Tohru Kiryu

Sensation of presence and cybersickness in applications of virtual reality for advanced rehabilitation.

Around three years ago, in the special issue on augmented and virtual reality in rehabilitation, the topics of simulator sickness was briefly discussed in relation to vestibular rehabilitation. Simulator sickness with virtual reality applications have also been referred to as visually induced motion sickness or cybersickness. Recently, study on cybersickness has been reported in entertainment, training, game, and medical environment in several journals. Virtual stimuli can enlarge sensation of presence, but they sometimes also evoke unpleasant sensation. In order to safely apply augmented and virtual reality for long-term rehabilitation treatment, sensation of presence and cybersickness should be appropriately controlled. This issue presents the results of five studies conducted to evaluate visually-induced effects and speculate influences of virtual rehabilitation. In particular, the influence of visual and vestibular stimuli on cardiovascular responses are reported in terms of academic contribution.

Multivariate analysis of muscular fatigue during bicycle ergometer exercise

The purpose of this study is to estimate the endurance threshold in terms of muscular fatigue during bicycle ergometer exercise. The problems to be solved are induced by dynamic movement and the physiological variation of muscle activity: that is, the progression and impairment of muscle activity occur simultaneously. First of all, the authors used multichannel recordings of myoelectric (ME) signals to reduce the effect by the movement of a bipolar surface electrode relative to the innervation zones. Second, since even the different types of ME parameters contain redundant information on muscular fatigue, the authors used the principal component analysis (PCA) to represent the meaningful information by small dimensions. Moreover, the authors proposed a total evaluation pattern to discriminate muscular fatigue from progression of muscle force at a glance. The total evaluation pattern shows the proportion of first principal component, the components of the first eigenvector, and the correlation coefficients as a function of the work load. The assessment using the total evaluation pattern divided 8 subjects into 3 groups, whereas these subjects were not identified by a specific ME parameter.

Providing appropriate exercise levels for the elderly

We propose a unique fuzzy system design for adjusting the cycle ergometer work-load to each individuals physical work capacity. We observed the physical work capacity by measuring the heart rate and a muscular-fatigue-related index. A set of fuzzy membership functions was determined for three different phases during a trial of exercise with a progressively increasing workload. Since the available objective data was limited in describing changes in physical activities, the fuzzy rules for workload control were designed to reflect the different types and different time-scales of physical information. We examined 18 elderly people and periodically redesigned die fuzzy inference for eight selected persons over a seven-month period.

A muscular fatigue index based on the relationships between superimposed M wave and preceding background activity

A practical muscle fatigue index is studied in this paper using the correlation between the instantaneous frequencies (IFs) of the superimposed M wave and the mean power frequency (MPF) of the preceding background activity. A superimposed M wave is an M wave elicited during a sustained contraction and was recently introduced for studying muscle fatigue. The authors investigated the details of the distribution of a feature vector (mpf, if) in two-dimensional space. Their experimental results showed that MPF and IFs were closely correlated during the first phase of a short-term high-level sustained voluntary contraction and then became uncorrelated or sometimes showed negative correlation as muscular fatigue progressed. Combining the correlation coefficients and conventional myoelectric (ME) parameters, such as the MPF and the average rectified value of ME signals, the authors propose a fuzzy rule based muscular fatigue index that can be used for managing the inevitable variability among individual subjects collected as a group. Introducing fuzzy inference seemed effective, but further studies including detailed investigation of the level of voluntary effort, the muscle fiber type composition, and metabolic by-products will be needed to customize the membership functions and fuzzy rules more appropriately in each practical field.

AR modeling of myoelectric interference signals during a ramp contraction

The authors investigated the time-varying behavior of the autoregressive (AR) parameters in a myoelectric (ME) signal detected during a linear force increasing contraction. The AR parameters of interest mere the reflection coefficients, the AR model spectrum, and the prediction errors. The authors used well-conditioned ME signals for which the complete time record of the motor units firings was available. In addition, the influence of the recruitment of a new motor unit, the conduction velocity of action potentials, and additive broad-band noise were investigated using simulated ME signals. The simulated ME signals were constructed from a selected group of the available motor unit action potential trains. The results revealed that, as the contraction progressed, the AR parameters displayed a time-varying behavior which coincided with the recruitment of newly recruited motor units whose spectrum of the waveform differed from that of the rest of the ME signal. This property of the AR parameters was obscured by the presence of broad-band noise and low-amplitude motor unit action potentials, both of which are more pronounced during low-level force contractions.<<ETX>>

A Method of High Bit-Rate Data Hiding in Music Using Spline Interpolation

Acoustical signals in digital form can include additional information, this information is separate from the original signal even though they are both stored in a same file. Methods for storing additional information into the original acoustical signal itself have been investigated. Their bit-rate is at most several hundred bit per second. This paper proposes a new method for digital watermarking with higher bit-rate. Its information hiding and detection method is based on spline interpolation. As a result of listening experiment, bit-rate of above 1 kbps was achieved without audible deterioration.

Low-cost, email-based system for self blood pressure monitoring at home.

We have developed a low-cost monitoring system, which allows subjects to send blood pressure (BP) data obtained at home to health-care professionals by email. The system consists of a wrist BP monitor and a personal computer (PC) with an Internet connection. The wrist BP monitor includes an advanced positioning sensor to verify that the wrist is placed properly at heart level. Subjects at home can self-measure their BP every day, automatically transfer the BP data to their PC each week, and then send a comma-separated values (CSV) file to their health-care professional by email. In a feasibility study, 10 subjects used the system for a mean period of 207 days (SD 149). The mean percent achievement of measurement in the 10 subjects was 84% (SD 12). There was a seasonal variation in systolic and diastolic BP, which was inversely correlated with temperature. Eight of the 10 subjects evaluated the system favourably. The results of the present study demonstrate the feasibility of our email-based system for self-monitoring of blood pressure. Its low cost means that it may have widespread application in future home telecare studies.

An Internet-based cycle ergometer system by using distributed computing

With a rapidly increasing elderly population, it is required to offer a safe and optimal exercise environment for them to keep themselves healthy. In this paper, we present an Internet-based cycle ergometer system that supports an appropriate personal fitness process for individual elderly persons. Because there are great individual differences for each elderly person when they perform a cycle ergometer exercise, and their physical activities vary slightly from day to day, it is necessary to support appropriate workload control continuously. To achieve high availability and real time execution assistance, Internet technology has been employed. By distributing the system into different working units and implementing those units at different places on the Internet, the system gained great flexibility and efficiency. It is conceivable for each person to continuously exercise by using our proposed system at any time and at any possible place.

A muscle fatigue index based on the relationship between preceding background activity, and myotatic reflex response (MRR)

An index of muscular fatigue was developed using the myotatic reflex response (MRR). The MRR of masseter muscles is evoked by periodical mechanical chin tapping during clenching. The MRR waveform is composed of somewhat synchronized action potentials of muscle fibers. The authors estimate the change of the MRR waveform due to fatigue using the instantaneous frequency pattern (IFP) with the Hilbert transform. As a result, the features of IFP were different from the monotonic changes that have been observed by the conventional fatigue indices. That is, a plateau IFP was observed ahead of considerable fatigue, whereas the IFP showed a monopeak pattern during the other phase of an exercise. Also, the relationship between the preceding background mean power frequency and the instantaneous frequency around the first part of the MRR waveform was nonlinear during the whole process of fatigue. These features may allow the authors to estimate the degree of fatigue at each time instant.<<ETX>>

Personal customizing exercise with a wearable measurement and control unit

BackgroundRecently, wearable technology has been used in various health-related fields to develop advanced monitoring solutions. However, the monitoring function alone cannot meet all the requirements of customizing machine-based exercise on an individual basis by relying on biosignal-based controls. We propose a new wearable unit design equipped with measurement and control functions to support the customization process.MethodsThe wearable unit can measure the heart rate and electromyogram signals during exercise performance and output workload control commands to the exercise machines. The workload is continuously tracked with exercise programs set according to personally customized workload patterns and estimation results from the measured biosignals by a fuzzy control method. Exercise programs are adapted by relying on a computer workstation, which communicates with the wearable unit via wireless connections. A prototype of the wearable unit was tested together with an Internet-based cycle ergometer system to demonstrate that it is possible to customize exercise on an individual basis.ResultsWe tested the wearable unit in nine people to assess its suitability to control cycle ergometer exercise. The results confirmed that the unit could successfully control the ergometer workload and continuously support gradual changes in physical activities.ConclusionThe design of wearable units equipped with measurement and control functions is an important step towards establishing a convenient and continuously supported wellness environment.