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Objective To study effects of backpack gravity center position on kinetics and kinematics of lower-extremity joints in parachuting landing and evaluate the injuries. Methods Seven participants performed parachuting landing with backpack gravity center on three positions: low-back (position 1), upper-back (position 2) and abdomen (position 3). Results The peak vertical ground reaction force (GRF) with backpack on position 2 was significantly lower than that on position 1. The joint moment on sagittal plane of the hip with backpack on position 2 was significantly higher than that on position 1 and position 3. The joint energy absorption of the hip with backpack on position 2 was significantly higher than that on position 1. The angular displacement of the hip on sagittal plane with backpack on position 2 was significantly higher than that on position 1 and was significantly lower than that on position 3. The angular velocity of the hip on sagittal plane with backpack on position 2 was significantly lower than that on position 3. Conclusions Different positions of backpack gravity center could significantly influence kinetic and kinematic parameters of the hip. Backpack gravity center on upper-back position could decrease the lower-extremity injuries. The results can provide evidences for evaluating backpack gravity center and decreasing injuries in parachuting landing.
RESUMO
Objective To investigate the effects of unevenly-distributed backpack loads on human physiological parameters as compared to the traditional centrally-placed load at the backpack bottom. Methods For the unevenly-distributed load mode, the backpack was divided into four spaces including top right, top left, bottom right and bottom left. The loads were divided into two parts proportionally (1/2∶1/2, 1/4∶3/4 and 3/4∶1/4) and placed at the bottom left and top right of the backpack, respectively. The remaining two spaces were filled with the plastic foam. Ten healthy volunteers performed 30-min walking trials on the treadmill at the speed of 1.1 m/s with the backpack load equal to 10% body weight (BW). The changes of subjects’ body posture, muscle fatigue, heart rate, blood pressure before and after the trial, as well as the electromyography (EMG) changes at 0, 5, 10, 15 min after the trial were measured by the Bortec AMT-8 and the NDI Optotrak Certus. Results The muscle fatigue of right upper trapezius and forward-leaning angle increased as the loads at top right of the backpack increased. However, the muscle fatigue in the new mode of backpack load distribution showed no significant differences as compared to the traditional mode under the same backpack loads. The new mode with the load ratio of 3/4∶1/4 had no significant effects on posture. The new mode with the load ratio of 1/2∶1/2 could contribute to the decrease of heart rate and blood pressure as compared to the traditional mode. Conclusions Adopting a new and more reasonable load distribution mode can guarantee the body posture unaffected by the backpack loads, and decrease heart rate and blood pressure. Therefore, the cross and evenly distributed load mode is recommended for the backpack design.
RESUMO
@#Objective To develop an alignment technique based on the movement of body gravity center. Methods As join forces in the system of balance is zero, the position of body gravity center can be calculated by body gravity which is taken from weight sensors, by the special software. Meanwhile, the position of body gravity will be sent to control unit, which can be transformed to driving signal of motor. The sliding table with laser, linked to motor, can make pursuit movement following with body gravity. A precise alignment can be made as the movement of body gravity. The balance function test is also used to make an assistant estimate for the alignment. Results and Conclusion An alignment technique has been developed for the fit of prosthesis and orthotics.
RESUMO
Objective To develop an alignment technique based on the movement of body gravity center. Methods As join forces in the system of balance is zero, the position of body gravity center can be calculated by body gravity which is taken from weight sensors, by the special software. Meanwhile, the position of body gravity will be sent to control unit, which can be transformed to driving signal of motor. The sliding table with laser, linked to motor, can make pursuit movement following with body gravity. A precise alignment can be made as the movement of body gravity. The balance function test is also used to make an assistant estimate for the alignment. Results and Conclu-sion An alignment technique has been developed for the fit of prosthesis and orthotics.
RESUMO
El análisis espacial y temporal de larvas de jurel Trachurus murphyi en el mar peruano entre los años 1966 y 2010 confirma su presencia constante durante todo el periodo estudiado. En general, en este periodo la abundancia de larvas de jurel T. murphyi muestra una tendencia ligeramente ascendente destacándose cambios en la distribución espacial y una alta variabilidad interanual, con cortos periodos de alta abundancia promedio, intercalados con periodos más prolongados y de baja abundancia. El promedio anual estimado varió entre 3 y 79 larvas/m². La distribución espacial presentó tres periodos importantes: uno con mayores densidades de larvas al sur de los 14°S, entre 1970 y 1979; cambió hacia el norte de esta latitud, entre 1980 y 1999; y otro de mayor densidad al sur de los 18°S, en el último periodo 2000 - 2010. Los centros de gravedad de la distribución de larvas presentaron tres periodos muy notorios: fueron más costeros hacia el sur de los 14°S, entre 1966 y1978; más oceánicos y al norte de los 14°S, entre 1979 y 1994; y con una posición intermedia entre 1995 - 2010. Se discute la relación entre la distribución de las larvas con las variables oceanográficas y la distribución de T. murphyi adultos y juveniles, además se destaca que el mar del Perú es un centro principal y permanente de actividad reproductiva de esta especie.
Constant presence of Jack mackerel Trachurus murphyi larvae in the Peruvian sea between 1966 and 2010 was confirmed by an analysis of their spatial and temporal variability. In general, there is a slight positive trend in abundance of Jack mackerel T. murphyi larvae, with noticeable changes in their spatial distribution and high interannual variability. High abundance of larvae is observed in some years, which are usually followed by a longer sequence of poor abundance years. Yearly averages varied between 3 and 79 larvae/m². The spatial distribution of average larvae density showed three notorious periods along time: the first between 1970 and 1979 with higher larvae densities south of 14°S; the second between 1980 and 1999 with the higher densities to the north of 14°S; and the third between 2000 and 2010 with higher densities south of 18°S. The displacement of the centers of gravity of the spatial distribution marked three noticeable periods: between 1966 and 1978 were more coastal, south of 14°S; between 1979 and 1994 more oceanic and north of 14°S; and between 1995 and 2010 which were at an intermediate position. The relationship of larvae density with oceanographic variables as well as with the distribution of adult and juvenile Jack mackerel T. murphyi are discussed, stressing the observation that there is a main center of permanent spawning activity of this species in Peruvian waters.
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A study was conducted to investigate the effects of a sagittal position of the body gravity center (GCP) and manual weight-load on postural control during rapid arm-lifting. The subjects were five males aged 21 to 36 years. They stood on a force plate while maintaining the GCP at 30%, 45% and 60% from the heel, regarding the fool length as 100%, and anteriorly lifted both arms spontaneously as rapidly as possible. These trials were carried out ten times under a 5 kg weight or no weight. EMGs of the biceps femoris muscle (BFM) and anterior deltoid muscle (ADM), the fluctuation of the center of foot pressure (CFP) and body motion were analyzed by focusing on their time sequences.<BR>At 45% and 60% GCP the BFM action started prior to the ADM action, whereas at 30% GCP it tended to lag behind. The lag times under no weight were 13.9±12.75 ms (mean±SD) at 30% GCP, -32.7±18.18 ms at 45% GCP and -46.0±19.40 ms at 60% GCP. Those under 5 kg weight were 15.0±11.40 ms at 30% GCP, -22.0±6.74 ms at 45% GCP and -28.9±7.63 ms at 60% GCP. These results indicate that the anticipatory action of the muscle related to postural control arises only at specific GCPs.<BR>The difference of starting points for BFM action to ADM action showed no significant difference between 45% and 60% GCP for either as 5 kg or no weight. The CFP position moving in a forward direction during arm-lifting showed a marked difference between 45% and 60% GCP. The time for arm-lifting showed a marked difference between 5 kg and no weight. These results suggest that the starting point of anticipatory muscle action related to postural control does not change according to the magnitude and time course of the distance to the body equilibrium as a result of arm-lifting.