PurposesThe present study investigated whether a combination of the thickness and hardness of muscles without muscle tension can be used to estimate muscle strength during knee extension in adult males and females.MethodsSeventy-two males and thirty-three females, whose ages ranged from 18 to 35 years, participated in this study. We measured muscle thickness and hardness in the right anterior region of the thigh (rectus femoris muscle and vastus intermedius muscle) without muscle tension using an ultrasound muscle hardness meter, and the maximal voluntary isometric contraction of right knee extension (MVIC). The changing ratios (%) of the tissue thickness before compression to those during compression (compression ratio) are calculated as an index of the hardness. Higher ratio indicates a harder muscle compared with that of other individuals showing the same muscle thickness.ResultsIn male group, although the MVIC had significantly positive correlation to both muscle thickness (r=0.412, p<0.01) and compression ratio (r=0.233, p<0.05), their variables also had correlation mutually. In the female group, the MVIC has significantly positive correlation to only compression ratio (r=0.499, p<0.01), not muscle thickness (r=0.225, n.s.). On multiple linear regression analysis, the combination of two parameters (muscle thickness and compression ratio) allowed more accurate estimation of MVIC (r=0.573, p<0.01) in the female group.ConclusionThese findings suggested that the combination of muscle thickness and hardness is capable of effectively estimating muscle strength especially in females.

We have developed a pupil-corneal reflection method-based gaze detection system, which allows large head movements and achieves easy gaze calibration. This system contains two optical systems consisting of components such as a camera and a near-infrared light source attached to the camera. The light source has two concentric LED rings with different wavelengths. The inner and outer rings generate bright and dark pupil images, respectively. The pupils are detected from a difference image created by subtracting the bright and dark pupil images. The light source also generates the corneal reflection. The 3-D coordinates of the pupils are determined by the stereo matching method using two optical systems. The vector from the corneal reflection center to the pupil center in the camera image is determined as r. The angle between the line of sight and the line passing through the pupil center and the camera (light source) is denoted as θ. The relationship θ =k |r| is assumed, where k is a constant. The theory implies that head movement of the user is allowed and facilitates the gaze calibration procedure. In the automatic calibration method, k is automatically determined while the user looks around on the PC screen without fixating on any specific calibration target. In the one-point calibration method, the user is asked to fixate on one calibration target at the PC screen in order to correct the difference between the optical and visual axes. In the two-point calibration method, in order to correct the nonlinear relationship between θ and |r|, the user is asked to fixate on two targets. The experimental results show that the three proposed calibration methods improve the precision of gaze detection step by step. In addition, the average gaze error in the visual angle is less than 1° for the seven head positions of the user.

Abstract:The present study investigated the effects of touch button size on touchscreen operability and compared these effects between young adult and elderly participants. A total of 21 young adults (aged 22.3 ± 1.5 years) and 20 elderly adults (aged 68.1 ± 4.9 years) were recruited and asked to press square number buttons (from 0 to 9) on an experimental touchscreen with their right index finger. The buttons' size changed during the experiment with six conditions (6, 8, 10, 12, 14 and 16 mm). It was found that a decrease of the button size to 10 mm or below tended to increase the operation time and error rate, whereas it decreased the subjective overall operability of the touchscreen. Such effects were greater in the elderly adults than in the young adults. In addition, the reaction positions on the buttons were found to be close to the right side of them, which led the fingertip to approach the right outline of the buttons. These findings suggest that the use of small touch buttons should be minimised on touchscreens, especially for elderly users.

The quantification of muscle volume can be used to estimate muscular strength. Therefore, we developed a flexible measuring system for muscle volume using ultrasonog-raphy. In the measuring process, subjects are not required to perform any muscular contraction, so it is completely safe and particularly suitable for elderly people. The ultrasound probe is installed on a mechanical arm, and continuously scans fragmental images along the body surface. The measured images are then composed into a wide area cross-sectional image. However, the muscle area measured by our system was slightly smaller than that measured by MRI. because the ultrasound probe contacted the body surface with a little pressure during the measurement. The strain then decreases the total image size and its circumference. This paper introduces our developed system and proposes a new calibration method for the muscle area in the thigh based on its circumference.

Quantification of muscle volume can be used as a means for the estimation of muscle strength. Its measuring process does not need the subject's muscular contractions so it is completely safe and particularly suited for elderly people. Therefore, we have developed a flexible measuring system for muscle volume using ultrasonography. In this system, an ultrasound probe is installed on a link mechanism which continuously scans fragmental images along the human body surface. These images are then measured and composed into a wide area cross-sectional image based on the spatial compounding method. The flexibility of the link mechanism enables the operator to measure the images under any body postures and body site. The spatial compounding method significantly reduces speckle and artifact noises from the composed cross-sectional image so that the operator can observe the individual muscles, such as Rectus femoris, Vastus intermedius, and so on, in detail. We conducted the experiments in order to examine the advantages of this system we have developed. The experimental results showed a high accuracy of the measuring position which was calculated using the link mechanism and presented the noise reduction effect based on the spatial compounding method. Finally, we confirmed high correlations between the MRI images and the ones of the developed system to verify the validity of the system.