A comparison of methods to determine center of mass during pregnancy

Sensory integration and segmental control of posture during pregnancy

BACKGROUND

Approximately 25% of pregnant people fall, yet the underlying mechanisms of this increased fall-risk remain unclear. Prior studies examining pregnancy and balance have utilized center of pressure analyses and reported mixed results. The purpose of this study was to examine sensory and segmental contributions to postural control throughout pregnancy using accelerometer-based measures of sway.

METHODS

Thirty pregnant people (first trimester: n = 10, second trimester: n = 10, third trimester: n = 10) and 10 healthy, nonpregnant control people stood quietly for one minute in four conditions: eyes open on a firm surface, eyes closed on a firm surface, eyes open on a foam pad, and eyes closed on foam. Postural sway was quantified using the root mean square accelerations in the anterior-posterior and medial-lateral directions from an inertial sensor at the lumbar region. Sensory sway ratios, segmental coherence and co-phase, were calculated to assess sensory contributions and segmental control, respectively.

FINDINGS

Pregnant people did not display greater sway compared to healthy, nonpregnant controls. There were no group differences in vestibular, visual, or somatosensory sway ratios, and no significant differences in balance control strategies between pregnant and nonpregnant participants across sensory conditions.

INTERPRETATION

The small effects observed here contrast prior studies and suggest larger, definitive studies are needed to assess the effect of pregnancy on postural control. This study serves as a preliminary exploration of pregnant sensory and segmental postural control and highlights the need for future to hone the role of balance in fall risk during pregnancy.

Different neurocognitive controls modulate obstacle avoidance through pregnancy

Understanding why falls during pregnancy occur at over 25% rate over gestation has clinical impacts on the health of pregnant individuals. Attention, proprioception, and perception of the environment are required to prevent trips and falls. This research aimed to understand how the changes to these neurocognitive processes control obstacle avoidance through gestation. Seventeen pregnant participants were tested five times in 6-week intervals. Participants walked an obstacle course (OC), and we analyzed the crossings over obstacles that were set to 10% of participants' body height. Participants also performed an attentional network test (ANT: performance of specific components of attention), an obstacle perception task (OP: ability to visually define an obstacle and translate that to a body posture), and a joint position sense task (JPS: ability to recognize and recreate a joint position from somatosensation). In the OC task, average leading and trailing foot crossing heights significantly reduced by 13% and 23% respectively, with no change in variation, between weeks 13 and 31 of pregnancy, indicating an increased risk of obstacle contact during this time. The variability in minimum leading foot distances from the obstacle was correlated with all three neurocognition tasks (ANT, OP, and JPS). Increased fall rates in the second and third trimesters of pregnancy may be driven by changes in attention, with additional contributions of joint position sense and environmental perception at various stages of gestation. The results imply that a holistic examination on an individual basis may be required to determine individual trip risk and appropriate safety modifications.

Determining fall risk change throughout pregnancy: the accuracy of postpartum survey and relationship to fall efficacy

All epidemiological studies on pregnancy fall risk to date have relied on postpartum recall. This study investigated the accuracy of postpartum recall of falls that were reported during pregnancy, including assessment of fall efficacy as a possible reason for recall inaccuracy. Twenty participants reported fall experiences weekly during pregnancy, but one participant was excluded as an outlier. A fall efficacy questionnaire was completed every six weeks during pregnancy. A postpartum survey to mimic previous studies (Dunning, Lemasters, and Bhattacharya 2010; Dunning et al. 2003) was delivered to determine recall accuracy. Postpartum recall of fall events each gestational month matches the previous study (Dunning, Lemasters, and Bhattacharya 2010). However, recall of falls is 16% underestimated and recall of all fall events is 30% overestimated in postpartum survey. There is a slight relationship between fall efficacy and true falls, but not between fall efficacy and fall recall. Our study suggests fall risk needs to be intermittently surveyed throughout pregnancy rather than assessed via postpartum survey.Practitioner summary: This study investigated the accuracy of postpartum survey of fall risk during pregnancy and the possibility of fall efficacy as a covariate. We used three corresponding surveys. We found inaccuracies in postpartum survey, not explain by fall efficacy.

Effect of pregnancy on anthropometrics, comfort, and functional performance for women living with transfemoral limb loss: Case report

Women living with limb loss (amputees) have unique needs that increase during pregnancy. Comfort, pain, and activity are exponentially compromised. Changes in mass and altered center of gravity increase the likelihood of falls and compromise safety for the mother and unborn baby. Subjective and physical functional performance measures data was collected through 2 separate pregnancies on a 36-year-old woman with a right transfemoral amputation. Physiological changes during pregnancy effected comfort, pain, and functional performance. Clinical practice guidelines for prosthetic management should be established to include protocols such as adjustment schedules, specialized socket design, and necessary component changes throughout the course of pregnancy.

Upper extremity kinematics during walking gait changes through pregnancy

BACKGROUND

Thirty percent of adults in the United States use wearable fitness devices as of 2020 [1], such as fitness watches, to monitor and track health and physical activity parameters. Physical changes during pregnancy may impact wrist worn device accuracy. The arms may be needed as compensation during walking because thorax axial rotation may be inhibited by pelvic tilt during pregnancy [2].

METHODS

To examine arm motion changes, twenty-three pregnant women (28 ± 4 y) were tested in four-week intervals ( ± 2 weeks) at 18-, 22-, 26-, 30- and 34-weeks' gestation. Kinematic data were measured during self-selected speed walking. Segment angles and angular velocities were analyzed over time. Linear regressions were used to analyze the correlations between arm motion and the other kinematic variables.

RESULTS

Arm range of motion significantly increased (p = 0.006) over gestation, but leg, thorax, and pelvis range of motions did not significantly change. Arm range of motion was correlated with pelvis (r² =0.311, p = 0.001, β = 1.724) and leg (r² = 0.285, p = 0.004, β = 1.520) range of motion and gait velocity (r² =0.566, p = 0.001, β = 39.110). Arm velocities significantly increased (p < 0.012), as did leg velocities (p < 0.022) over gestation time, but thorax and pelvis rotational velocities did not significantly change over time. Arm velocity was correlated with leg velocity in both flexion (r² =0.598, p = 0.001, β = 1.61) and extension (r² =0.568, p = 0.001, β = 1.35).

SIGNIFICANCE

Arm swing increases over the course of gestation during walking, which does not follow the exact pattern of changes seen in the legs, thorax, and pelvis. These results show that a typical gait analysis of lower body motions may miss important biomechanical changes or compensations at different points over pregnancy. Future studies should examine why these changes may occur. Studies should also be conducted to see if arm changes impact outcome parameters from fitness watches and affect their validity as an exercise tracker during pregnancy.

Pregnancy-related sensory deficits might impair foraging in echolocating bats

BACKGROUND

Reproduction entails substantial demands throughout its distinct stages. The mammalian gestation period imposes various energetic costs and movement deficits, but its effects on the sensory system are poorly understood. Bats rely heavily on active sensing, using echolocation to forage in complete darkness, or when lighting is uncertain. We examined the effects of pregnancy on bat echolocation.

RESULTS

We show that pregnant Kuhl's pipistrelles (Pipistrellus kuhlii) altered their echolocation and flight behavior. Specifically, pregnant bats emitted longer echolocation signals at an ~ 15% lower rate, while flying more slowly and at a lower altitude compared to post-lactating females. A sensorimotor foraging model suggests that these changes could lead to an ~ 15% reduction in hunting performance during pregnancy.

CONCLUSIONS

Sensory deficits related to pregnancy could impair foraging in echolocating bats. Our study demonstrates an additional cost of reproduction of possible relevance to other sensory modalities and organisms.

How Does the Lumbopelvic Complex Cope with the Obstetrical Load during Standing? Ergonomic Aspects of Body Posture in Pregnant Women

Pregnancy induces numerous modifications in the musculoskeletal system of the female body. Since one of the essential roles of the lumbopelvic structure is to support mechanical loads in the upright position, this study was designed to simulate the response of this complex to the growing foetus in pregnant women. The authors hypothesized that posture (i.e., lordosis and muscle involvement) under pregnancy conditions might be adjusted to minimize the demands of the obstetrical load. The analysis of the load on the musculoskeletal system during gestation was made based on numerical simulations carried out in the AnyBody Modeling System. The pregnancy-related adjustments such as increased pelvic anteversion and increased lumbar lordosis enhance the reduction of muscle activation (e.g., erector spinae, transversus abdominis or iliopsoas), muscle fatigue and spinal load (reaction force). The results may help develop antenatal exercise programs targeting core strength and pelvic stability.

Self-selection of gestational lumbopelvic posture and bipedal evolution

BACKGROUND

Not all pregnant women seem to select the more curved lumbopelvic posture that their sexual dimorphic anatomy allows even though many previous researchers have assumed lumbopelvic curvature to be standard during pregnancy. This study is vital to understanding coevolution of lumbopelvic sexual dimorphism and bipedalism, and understanding some clinical implications of intervening in gestational posture changes.

RESEARCH QUESTIONS

Are there anthropometric changes that correspond with selection of lumbopelvic curvature change during pregnancy? What are the biomechanical costs and benefits of gestational lumbopelvic curvature change?

METHODS

Twenty pregnant women were tested at five different times in the 2nd and 3rd trimesters of pregnancy. Lumbopelvic posture, standing kinetics and gait kinetics were measured longitudinally. Additionally, we modeled the effects on standing and gait without lumbopelvic postural changes, but with anthropometric changes, for each individual.

RESULTS

We found greater lumbopelvic angulation to correspond with a shorter body height (6 cm difference between groups, p = 0.048) and deeper 2nd trimester abdomen (2 cm difference between groups, p = 0.013). Lumbopelvic angulation lowers support requirements (in standing and walking (6% lower support impulse, p = 0.056), but at the cost of shifting the propulsive actions to a less efficient pulling action rather than pushoff (13 % reduction in pushoff time, p = 0.001). We observed minimal effects on walking kinematics and balance control.

SIGNIFICANCE

Our findings suggest the evolutionary advantage of the female lumbopelvic unit is the adaptability it provides to adjust for the individual needs of the pregnant woman. We discuss multiple potential contributing factors that may have shaped hominin female lumbopelvic evolution and are involved in self-selecting lumbopelvic posture.

Shoulder and elbow requirements during sagittal reach as a result of changing anthropometry throughout pregnancy

During pregnancy, anthropometric and physiological changes can result in difficulty reaching for and lifting everyday objects. The aims of this study were to determine the changes in sagittal plane anterior reach space (SPARS) and shoulder/elbow strength requirements throughout pregnancy. Seventeen participants were tested through a longitudinal observational cohort study between 16 and 36 weeks gestation in four-week intervals. A 25% decrease in SPARS was observed at the L3-4 torso height. Combined with arm mass increases, shoulder and elbow moment requirements at the minimum and maximum static reach distances significantly increased. However, inverse dynamics analysis determined that mass gains in the arm alone only minimally impact dynamic shoulder moments. Additionally, torso flexion increases throughout pregnancy demonstrates that women are attempting to compensate for decreased SPARS, possibly indicating the additional perceptual importance of reach space in accommodations for pregnant workers.

Development of Machine Learning Algorithms for the Determination of the Centre of Mass

The study of the human body and its movements is still a matter of great interest today. Most of these issues have as their fulcrum the study of the balance characteristics of the human body and the determination of its Centre of Mass. In sports, a lot of attention is paid to improving and analysing the athlete’s performance. Almost all the techniques for determining the Centre of Mass make use of special sensors, which allow determining the physical magnitudes related to the different movements made by athletes. In this paper, a markerless method for determining the Centre of Mass of a subject has been studied, comparing it with a direct widely validated equipment such as the Wii Balance Board, which allows determining the coordinates of the Centre of Pressure. The Motion Capture technique was applied with the OpenPose software, a Computer Vision method boosted with the use of Convolution Neural Networks. Ten quasi-static analyses have been carried out. The results have shown an error of the Centre of Mass position, compared to that obtained from the Wii Balance Board, which has been considered acceptable given the complexity of the analysis. Furthermore, this method, despite the traditional methods based on the use of balances, can be used also for prediction of the vertical position of the Centre of Mass.

Correlations between joint kinematics and dynamic balance control during gait in pregnancy

BACKGROUND

Dynamic balance control degrades during pregnancy, but it is not yet understood why. Mechanical aspects of the body should directly affect walking balance control, but we have recently published papers indicating that weight gains during pregnancy explain very little dynamic balance changes. Our goal was to determine if lower extremity joint kinematic changes are an indicator of walking balance control. This information is vital to understanding the route by which pregnancy increases fall risk.

METHODS

Twenty-three pregnant women were tested at five different times in the 2nd and 3rd trimesters of pregnancy. Participants performed walking trials at a self-selected pace. Motion capture was used to measure joint kinematics (discrete and coordination variables) and body center of mass motion. Changes over time were statistically analyzed. Correlations between kinematics and walking balance were modelled with hierarchical multiple regression models.

RESULTS

As pregnancy progresses, it appears that a more flexed hip posture could be driving lower extremity kinematic changes toward increased coordination between joints and increased knee and ankle motions. Walking balance changes were also detected through increased COM motion (lateral range of motion and velocity) in the lateral directions. However, there was little correlation between kinematic and balance changes (r² < 0.4). Strong correlations were only observed when all kinematics (including those that don't ubiquitously change during pregnancy) were used in the regression model (r² > 0.7).

SIGNIFICANCE

Our findings suggest that walking balance control is not altered by a common kinematic change between all pregnant women. While increased lateral center of mass motion should be expected with pregnancy, the kinematics leading to this increase may be person-specific. The cause of dynamic imbalance in each pregnant women (physiological, mechanical, and neurocognitive) may play an important role in determining the kinematic means by which lateral center of mass motion increases.

Changes in segmental mass and inertia during pregnancy: A musculoskeletal model of the pregnant woman

BACKGROUND

One in four pregnant women falls at least once during her pregnancy. During pregnancy, the body undergoes tremendous vascular, hormonal, physiological, and psychological changes to accommodate the growing fetus. The pregnancy-induced mass gain of 10 to 25 kg is not evenly distributed and results in a large change in mass distribution and shift in segmental centers of mass. To accurately understand how the change in mass distribution leads to an increase in fall events, a musculoskeletal model of the pregnant body is necessary. Generic musculoskeletal models cannot accurately represent the morphology of pregnant women and the study of postural stability of pregnant women is limited by the lack of adapted musculoskeletal models.

RESEARCH QUESTION

Could a model reflecting the change in segmental inertia during pregnancy explain the pregnancy-related risk of falling?

METHODS

We built a musculoskeletal model of the pregnant women, combining literature anthropomorphic measurements with generic models. We optimized the dimensions of the anthropomorphic model shapes to fit the average measurements of 25 pregnant women. The mass, center of mass, and inertia of each segment are then computed throughout pregnancy. Finally, the stance phase of a gait cycle was modeled using the pregnancy-specific and the generic models. The ankle, knee, hip and lumbar joint moments during gait were compared between the two models.

RESULTS

The built musculoskeletal model of the pregnant woman includes changes in mass and geometry of the thorax, pelvis, thighs, and legs. The model reproduces the change in lumbar curvature during pregnancy. Gait simulation results show a limited impact of pregnancy on the ankle, knee, and hip moment, but a large impact on the lumbar moment.

SIGNIFICANCE

Such a musculoskeletal model will help elucidate the mechanisms leading to falls or low back pain during pregnancy.

An analysis of postpartum walking balance and the correlations to anthropometry

BACKGROUND

Falls caused by balance issues during pregnancy are quite common, and these issues can continue postpartum, potentially posing a danger to both the mother and baby. While there has been research on changes to walking gait during pregnancy, walking balance in the postpartum period has yet to be examined. Therefore, the aims of this study were to examine if balance changes persist in postpartum and the contribution of anthropometry changes.

METHODS

This was done through longitudinal observational cohort study at 16 and 40 weeks gestation and at four-week intervals postpartum. Balance was measured as lateral center of mass motion during treadmill walking, and recorded with motion capture cameras following anthropometric measurements. Balance variables were statistically analyzed to observe how they changed over time. Hierarchical regression analyses determined correlations between balance and anthropometry.

RESULTS

Balance was observed to improve significantly just following birth. Additionally, there were changes that continued to indicate improvement throughout the postpartum period. Anthropometry changes were significantly, but minimally, correlated with balance changes.

SIGNIFICANCE

Many women begin to return to normal activities soon after birth. With women participating in various forms of exercise, potentially rigorous work requirements, and tasks around the home, it is important that they, their medical providers, and employers understand and consider the continued risks of imbalance.

Stand-to-sit kinematic changes during pregnancy correspond with reduced sagittal plane hip motion

BACKGROUND

The stand-to-sit motion has been linked to falls during pregnancy. It is also used in the clinical evaluation of functional performance. The physical and physiological changes during pregnancy may necessitate a change in stand-to-sit kinematic performance. Therefore, this study was conducted to evaluate the longitudinal changes to stand-to-sit kinematics during pregnancy.

METHODS

Fifteen pregnant women were tested in 4-week intervals from 16 weeks to 36 weeks gestational age. They performed a 60-second trial of semi-continuous stand-to-sit motion. Sagittal plane motions at the ankle, knee, spine, and shoulders were measured. Additionally, three-dimensional hip motion was measured. Discrete variables (e.g. range of motion) and joint coordinations (through vector coding) were analyzed over time through a linear mixed model analysis.

FINDINGS

The results indicate a shift away from sagittal hip motion throughout pregnancy. Hip range of motion and standing angle changed in favor of spine motion. Joint coordination shifted from hip dominant to spine- and shoulder-dominate coordination just before the start of sitting motion. Hip-knee joint coordination just before seat contact shifted from hip to a knee-dominant motion during pregnancy.

INTERPRETATION

Discrete variable changes in the entire stand-to-sit motion seem to be driven by initial standing posture related to an increase in gestational lordosis. Likewise, standing joint coordination shift to upper body motion can be attributed to gestational lordosis limiting functional ability around the hip. The shift in motion away from the hip may provide insight into why both fall rates and low back pain rates increase during stand-to-sit during pregnancy.

Anthropometry, standing posture, and body center of mass changes up to 28 weeks postpartum in Caucasians in the United States

BACKGROUND

Anthropometric models are used when body center of mass motion is calculated for assessment of dynamic balance. It is currently unknown how body segments and posture change in the postpartum period. Therefore, this study was conducted to evaluate the longitudinal changes in anthropometry, center of mass, and standing posture postpartum.

METHODS

Seventeen pregnant women were tested at nine different times: 16-20 weeks and 36-40 weeks gestation, and then in 4-week intervals from childbirth to 28 weeks postpartum. Anthropometry was measured and then participants conducted a static standing and static laying trial. Force plate data and motion capture data were used in combination with anthropometry to calculate the masses of individual segments and the body center of mass. Change over time was determined through a linear mixed model analysis.

RESULTS

Anthropometric changes related to the abdomen or fluid retention during pregnancy immediately regress to early pregnancy levels following childbirth. However, other changes related to breast tissue and fat deposits persist postpartum. As such, masses of different segments affect an anthropometric model for center of mass calculation, and body center of mass changes in the lateral and anterior directions postpartum. Vertical body center of mass position was unaffected.

SIGNIFICANCE

Increased postpartum breast mass may be the cause of persistent lordotic curvature changes in the lumbar spine. There is potential that this affects postpartum back pain. Future research should explore how body center of mass changes postpartum for individuals that do not breast feed, and thus may not have significant breast mass postpartum.

Walking balance on a treadmill changes during pregnancy

BACKGROUND

Altered standing balance during pregnancy has been previously reported. To date, body center of mass (bCOM) motion has not been used to track balance changes in this population. We recently compared three methods to determine the torso center of mass (tCOM) location (via force plate acquired center of pressure calculation, using Pavol surface anthropometry measurements, and a combination of the two) to use in calculating the bCOM during pregnancy.

RESEARCH QUESTION

This current research explored two questions: (1) does walking balance change during pregnancy, and (2) do the methods for identifying tCOM location affect the resulting balance measures?

METHODS

Fifteen pregnant women were recruited to perform 60-second trial of treadmill walking at 4-week intervals from 12 weeks gestation until delivery. Walking balance was measured as bCOM motion within the base of support. Gestation time and anthropometric model (force plate, Pavol, and combination) were repeated-measures independent variables in a general linear mixed model analysis.

RESULTS

There was a significant decrease in walking balance during pregnancy. As gestation progressed, we observed non-linear changes in the bCOM motion within the base of support over time, with some changes starting early in pregnancy and others not starting until late 2^nd trimester. The anthropometric model used to locate the bCOM significantly influences balance measures. The results of this study indicate that the force plate method is more appropriate for locating the tCOM in the anterior and lateral directions.

SIGNIFICANCE

The results of this study will inform clinicians and patients about the gestational stage-associated changes in balance during pregnancy that increase the risk of falling and injury. Researchers should also carefully consider the method for locating the bCOM.