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This study aimed to analyze and compare the hip, knee, and elbow joint movements during the double poling (DP) technique in cross-country skiing using a wearable inertial measurement unit (IMU) sensor on a real snow skiing track. Six national players (NP) and five college players (CP) participated in this study. The joints angles were calculated using the data from IMU sensors on a 145 m skiing course with 10° slope using the DP technique. In addition, the parameters of the DP phase were estimated. Then, all parameters were compared between the NP and CP groups. The hip and knee joint angles in the NP groups were significantly larger than the CP groups. However, there was no intergroup difference in elbow joint range of motion (ROM). Moreover, the cycle length and cycle velocity was higher in the NP group than the CP group. The results showed that the NP group had higher speed and longer cycle length with greater flexion angles in the hip and knee joints. The wearable IMU sensor was used to analyze the motions during DP skiing on the snow skiing slope, which can provide more realistic detailed analysis of the skiing movements. This study provides the comparison analysis of the main parameters between the two different skilled skiers groups, which may help coaches and players improve skiing performance.

Various treatment devices or tables have been developed for generating axial rotation of the lumbar spine during spinal mobilization. However, the effects of the design of such treatment devices on the axial rotation of the lumbar spine have not been thoroughly investigated. In this study, the influences of the location of the treatment table rotational axis on the biomechanical behaviors of the lumbar spine were investigated for spinal mobilization using finite element analysis. The axial rotation of spinal mobilization with a supine posture on a treatment table was simulated. The sacrum was rotated by 10° along the axial rotation axis. The initial axis location was around the posterior edge of the nucleus pulposus of the L5–S intervertebral disc. The axis location was varied in the posterior direction from 0 to 200 mm in increments of 50 mm. Changes in the spine biomechanics, such as the intersegmental rotation, intradiscal pressure, and stresses on the ligaments and fibers of the annulus fibrosus, were investigated. Upon movement of the rotation axis towards the posterior direction, (1) the rotation angle along the lateral bending direction increased, (2) the intradiscal pressure increased, (3) the stresses on fibers of the annulus fibrosus and ligaments increased, and (4) the facet joint forces increased. Based on these findings, we conclude that careful consideration of the rotation axis location is important and necessary in the development of treatment beds for spinal manipulation.

The primary aim was to investigate serial changes in the mechanical properties of the pectoralis major (PM), upper trapezius (UT), and sternoclavicular mastoid muscle (SCM) in breast cancer patients undergoing radiotherapy (RT) using a hand-held myotonometer. The secondary aims were to determine changes in subjective symptoms and to identify correlation with subjective results. A total of 42 breast cancer patients were enrolled in this longitudinal prospective study. Muscle properties of the PM, UT, and SCM were evaluated before RT, immediately after RT, and 4 months post-RT. Subjective symptom scales of pain and stiffness at rest/stretch of each muscle were evaluated. The PM showed significant side-to-side differences; the affected PM showed increased tone, stiffness, and decreased elasticity compared with the unaffected PM. The affected PM and UT showed significant time-dependent interactions. Stiffness of the affected PM at stretching was significantly higher 4 months post-RT than baseline. Only the tone and elasticity of the affected PM were correlated with subjective symptoms. In breast cancer patients who received RT after surgery, increased tone, stiffness, and decreased elasticity were observed in the affected PM compared with the unaffected side, which sustained four months post-RT. Change in muscle properties immediately after RT preceded subjective stiffness, which worsened significantly 4 months post-RT compared with baseline.

Swing tempo, rhythm and swing plane are shown to be important in maintaining the performance. However, nearly all studies utilized optical motion capture system for the planar behavior of golf swings and the movement of the club. The primary aim of this study was to develop inertial measurement unit sensor-based swing motion analysis algorithm, and validate against an optical motion camera system by comparing the estimated clubhead trajectories during the golf swing. Then, the tempo, rhythm and functional swing plane were investigated using a validated wearable inertial sensor. Fourteen male golfers performed repeated swings for three clubs (driver, 7-iron, and wedge) and at three distances (30 m, 50 m, and 70 m using the wedge). The swing tempo of all the participants was consistent across different clubs. The swing rhythm tends to decrease for club types with less carrying distance. The functional swing plane slope tends to decrease for club types with greater carrying distance. Our study demonstrated a potential application of a wearable inertial measurement unit system for analyzing golf performance parameters.

For golf swing, the soft tissue structure resisting joint compression and internal rotation of the knee at low flexion angle may be susceptible for a lead knee injury. Therefore, anterior cruciate ligament (ACL) rupture is one of the potential injuries that may occur from repeated stress during golf. The current study was purposed to investigate the biomechanical factors that lead to high ACL load in the lead knee during golf swing. The joint kinematic data of the lead leg and trunk, joint kinetic data of the lead knee, ground reaction force, and the external knee moments were compared between the low and high ACL loading groups. The results demonstrated an increased amount of frontal plane moment arm and external knee adduction (varus) moment just after ball impact for the high ACL loading group. These observations were associated with a characteristic difference in the upper body motion and were the main contributors to the elevated ACL force of the lead knee. The mechanism that generates a high amount of ACL loading during golf swing, which involves the application of external knee adduction moment just after ball impact, may differ from conventional non-contact ACL injury mechanisms that associated with dynamic valgus loading during injury circumstance.

In golf, the trunk and pelvis kinematic variables are often related to measures of performance due to the highly complex and multi-joint movements involved in swings. However, it is unclear how specific body segments or joints contributed to the golf performance parameters. Therefore, the purpose of this study was to identify the key joints, including those of the upper and lower trunk, that are associated with golf performance parameters, such as X-Factor and pelvis motion. A motion capture system was used to obtain three-dimensional kinematics of golf swings performed by 10 low handicap male golfers. Based on regression analysis, right knee adduction, right shoulder external rotation and left elbow extension in ball address to top of the backswing and left knee adduction and lower trunk right bending with left rotation in top of the backswing to end of follow-through were presented as predictor variables for the X-Factor. For pelvis movement, a greater number of joint angles were associated with pelvis posterior tilt during backswing and pelvis motion to target with right rotation during downswing/follow-through. This study provides fundamental details of the movement mechanisms of major joints, as well as their relationships with performance parameters. Such understanding can be combined with training to improve the golfing skill and prevent possible injuries.

Instability of the forearm is a complex problem that leads to pain and limited motions. Up to this time, no universal consensus has yet been reached as regards the optimal treatment for forearm instability. In some cases, conservative treatments are recommended for forearm instability injuries. However, quantitative studies on the conservative treatment of forearm instability are lacking. The present study developed a finite element model of the forearm to investigate the contribution of the distal radioulnar joint stabilizer on forearm stability. The stabilizer was designed to provide stability between the radius and ulna. The forearm model with and without the stabilizer was tested using the pure transverse separation and radial pull test for the different ligament sectioned models. The percentage contribution of the stabilizer and ligament structures resisting the load on the forearm was estimated. For the transverse stability of the forearm, the central band resisted approximately 50% of the total transverse load. In the longitudinal instability, the interosseous membrane resisted approximately 70% of the axial load. With the stabilizer, models showed that the stabilizer provided the transverse stability and resisted almost 1/4 of the total transverse load in the ligament sectioned models. The stabilizer provided transverse stability and reduced the loading on the ligaments. We suggested that a stabilizer can be applied in the conservative management of patients who do not have the gross longitudinal instability with the interosseous membrane and the triangular fibrocartilage complex disruption.

Technological advances in wireless communications, miniaturized sensors, and low-power electronics have made it possible to implement integrated wireless body area networks (WBANs). These developments enable the applications of wireless wearable systems for diagnosis, health monitoring, rehabilitation, and dependency care. Across the current range of commercial wearable devices, the products are not firmly fixed to the human body. To minimize data error caused by movement of the human body and to achieve accurate measurements, it is essential to bring the wearable device close to the skin. This paper presents the implementation of a patch-type, six-axis inertial measurement unit (IMU) with wireless communication technology. The device comprises hard-electronic components on a stretchable elastic substrate for application in epidermal electronics, to collect precise data from the human body. Instead of the commonly used cleanroom processes of implementing devices on a stretchable substrate, a simple and inexpensive &ldquo, cut-solder-paste&rdquo, method is adopted to fabricate complex, convoluted interconnections. Thus, the signal distortions in the proposed device can be minimized during various physical activities and skin deformations when used in gait analysis. The inertial sensor data measured from the motion of the body can be sent in real-time via Bluetooth to any processing unit enabled with such a widespread standard wireless interface. For performance evaluation, the implemented device is mounted on a rotation plate in order to compare performance with the conventional product. In addition, an experiment on joint angle estimation is performed by attaching the device to an actual human body. The preliminary results of the device indicate the potential to monitor people in remote settings for applications in mobile health, human-computer interfaces (HCIs), and wearable robots.

When a person plays a musical instrument, sound is produced and the integrated frequency and intensity produced are perceived aurally. The central nervous system (CNS) receives defective afferent signals from auditory systems and delivers imperfect efferent signals to the motor system due to the noise in both systems. However, it is still little known about auditory-motor interactions for successful performance. Here, we investigated auditory-motor interactions as multi-sensory input and multi-motor output system. Subjects performed a constant force production task using four fingers in three different auditory feedback conditions, where either the frequency (F), intensity (I), or both frequency and intensity (FI) of an auditory tone changed with sum of finger forces. Four levels of uncertainty (high, moderate-high, moderate-low, and low) were conditioned by manipulating the feedback gain of the produced force. We observed performance enhancement under the FI condition compared to either F or I alone at moderate-high uncertainty. Interestingly, the performance enhancement was greater than the prediction of the Bayesian model, suggesting super-optimality. We also observed deteriorated synergistic multi-finger interactions as the level of uncertainty increased, suggesting that the CNS responded to increased uncertainty by changing control strategy of multi-finger actions.

Chu, E, Kim, Y-S, Hill, G, Kim, YH, Kim, CK, and Shim, JK. Wrist resistance training improves motor control and strength. J Strength Cond Res 32(4): 962-969, 2018-The aim of this study was to investigate the effects of a 6-week direction-specific resistance training program on isometric torque control and isokinetic torque strength of the wrist joint. Nineteen subjects were randomly assigned to either the wrist training group (n = 9) or the control group (n = 10). The training group performed wrist exercises in 6 directions (flexion, extension, pronation, supination, radial deviation, and ulnar deviation), whereas the control group did not. Data were collected on the isometric torque control, 1-repetition maximum (1RM) strength, and isokinetic maximum torque (angular velocity of 60° per second wrist movements) before and after 6 weeks of resistance training and at 2-week intervals during training. The training group showed significant decreases in isometric torque control error in all 6 directions after 2 weeks of resistance training, whereas the control group did not show significant increase or decrease. After 4 weeks of training, the training group showed significant increases in maximum strength in all 6 directions as assessed by 1RM strength and isokinetic strength tests, whereas the control group did not show any statistically significant changes. This study shows that motor control significantly improves within the first 2 weeks of resistance training, whereas the wrist strength significantly improves within the first 4 weeks of resistance training. Based on the findings of this study, coaches and trainers should consider wrist resistance training to improve athletes' muscular strength and control of the wrist muscles.

The X-ray-based reconstruction methods using anterior-posterior (AP) and lateral (LAT) images assumes that the angle between the AP and LAT images is perpendicular. However, it is difficult to maintain the perfect perpendicular angle between the AP and LAT images when taking those two images sequentially in real situations. In this study, the robustness of a three-dimensional (3D) whole spine reconstruction method using AP and LAT planar X-ray images was analyzed by investigating cases in which the AP and LAT images were not taken perpendicularly. 3D models of the patient-specific spine from five subjects were reconstructed using AP and LAT X-Ray images and the 3D template models of C1 to L5 vertebrae based on B-spline free-form deformation (FFD) technology. The shape error, projected area error, and relative error in length were quantified by comparing the reconstructed model (FFD model) to the reference model (CT model). The results indicated that the reconstruction method might be considered robust in case that there is a small angular error, such as 5°, between the AP and LAT images. This study suggested that simple technical indications to obtain the perpendicular AP and LAT images in real situations can improve accuracy of 3D spine reconstruction.

The human cervical spine is a complex structure that is the most frequently injured site among all spinal injuries. Therefore, understanding of the cervical spine injury and dysfunction, and also biomechanical response to external stimuli is important. Finite element (FE) modeling can help researchers to access the internal stresses and strains in the bones, ligaments and soft tissues more realistically, and it has been widely adopted for spine biomechanics research. Although in recent years numerous techniques have been developed, there are no recent literature reviews on FE models of the cervical spine. Our objective was to present recent advances in FE modeling of the human cervical spine in terms of component modeling, material properties, and validation procedures. Model applications and further development are also discussed. The integration of new technologies will allow us to generate more accurate and comprehensive model of the cervical spine, which can increase efficiency and model applicability. Finally, the FE modeling can help to facilitate diagnosis, treatment, and prevention technologies for cervical spine injuries.

In order to clearly understand the injury mechanism of the Lateral ankle sprain (LAS), we purposed to evaluate the ligament strains in the human ankle joint during the real accidental events of LAS. Three different accidental ankle sprain cases were selected based on their reported motions, which are rarely captured under laboratory settings. The ligament strains were investigated using a computational ankle joint model based on the kinematic data from these case reports. Our result revealed that the excessive ankle inversion coupled with slight internal rotation could lead to LAS. Therefore, the ankle inversion and internal rotation should be primarily considered in LAS studies. This study quantitatively contributes to our understanding of the LAS mechanism in sport and clinical research.

The main principle of open-wedge high tibial osteotomy (HTO) is to shift the weight-bearing line of the knee joint in order to decompress the degenerated compartment and delay osteoarthritis (OA). In this study, the resultant contact forces on the medial compartment, lateral compartment, and total tibiofemoral joint were analyzed during gait for five OA patients before and after HTO in order to fully understand the effect and mechanism of HTO for the OA knee. The compressive, lateral-medial shear, and anteriorposterior shear force components of the joint force, as well as the ratio of the medial contact force to the lateral contact force, were investigated using inverse dynamic and multi-body dynamic models. Medial open-wedge HTO improved the balance of medial and lateral contact forces on the tibiofemoral joint, which demonstrated the purpose of HTO provided by clinical studies and the outcomes of a computational study. In addition to the compressive contact force, the lateral-medial shear force was also reduced during the stance phase of walking after HTO. The technology in this study provides a fundamental tool to evaluate the outcomes of HTO by considering daily and sports activities.

Study design A biomechanical comparison among the intact C2 to C7 segments, the C5 to C6 segments implanted with fusion cage, and three different artificial disc replacements (ADRs) by finite element (FE) model creation reflecting the entire cervical spine below C2. Objective The aim of this study was to analyze the biomechanical changes in subaxial cervical spine after ADR and to verify the efficacy of a new mobile core artificial disc Baguera C that is designed to absorb shock. Summary of background data Scarce references could be found and compared regarding the cervical ADR devices' biomechanical differences that are consequently related to their different clinical results. Methods One fusion device (CJ cage system, WINNOVA) and three different cervical artificial discs (Prodisc-C Nova (DePuy Synthes), Discocerv (Scient'x/Alphatec), Baguera C (Spineart)) were inserted at C5-6 disc space inside the FE model and analyzed. Hybrid loading conditions, under bending moments of 1 Nm along flexion, extension, lateral bending, and axial rotation with a compressive force of 50 N along the follower loading direction, were used in this study. Biomechanical behaviors such as segmental mobility, facet joint forces, and possible wear debris phenomenon inside the core were investigated. Results The segmental motions as well as facet joint forces were exaggerated after ADR regardless of type of the devices. The Baguera C mimicked the intact cervical spine regarding the location of the center of rotation only during the flexion moment. It also showed a relatively wider distribution of the contact area and significantly lower contact pressure distribution on the core than the other two devices. A "lift off" phenomenon was noted for other two devices according to the specific loading condition. Conclusion The mobile core artificial disc Baguera C can be considered biomechanically superior to other devices by demonstrating no "lift off" phenomenon, and significantly lower contact pressure distribution on core. Level of evidence N/A.

The push-off mechanism to generate forward movement in skating has been analyzed by using high-speed cameras and specially designed skates because it is closely related to skater performance. However, using high-speed cameras for such an investigation, it is hard to measure the three-dimensional push-off force, and a skate with strain gauges is difficult to implement in the real competitions. In this study, we provided a new method to evaluate the three-dimensional push-off angle in short-track speed skating based on motion analysis using a wearable motion analysis system with inertial measurement unit sensors to avoid using a special skate or specific equipment insert into the skate for measurement of push-off force. The estimated push-off angle based on motion analysis data was very close to that based on push-off force with a small root mean square difference less than 6% when using the lateral marker in the left leg and the medial marker in the right leg regardless of skating phase. These results indicated that the push-off angle estimation based on motion analysis data using a wearable motion capture system of inertial measurement unit sensors could be acceptable for realistic situations. The proposed method was shown to be feasible during short-track speed skating. This study is meaningful because it can provide a more acceptable push-off angle estimation in real competitive situations.