Jin-Seung Choi

Relationship between Lower -Limb Joint Angle and Muscle Activity due to Saddle Height during Cycle Pedaling

The purpose of this study was to investigate the effects of different saddle heights on lower-limb joint angle and muscle activity. Six elite cyclists(age: , height: , weight: , cycle career: ) participated in three min. submaximal(90 rpm) pedaling tests with the same load and cadence based on saddle heights where subject`s saddle height was determined by his knee flexion angle when the pedal crank was at the 6 o`clock position. Joint angles(hip, knee, ankle joints) and the activity of lower limb muscles(biceps femoris(BF), vastus lateralis(VL), tibialis anterior(TA) and gastrocnemius medial(GM)) were compared by measuring 3D motion and electromyography(EMG) data. Results showed that there were significant differences in minimum hip & knee joint angle and range of motion of hip and knee joint between saddle heights. Onset timing and integrated EMG of only BF among 4 muscles were significantly different between saddle heights. Especially there was a negative relationship between minimum hip joint angle and onset timing of BF in most subject, which means that onset timing of BF became fast as the degree of bending of the hip joint became larger by saddle height. Optimal pedaling will be possible through increased amount of muscle activation due to the appropriate burst onset timing by proper pedaling posture with adjusted saddle height.

Development of Gait Event Detection Algorithm using an Accelerometer

The purpose of this study was to develop and automatic gait event detection algorithm using single accelerometer which is attached at the top of the shoe. The sinal vector magnitude and anterior-posterior(x-axis) directional component of accelerometer were used to detect heel strike(HS) and toe off(TO), respectively. To evaluate proposed algorithm, gait event timing was compared with that by force plate and kinematic data. In experiment, 7 subjects performed 10 trials level walking with 3 different walking conditions such as fast, preferred & slow walking. An accelerometer, force plate and 3D motion capture system were used during experiment. Gait event by force plate was used as reference timing. Results showed that gait event by accelerometer is similar to that by force plate. The distribution of differences were spread about for HS and for To and most error was existed consistently prior to 20ms. The difference between gait event by kinematic data and developed algorithm was small. Thus it can be concluded that developed algorithm can be used during outdoor walking experiment. Further study is necessary to extract gait spatial variables by removing gravity factor.

The Differences of the Normalized Jerk According to Shoes, Velocity and Slope During Walking

The purpose of this study was to evaluate normalized jerk according to shoes, slope, and velocity during walking. Eleven different test subjects used three different types of shoes (running shoes, mountain climbing boots, and elevated forefoot walking shoes) at various walking speeds(1.19, 1.25, 1.33, 1.56, 1.78, 1.9, 2, 2.11, 2.33m/sec) and gradients(0, 3, 6, 10 degrees) on a treadmill. Since there were concerns about using the elevated forefoot shoes on an incline, these shoes were not used on a gradient. Motion Analysis (Motion Analysis Corp. Santa Rosa, CA USA) was conducted with four Falcon high speed digital motion capture cameras. Utilizing the maximum smoothness theory, it was hypothesized that there would be differences in jerk according to shoe type, velocity, and slope. Furthermore, it was assumed that running shoes would have the lowest values for normalized jerk because subjects were most accustomed to wearing these shoes. The results demonstrated that elevated forefoot walking shoes had lowest value for normalized jerk at heel. In contrast, elevated forefoot walking shoes had greater normalized jerk at the center of mass at most walking speeds. For most gradients and walking speeds, hiking boots had smaller medio-lateral directional normalized jerk at ankle than running shoes. These results alluded to an inverse ratio for jerk at the heel and at the COM for all types of shoes. Furthermore, as velocity increased, medio-lateral jerk was reduced for all gradients in both hiking boots and running shoes. Due to the fragility of the ankle joint, elevated forefoot walking shoes could be recommended for walking on flat surfaces because they minimize instability at the heel. Although the elevated forefoot walking shoes have the highest levels of jerk at the COM, the structure of the pelvis and spine allows for greater compensatory movement than the ankle. This movement at the COM might even have a beneficial effect of activating the muscles in the back and abdomen more than other shoes. On inclines hiking boots would be recommended over running shoes because hiking boots demonstrated more medio-lateral stability on a gradient than running shoes. These results also demonstrate the usefulness of normalized jerk theory in analyzing the relationship between the body and shoes, walking velocity, and movement up a slope.

Finite element analysis of the femur during stance phase of gait based on musculoskeletal model simulation

In this study, the accuracy of the inputs required for finite element analysis, which is mainly used for the biomechanical analysis of bones, was improved. To ensure a muscle force and joint contact force similar to the actual values, a musculoskeletal model that was based on the actual gait experiment was used. Gait data were obtained from a healthy male adult aged 29 who had no history of musculoskeletal disease and walked normally (171 cm height and 72 kg weight), and were used as inputs for the musculoskeletal model simulation to determine the muscle force and joint contact force. Among the phases of gait, which is the most common activity in daily life, the stance phase is the most affected by the load. The results data were extracted from five events in the stance phase: heel contact (ST1), loading response (ST2), early mid-stance (ST2), late mid-stance (ST4), and terminal stance (ST5). The results were used as the inputs for the finite element model that was formed using 1.5mm intervals computed tomography (CT) images and the maximum Von-Mises stress and the maximum Von-Mises strain of the right femur were examined. The maximum stress and strain were lowest at the ST4. The maximum values for the femur occurred in the medial part and then in the lateral part after the mid-stance. In this study, the results of the musculoskeletal model simulation using the inverse-dynamic analysis were utilized to improve the accuracy of the inputs, which affected the finite element analysis results, and the possibility of the bone-specific analysis according to the lapse of time was examined.

Driving Performance Changes of Middle-Aged Experienced Taxi Drivers Due to Distraction Tasks during Unexpected Situations

This study investigated the effects of distraction tasks—such as sending a text message with a cellphone and searching navigation with car navigation system—on the driving performance of 29 highly experienced taxi drivers in their 50 s. All participants were instructed to drive using a driving simulator for 2 min. while maintaining a constant distance from the vehicle in front and a constant speed. Participants drove without any distractions for the first minute. For an additional minute, they performed Driving Only or performed a task while driving (Driving + Sending Text Message or Driving + Searching Navigation). An unexpected situation, in which the participant had to stop abruptly due to a sudden stop of the preceding vehicle, occurred during this period. Driving performance during the unexpected situation was evaluated by car control variables, medial-lateral coefficient of variation and brake time, and by motion variables such as the jerk-cost function. Compared to Driving Only, jerk-cost function, medial-lateral coefficient of variation, and brake time increased during Driving + Sending Text Message or Driving + Searching Navigation.

Technical Note : Development of Electric Riding Machine for Cycle Fitting

The purpose of this study was to develop an electric riding machine for cycle fitting to control riding posture easily, to measure frame size quantitatively, and to overcome disadvantages of the traditional systems. The electric riding machine consisted of actuator, load controller, and display & control unit. The actuator unit by BLDC(BrushLess Direct Current) motor drives the saddle height up and down, the crank forward and backward, the handlebar up and down, and the handlebar forward and backward. The load controller unit controls loads by Eddy current controller with electromagnet and aluminum circular plate. The display & control unit consisted of frame size controller and display panel which shows top tube length(485~663mm), head tube length(85~243mm), seat tube length(481~671mm), and seat tube angle(). The range of frame size control for developed electric riding machine did not have difference compared to traditional commercial systems, but quantitative and precise control with 0.1 mm length and angle was possible through digital measurement. Unlike traditional commercial systems, frame size control was possible during riding through motor driven method, thus fitting duration decreased. It is necessary for further improvement to have feedback from users. It is believed that developed electric riding machine can help to develop domestic fitting system.

Changes in simple visual matching task performance and physiological signals in intellectually and developmentally disabled people due to administration of highly concentrated oxygen

BACKGROUNDnThis study attempted to identify the effect of administration of highly concentrated oxygen on simple visual matching task performance, blood oxygen saturation [SpO2 (%)], and heart rate [HR (bpm)] of intellectually and developmentally disabled people.nnnMETHODSnNineteen intellectually and developmentally disabled people (mean age 30.6 ± 5.7 years) participated in an experiment consisting of a simple visual matching task performed under 21% and 92% oxygen. SpO2 and HR were measured under both oxygen conditions.nnnRESULTSnWhen 92% oxygen was supplied, the response time decreased, SpO2 increased, and HR decreased compared to the vales obtained using 21% oxygen. The response time decreased for subjects with a high SpO2 and HR during the simple visual matching task phase.nnnCONCLUSIONnThis result supports the hypothesis that administration of highly concentrated oxygen can positively affect the cognitive performance of intellectually and developmentally disabled people.

Correlation between cognitive ability measured by response time of 1‐back task and changes of SpO2 by supplying three different levels of oxygen in the elderly

Aim:u2003 This study investigated the correlation between response time of the 1‐back task and changes of blood oxygen saturation (SpO2) by supplying three different levels of oxygen (21%, 1u2003L/min; 93%, 1u2003L/min; 93%, 5u2003L/min) in the elderly.

Simple Camera-based Evaluation System for Lower Limb Alignment during Pedalling

The present invention relates to a camera-based cycle pedaling lower limb alignment evaluation system and a method thereof. More particularly, the present invention relates to a camera-based cycle pedaling lower alignment evaluation system which can quantitatively measure the trajectory of a vertical direction, the inner and outer part of knee joints which closely relates to the vertical alignment of limbs through a front photography in pedaling. In the present invention relating to a camera-based cycle pedaling lower limb alignment evaluation system using image data, a reflection mark for photographing the change of the trajectory of the knee joints in the frontal plane with respect to the vertical alignment of the lower limb in the pedaling. [Reference numerals] (AA) Front camera; (BB) Trajectory of frontal plane; (CC) Measure the pattern of the knee joint trajectory; (DD) Lateral camera; (EE) Angle of sagittal plane; (FF) Calculate the angle of hip, knee joint, and ankle joint; (S110) Set an image; (S112) Set the camera(front side, lateral side); (S114) Set the region of interest(ROI); (S120) Obtain a marker trajectory; (S122) Obtain the image; (S124) Recognize a marker

Comparison of Kinematic Factors between Old and Young People during Walking on Level and Uneven Inclined Surfaces

The purpose of this study was to investigate the changes in walking pattern of the elderly during inclined walkway with uneven surfaces and level walking. 10 young(26.3±1.3 years, 174.3±5.3 cm, 69.5±9.5 kg) and 13 elderly(72.4±5.2 years, 164.5±5.4 cm, 66.1±9.6 kg) male subjects were participated in the experiment. Experiment consisted of 2 walking conditions: horizontal and inclined walkway with uneven surfaces. 3D motion capturing system were used to acquire and analyze walking motion data with sampling frequency of 120 Hz. To compare differences between conditions, kinematic variables(walking speed, stance-swing ratio, hip joint angle, knee joint angle, ankle joint angle, pelvic rotation angle) were used. Results showed that there were some changes of elderly walking pattern in inclined walkway with uneven surfaces: hip joint(adduction and rotation) and pelvic movement pattern. These changes by inclination and surface may affect gait pattern of young subjects as well as elderly subjects. However, in case of elderly it revealed more unstable gait than the young. Further study is necessary to clarify changes in walking pattern for elderly by considering various gait variables including head movement and various walkway conditions.