The human foot contains a large number of bones, which form joints that can be moved consciously, as well as joints that move only slightly in an unconscious manner. While many studies have investigated the changes in unconsciously moved joints collectively by examining the wide region of the medial longitudinal arch, very few studies have investigated the constituent parts such as the first tarsometatarsal joint (an unconsciously moved joint). Furthermore, the commonly used methods of measurement based on motion capture or fluoroscopy have a problem associated with difficulties in preparing the measuring environment. To measure the dynamic deformation of the first tarsometatarsal joint, which is a part of the medial longitudinal arch, we used flexible polymer curvature sensors that convert the bending curvature to voltage. We attached three of these curvature sensors to measure the deformation of the joint in multiple planes. Twelve healthy adult males (aged 22.6±1.2 years) participated in the experiment, in which they were asked to walk barefoot on a treadmill. The measurements obtained showed dynamic and multi-planar deformation at the first tarsometatarsal joint. We confirmed that the tendency of deformation of the foot structure changes sensitively depending on the state of the foot.
The purpose of this study was to clarify the elasticity of the anterior tibial muscle depending on the contraction level. System identification technique was applied to an evoked mechanomyogram (MMG) and dorsiflex torque at a low level of isometric contraction. Electrical stimulation was applied to the common peroneal nerve when the subject maintained contraction levels at 0 (resting state), 5, 10, 20, and 30% of the maximum voluntary contraction. The evoked MMG and dorsiflex torque were measured with an acceleration sensor and a strain gauge load cell, respectively. Stimulation was conducted using 31 monopolar rectangle pulses with an interpulse interval of 1 s, and at supramaximal strength. The evoked MMGs and dorsiflex torques were averaged synchronously. System identification was performed using a singular value decomposition method. The undamped natural frequency of the system was calculated from the poles of the transfer function. The evoked MMG and dorsiflex torque in isometric contraction approximated well with a sixth-and a second-order model, respectively. The MMG peak-to-peak and the dorsiflex torque amplitude during isometric contraction decreased as the contraction level increased. The highest and intermediate natural frequencies of the sixth-order model of the evoked MMG (f1, and f2, respectively) tended to decrease as the contraction level increased. These decreases might reflect extension of the subcutaneous tissue. The lowest undamped natural frequency (f3) increased as the contraction level increased. This increase might reflect an increase in muscle stiffness. In conclusion, the muscle elasticity during isometric contraction was elucidated by the proposed method.
When humans swallow, swallowing sounds occur at the larynx. Since swallowing sounds can be measured noninvasively, these sounds are expected to be useful for testing swallowing ability. By analyzing these sounds, researchers have attempted to elucidate the mechanisms and the acoustic characteristics of the swallowing sounds. However, little research has been done which utilizes swallowing sounds to measure how much food or liquid is being swallowed. If the amount of food or drink being swallowed can be measured quantitatively, some diseases may be prevented by monitoring eating habits. The purpose of this research was to estimate the volume of water swallowed by analyzing swallowing sounds. First, swallowing sounds were recorded by applying a microphone on the skin surface above the thyroid cartilage when volumes of 5mL, 10mL and 15mL were swallowed by a subject. Fifty measurements were obtained. Second, signal processing methods such as smoothing, linear prediction analysis, Fourier transform and wavelet transform were applied to the swallowing sounds. Eighty-eight feature variables that may reflect the amount of water swallowed were obtained from the results. Using principal component analysis, the number of feature variables was reduced from 88 to 13. Finally, the estimated volume of water swallowed was evaluated using support vector machines. The volume of water was accurately identified with a probability of 72% for volumes between 5mL and 10mL, a probability of 84% for volumes between 10mL and 15mL, and a probability of 88% for volumes between 5mL and 15mL. When the same analysis was performed in several human subjects, the precision of classifying volume of water decreased, which may suggest individual differences in movements of the larynx and pharynx during swallowing.
We examined whether auditory steady-state response (ASSR), which is known as a lower-order brain response, can be modulated by expectations accompanying the progression of a musical phrase. We fabricated musical melodies consisted of seven tones, the amplitudes of which were modulated at 40Hz, under two conditions:the final (7th) tone was either congruent or incongruent with respect to the musical context of the melodies. Two control experiments were also conducted. The objective of one control experiment was to investigate the effect of the preceding sound (6th) on the final tone (7th) by presenting two final tones (6th and 7th) extracted from the melodies, and the objective of the other control experiment was to investigate the effect of hearing a pitch itself by presenting a tone sequence of ascending and descending scales between A♭5 and C7. The ASSR source strengths were estimated by magnetoencephalography. The strength of the 7th tone of the melodies was significantly larger in the incongruent condition than in the congruent condition. This difference could not be explained by effects of the preceding sound and pitch of the target tone, suggesting that ASSR was modulated by musical expectancy.