Kristiina M. Valter McConville

Arm movement improves performance in clinical balance and mobility tests

Previous studies have suggested that arm movements can contribute to preventing the loss of balance or falls, and that aging affects the functions of arm movements. Clinical balance and mobility tests may be able to detect such aging effects. As the first step to approaching this question, the purpose of this pilot study was to investigate the effects of arm movements on the performance of clinical balance and mobility tests. Ten participants were evaluated in four clinical tests: (1) Maximal Step Length Test (MST), (2) Step Test (ST), (3) Timed Up and Go Test (TUG), and (4) Walk along an Elliptical Line (WEL). Each test was performed with free and limited arm movement and the outcomes were compared. Statistical analysis indicated a significant improvement in test performance when arms were used freely for three out of four tests (MST, ST and TUG), with inconclusive results on WEL. This pilot study showed improved performance on the clinical balance and mobility tests, suggesting that the contribution of arm movements is sufficiently large to be detected. This implies a feasibility for novel usage of clinical balance and mobility tests, i.e., to test the effectiveness of arm usage in balance and mobility.

An informational approach to sensory adaptation

SummaryConcepts from information theory can enhance our understanding of perceptual processes by providing a unified picture of the process of perception. A single equation is shown to embrace adaptation phenomena, stimulus-response relations, and differential thresholds. Sensory adaptation is regarded as representing a gain in information by the receptor. It is calculated that for constant stimuli in the form of step inputs, insects and arachnids obtain approximately the same amount of information per stimulus from their respective environments as do human beings.

Trunk control impairment is responsible for postural instability during quiet sitting in individuals with cervical spinal cord injury.

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.

Video game-based neuromuscular electrical stimulation system for calf muscle training: A case study

A video game-based training system was designed to integrate neuromuscular electrical stimulation (NMES) and visual feedback as a means to improve strength and endurance of the lower leg muscles, and to increase the range of motion (ROM) of the ankle joints. The system allowed the participants to perform isotonic concentric and isometric contractions in both the plantarflexors and dorsiflexors using NMES. In the proposed system, the contractions were performed against exterior resistance, and the angle of the ankle joints was used as the control input to the video game. To test the practicality of the proposed system, an individual with chronic complete spinal cord injury (SCI) participated in the study. The system provided a progressive overload for the trained muscles, which is a prerequisite for successful muscle training. The participant indicated that he enjoyed the video game-based training and that he would like to continue the treatment. The results show that the training resulted in a significant improvement of the strength and endurance of the paralyzed lower leg muscles, and in an increased ROM of the ankle joints. Video game-based training programs might be effective in motivating participants to train more frequently and adhere to otherwise tedious training protocols. It is expected that such training will not only improve the properties of their muscles but also decrease the severity and frequency of secondary complications that result from SCI.

Anticipation of direction and time of perturbation modulates the onset latency of trunk muscle responses during sitting perturbations

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.

Evaluation of Protective Gloves and Working Techniques for Reducing Hand-arm Vibration Exposure in the Workplace

Evaluation of Protective Gloves and Working Techniques for Reducing Hand‐arm Vibration Exposure in the Workplace: Matija MILOSEVIC, et al. Electrical and Computer Engineering Department, Ryerson University, Canada—

Trunk muscle co-activation using functional electrical stimulation modifies center of pressure fluctuations during quiet sitting by increasing trunk stiffness.

BackgroundThe 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.MethodsThe 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.ResultsIn 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.ConclusionsThe 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.

Abdominal muscle behavior and motion sickness during paired visual input with roll motion

The study of seated balance, specifically in relation to wheelchair propulsion has the potential to lead to the prevention and treatment of musculoskeletal injuries. To date little study has been done which analyzes the activity of abdominal and back muscles in relation to postural behavior and balance during sitting balance. In this pilot study, the effect of motorized rotational roll movement was analyzed on two subjects with and without visuals in both directions of the individuals. The corresponding muscle activity was recorded by surface electromyography (EMG) in the presence and absence of visual scenery. An assessment of how muscle activity was affected by virtual reality was also conducted, and motion sickness during paired visual input with motion was also examined. The results showed that the dominant factors in abdominal muscle activity were the acceleration and speed of rotational motion and an increase of 20.8% in muscle activity was observed. The results also suggested that motion of the subject with respect to visual display had an inhibitory effect on the motion perception. The findings also suggested that visual scenery during rotational motion had a small effect on the subjects (4.2%), which was possibly caused by placing focus away from maintaining balance. Finally, the study confirmed that the duration of motion with visuals was a major contributor to motion sickness.