Center Of Mass Acceleration Research Articles

Centre of mass control is reduced in older people when descending stairs at an increased riser height

BackgroundMaintaining body centre of mass (CoM) lowering velocity within manageable/safe limits during stair descent can be problematic for older individuals due to reduced ranges of motion at the involved joints (ankle and knee) and a reduced ability to generate adequate joint moments at the extremes in joint ranges of motion. These problems are likely to magnify in circumstances where the distance of lowering increases, or when misjudging the height of lowering. Research questionHow does a 50% increase in standard stair riser-height affect control of CoM velocity and acceleration of older people during stair descent? MethodsFifteen older (75 ± 3 years) and seventeen young (25 ± 4 years) healthy adults descended a 4-step staircase, at two riser-heights: 170 mm, 255 mm. Changes in peak vertical CoM acceleration and velocity, and lower-limb joint kinetics (moments, work) during landing and lowering phases of stair descent were assessed using a mixed-design repeated measures analysis of variance. ResultsPeak CoM accelerations and velocities during landing and lowering were lower in older compared to young adults and increased in both groups at 255 mm riser-height. Duration of lowering also increased, particularly for older adults. Peak ankle moments during landing and lowering, which were lower in older compared to young adults, increased when descending from 255 mm riser-height, whilst the peak knee moment reduced. Both groups produced increased landing-limb negative (eccentric) ankle joint work when descending from 255 mm, but increases were greater for older adults (87.8%) compared to young (76.1%). SignificanceDescending stairs became more challenging in both age groups as riser-height increased. Older adults adopted a strategy of reducing CoM velocity to lessen the eccentric landing demands. In both groups, but more so older adults, there was a greater reliance on using leading-limb eccentric plantarflexion at 255 mm riser-height compared to 170 mm, to arrest/control increased downward CoM velocity and acceleration during landing.

Red muscle activity in bluegill sunfish Lepomis macrochirus during forward accelerations

Fishes generate force to swim by activating muscles on either side of their flexible bodies. To accelerate, they must produce higher muscle forces, which leads to higher reaction forces back on their bodies from the environment. If their bodies are too flexible, the forces during acceleration could not be transmitted effectively to the environment, but fish can potentially use their muscles to increase the effective stiffness of their body. Here, we quantified red muscle activity during acceleration and steady swimming, looking for patterns that would be consistent with the hypothesis of body stiffening. We used high-speed video, electromyographic recordings, and a new digital inertial measurement unit to quantify body kinematics, red muscle activity, and 3D orientation and centre of mass acceleration during forward accelerations and steady swimming over several speeds. During acceleration, fish co-activated anterior muscle on the left and right side, and activated all muscle sooner and kept it active for a larger fraction of the tail beat cycle. These activity patterns are both known to increase effective stiffness for muscle tissue in vitro, which is consistent with our hypothesis that fish use their red muscle to stiffen their bodies during acceleration. We suggest that during impulsive movements, flexible organisms like fishes can use their muscles not only to generate propulsive power but to tune the effective mechanical properties of their bodies, increasing performance during rapid movements and maintaining flexibility for slow, steady movements.

Quiet standing: The Single Inverted Pendulum model is not so bad after all.

In the study of balance and postural control the (Single) Inverted Pendulum model (SIP) has been taken for a long time as an acceptable paradigm, with the implicit assumption that only ankle rotations are relevant for describing and explaining sway movements. However, more recent kinematic analysis of quiet standing revealed that hip motion cannot be neglected at all and that ankle-hip oscillatory patterns are characterized by complex in-phase and anti-phase interactions, suggesting that the SIP model should be substituted by a DIP (Double Inverted Pendulum) model. It was also suggested that DIP control could be characterized as a kind of optimal bi-axial active controller whose goal is minimizing the acceleration of the global CoM (Center of Mass). We propose here an alternative where active feedback control is applied in an intermittent manner only to the ankle joint, whereas the hip joint is stabilized by a passive stiffness mechanism. The active control impulses are delivered to the ankle joint as a function of the delayed state vector (tilt rotation angle + tilt rotational speed) of a Virtual Inverted Pendulum (VIP), namely a pendulum that links the ankle to the CoM, embedded in the real DIP. Simulations of such DIP/VIP model, with the hybrid control mechanism, show that it can reproduce the in-phase/anti-phase interaction patterns of the two joints described by several experimental studies. Moreover, the simulations demonstrate that the DIP/VIP model can also reproduce the measured minimization of the CoM acceleration, as an indirect biomechanical consequence of the dynamic interaction between the active control of the ankle joint and the passive control of the hip joint. We suggest that although the SIP model is literally false, because it ignores the ankle-hip coordination, it is functionally correct and practically acceptable for experimental studies that focus on the postural oscillations of the CoM.

Towards a wearable monitoring tool for in-field ice hockey skating performance analysis

The capturing of movements by means of wearable sensors has become increasingly popular in order to obtain sport performance measures during training or competition. The purpose of the current study was to investigate the feasibility of using body worn accelerometers to identify previous highlighted performance related biomechanical changes in terms of substantial differences across skill levels and skating phases. Twenty-two ice hockey players of different caliber were equipped with two 3D accelerometers, located on the skate and the waist, as they performed 30 m forward skating sprints on an ice rink. Two measures of the temporal stride characteristics (contact time and stride time) and one measure of the propulsive power (stride propulsion) of a skating stride were calculated and checked for discriminating effects across (i) skill levels and (ii) sprint phases as well as for their (iii) strength of association with the sprint performance (total sprint time). High caliber players showed an increased stride propulsion (+22%, P < 0.05) and shorter contact time (−5%, P < 0.05). All three analysed variables highlighted substantial biomechanical differences between the accelerative and constant velocity phases (P < 0.05). Stride propulsion of acceleration strides primarily correlated to total sprint time (r = −0.57, P < 0.05). The results demonstrate the potential of accelerometers to assess skating technique elements such as contact time or elements characterizing the propulsive power such as center of mass acceleration, to gauge skating performance. Thus, the findings of this study might contribute to establishing wearable sensors for in-field ice hockey skating performance analysis.

Dynamic walking stability of elderly people with various BMIs

BackgroundFalls are one of the major causes of injury in the elderly. Obesity may be related to the risk of falling. Understanding the dynamic stability mechanisms of obese elderly people during gait is important as it may be associated with fall protection. Research questionDoes obesity affect the dynamic walking stability of elderly people? MethodsThis is a prospective study. Fifty-three elderly participants, aged 60–82 years, were categorized into body mass index (BMI) groups. In single-limb support experiments, the center of mass velocity (COMv), center of mass acceleration (COMa), region of velocity stability (ROSv) and region of acceleration stability (ROSa) were calculated using kinematic data sampled from a motion analysis system. In addition, all participants were assessed for the dynamic balance ability test scale (DBATS). Statistical analyses were performed by one-way ANOVA, Kruskal–Wallis/Wilcoxon nonparametric tests, or bivariate Pearson/Spearman correlation analysis. ResultsDuring walking, peak COMv and COMa decreased with increasing BMI (Normal BMI: 1.20 ± 0.14 m/s, 1.66 ± 0.36 m/s2; High BMI: 1.14 ± 0.11 m/s, 1.56 ± 0.30 m/s2; Higher BMI: 1.04 ± 0.15 m/s, 1.47 ± 0.25 m/s2). At toe-off (TO), the normalized participants’ center of mass (COM) is significantly more anterior in the Higher BMI group (Normal BMI: -0.30 ± 0.09, High BMI: -0.23 ± 0.07, Higher BMI: -0.16 ± 0.10), their normalized COMv and COMa (Normal BMI: 1.40 ± 0.16, 0.53 ± 0.11; High BMI: 1.33 ± 0.13, 0.49 ± 0.11; Higher BMI: 1.21 ± 0.16, 0.46 ± 0.11) are slower. The mean DBATS score of the Higher BMI group was the highest, indicating the weakest dynamic balance ability. SignificanceThe COM dynamic stability parameters indicate that obesity may worsen balance, with the peak COMv and ROSv most affected. With increasing BMI, the dynamic stability and balance of elderly people both decreased.

Strength Training Effects on Muscle Forces and Contributions to Whole-Body Movement in Cerebral Palsy

Strength training is often prescribed for children with cerebral palsy (CP); however, links between strength gains and mobility are unclear. Nine children (age 14 ± 3 years; GMFCS I-III) with spastic CP completed a 6-week strength-training program. Musculoskeletal gait simulations were generated for four children to assess training effects on muscle forces and function. There were increases in isometric joint strength, but no statistical changes in fast-as-possible walking speed or endurance after training. The walking simulations revealed changes in muscle forces and contributions to body center of mass acceleration, with greater forces from the hip muscles during walking most commonly observed. A progressive strength-training program can result in isometric and dynamic strength gains in children with CP, associated with variable mobility outcomes.

A Method for Bipedal Robot Locomotion Control along an Arbitrary Trajectory

This paper presents an algorithm for stable bipedal walking control along an arbitrary curve. The algorithm starts with a foot planner, which takes a parametrically defined desired path as an input and calculates feet positions and orientations at each step. Zero moment point (ZMP) concept is used for robot stability control. The dynamics of the robot is modeled as a running cart on a table. Given the reference ZMP trajectory, ZMP tracking servo controller based on preview control theory is used to calculate robot’s center of mass (CoM) trajectory. The preview controller is made of three terms: the integral error of ZMP, the state feedback proportional to a current state vector and the preview action which takes into account future values of the desired ZMP position. We propose robot’s state estimator based on linear Kalman filter with measured CoM acceleration and position as system inputs. Swing foot trajectories are calculated using trigonometric functions, since they are simple and can provide zero velocities at contact moments. We put some additional constraints on a system by assuming that there is no forward-backward inclination of the robot trunk and swing foot is always parallel to the ground. To avoid kinematic limits in hip and ankle roll joints we calculate a minimal angle to rotate robot trunk in frontal plane. After position and orientation of robot trunk and swing foot are found we apply inverse kinematics solution for robot legs to get robot joint angles. Finally, joint angles are sent to robot actuators. Software package based on ROS operating system was developed for AR601 robot. Verification tests were executed with robot model in Gazebo simulator. The robot successfully completed series of experiments confirming modelling results.

Simultaneous Prevention of Rotational and Translational Slip for a Humanoid Robot

Slip often occurs in humanoid robot walking, especially when the robot walks on a low friction floor or walks fast. Unexpected slip may cause the robot to fall and then sustain damage. In real environments, rotational and translational slip phenomena can happen during biped walking. Previous studies have mainly focused on solving these problems independently. In this paper, we propose strategies for simultaneous rotational and translational slip prevention based on a three mass model, which takes into account the effect of the swing leg. The rotational slip is prevented through a bionic walking pattern generator which mimics the yaw moment compensation mechanism of a human. The translational slip is eliminated through a novel reaction force ratio reduction control with the compensation of CoM (center of mass) acceleration. The effectiveness of the presented strategies is validated by simulations and experiments with an actual humanoid robot.

Potential of muscles to accelerate the body during late-stance forward progression in individuals with knee osteoarthritis

Many individuals with knee osteoarthritis (OA) generate low forward center of mass (COM) acceleration during the late stance phase, consequently making it difficult to walk fast. This study analyzed individual muscle contributions to forward COM acceleration and the muscle potential (i.e., acceleration by unit force) to clarify whether reduced acceleration was related to decreased muscle potential of forward progression by the triceps sure. Twelve individuals with knee OA and 12 healthy age-matched individuals participated in this study. All participants underwent kinetic measurements during normal gait. The simulation involved 92 Hill-type muscle–tendon units with 23 degrees of freedom. We analyzed how each muscle contributed to forward COM acceleration during the 70–100% stance phase using an induced acceleration analysis. Next, the muscle potential of forward COM acceleration was calculated. Our results showed that individuals with knee OA had significantly lower forward COM acceleration with the soleus, gastrocnemius, and iliopsoas muscles compared with controls. Lower muscle potential in the soleus was found in those with knee OA. These findings implied that improving the contribution of the soleus to forward body progression would be effective for increasing the gait speed of those with knee OA during the late stance phase.

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.

Running patterns for male and female competitive and recreational runners based on accelerometer data

ABSTRACTThe purpose of this study was to classify runners in sex-specific groups as either competitive or recreational based on center of mass (CoM) accelerations. Forty-one runners participated in the study (25 male and 16 female), and were labeled as competitive or recreational based on age, sex, and race performance. Three-dimensional acceleration data were collected during a 5-minute treadmill run, and 24 features were extracted. Support vector machine classification models were used to examine the utility of the features in discriminating between competitive and recreational runners within each sex-specific subgroup. Competitive and recreational runners could be classified with 82.63 % and 80.4 % in the male and female models, respectively. Dominant features in both models were related to regularity and variability, with competitive runners exhibiting more consistent running gait patterns, but the specific features were slightly different in each sex-specific model. Therefore, it is important to separate runners into sex-specific competitive and recreational subgroups for future running biomechanical studies. In conclusion, we have demonstrated the ability to analyze running biomechanics in competitive and recreational runners using only CoM acceleration patterns. A runner, clinician, or coach may use this information to monitor how running patterns change as a result of training.

Aging may negatively impact movement smoothness during stair negotiation

Stairs represent a barrier to safe locomotion for some older adults, potentially leading to the adoption of a cautious gait strategy that may lack fluidity. This strategy may be characterized as unsmooth; however, stair negotiation smoothness has yet to be quantified. The aims of this study were to assess age- and task-related differences in head and body center of mass (COM) acceleration patterns and smoothness during stair negotiation and to determine if smoothness was associated with the timed “Up and Go” (TUG) test of functional movement. Motion data from nineteen older and twenty young adults performing stair ascent, stair descent, and overground straight walking trials were analyzed and used to compute smoothness based on the log-normalized dimensionless jerk (LDJ) and the velocity spectral arc length (SPARC) metrics. The associations between TUG and smoothness measures were evaluated using Pearson’s correlation coefficient (r). Stair tasks increased head and body COM acceleration pattern differences across groups, compared to walking (p < 0.05). LDJ smoothness for the head and body COM decreased in older adults during stair descent, compared to young adults (p ≤ 0.015) and worsened with increasing TUG for all tasks (−0.60 ≤ r ≤ −0.43). SPARC smoothness of the head and body COM increased in older adults, regardless of task (p < 0.001), while correlations showed improved SPARC smoothness with increasing TUG for some tasks (0.33 ≤ r ≤ 0.40). The LDJ outperforms SPARC in identifying age-related stair negotiation adaptations and is associated with performance on a clinical test of gait.

Development of the procedure for verifying the feasibility of designing an active suspension system for transport carriages

We have proposed techniques using which made it possible to solve a nonlinear algebraic Riccati equation for dynamic systems with degrees of freedom. A constraint was imposed on the structure of a designed railroad carriage. We employed, as an analogue, a symmetrical carriage whose suspension system contains elastic-dissipative links with linear characteristics. This allowed us to devise a procedure for designing a suspension system for a railroad carriage. The criterion when choosing the weight coefficients of quality was the requirement to ensure comfortable conditions for passengers and a locomotive crew. Therefore, the system must experience an oscillatory process with small amplitudes; the frequency of natural oscillations of the body should not exceed 2 Hz. We have performed decomposition of the dynamic programming method for continuous stochastic systems, which made it possible to develop a procedure for a phased suspension system design. The procedure is suitable for use when designing suspensions for carriages running at regular and high-speed speed. The first stage implies designing a passive suspension system. The second stage involves a validation of the feasibility of designing devices to control parameters of the elastic-dissipative links in a suspension system of transport carriages using the optimal Kalman-Bucy filters. The modeling proved that control over parameters of elastic-dissipative links improves the dynamics of transport carriages. Damping control alone could reduce the body's center of mass acceleration by more than two times and hence decrease dynamic loads in the system. The Kalman-Bucy algorithm makes it possible to obtain optimal parameters of the elastic-dissipative links in a suspension system in complex dynamic systems. The procedure could be used independently and as part of the technique for a phased design of the suspension system. The procedure was demonstrated using test examples. The procedure is implemented in the simulation system. Control over parameters of the elastic-dissipative links in a suspension system of transport carriages would make it possible, first, to create comfortable working conditions for a locomotive crew and passengers, second, to improve operation reliability and motion safety of rolling stock by reducing dynamic loads.

An accurate estimation of the horizontal acceleration of a rower’s centre of mass using inertial sensors: a validation

For a valid determination of a rower’s mechanical power output, the anterior–posterior (AP) acceleration of a rower’s centre of mass (CoM) is required. The current study was designed to evaluate the accuracy of the determination of this acceleration using a full-body inertial measurement units (IMUs) suit in combination with a mass distribution model. Three methods were evaluated. In the first two methods, IMU data were combined with either a subject-specific mass distribution or a standard mass distribution model for athletes. In the third method, a rower’s AP CoM acceleration was estimated using a single IMU placed at the pelvis.Experienced rowers rowed on an ergometer that was placed on two force plates, while wearing a full-body IMUs suit. Correspondence values between AP CoM acceleration based on IMU data (the three methods) and AP CoM acceleration obtained from force plate data (reference) were calculated. Good correspondence was found between the reference AP CoM acceleration and the AP CoM accelerations determined using IMU data in combination with the subject-specific mass model and the standard mass model (intraclass correlation coefficients [ICC] > 0.988 and normalized root mean square errors [nRMSE] 3.81%). Correspondence was lower for the AP CoM accelerations determined using a single pelvis IMU (0.877 < ICC < 0.960 and 6.11% < nRMSE < 13.61%).Based on these results, we recommend determining a rower’s AP CoM acceleration using IMUs in combination with the standard mass model. Finally, we conclude that accurate determination of a rower’s AP CoM acceleration is not possible on the basis of the pelvis acceleration only.

Improved determination of mechanical power output in rowing: Experimental results

ABSTRACTIn rowing, mechanical power output is a key parameter for biophysical analyses and performance monitoring and should therefore be measured accurately. It is common practice to estimate on-water power output as the time average of the dot product of the moment of the handle force relative to the oar pin and the oar angular velocity. In a theoretical analysis we have recently shown that this measure differs from the true power output by an amount that equals the mean of the rower’s mass multiplied by the rower’s center of mass acceleration and the velocity of the boat. In this study we investigated the difference between a rower’s power output calculated using the common proxy and the true power output under different rowing conditions. Nine rowers participated in an on-water experiment consisting of 7 trials in a single scull. Stroke rate, technique and forces applied to the oar were varied. On average, rowers’ power output was underestimated with 12.3% when determined using the common proxy. Variations between rowers and rowing conditions were small (SD = 1.1%) and mostly due to differences in stroke rate. To analyze and monitor rowing performance accurately, a correction of the determination of rowers’ on-water power output is therefore required.

Comparison of segmental analysis and sacral marker methods for determining the center of mass during level and slope walking

BackgroundA human’s center of mass (COM) is a widely used parameter in both clinical and practical applications. The segmental analysis method for determining the COM is considered the gold standard but is difficult to apply in a real environment. Research questionThe purpose of this study was to confirm the efficacy of an alternative COM determination method—the sacral marker method—by comparing segmental analysis and sacral marker method results in three dimensions during level or slope walking. MethodsTen healthy young subjects (age = 24.0 ± 4.5 yr, height = 174.5 ± 5.9 cm, and weight = 66.9 ± 9.4 kg) participated in the study. Each participant was monitored using a Helen Hayes full-body marker set and asked to walk on level and sloped (7°) terrain. The markers’ trajectories were subsequently recorded. Each participant’s COM was determined using segmental analysis and sacral marker methods via calculation and direct measurement, respectively. ResultsComparative results indicated no significant differences (p > 0.05) between the segmental analysis and sacral marker method results for the COM displacement, velocity, or acceleration in the fore-aft and vertical directions. Conversely, significant differences (p < 0.05) between the two methods were observed for the COM displacement and acceleration in the medial-lateral direction, suggesting kinematic differences. SignificanceBased on this latter finding, caution should be exercised when determining COM kinematics using the sacral marker method.

Effects of task velocity and center of mass acceleration during Y-Balance Test in elderly females with good and poor visual acuity.

[Purpose] To explore the effects of good binocular visual acuity (BVA) compared to poor BVA, reach distance, task velocity, and center of mass (COM) acceleration were evaluated in elderly females performing the Y-Balance Test (YBT) using a cross-sectional design. [Subjects and Methods] A total of 13 participants had BVA of ≥0.4 log of the minimum angle of resolution (logMAR) (poor BVA group), and the other 13 had BVA of ≤0.3 logMAR (good BVA group). An accelerometer was attached over participants’ L3 spinous process, and they then performed the YBT. [Results] The normalized reach distances in the three directions among the good BVA group were longer than those among the poor BVA group. The task velocity in the good BVA group was significantly higher, whereas COM acceleration in the A direction was significantly lower compared with the poor BVA group. [Conclusion] Visual status must be considered when older adult individuals undergo physical therapy and functional training to ensure that healthcare professionals can better assist older adult women.

Effects of fatigue on center-of-mass acceleration during a prolonged overground run

Objective: The aim of this study was to assess for fatigue related changes in center-of-mass (COM) acceleration during a prolonged overground run in a group of healthy male runners using a tri-axial accelerometer attached to a runner’s low back. Methods: Thirty healthy male runners’ performed an eight kilometer (20 laps) overground time trial paced run on a 400 meter athletics track. Kinematic measures assessed regularly throughout the run included signal energy and acceleration impulse in the anteroposterior (AP), mediolateral (ML) and vertical (VT) directions, contact time (CT) and step frequency. A repeated measures analysis of variance comparing each data collection point to the initial was used to identify fatigue related changes. Results: Compared to initial measurement, CT significantly increased during laps six to 18 in addition to significant increases in ML signal energy and decreases in AP impulse identified from lap four to 20. Conclusion: A tri-axial accelerometer was able to identify changes in ML and AP COM acceleration measures plus a runner’s CT indicating fatigue was impacting a runner throughout a prolonged run. Limited changes in VT acceleration measures were identified suggesting biomechanical fatigue related running changes predominately occur in the horizontal plane. Future research investigating the effects of fatigue on running should use frequent and regular data collection to identify fatigue related running changes.

Probing stellar binary black hole formation in galactic nuclei via the imprint of their center of mass acceleration on their gravitational wave signal

Multi-frequency gravitational wave (GW) observations are useful probes of the formation processes of coalescing stellar-mass binary black holes (BBHs). We discuss the phase drift in the GW inspiral waveform of the merging BBH caused by its center-of-mass acceleration. The acceleration strongly depends on the location where a BBH forms within a galaxy, allowing observations of the early inspiral phase of LIGO-like BBH mergers by the Laser Interferometer Space Antenna (LISA) to test the formation mechanism. In particular, BBHs formed in dense nuclear star clusters or via compact accretion disks around a nuclear supermassive black hole in active galactic nuclei would suffer strong acceleration, and produce large phase drifts measurable by LISA. The host galaxies of the coalescing BBHs in these scenarios can also be uniquely identified in the LISA error volume, without electromagnetic counterparts. A non-detection of phase drifts would rule out or constrain the contribution of the nuclear formation channels to the stellar-mass BBH population.

Comparison of the COM-FCP inclination angle and other mediolateral stability indicators for turning

BackgroundStudies have shown that turning is associated with more instability than straight walking and instability increases with turning angles. However, the precise relationship of changes in stability with the curvature and step length of turning is not clear. The traditional center of mass (COM)-center of pressure (COP) inclination angle requires the use of force plates. A COM-foot contact point (FCP) inclination angle derived from kinematic data is proposed in this study as a measure of the stability of turning.MethodsIn order to generate different degrees of stability, we designed an experiment of walking with different curvatures and step lengths. Simultaneously, a novel method was proposed to calculate the COM-FCP inclination angles of different walking trajectories with different step lengths for 10 healthy subjects. The COM-FCP inclination angle, the COM acceleration, the step width and the COM-ankle inclination angles were statistically analyzed.ResultsThe statistical results showed that the mediolateral (ML) COM-FCP inclination angles increased significantly as the curvature of the walking trajectories or the step length in circular walking increased. Changes in the ML COM acceleration, the step width and the ML COM-ankle inclination angle verified the feasibility and reliability of the proposed method. Additionally, the ML COM-FCP inclination angle was more sensitive to the ML stability than the ML COM-ankle inclination angle.ConclusionsThe work suggests that it is more difficult to keep balance when walking in a circular trajectory with a larger curvature or in a larger step length. Essentially, turning with a larger angle in one step leads to a lower ML stability. A novel COM-FCP inclination angle was validated to indicate ML stability. This method can be applied to complicated walking tasks, where the force plate is not applicable, and it accounts for the variability of the base of support (BOS) compared to the COM-ankle inclination angle.