep. Serotonergic drugs are known to increase nocturnal EMs. Few studies have quantified sleep EMs due to technical complexity. We investigated the effects of serotonergic drugs on slow EMs in sleeping patients using an objective automated EM quantification tool. METHODS: We studied patients who had polysomnograms for clinical assessment. We identified 5 sertraline, 7 citalopram, and 4 fluoxetine users who were not using other psychoactive medications. Controls were 10 age-matched patients on no medications. An automated objective EM detection tool was developed. The first and last 5 min of each sleep stage were assessed. ANOVA was used to assess the effects of time, stage, and medication. RESULTS: No differences were noted between SSRI users and controls in demographics. Medications were associated with more slow EMs compared to controls (p<0.05). Among SSRI users, a non-statistical trend was noted for increasing slow EMs in the following pattern: sertralineAsunto(s)
Procesamiento Automatizado de Datos/métodos
, Electrooculografía/métodos
, Trastornos de la Motilidad Ocular/inducido químicamente
, Trastornos de la Motilidad Ocular/diagnóstico
, Inhibidores Selectivos de la Recaptación de Serotonina/efectos adversos
, Anciano
, Análisis de Varianza
, Estudios de Casos y Controles
, Presión de las Vías Aéreas Positiva Contínua/métodos
, Depresión/tratamiento farmacológico
, Depresión/fisiopatología
, Electroencefalografía/métodos
, Electromiografía
, Femenino
, Humanos
, Estudios Longitudinales
, Masculino
, Persona de Mediana Edad
, Polisomnografía/métodos
RESUMEN
This study considers the use of hand-held power tools and the exposure of a large number of employees to hand-arm vibrations in work settings as well as the harmful effects that such exposure has on health and safety. The major objective of the project was the development of a diagnostic device for the detection and monitoring of the vibrations produced during work activities in a natural working environment and to analyze the impact of the vibrations on workers during different work operations. The developed device for vibration monitoring is based on the latest generation MEMS tri-axis accelerometer with a wireless link with the PC station. This study demonstrates the use of the device in evaluating the level of protection that gloves provide concerning the level of vibrations during work operations. The initial evaluation shows that the proposed solution provides an effective multifunctional, low-cost diagnostic device for vibration measurement in natural work settings. Preliminary results indicate that the developed device could be used for health and safety studies, evaluation of protective equipment, and ongoing monitoring in a natural working environment, and in this way may lead to more effective prevention and management of the risks associated with exposure to workplace vibrations.