Average Center Of Mass Research Articles

대학 여자 멀리뛰기 엘리트 선수와 아마추어 선수의 각운동량 비교분석

The purpose of this study was to compare and analyze the angular momentum of the lower extremities and upper extremities and the resultant velocity of the COM(center of mass) in the long jump motions of elite female long jump athletes and amateur athletes. This study obtained the following results. First, the average angular momentum of the right arm of the elite female long jump athlete and amateur athlete during the long jump action was high in all events except Event 4, Event 5, and Event 6, and there was a significant difference in Event 8. Second, the average angular momentum of the left arm during the long jump of elite female long jump athletes and amateur athletes was high in all events except Event 3, Event 4, and Event 5, and there was a significant difference in Event 8. Third, the average angular momentum of the right leg of the elite female long jump athlete and amateur athlete during the long jump was high in all events except for Event 3 and Event 4. There was a significant difference between Event 3 and Event 8. Fourth, the average angular momentum of the left leg of the elite female long jump athlete and amateur athlete during the long jump operation was high in all Events except Event 1 and Event 5, and there was a significant difference in Event 8. Fifth, the average COM resultant velocity of the elite female long jump athlete and amateur athlete during the long jump action showed that the average COM resultant velocity of all Event elite athlete was high, showing a significant difference.

Geometric and Dosimetric Changes in Tumor and Lung Tissue During Radiotherapy for Lung Cancer With Atelectasis.

Background and PurposeThis article retrospectively characterized the geometric and dosimetric changes in target and normal tissues during radiotherapy for lung cancer patients with atelectasis.Materials and MethodsA total of 270 cone beam computed tomography (CBCT) scans of 18 lung patients with atelectasis were collected. The degree and time of resolution or expansion of the atelectasis were recorded. The geometric, dosimetric, and biological changes in the target and lung tissue were also quantified.ResultsThere were two patients with expansion, four patients with complete regression, six patients with partial regression, and six patients with no change. The time of resolution or expansion varied. The tumor volume increased by 3.8% in the first seven fractions, then decreased from the 9th fraction, and by 33.4% at the last CBCT. In the LR direction, the average center of mass (COM), boundaries of the tumors gradually shifted mediastinally. In the AP direction, the COM of the tumors was shifted slightly in the posterior direction and then gradually shifted to the anterior direction; the boundaries of the tumors all moved mediastinally. In the SI direction, the COM of the tumors on the right side of the body was substantially shifted toward the head direction. The boundaries of the tumors varied greatly. D2, D98, Dmean, V95, V107, and TCP of the PTV were reduced during radiotherapy and were reduced to their lowest values during the last two fractions. The volume of the ipsilateral lung tended to increase gradually. The V5, V10, V20, V30, V40, and NTCP of the total lung gradually increased with the fraction.ConclusionsFor most patients, regression of the atelectasis occurred, and the volume of the ipsilateral lung tended to increase while the tumor volume decreased, and the COM and boundary of the tumors shifted toward mediastinum, which caused an insufficient dose to the target and an overdose to the lungs. Regression or expansion may occur for any fraction, and it is therefore recommended that CBCT be performed at least every other day.

A Comparison of Squatting Exercise on a Centrifuge and With Earth Gravity.

Purpose: Long-duration space missions require countermeasures against the muscular wasting and cardiovascular deconditioning associated with microgravity. Replacing gravitational acceleration by means of centrifugation is a promising alternative as it challenges all physiological systems at once. The aim of this study is to examine the metabolic energy costs of squatting on a centrifuge in comparison with squatting in an upright standing posture under natural gravity.Methods: 24 subjects (11 male, 13 female) performed continuous squatting exercise for 9 min with increasing cadence (10, 12, and 15 squats min-1). This was done under three conditions: Upright under natural gravity and lying supine on a centrifuge at two radii (2.5 and 3.5 m) at 1 g of centrifugal acceleration at the subject’s average center of mass during the exercise.Results: Generally, subjects did not suffer from motion sickness. Exercise under natural gravity led to a higher Δ V’O2/body mass (7.1 ± 2.0, ml min-1 kg-1, mean ± SD) compared with exercise on the centrifuge (6.1 ± 1.6, ml min-1 kg-1, mean ± SD). Exercise efficiency was also reduced under natural 1 g at 28.2 ± 1.0% compared to 40.4 ± 1.5% on the centrifuge. As expected, oxygen consumption increased with increasing cadences. The Coriolis effect had a negligible impact as there was no significant difference in V’O2 between the two radii. However, during centrifugation and upward movement the right leg was more loaded than the leg left and vice versa during downward movement (centrifuge running clockwise looking down, so to the subjects’ right).Conclusion: The lower V’O2 on the centrifuge may be attributed to the unloading of trunk muscles while subjects were lying on the sled, which in the upright condition leaning against the sled were still working to stabilize the torso. Subjects tolerated high rotational rates combined with exercise very well.

Dynamic balance in elite karateka

In karate, balance control represents a key performance determinant. With the hypothesis that high-level athletes display advanced balance abilities, the purpose of the current study was to quantitatively investigate the motor strategies adopted by elite and non-elite karateka to maintain balance control in competition. The execution of traditional karate techniques (kihon) in two groups of elite Masters (n=6, 31±19years) and non-elite Practitioners (n=4, 25±9years) was compared assessing body center of mass (CoM) kinematics and other relevant parameters like step width and angular joint behavior.In the considered kihon sequence, normalized average CoM height was 8% lower (p<0.05), while CoM displacement in the horizontal direction was significantly higher in Masters than in Practitioners (2.5 vs. 1.9m, p<0.05), as well as CoM average velocity and rms acceleration (p<0.05). Step width was higher in Masters in more than half of the sequence steps (p<0.05).Results suggest that elite karateka showed a refined dynamic balance control, obtained through the increase of the base of support and different maneuvers of lower limbs. The proposed method could be used to objectively detect talented karateka, to measure proficiency level and to assess training effectiveness.

Body sway and performance at competition in male pistol and rifle Olympic shooters

Summary Study aim: We examine the body sway differences between a) pistol and rifle and b) elite and national level senior male Olympic shooters, as well as the possible relation between body sway and performance at competition in Olympic shooting. Material and methods: Two body sway tests (feet together and feet apart) were performed by 28 Spanish male senior Olympic shooters just before competition. Performance was measured as the actual score at competition. Total center of mass (COM) areas and average/maximum COM velocities were calculated from force platform data. ANCOVA tests were implemented with age as a covariable. The non-parametric test U of Mann Whitney was used to study the differences between national and elite shooters. Pearson correlations were used to examine the relation between performance and total COM area. Results: At the feet apart position, rifle and elite shooters were found to have statistically less body sway than pistol and national level shooters respectively (total COM areas: F1,25 = 6.7; p &lt; 0.05, and Z = 2.36; p &lt; 0.01). No statistically significant differences were found regarding the feet together position, regardless the level or discipline (total COM areas: F1,25 = 1.49 ; p &gt; 0.05; 1 – β = 0.22, average COM velocities: F1,25 = 0.58; p &gt; 0.05; 1 – β = 0.11, maximum COM velocities: F1,25 = 0.03; p &gt; 0.05; 1 – β = 0.05). No significant relation was found between body sway and performance at competition (feet together: r = 0.13, feet apart: r = 0.14, p &gt; 0.05). Age and body sway were not found to be significantly correlated (F1,25 = 0.23; p &gt; 0.05; 1 – β = 0.08). Conclusions: Easy to carry out, non-specific body sway tests can be used for the selection of novice shooters.

Gait stability improvement after fusion surgery for adolescent idiopathic scoliosis is influenced by corrective measures in coronal and sagittal planes

To achieve optimal results after fusion for adolescent idiopathic scoliosis (AIS), radiographic parameters must be aligned with motion and performance. The effects of fusion on balance are poorly understood. Center of mass (COM) excursion and instantaneous interaction with center of pressure (COP) provides information about patients’ balancing ability during gait. This study investigates the interaction between COM and COP (COM–COP) in AIS patients before and one year after spine fusion and determines what radiographic goals predict restoration of harmonious COM–COP. This was a prospective study that investigated sixteen adolescents with AIS curvature >30˚ requiring surgical correction. Clinical outcomes measures, X-rays, and 3D motion-capture gait analysis were collected. Sagittal and coronal COM and COP offsets and inclination angles were calculated from positional data. COM excursion was calculated as peak COM displacement based on mediolateral and vertical deviation from a line fitted to the patient’s path. Radiographic parameters were measured to determine variables predictive of change in COM excursion. Post-operatively, average COM peak displacement decreased (42.6 to 13.1mm, p=0.001) and COM peak vertical displacement remained unchanged (17.0 to 16.3mm, p=0.472). COM–COP inclination angles reduced in the coronal, but not sagittal plane. Coronal lower extremity peak inclination angles reduced (8.8˚ to 7.5˚, p=0.025), correlating with C7 plumb-line offset (R=0.581, p=0.018). Thoracic Cobb, thoracic kyphosis, and C7 plumb-line were predictors of change in COM excursion. Mediolateral COM excursion post-surgery may reflect an attempt to reduce kinetic demands with improved spinal alignment. Although AIS correction has historically focused on the coronal plane, sagittal parameters may be more important for motion than previously theorized.

Dynamic Sagittal Plane Trunk Control During Anterior Cruciate Ligament Injury

Background: Recent studies have demonstrated that trunk control likely plays a role in anterior cruciate ligament (ACL) injury. Yet, the majority of ACL research remains focused on the lower limb, with limited information on the trunk position at the time of injury. Hypotheses: Athletes experiencing a noncontact ACL injury after a 1-legged landing position their center of mass (COM) more posterior from the base of support (BOS) at initial ground contact in comparison with uninjured athletes. The distance from the COM to the BOS (COM_BOS) is larger in female, as compared with male, athletes during 1-legged landing. Study Design: Case control study; Level of evidence, 3. Methods: Movie captures of 20 athletes performing a 1-legged landing maneuver resulting in a torn ACL were compared with matched (for gender, sport, and activity just before landing) movie captures of 20 athletes performing a similar maneuver that did not result in an ACL disruption (controls). The COM_BOS, trunkG angle, and limbG angle (both relative to the gravity vector) were measured in the sagittal plane at initial ground-foot contact. A 2-way ANOVA (injury status × gender) was used to examine the hypotheses. Results: There was a significant difference in all 3 measures based on injury status but not on gender. The COM_BOS, normalized by femur length, and limbG angle were greater (Δ = 0.9, P < .001 and Δ = 16°, P = .004, respectively), and the trunkG angle was smaller (Δ = 12°, P = .016) in the participants who sustained an ACL injury as compared with controls. The average COM was calculated as 38 cm more posterior relative to the BOS in the participants who sustained an ACL injury as compared with controls. Conclusion: Landing with the COM far posterior to the BOS may be a risk factor for noncontact ACL injury and potentially can be addressed in prevention programs.

Mechanics and energetics of step-to-step transitions isolated from human walking

We isolated step-to-step transitions from other contributors to walking mechanics using a cyclical rocking task and then examined the contribution of individual joints to the total work required to redirect the velocity of the center of mass (COM). Nine participants were instructed to rock backward and forward in the sagittal plane, eliminating the need to swing the legs and progress forward. To systematically increase the required work, we increased step length from 60 to 100% of leg length, keeping rocking frequency constant. The individual limbs method quantified the COM work and the joint power method apportioned the COM work among its various sources. As predicted by a physics-based model, we found that work in rocking was performed mainly during the step-to-step transitions and increased strongly with step length. We also found that increases in the average COM work rate exacted a proportional metabolic cost. The similar patterns of COM work and COM work rate during rocking and walking support the use of rocking to isolate the mechanics of step-to-step transitions. We found that the ankle was the main joint contributing to the positive work required to redirect the COM velocity during forward rocking. At the longest length, it accounted for 88% of the work performed by the trailing leg joints. Interestingly, the summed contribution of ankle, knee and hip joint work accounted for only 39% of the front leg negative COM work during the forward transition, suggesting that most of the collision work is performed by passive tissue.

Nuclear bremsstrahlung and its radiation effects in fusion reactors

Nucleons, i.e. protons or neutrons, are emitted in many fusion processes of light nuclei. The fusion-generated nucleons can in turn fuse with or be captured by an un-reacted nuclear fuel, for example deuterium. The fusion reaction occurs at an average center of mass (COM) energy of 10 keV (thousand electron volts) or more in a typical fusion reactor. At such a relative low COM energy, the proton and deuteron are in a state where the relative angular momentum approaches zero, or an s-wave state. The single gamma radiation process is thus suppressed due to the conservation of parity. Instead, the gamma ray (typically of the order of a few MeV or more) released is likely to be accompanied by soft x-ray photons from a nuclear bremsstrahlung process, which generates continuous x-ray radiation peaked around a few hundred eV to a few keV. The average photon energy and spectrum properties of such a process is calculated with a semiclassical approach. This phenomenon may cause additional parasitic issues to a fusion reactor, while also opening up the possibility of new plasma diagnostics.

SU-GG-J-02: 3D Lung Tumor Motion Tracking Using MV Cone-Beam CT Acquisition with Synchronized Respiratory Monitoring

Purpose: Raw cone‐beam CT data consists of projection images acquired sequentially during gantry rotation. For lungimaging, respiratory motion is recorded in the projections, but is lost during back‐projection reconstruction. The goal of this study was to measure the 3D respiratory motion of lungtumors from the raw MV cone‐beam CT (MVCBCT) projection data. Method and Materials: A respiratory signal was captured using an external surrogate (Anzai/Siemens) during MVCBCT acquisition (MVision, Siemens) and time‐synchronized with the projection data using the beam pulse signal. Projection images were processed to enhance anatomical structures then the lungtumor was segmented automatically. The tumor center‐of‐mass (COM) in the rotating coordinate system of the flat panel detector was computed for each projection frame. The respiratory signal amplitude was used to sort projections into 10 respiratory phase bins. Projections within each phase bin were analyzed in a pair‐wise manner by trigonometric triangulation yielding multiple measures of the tumor COM. A weighted average COM was computed for each phase, with greater weight given to measures obtained from projection pairs with larger angular perspective. Results: Tests on phantoms containing point structures validated the accuracy (2 mm) of the methodology. Clinical MVCBCT of a patient with two lungstumors yielded measures of the tumor centers' motion over the respiratory cycle, which agreed well with tumor motions measured from kV‐4DCT. Conclusion: The analysis presented here gleans additional dynamic 3D information that is unique from the time‐averaged 3D structure normally reconstructed in CBCT; and it is obtained without any additional radiation dose when CBCT is used for static IGRT. This method could prove useful for near real‐time calibration/verification of the correlation between surrogate and tumor respiratory motion immediately prior to 4D treatment delivery. It may also be used for automated online motion tracking during rotational dynamic treatment delivery.

Variability Among Breast Radiation Oncologists in Delineation of the Postsurgical Lumpectomy Cavity

Partial breast irradiation (PBI) is becoming more widely used. Accurate determination of the surgical lumpectomy cavity volume is more critical with PBI than with whole breast radiation therapy. We examined the interobserver variability in delineation of the lumpectomy cavity among four academic radiation oncologists who specialize in the treatment of breast cancer. Thirty-four lumpectomy cavities in 33 consecutive patients were evaluated. Each physician contoured the cavity and a 1.5-cm margin was added to define the planning target volume (PTV). A cavity visualization score (CVS) was assigned (1-5). To eliminate bias, the physician of record was eliminated from the analysis in all cases. Three measures of variability of the PTV were developed: average shift of the center of mass (COM), average percent overlap between the PTV of two physicians (PVO), and standard deviation of the PTV. Of variables examined, pathologic resection volume was significantly correlated with CVS, with larger volumes more easily visualized. Shift of the COM decreased and PVO increased significantly as CVS increased. For CVS 4 and 5 cases, the average COM shift was 3 mm and 2 mm, respectively, and PVO was 77% and 87%, respectively. In multiple linear regression, pathologic diameter >4 cm and CVS > or =3 were significantly associated with smaller COM shift. When CVS was omitted from analysis, PVO was significantly larger with pathologic diameter > or =5 cm, days to planning <36, and older age. Even among radiation oncologists who specialize in breast radiotherapy, there can be substantial differences in delineation of the postsurgical radiotherapy target volume. Large treatment margins may be prudent if the cavity is not clearly defined.

Enhanced Transport of Atrazine Under Irrigation with Effluent

AbstractEnhanced transport of atrazine (2‐chloro‐4‐(ethylamino)‐6‐(isopropylamino)‐s‐triazine; C8H14CIN5) applied to a corn (Zea mays L.) field was observed after irrigation with secondary effluent. Cores to 4 m were obtained from 10 effluent‐irrigated and 10 high‐quality water‐irrigated plots after two growing seasons and two winter rainy seasons. In most of the effluent‐irrigated cores, atrazine was widely distributed with depth, with an average center of atrazine mass at 115 ± 39 cm and a mean variance around the center of mass of 142 cm. In the high‐quality water‐irrigated cores, atrazine was concentrated in the upper soil horizons with an average center of mass at 63 ± 64 cm and a mean variance around the center of mass of 58 cm. The mean centers of atrazine mass in the effluent‐irrigated profiles and high‐quality water‐irrigated profiles are significantly different (Student's t‐test, P = 0.06). The equilibrium sorption isotherm for atrazine in the presence of high‐quality water was nonlinear, with a Freundlich n of 0.87 and a distribution coefficient (Kf) of 1.07. The atrazine isotherm in the presence of effluent had a similar n (0.86) but a significantly lower Kf of only 0.93. Atrazine at a rate of 4 mg/kg−1 was added to soil columns filled with the &lt; 1‐mm size fraction of the 0 to 30‐cm horizon of soil from an uncultivated site adjacent to the field site. Three replicate columns were leached with 0.85 pore volumes of either secondary effluent or 0.005 M CaCl2 solution at constant head. Atrazine in the effluent‐treated columns was more strongly leached from the upper columns and peaked at higher concentrations lower in the columns.

Wheel chair karate

In karate, balance control represents a key performance determinant. With the hypothesis that high-level athletes display advanced balance abilities, the purpose of the current study was to quantitatively investigate the motor strategies adopted by elite and non-elite karateka to maintain balance control in competition. The execution of traditional karate techniques (kihon) in two groups of elite Masters (n = 6, 31 ± 19 years) and non-elite Practitioners (n = 4, 25 ± 9 years) was compared assessing body center of mass (CoM) kinematics and other relevant parameters like step width and angular joint behavior.In the considered kihon sequence, normalized average CoM height was 8% lower (p < 0.05), while CoM displacement in the horizontal direction was significantly higher in Masters than in Practitioners (2.5 vs. 1.9 m, p < 0.05), as well as CoM average velocity and rms acceleration (p < 0.05). Step width was higher in Masters in more than half of the sequence steps (p < 0.05).Results suggest that elite karateka showed a refined dynamic balance control, obtained through the increase of the base of support and different maneuvers of lower limbs. The proposed method could be used to objectively detect talented karateka, to measure proficiency level and to assess training effectiveness.