Development of a three-degrees-of-freedom moveable platform for providing postural perturbations.

The purpose of this study was to design and develop a three-degrees-of-freedom moveable platform to provide postural perturbations for balance assessment and training. The platform consists of three motion mechanisms, which can provide forward-backward translation, upward-downward tilt, and clockwise-counterclockwise rotation. This platform can move in any of its degrees of freedom separately or simultaneously. The precision and accuracy of the platform movement were examined by calculating the standard deviations in repeated trials and comparing the real amplitude and velocity of the movement with the preset values. All the standard deviations in repeated trials were small in that the variation coefficients were less than 2 per cent, except that in the highest-velocity test, and all the mean differences were less than 1 mm for translational and 1 degree for tilt or rotational perturbations. The results demonstrated that the platform is a reliable and valid instrument for providing postural perturbations. The preliminary investigation of the kinematic postural responses to translational and tilt perturbation showed that this platform is a useful apparatus for balance research. Potential applications of this platform include investigation of the postural responses to yaw rotation or any combination of its degrees of freedom and studying the effects of perturbation-based balance-training programmes provided by this platform.

Elbow load with various forearm positions during one-handed pushup exercise.

This is the first study of the one-handed pushup, and tries to show the effects of forearm rotations. Previous studies of elbow loading have focused on passive loading and small loads, because data from large loads during active exercise is not easy to obtain. In order to investigate the biomechanical impact of hand position on the elbow and the potential trauma mechanisms of outstretched elbow, joint loading across the elbow was analyzed for three forearm rotational positions, neutral, 90 degrees internal rotation and 90 degrees external rotation. Both kinematic and kinetic data were collected from eight volunteers by the Motion Analysis System and a Kistler Force Plate. Statistical analysis of the data delineates the relationship between elbow joint load and hand rotational position during one-handed pushup, and also provides useful biomechanical information for this challenging exercise. The axial and valgus stresses and forces are the major concerns. The peak axial forces exerted on the elbow joint averaged 65 % of the body weight when the hand position was neutral, and was significantly reduced with the hand rotated either internally or externally. The peak valgus shear force with the hand externally rotated was 50 % greater than the other two positions. Thus, outward rotation of the hand is a stressful position that should be avoided during one-handed pushup exercise or forward falls with outstretched hands in order to reduce the risk of elbow injuries.

Effect of elbow flexion on upper extremity impact forces during a fall.

OBJECTIVE: The overall objectives are to develop a biomechanical model for a simulated fall with outstretched hand. DESIGN: Cross-sectional study involving young healthy volunteers in a university research laboratory setting. BACKGROUND: Little is known about the factors which influence fracture risk during a fall on outstretched hand. METHODS: A group of 11 male subjects volunteered for this investigation. A set of eight reflective markers was placed bilaterally on selected anatomic landmarks. Subjects were suspended with both elbows extended and wrists dorsiflexed, preparing to impact the ground and force plates from two different fall heights: 3 and 6 cm. Two different postures for the elbows were employed. In the elbow extension experiment, the elbows were extended at all times. In the elbow flexion experiment, the elbows were extended at impact, but then flexed immediately, as though in the initial downward phase of a push-up exercise. RESULT: Increasing the fall height significantly increased the upper extremity axial forces by 10% and 5%. No significantly different differences were found in the axial forces applied to the wrist, elbow or shoulder between the elbow flexion and elbow extension trials, but the elbow mediolateral shear force was 68% larger (P=0.002) in the extension trials. CONCLUSIONS: Performing an elbow flexion movement at impact reduces the first peak impact force value and postpones the maximum peak value. Although changing the fall arrest strategy from elbow extension to elbow flexion did not affect the peak impact force on the hand, it did require substantially greater elbow and shoulder muscle strengths. RELEVANCE: This paper yields insights into how the physical demands of arresting mild falls may relate to upper extremity muscle capacity, joint dislocation and bony fracture.

Sit-to-stand at different periods of pregnancy.

OBJECTIVE: This study was performed to determine the biomechanics of chair rising by pregnant women. DESIGN: Relative body joint position and ground reaction forces were measured by a motion analysis system and one force plate. BACKGROUND: Physiological and psychological changes during pregnancy impose postural demands and limit the performance of daily living activities such as rising from sitting to standing position. METHODS: Twenty-four pregnant women, divided into three groups, were studied performing sit-to-stand transition from an armless and adjustable chair. By kinematic and kinetic analysis, the angles and moments of hip, knee and ankle joints were investigated. RESULTS: The chair height has great influence on knee joint and hip joint moments, but less on ankle joints. In the third trimester for all chair heights, because of a marked increase in abdominal depth, the maximum hip moment is significantly less than that in first trimester, while the maximum knee moment is significantly larger. Pregnant women in third trimester produced larger knee moment during sit-to-stand transition from lower chair height. CONCLUSIONS: The mechanism of sit-to-stand is affected by the physical changes of pregnant women at different periods of pregnancy, e.g. increased loading of knee joint and decreased hip joint moment, especially in the last trimester period of pregnancy.

[Glucose and lipid metabolism in patients with polycystic ovary syndrome].

Glucose and lipid metabolism were studied in 30 patients with polycystic ovary syndrome (PCOS), divided into obese (n = 17) and non-obese (n = 13) groups according to BMI > 27 or < 24. Another 30 healthy controls were also divided into obese (n = 14) and nonobese (n = 16) normal groups on the same index. Cubital venous blood was drawn from each participant for oral glucose tolerance test (OGTT), insulin and lipid profile determination, for PCOS groups at the end of 3 months amenorrhea and control groups within the first 10 days of the menstrual cycle. The results showed: (1) the PCOS groups had much higher insulin level before and after OGTT than the normal groups. There was a significant positive correlation between fasting insulin level and testosterone concentration; (2) in lipid profile, the triglyceride levels in both obese groups were significantly higher than that in the non-obese groups, in whom a strong positive correlation between triglyceride and BMI was found. It is concluded that the obese and non-obese PCOS were correlated with insulin alteration, and the changed serum lipid in obese PCOS patients might be the effect of obesity but not PCOS.