Maximum Center Of Mass Research Articles

Sensitivity of subject-specific upper body musculoskeletal model predictions to mass scaling methods

Accurate predictions of spinal loads in subject-specific musculoskeletal models require precise body segment parameters, including segment mass and center of mass (CoM) locations. Existing upper body models often assume a constant percentage of total body mass to calculate segmental masses, disregarding inter-individual variability and limiting their predictive capacity. This study evaluated the sensitivity of subject-specific upper body musculoskeletal model predictions to body mass scaling methods. The upper body segmental masses and corresponding CoM of six male subjects with varying body mass indices were computed using two mass scaling methods: the constant-percentage-based (CPB) scaling method, commonly used in AnyBody software; and our recently developed body-shape-based (BSB) method. Subsequently, these values were used by a validated musculoskeletal model to predict the muscle and disc forces in upright and flexed postures. The discrepancies between the results of the two scaling methods were compared across subjects and postures. Maximum deviations in thorax masses reached up to 7.5% of total body weight (TBW) in overweight subjects, while maximum CoM location differences of up to 35 mm were observed in normal weight subjects. The root mean squared errors (RMSE) of the CPB results, calculated with the BSB results as baseline, showed that the muscle and shear forces of the two scaling methods were quite similar (<4.5% of TBW). Though, there were small to moderate differences in compressive forces (6.5–16.0% of TBW). Thus, the compressive forces predicted with CPB method should be used with caution, particularly for overweight and obese subjects.

Late-cueing of gait tasks on an uneven brick surface impacts coordination and center of mass control in older adults

BackgroundChanging directions while walking (turning gait), often with little planning time, is essential to navigating irregular surfaces in the built-environment. It is unclear how older adults reorient their bodies under these constraints and whether adaptations are related to declines in physiological characteristics. Research questionThe aims of this study were to (1) investigate whether surface irregularity, late-cueing, and age negatively affect coordination, kinematics, and center of mass (COM) movement during 90° turning gait and (2) determine if adaptations correlate with declines in strength, balance, and reaction-time. MethodsEighteen young (18–35 years) and sixteen older (65+ years) healthy adults participated in the study. Retro-reflective marker and trunk-accelerometry data were used to compute upper-body segmental reorientation timing, upper-body kinematics, and COM movement characteristics. Balance scores, lower-limb strength, and choice-reaction-times were also recorded. ResultsYoung and older adults maintained a cranial-caudal (head, shoulders, pelvis) reorientation sequence (p ≤ 0.018), lowered head pitch (uneven surface; young p = 0.035 and old p < 0.001), increased maximum COM acceleration (uneven surface and late-cueing; p ≤ 0.002), and decreased COM smoothness (uneven surface; p < 0.001). Young adults increased shoulder roll (uneven surface and late-cueing; p ≤ 0.008). Reduced stride regularity (late-cueing) was observed in older (p < 0.001), compared to young (p = 0.017), adults. Declines in strength (p ≤ 0.040) and balance (p = 0.018) were correlated with gait adaptations of older adults. SignificanceLate-cueing on an uneven surface is challenging for older adults. These challenges are exacerbated by strength and balance deficits.

Biomechanical Role of the Hip in Maintaining Balance during Standing Forward Reach

During reactions to external anterior-posterior (AP) postural perturbations, it has been demonstrated that the hip strategy (HS) is employed only when balance risk is high and the ankle strategy (AS) is inadequate. In quiet standing the ankle plays a major role in maintenance of AP balance while the role of the hip is limited to medial-lateral (ML) control. This has led to the hypothesis that use of HS during self-initiated AP movements that are relatively safe or involve small center of mass (COM) excursions indicates poor balance, possibly due to deficits in ankle musculature. Consequently, comprehensive balance tests like BESTest focus on hip strength in the frontal plane and ankle strength in the sagittal plane. PURPOSE: To elucidate the biomechanical role of the hip during self-initiated standing forward reach. This movement pattern is used in several clinical balance screens including BESTest, Berg Balance Scale and Functional Reach Test. METHODS: 5 healthy young participants stood with their right shoulder flexed to 90°. A yardstick was placed parallel to the floor at the level of the acromion. They were instructed to reach forward as far as possible without taking a step and without raising their heels off the floor. 3 trials each were collected with 2 different instructions - do not bend the hip (AS) and bend the hip (HS). 2 force plates and an 11 camera motion capture system were used to obtain joint angles and moments, and whole-body COM and center of pressure (COP) excursions. RESULTS: Reach distance normalized by height was significantly higher during HS (Δ= 4.5±1.3 cm; p=0.008). This was accompanied by a significantly higher peak hip extensor moment (Δ= 0.41±0.13 Nm/kg; p=0.014). However, the maximum COM and COP excursions and peak ankle plantarflexor moment were not significantly different between strategies. CONCLUSIONS: Using HS allowed participants to reach further without increasing the balance risk as assessed by COM and COP excursions. Based on these findings, it is likely that in a functional situation where an individual is required to reach a fixed distance, using HS will achieve the goal with smaller COP and COM excursions compared to AS. Therefore, use of HS may not necessarily be a last resort indicating absence of ankle strength and the hip should not be ignored during assessment and retraining of AP balance.

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.

Compensations during Unsteady Locomotion.

Locomotion in a complex environment is often not steady, but the mechanisms used by animals to power and control unsteady locomotion (stability and maneuverability) are not well understood. We use behavioral, morphological, and impulsive perturbations to determine the compensations used during unsteady locomotion. At the level both of the whole-body and of joints, quasi-stiffness models are useful for describing adjustments to the functioning of legs and joints during maneuvers. However, alterations to the mechanics of legs and joints often are distinct for different phases of the step cycle or for specific joints. For example, negotiating steps involves independent changes of leg stiffness during compression and thrust phases of stance. Unsteady locomotion also involves parameters that are not part of the simplest reduced-parameter models of locomotion (e.g., the spring-loaded inverted pendulum) such as moments of the hip joint. Extensive coupling among translational and rotational parameters must be taken into account to stabilize locomotion or maneuver. For example, maneuvers with morphological perturbations (increased rotational inertial turns) involve changes to several aspects of movement, including the initial conditions of rotation and ground-reaction forces. Coupled changes to several parameters may be employed to control maneuvers on a trial-by-trial basis. Compensating for increased rotational inertia of the body during turns is facilitated by the opposing effects of several mechanical and behavioral parameters. However, the specific rules used by animals to control translation and rotation of the body to maintain stability or maneuver have not been fully characterized. We initiated direct-perturbation experiments to investigate the strategies used by humans to maintain stability following center-of-mass (COM) perturbations. When walking, humans showed more resistance to medio-lateral perturbations (lower COM displacement). However, when running, humans could recover from the point of maximum COM displacement faster than when walking. Consequently, the total time necessary for recovery was not significantly different between walking and running. Future experiments will determine the mechanisms used for compensations during unsteady locomotion at the behavioral, joint, and muscle levels. Using reduced-parameter models will allow common experimental and analytical frameworks for the study of both stability and maneuverability and the determination of general control strategies for unsteady locomotion.

Postural reactions following forward platform perturbation in young, middle-age, and old adults

The aim of the study was to examine how individuals of different ages react to forward balance perturbations. Thirty-six volunteers, divided into four groups [young (YA), middle-age (MA 40 and MA 50), and old (OA) adults], stood on a platform that was either kept stationary, moved backward, or moved forward. EMG onset, EMG time-to-peak, iEMG, and agonist–antagonist co-activation, as well as cumulative angular excursion, maximum center of mass (CM) backward displacement, and CM time-to-reversal were assessed after forward translations. Postural synergies were assessed using principal component analysis (PCA). The results showed that OA activated their muscles later than YA [TA = 25 ms, RF = 17 ms] and OA and MA 50 reached the peak of activation later than YA [MA 50:TA = 23 ms, RF = 32 ms, OA:TA = 28 ms, RF = 21 ms]. Moreover, OA kept a higher level of activation longer than all younger groups. No differences among groups were observed in co-activation, kinematic, and PCA variables. We conclude that changes in temporal EMG patterns can be seen in the fifth decade. However, such changes have no effect on the CM horizontal displacement and CM time-to-reversal after perturbation, which cannot be justified by the use of different postural synergies, suggesting that temporal aspects of muscle activation could play a minor role in controlling excessive CM displacements after perturbations.

소프트볼 좌타자들의 효율적인 타격을 위한 운동역학적 분석

Here are the following results of the kinematic analysis for a left handed softball batter. For an efficient left handed softball bat, the total moving time of the center of mass (COM) must not be fast and the sliding time must be reduced and the movement slow. Also for accurate impact, the follow through swing must be fast, the nose movement up and down is approximately 2cm and the stride length is about 70cm. During the stride the COM movement in the vertical plane needs to be minimized and lower the players body. From the impact to the follow through phase the right leg must be maximally extended so that maximum COM velocity can be increased. The maximum bat speed must arise before the impact and the orientation must be so that the small side contacts with the ball. The trunk angle is about 90 degrees, the wrist angle is about 80 degrees and it must not be un-cocked until after impact. At impact the left knee must be flexed to support the body until the follow through swing where the right leg must be fully extended to maintain a posture to increase the torque. At the take back point the left foot must be focused on and pulled in towards the body while at the impact point the left foot pushes the ground ensuring a strong torque. Finally the right foot pushing towards the home plate while there is maximum knee extension and by the left foot axis the trunks torque must be used to increase the efficiency and power for batting.

Toward Endografting of the Ascending Aorta: Insight into Dynamics Using Dynamic Cine-CTA

To evaluate pulsatility and movement along the ascending thoracic aorta using dynamic electrocardiographically-gated 64-slice cine computed tomographic angiography (CTA). Diameter and area change and center of mass (COM) movement of the ascending thoracic aorta was determined per cardiac cycle in 15 patients at surgically relevant anatomical levels: (A) 5 mm distal to the coronary arteries, (B) 5 mm proximal to the innominate artery, and (C) halfway up the ascending aorta. Additionally, COM movement was determined 1 cm (level P) and 2 cm (level Q) distal from the origins of the innominate, left carotid, and left subclavian arteries. Eight gated datasets covering the cardiac cycle were used to reconstruct images at each level perpendicular to the aortic lumen. The distance between important anatomical landmarks was determined. All levels showed significant cardiac cycle-induced diameter and area changes (p<0.001), with the largest pulsatility 5 mm distal to the coronary arteries. Mean maximum diameter changes were (A) 17.4%+/-4.8% (range 7.5%-27.5%), (B) 13.9%+/-3.5% (range 10.6%-25.0%), and (C) 12.9%+/-3.4% (8.3%-19.6%). Mean area changes were (A) 12.7%+/-5.5% (range 4.3%-21.8%), (B) 7.5%+/-2.0% (range 4.1%-11.0%), and (C) 5.6%+/-2.2% (range 1.9%-11.4%). Mean maximum COM movements were (A) 6.1+/-2.0 mm (range 2.7-9.0), (B) 2.3+/-1.1 mm (range 1.1-5.6), and (C) 3.6+/-1.5 mm (range 1.4-6.5). Mean COM movements of the innominate, left carotid, and left subclavian arteries, respectively, were (P) 1.9+/-0.7 mm (range 0.9-3.7), 2.4+/-0.6 mm (range 1.4-3.3), and 1.9+/-0.6 mm (range 0.8-2.8), and (Q) 1.8+/-0.7 mm (range 0.8-3.5), 1.8+/-0.6 mm (range 0.8-2.7), 1.9+/-0.6 mm (range 1.1-3.4). The dynamics of the ascending thoracic aorta and the arch vessels are impressive, showing a wide range of 3-dimensional motions. Future ascending arch branched and fenestrated thoracic endograft designs must consider this active local environment, as it may have implications for durability, sealing, and ultimate clinical success.

Influence of footwear midsole material hardness on dynamic balance control during unexpected gait termination

The purpose of this study was to determine the influence of different midsole hardnesses on dynamic balance control during unexpected gait termination. Twelve healthy young female adults were asked to walk along an 8-m walkway, looking straight ahead. During 25% of the trials, they were signaled (via an audio buzzer) to terminate gait within the next two steps. The four experimental conditions were: (1) soft (A15); (2) standard (A33); (3) hard (A50); (4) barefoot. Center of mass (COM) position relative to the lateral base of support (BOS), center of mass-center of pressure (COM-COP) difference and vertical loading rate were used to evaluate the influence of midsole material on dynamic balance control. The results were a decrease in the medial-lateral range of COM with respect to the lateral BOS, a reduction in the maximum COM-COP difference and an increase in the vertical loading rate due to the presence and hardness level of the midsole material when compared to the barefoot condition. The primary outcomes of this study have illustrated the influence of midsole hardness as an impediment to dynamic balance control during responses to gait termination. In conclusion, the present study suggests that variations in midsole material and even the presence of it, impairs the dynamic balance control system.

15.26 Control of dynamic stability during gait termination on a moving surface in Parkinson's disease

The purpose of this study was to determine the influence of different midsole hardnesses on dynamic balance control during unexpected gait termination. Twelve healthy young female adults were asked to walk along an 8-m walkway, looking straight ahead. During 25% of the trials, they were signaled (via an audio buzzer) to terminate gait within the next two steps. The four experimental conditions were: (1) soft (A15); (2) standard (A33); (3) hard (A50); (4) barefoot. Center of mass (COM) position relative to the lateral base of support (BOS), center of mass − center of pressure (COM − COP) difference and vertical loading rate were used to evaluate the influence of midsole material on dynamic balance control. The results were a decrease in the medial–lateral range of COM with respect to the lateral BOS, a reduction in the maximum COM − COP difference and an increase in the vertical loading rate due to the presence and hardness level of the midsole material when compared to the barefoot condition. The primary outcomes of this study have illustrated the influence of midsole hardness as an impediment to dynamic balance control during responses to gait termination. In conclusion, the present study suggests that variations in midsole material and even the presence of it, impairs the dynamic balance control system.