Yu Okubo

Fatigue Alters Landing Shock Attenuation During a Single-Leg Vertical Drop Jump

Background: Landings in fatigue conditions are considered to be one of the factors that cause noncontact anterior cruciate ligament (ACL) injury. Additionally, it is known that fatigue alters lower extremity landing strategies and decreases the ability to attenuate shock during landing. Purpose: To determine characteristics of knee kinematics and shock attenuation during the landing phase of a single-leg vertical drop jump in a fatigued condition. The hypothesis was that knee kinematics during the landing phase of a single-leg vertical drop jump would demonstrate a significant difference between before and after fatigue. Study Design: Controlled laboratory study. Methods: Thirty-four college females participated in this experiment. They were randomly assigned to either the fatigue (n = 17) or control group (n = 17). The fatigue group performed the single-leg vertical drop jump before and after the fatigue protocol, which was performed on a bike ergometer. Knee kinematics data were obtained from the 3-dimensional motion analysis system. The ratio of each variable (%) was calculated, comparing the pre- to postfatigue protocol. Unpaired t tests were used to compare changes in kinematic variables between the fatigue-induced group and control group. Results: Peak knee flexion angular velocity increased significantly in the fatigue group (106.1% ± 8.0%) in comparison with the control group (100.7% ± 6.6%) (P < .05). However, peak knee flexion angle and acceleration had no differences between each group. Peak knee adduction/abduction angle, velocity, and acceleration also had no differences between each group. Conclusion: Fatigue decreased the ability to attenuate shock by increasing angular velocity in the direction of knee flexion during single-leg drop jump landing. These findings indicate the need to evaluate the ability to attenuate shock by measuring knee flexion angular velocity when fatigue is considered. Clinical Relevance: Measuring knee angular velocity during landings might be an important evaluation parameter in the consideration of the knee injury prevention.

Trunk muscle activity while lifting objects of unexpected weight

OBJECTIVE To determine trunk muscle activity when lifting an object of greater weight than expected, which may contribute to the development of low back pain. DESIGN Electromyographic evaluation of trunk muscle activity. SETTING University of Tsukuba, Spine laboratory. PARTICIPANTS Eleven healthy men with a mean age of 24 (SD 2) years. INTERVENTIONS Trunk muscle activity was measured when subjects lifted an object with their right arm in immediate response to a light stimulus. Surface and wire electrodes were used to measure the activity of the rectus abdominis, external oblique and erector spinae muscles, and the transversus abdominis and lumbar multifidus muscles, respectively. The lifting tests were performed in three different settings: lifting an expected 1-kg object, lifting an unexpected 4-kg object (erroneously expected to weigh 1 kg), and lifting an expected 4-kg object. MAIN OUTCOME MEASURES The muscle activity induced when subjects lifted objects of different weights was compared by calculating the root mean square (RMS) of muscle activity at rest and % maximum voluntary contraction. RESULTS When the subjects were aware of the weight of the object to be lifted, the activity of the external oblique, transversus abdominis, erector spinae and lumbar multifidus muscles increased immediately after lifting. When the subjects were not aware of the weight of the object to be lifted, the increase in muscle activity was delayed (P<0.05). CONCLUSIONS Trunk muscles may not be able to function appropriately when individuals lift an object that is much heavier than expected.

The effect of dynamic stretching on hamstrings flexibility with respect to the spino-pelvic rhythm

OBJECTIVES To ascertain the dynamic stretch effects of flexibility of the hamstrings on lumbar spine and pelvic kinematics. BACKGROUND Tight hamstrings are positively correlated with low back pain. However, it is unclear how flexibility of the hamstrings affects spino-pelvic rhythm. METHODS Twelve healthy men participated in the study. The straight leg raising (SLR) angle, finger floor distance (FFD), and spino-pelvic rhythm was measured before and after the 6-week stretching protocol. The forward bending task was divided into 4 phases. The paired t-test was used to determine significant differences before and after the FFD, SLR angle, lumbar motion, and pelvic motion, and spino-pelvic rhythm in each phase (p<0.05). RESULTS After 6 weeks of stretching, significant improvements were seen in the FFD with maximum forward bending and in the SLR angle. Total pelvic rotation was also significantly increased in contrast to total lumbar flexion. A decreased spino-pelvic ratio was seen in the final phase. CONCLUSION Dynamic stretching could change the spino-pelvic rhythm to a pelvis-dominant motion, indicating that flexible hamstrings are important for preventing low back pain.

Noninvasive evaluation of trunk muscle recruitment after trunk exercises using diffusion-weighted MR imaging

PURPOSE We evaluated trunk muscle recruitment in abdominal and back exercises with magnetic resonance (MR) diffusion-weighted imaging. METHODS Twelve men performed bent-knee sit-up, crunch, trunk lateral flexion, and trunk extension exercises. We obtained axial diffusion-weighted images of the trunk before and after each exercise using a 1.5-tesla MR system, calculated apparent diffusion coefficient (ADC) values from the right and left rectus abdominis, lateral abdominal, psoas major, quadratus lumborum, and intrinsic back muscles to evaluate the activity of these muscles during each exercise, and compared ADC values before and after exercise using a paired t-test. RESULTS The ADCs of the rectus abdominis (right, +19.1%; left, +11.7%), lateral abdominal (right, +15.5%; left, +14.1%), and psoas major (right, +14.8%; left, +15.9%) muscles on both sides increased after the bent-knee sit-up (P < 0.01). The ADCs of the rectus abdominis (right, +16.8%; left, +10.2%) and lateral abdominal (right, +8.4%; left, +7.0%) muscles on both sides increased after the crunch exercise (P < 0.01). Trunk lateral flexion resulted in increased ADC on only the right side of all of the muscles (rectus abdominis, +12.3%; lateral abdominal muscles, +20.3%; quadratus lumborum, +17.1%; intrinsic back muscles, +12.0%; psoas major, +15.4%) (P < 0.01). The ADCs of the lateral abdominal (right, +5.2%; left, +5.6%), quadratus lumborum (right, +6.0%; left, +3.0%), and intrinsic back (right, +13.2%; left, +14.6%) muscles on both sides were elevated after trunk extension (right lateral abdominal muscles and left quadratus lumborum, P < 0.05; other muscles, P < 0.01). CONCLUSION Diffusion-weighted imaging reveals the recruitment patterns of superficial and deep trunk muscles in abdominal and back exercises through exercise-induced activation in intramuscular water movement.

Immediate Effects of Different Trunk Exercise Programs on Jump Performance

The aim of this study was to investigate the immediate effects of trunk stabilization exercise (SE) and conventional trunk exercise (CE) programs on jump performance. 13 adolescent male soccer players performed 2 kinds of jump testing before and immediate after 3 experimental conditions: SE, CE, and non-exercise (NE). The SE program consisted of the elbow-toe, hand-knee, and back bridge, and the CE program consisted of the sit-up, sit-up with trunk rotation and back extension. Testing of a countermovement jump (CMJ) and rebound jump (RJ) were performed to assess jump performance. Jump height of the CMJ and RJ-index, contact time, and jump height of the RJ were analyzed. The RJ index was improved significantly only after SE (p=0.017). However, contact time and jump height did not improve significantly in the SE condition. Moreover, no significant interaction or main effects of time or group were observed in the CMJ. Consequently, this study showed the different immediate effect on the RJ between the SE and CE, and suggested the possibility that the SE used in this study is useful as a warm-up program to improve the explosive movements.

Deep abdominal muscle thickness measured under sitting conditions during different stability tasks.

[Purpose] This study was conducted to investigate ultrasonically determined changes in the thickness of the transversus abdominis and internal oblique muscles during different sitting conditions. [Subjects and Methods] Twenty healthy men volunteered to participate in this study. Four different sitting conditions including (A) sitting, (B) sitting with left hip flexion, (C) sitting with an abdominal hollowing maneuver (AHM), and (D) sitting with an AHM and left hip flexion, were used. Subjective exercise difficulty was evaluated. [Results] Transversus abdominis and internal oblique muscle thicknesses significantly differed between conditions, with significantly greater thickness between positions from (A) to (D). Stability of the surface when sitting had no effect on the muscle thickness of the transversus abdominis. By contrast, sitting on an unstable surface caused an increase in muscle thickness of the internal oblique in each condition. The subjects reported progressively increasing difficulty in performing each exercise in a stable position from (A) to (D), while the difficulty in an unstable position was significantly different between (A) and (B), and between (C) and (D). [Conclusion] Our findings suggest that task (B) on a stable surface should be chosen for maximal activation of transversus abdominis without inducing overactivation of the internal oblique muscle.

Abdominal Muscle Activity During a Standing Long Jump

STUDY DESIGN Experimental laboratory study. OBJECTIVES To measure the activation patterns (onset and magnitude) of the abdominal muscles during a standing long jump using wire and surface electromyography. BACKGROUND Activation patterns of the abdominal muscles, especially the deep muscles such as the transversus abdominis (TrA), have yet to be examined during full-body movements such as jumping. METHODS Thirteen healthy men participated. Wire electrodes were inserted into the TrA with the guidance of ultrasonography, and surface electrodes were attached to the skin overlying the rectus abdominis (RA) and external oblique (EO). Electromyographic signals and video images were recorded while each subject performed a standing long jump. The jump task was divided into 3 phases: preparation, push-off, and float. For each muscle, activation onset relative to the onset of the RA and normalized muscle activation levels (percent maximum voluntary contraction) were analyzed during each phase. Comparisons between muscles and phases were assessed using 2-way analyses of variance. RESULTS The onset times of the TrA and EO relative to the onset of the RA were -0.13 ? 0.17 seconds and -0.02 ? 0.07 seconds, respectively. Onset of TrA activation was earlier than that of the EO. The activation levels of all 3 muscles were significantly greater during the push-off phase than during the preparation and float phases. CONCLUSION Consistent with previously published trunk-perturbation studies in healthy persons, the TrA was activated prior to the RA and EO. Additionally, the highest muscle activation levels were observed during the push-off phase.

Piriformis electromyography activity during prone and side-lying hip joint movement

[Purpose] To measure electromyographic activity of the piriformis using fine-wire electrodes during 7 hip movements. [Subjects and Methods] Eleven healthy men, without severe low back pain or lower limb injury, participated in this study. Fine-wire electrodes were inserted into the piriformis and surface electrodes were attached to the muscles in the hip region and the trunk muscles on the dominant arm side. Electromyographic signal amplitude was measured during 7 hip movements: side-lying external rotation in hip neutral position, side-lying abduction in hip neutral position, side-lying abduction in hip external rotation, side-lying abduction in hip internal rotation, prone extension in hip neutral position, prone extension in hip external rotation, and prone extension in hip internal rotation. Repeated-measures one-way analysis of variance was used to examine electromyographic activity in each of the 7 hip movements. [Results] Piriformis electromyographic activity was highest during prone hip extension in external rotation. Both the superior and inferior portions of the gluteus maximus were also highly activated during prone hip extension in external rotation. [Conclusion] Prone hip extension in external rotation induced high electromyographic activity in the piriformis and superior and inferior gluteus maximus muscles.

Does trampoline or hard surface jumping influence lower extremity alignment

[Purpose] To determine whether repetitive trampoline or hard surface jumping affects lower extremity alignment on jump landing. [Subjects and Methods] Twenty healthy females participated in this study. All subjects performed a drop vertical jump before and after repeated maximum effort trampoline or hard surface jumping. A three-dimensional motion analysis system and two force plates were used to record lower extremity angles, moments, and vertical ground reaction force during drop vertical jumps. [Results] Knee extensor moment after trampoline jumping was greater than that after hard surface jumping. There were no significant differences between trials in vertical ground reaction force and lower extremity joint angles following each form of exercise. Repeated jumping on a trampoline increased peak vertical ground reaction force, hip extensor, knee extensor moments, and hip adduction angle, while decreasing hip flexion angle during drop vertical jumps. In contrast, repeated jumping on a hard surface increased peak vertical ground reaction force, ankle dorsiflexion angle, and hip extensor moment during drop vertical jumps. [Conclusion] Repeated jumping on the trampoline compared to jumping on a hard surface has different effects on lower limb kinetics and kinematics. Knowledge of these effects may be useful in designing exercise programs for different clinical presentations.

Evaluation of Psoas Major and Quadratus Lumborum Recruitment Using Diffusion-Weighted Imaging Before and After 5 Trunk Exercises

• STUDY DESIGN: Controlled laboratory study, with a pretest‐posttest design. • BACKGROUND: Diffusion‐weighted imaging is a noninvasive magnetic resonance imaging technique that can be used to assess the recruitment of the psoas major (PM) and quadratus lumborum (QL). The recruitment of these muscles during trunk exercises has not been evaluated. • OBJECTIVE: To evaluate the diffusion of water movement in several trunk muscles using diffusion‐weighted imaging before and after specific trunk exercises and thereby to understand the level of recruitment of each muscle during each exercise. • METHODS: Nine healthy male participants performed the right side bridge, knee raise, and 3 front bridges, including the hand‐knee, elbow‐knee, and elbow‐toe bridges. Diffusion‐weighted imaging was performed before and after each exercise. After scanning, the apparent diffusion coefficient (ADC) map was constructed, and ADC values of the rectus abdominis, lateral abdominal muscles, QL, PM, and back muscles were calculated. • RESULTS: The right PM following the elbow‐toe bridge demonstrated the largest increase in ADC values, a change significantly greater than that demonstrated by the hand‐knee bridge (P<.001) and side bridge (P = .002) exercises. The ADC change in the right QL following the side bridge exercise was significantly larger than that of other exercises (P<.008). • CONCLUSION: Of the 5 exercises investigated, the elbow‐toe bridge and side bridge exercises elicit the greatest recruitment of the PM and QL, respectively.