[Purpose] The aim of this study was to examine the intrarater and interrater reliability of the Star Excursion Balance Test (SEBT), thereby increasing understanding of its efficient utilization. [Subjects and Methods] There were 67 subjects (49 female; 18 male). For the SEBT, eight lines were made using tape at 45-degree angles from the center of a circle. The experiment was conducted in the following order: the anterior, anterior-medial, medial, posterior-medial, posterior, posterior-lateral, lateral, and anterior-lateral directions. Intraclass correlation coefficients (ICC) (3,1) were used to evaluate the intrarater and interrater reliability (2,1) for each reach distance, while the standard error of measurement (SEM) and smallest detectable distance (SDD) were employed to assess absolute reliability. [Results] For intraratar reliability, the ICC values for all directions ranged from 0.88 to 0.96, SEM values ranged from 2.41 to 3.30, and SDD values ranged from 6.68 to 9.15. For interrater reliability, the ICC values for all directions ranged from 0.83 to 0.93, SEM values ranged from 3.19 to 4.26, and SDD values ranged from 8.85 to 11.82 [Conclusion] The SEBT is a highly reliable tool for measuring dynamic balance. Measurements for intrarater reliability are more reliable than measurements for interrater reliability. When measurement for eight directions was difficult, the SEBT was used. While the anterior, posteromedial, and posterolateral directions employed in the Y Balance Test KitTM can be utilized, this study recommends using the reverse Y Balance Test KitTM method with the posterior direction, not the anterior direction.

[Purpose] This study aimed to compare dynamic balance with respect to completing a single task while not using smartrphone function and completing two task while using different smartphone functions, therby preventing falls or injuries resulting from completion of dual tasks. [Subjects and Methods] The subjects of this study were 36 healthy males and females. The experiment was conducted for five situations: a Star Excursion Balance Test (SEBT) was performed (1) during single-tasking without a smartphone and during dual-tasking with a smartphone, (2) when listening to music using a smartphone, (3) when sending message using a smartphone, (4) when surfing the web using a smartphone, and (5) when playing a game using a smartphone. The condition were the same for all five experimentes. Random selection was done to prevent learing. All experiments were conducted three times, and the averaged values were used for analysis. The SEBT was performed in three directions: anterior, posterolateral, and posterormedial. In consideration the differences in leg length of the subjects, their actual leg length were measured to be used as percentages. Their leg length was measured from the anterior superior iliac spine of the femur to the medial malleolus. [Results] Compared with single task not done using a smartphone, dynamic balance statistically significantly changed for dual tasks done using a smartphone in all three directions. Dynamic balance decreased in all three directions when playing games, sending messages, web surfing, and listening to music. [Conclusion] Completing two tasks using a smartphone reduced cognitive ability, decreasing dynamic balance. Therefore, performing a single task rather than using the diverse functions of a smartphone while walking or working is considered a factor that can prevent falls and injuries.

Abstract.[Purpose] The purpose of the present study was to examine the immediate effects of passive hamstring stretching exercises on cervical spine range of motion and balance.[Subjects] The present study was conducted with 60 healthy university students without any musculoskeletal dysfunction as subjects. They were divided into an experimental group consisting of 30 subjects and a control group consisting of 30 subjects.[Methods] Cervical spine range of motion was measured using a cervical range of motion goniometer, and the stability test was conducted to assess balance. The experimental group were administered hamstring stretching with ankle dorsiflexion for 30 seconds three times, whereas the control group received the same treatment without ankle dorsiflexion. [Results] Cervical spine range of motion and balance immediately increased in the experimental group while there was no change in the control group.[Conclusion] The results show that hamstring muscle stretching exercises the fascia of the skeletal muscles of the human body and that the fascia are connected to each other by interactions of force. The human skeletal muscles interacted with each other to increase the flexion and extension range of motion of the cervical spine. In addition, the transfer of these forces to the stabilizer muscles of the pelvis and spine were the most important factor in the improvement of the subjects' balance.

[Purpose] This study aimed to compare dynamic balance ability according to foot shape, defined as normal, pronated, or supinated on the basis of the height of the medial arch. [Subjects] In this study, 14 subjects for the pronated foot group, 14 for the supinated foot group, and 14 for the normal foot group were selected from among 162 healthy university students by using the navicular drop test proposed by Brody. To measure dynamic balance ability, a star excursion balance test (SEBT) was conducted for each group, in which a cross-shaped line and lines at 45° in eight directions were drawn on the floor. In this study, only three directions were used, namely anterior, posterolateral, and posteromedial. The mean of the SEBT was calculated by measuring three times for each group, and the values were standardized using the following equation: measured value/leg length × 100. [Results] No significant differences in dynamic balance ability were found between the normal, pronated, and supinated foot groups. [Conclusion] No significant differences in dynamic balance ability according to the foot shape were found among the healthy university students with normal, pronated, and supinated feet.

[Purpose] The purpose of the present study was to examine the effects of squat exercises performed on different surfaces on the activity of the quadriceps femoris muscle in order to provide information on support surfaces for effective squat exercises. [Subjects and Method] Fourteen healthy subjects performed squat exercises for five seconds each on three different support surfaces: hard plates, foam, and rubber air discs. Their performance was measured using electromyography. As the subjects performed the squat exercises on each surface, data on the activity of the vastus medialis oblique and the vastus lateralis, and the vastus medials oblique/vastus lateralis ratio, were collected. [Results] The activity of the vastus medialis oblique and the vastus medialis oblique/vastus lateralis ratio were found to be statistically significantly higher on rubber air discs than when the squats were performed on hard plates or foam. [Conclusion] To activate the vastus medialis obilique, and to enhance the vastus medialis oblique/vastus lateralis ratio, unstable surfaces that are highly unstable should be selected.

Abstract.[Purpose] The purpose of the present study was to examine differences in ankle joint muscles' electromyographic activities at different instability levels of unstable surfaces in order to provide a scientific basis for unstable surface training. [Subjects and Method] Sixty healthy adult males and females participated in the present study, and they were equally and randomly assigned to a 2.0 psi group, a 1.5 psi group, and a 1.0 psi group. The subjects were instructed to take a standing posture on a 13 inch diameter rubber air disc inflated at different air pressure for 15 seconds. While the participants maintained their standing posture, the EMG signals of the tibialis anterior, the peroneus longus, and the medial gastrocnemius of the dominant lower limb were recorded to assess the muscle activities.[Results] The muscle activity of the tibialis anterior was the highest at 1.0 psi and showed significant differences from its muscle activities at 1.5 psi and 2.0 psi. The muscle activities of the peroneus longus and the medial gastrocnemius were highest at 1.0 psi and showed significant differences from the muscle activities at 2.0 psi. At all the pressures, the muscle activity of the tibialis anterior was the highest and that of the medial gastrocnemius was the lowest, although the differences were not statistically significant. [Conclusion] The results of the present study show that to trigger the co-contraction of all muscles involved in ankle joint stability, 1.0 psi or lower instability should be provided.

[Purpose] This study evaluated the effective selective activation method of the vastus medialis oblique for knee joint stabilization in patients with patellofemoral pain syndrome. [Subjects and Methods] Fifteen healthy college students (9 males, 6 females); mean age, height, and weight: 22.2 years, 167.8 cm, and 61.4 kg, respectively) participated. The knee angle was held at 60°. Muscle activities were measured once each during an ordinary squat and a squat accompanied by hip joint adduction. The muscle activities of the vastus medialis oblique and vastus lateralis were measured by electromyography for five seconds while maintaining 60° knee flexion. Electromyography signals were obtained at a sampling rate of 1,000 Hz and band pass filtering at 20–50 Hz. The obtained raw root mean square was divided by the maximal voluntary isometric contraction and expressed as a percentage. The selective activity of the vastus medialis oblique was assessed according to the muscle activity ratio of the vastus medialis oblique to the vastus lateralis. [Results] The activity ratio of the vastus medialis oblique was higher during a squat with hip joint adduction than without. [Conclusion] A squat accompanied by hip joint adduction is effective for the selective activation of the vastus medialis oblique.

Purpose] The purpose of this study was to examine the effect of forward head posture on ankle joint range of motion and static balance.[Subjects] The study subjects were on 51 healthy undergraduates (22 males and 29 females) who had not experienced cervical or shoulder pains, or hospital diagnosis of musculoskeletal dysfunction in the previous four weeks. [Methods] The cranial vertical angle (CVA) was measured to investigate forward head posture, and the Tetrax Portable Multiple System (Tetrax Ltd, 56 Miryam Ramat Gan, Sunlight, Israil) was used to measure static balance using the stability test index (STI). Distal dualer-IQ (JTECH Medical, USA) was used to measure ankle joint range of motion.[Results] Cranial vertical angle had an influence on ankle joint plantarflexion, but no influence on static balance. [Conclusion] Forward head posture was shown to transmit tension to the ankle joint through the superficial back-line, one of the myofascial meridians connected to the fascia, which suggests that tension in the neck muscles influence the ankle joints.