Relationship between Standing Trunk Extension Angle and Medial Elbow Injuries in Young Baseball Pitchers.

Purpose: The purpose of this study was to investigate the relationship between the standing trunk extension angle and medial elbow injuries. Subjects and methods: The study participants were 90 male baseball pitchers (10−12 years) belonging to youth baseball teams. Pitching elbow injuries were evaluated by an orthopedic surgeon using ultrasound scans and physical examination findings. A single optical three-dimensional motion analysis system was used for the trunk extension measurements, with three-dimensional coordinates captured. The overall, upper, and lower trunk angles were then analyzed. Results: Trunk extension angle during standing trunk extension was significantly smaller among participants who were positive for medial elbow injuries on ultrasound scans (positive: 71.4° ± 10.3°; negative: 75.7° ± 9.2°; t = 2.05, p < 0.05). The upper trunk extension angle was significantly smaller than the lower trunk extension angle among participants who were positive for medial elbow injuries on physical examination (upper: 33.0° ± 6.9°; lower: 41.2° ± 8.2°; t = −2.42, p < 0.05). Conclusions: Trunk extension angle during standing trunk extension is associated with medial elbow injuries. Evaluating the trunk extension angle as multiple segments rather than a single rigid body is valuable.

Elucidation of abductor digiti minimi activity in chronic ankle instability.

[Purpose] This study aimed to compare the muscle activity around the foot and ankle joints, notably of the abductor digiti minimi, between affected and unaffected sides of individuals with chronic ankle instability. [Participants and Methods] Twelve adult males with chronic ankle instability in one ankle (age, 27.7 ± 5.4 years; height, 172.5 ± 8.1 cm; weight, 67.5 ± 8.1 kg) were included and underwent surface electromyography assessments in multiple positions on both affected and unaffected sides. Measurements were obtained for eight muscles including the abductor digiti minimi. Each measurement included a 5-s segment of the stable waveform, with the root mean square-processed and normalized to the resting position set to 1. [Results] Abductor digiti minimi activity on the affected side was significantly reduced during maximal toe extension/abduction with both ankle dorsiflexion and plantarflexion. Peroneus longus activity on the affected side was significantly greater during maximal toe extension/abduction with ankle plantarflexion; peroneus longus and tibialis anterior muscle activities were significantly greater on the affected side during maximal toe extension/abduction with ankle dorsiflexion. [Conclusion] In the absence of load, muscle imbalance in the intrinsic and extrinsic muscles of the foot was suggested. However, no significant differences were observed under loading conditions.

Influence of motor instruction words on body movements in step-over motions.

[Purpose] To quantitatively analyze the characteristics of movements evoked by certain motor instruction words on the basis of measurements of ankle elevation and related body movements in step-over motion tasks. [Participants and Methods] Sixty-one healthy adult participants were presented with motor instructions and asked to step over an obstacle in accordance with the instructions. The motor instructions were as follows: "Raise your XX (body part) up YY (expression)" in four combinations using "thigh" and "knee" for body part and "high" and "firmly" for expression. Using Kinect to analyze movements, ankle elevation, trunk-anteversion angle, hip-flexion angle, and knee-flexion angle were measured and statistically processed. [Results] With respect to body part, there was no significant difference in the mean and standard deviation (individual variation) values for ankle elevation. With respect to expression, hip joint and knee joint were bent significantly more for "high" than for "firmly", and although the mean value for ankle elevation was high, ankle elevation standard deviation (individual variation) values were significantly lower for "firmly" than for "high". [Conclusion] Explicit motor instruction words such as "high" may be effective in improving performance, while ambiguous motor instruction words like "firmly" may be effective in stabilizing movements.

Relationship between gait speed and trunk muscles in frail elderly individuals.

[Purpose] The external and internal abdominal muscles may be related to gait speed; however, this has not yet been elucidated. In this study, we aimed to clarify the relationship between gait speed and trunk muscle thickness in elderly individuals. [Participants and Methods] The participants were 12 elderly individuals (4 males and 8 females, mean age 83.4 years old, SD ± 0.5) that attend a day service center. We measured the 5 m free gait speed, the 5 m fastest gait speed, and the thickness of five trunk muscles (the rectus abdominis [divided into three parts: upper, central, and lower], external oblique, internal oblique, transverse abdominis, and iliopsoas muscles). [Results] There were positive correlations between the free gait speed and the thickness of the lower rectus abdominis, internal oblique, and transverse abdominis muscles. There were also positive correlations between the fastest gait speed and the thickness of the lower rectus abdominis, internal oblique, and transverse abdominis muscles. [Conclusion] Incorporating muscle strength training of the lower rectus abdominis, internal oblique, and transverse abdominis muscles into existing lower limb muscle training protocols is important to effectively maintain the gait speed of elderly individuals.

Effect of standing postural deviations on trunk and hip muscle activity.

[Purpose] It is very important to consider effects that postural deviations has on muscle activity when treating low back pain. Therefore, activities of trunk and hip joint muscles in healthy adults while they attempted three postural conditions of neutral, sway-back, and lordosis was compared and evaluated in this study. [Subjects and Methods] The subjects comprised 17 healthy adult male volunteers. The muscle activity and spinal curve were measured while the subjects attempted different postural conditions (neutral, sway-back, and lordosis) as defined in the text. [Results] Activity of trunk and hip inner muscles was decreased in sway-back posture, and only activity of the trunk back muscles was increased in lordosis. [Conclusion] This results were suggested that postural deviations affected muscle control in the lumbo-pelvic area.

New evaluation index for the retainability of a swimmer's horizontal posture.

This study aims to investigate the effect of changes in buoyancy when a swimmer respires in a horizontal posture. We attempted to evaluate the levelness of swimmers' streamline posture by simultaneously measuring the lung capacity and buoyancy under water. The buoyancy was measured based on the changes in the vertical loads of the upper and lower limbs on the subjects' streamline posture under water. The horizontal x-axis as lung ventilation and the vertical y-axis as buoyancy forms a linear equation y = ax + b. The relation between hand (upper-limb) buoyancy and lung ventilation is defined as y = a1x + b1 and that between foot (lower-limb) buoyancy and lung ventilation as y = a2x + b2. Horizontal levelness was calculated as a ratio by dividing a2 by a1 using the inclination (a) values from these formulas for an underwater streamline posture. We defined this ratio as the breathing-balance (BB) ratio. Although the performance levels in the present study did not show any difference in the absolute quantity of air that humans can inhale in a streamline posture, the BB ratio was higher in a statistically significant manner in junior swimmers competing at international levels compared with the other groups of subjects (P < 0.001). This statistical difference in horizontal levelness, despite the absence of a noticeable difference in the absolute quantity of inhaled air, may be attributable to the way in which each person inhales and exhales air. Top-level junior swimmers that exhibited a high BB ratio might have inhaled in a way that would counteract the sinking of the lower limbs, for example, through abdominal respiration. When exhaling, on the other hand, they might have let out air gradually to mitigate the acceleration force involved in submerging the lower limbs.

Three-dimensional Scapular Kinematics During Arm Elevation in Massive Rotator Cuff Tear Patients.

OBJECTIVE: Rotator cuff tears can influence shoulder kinematics and severely impair function. However, there have been no studies on three-dimensional (3D) shoulder kinematics in massive rotator cuff tear (MRCT) patients. Hypothesizing that MRCT patients could demonstrate significantly changed scapular kinematics during arm elevation in the scapular plane, we compared 3D scapular kinematics in the scapular plane between MRCT patients and healthy elderly subjects. METHODS: We assessed 15 shoulders of 11 MRCT patients and 16 shoulders of 16 healthy subjects. With the subjects seated, we used an electromagnetic tracking system to calculate the upward rotation, posterior tilt, and internal rotation of the scapula at 10° increments from 30° to 120° with respect to the thorax. We performed two-way analysis of covariance with the initial position of the scapular motion as the covariate and performed multiple comparisons using the Bonferroni method. RESULTS: MRCT patients exhibited significantly higher scapular upward rotation than did the healthy subjects (P < 0.05). There were no significant differences between groups with regard to posterior tilt and internal rotation. CONCLUSIONS: This study indicated that when MRCT patients elevated their arms, they exhibited a significantly higher scapular upward rotation at low- to mid-range elevations compared with that of healthy subjects. This difference may have resulted from a compensatory effect in response to the decreased elevation torque caused by the loss of rotator cuff function. These results may assist rehabilitation strategies to improve active arm elevation in MRCT patients.

Lower muscle co-contraction in flutter kicking for competitive swimmers.

The purpose of this study was to examine the difference in muscle activation pattern and co-contraction of the rectus and biceps femoris in flutter-kick swimming between competitive and recreational swimmers, to better understand the mechanism of repetitive kicking movements during swimming. Ten competitive and 10 recreational swimmers swam using flutter kicks at three different velocities (100%, 90%, and 80% of their maximal velocity) in a swimming flume. Surface electromyographic signals (EMG) were obtained from the rectus (RF) and biceps femoris (BF), and lower limb kinematic data were obtained at the same time. The beginning and ending of one kick cycle was defined as when the right lateral malleolus reached its highest position in the vertical axis. The offset timing of muscle activation of RF in the recreational swimmers was significantly later at all velocities than in the competitive swimmers (47-48% and 26-33% of kick time of one cycle for recreational and competitive swimmers, respectively), although the kinematic data and other activation timing of RF and BF did not differ between groups. A higher integrated EMG of RF during hip extension and knee extension induced a higher level of muscle co-contraction between RF and BF in the recreational swimmers. These results suggest that long-term competitive swimming training can induce an effective muscle activation pattern in the upper legs.

Intracyclic velocity variation and arm coordination for different skilled swimmers in the front crawl.

The aim of this study was to examine whether the intracyclic velocity variation (IVV) was lower in elite swimmers than in beginner swimmers at various velocities, and whether differences may be related to arm coordination. Seven elite and nine beginner male swimmers swam front crawl at four different swimming velocities (maximal velocity, 75%, 85%, and 95% of maximal swimming velocity). The index of arm coordination (IDC) was calculated as the lag time between the propulsive phases of each arm. IVV was determined from the coefficient of variation of horizontal velocity within one stroke cycle. IVV for elite swimmers was significantly lower (26%) than that for beginner swimmers at all swimming velocities (p<0.01, 7.28 1.25% vs. 9.80 1.70%, respectively). In contrast, the IDC was similar between elite and beginner swimmers. These data suggest that IVV is a strong predictor of the skill level for front crawl, and that elite swimmers have techniques to decrease IVV. However, the IDC does not contribute to IVV differences between elite and beginner swimmers.