Abstract
[Purpose] This study aimed to determine whether a common left-right asymmetry exists in frontal plane movement during gait and to explore its relationship with resting standing posture. [Participants and Methods] Twenty-five healthy adult male participants with no history of surgery were assessed during standing and gait using a three-dimensional motion analysis system. The maximum lateral movement of the trunk and center of mass, peak of the vertical ground reaction force, and lateral position of the center of pressure were compared between the left and right stance phases. The relationship between asymmetry in standing posture and gait was also evaluated. [Results] Most participants exhibited a leftward thoracic deviation relative to the pelvis while standing. During gait, lateral movement of the center of mass, first peak of the vertical ground reaction force, and lateral position of the center of pressure were all significantly greater during the left stance phase compared with the right. Additionally, greater leftward thoracic deviation in the standing posture was associated with larger asymmetry in lateral trunk and center of mass movement during gait. [Conclusion] A consistent left-right asymmetry was observed in both resting standing posture and gait. Leftward thoracic deviation in standing appears to shift the center of mass to the left during gait, potentially contributing to inefficient gait patterns.
Keywords: Standing posture, Gait, Left-right asymmetry
INTRODUCTION
In clinical gait observations, we often encounter individuals with left-right asymmetry in trunk movement. The degree of left-right asymmetry varies from person to person. However, the greater the deviation of the trunk posture on the frontal plane is, the more pronounced the left-right asymmetry tends to be. Regarding this deviation of trunk posture, our research group has revealed that the thorax of many healthy adults is shifted to the left relative to the pelvis1,2,3). Previous studies4,5,6) that investigated the morphological and functional roles of the left and right legs in upright posture and gait reported that the left leg has a higher support capacity than does the right leg. Moreover, the left leg primarily contributes to maintaining an upright posture and functions as a supporting leg during stance and turning movements, whereas the right leg plays a leading role in initiating steps and controlling directional changes during gait. Based on these findings, it is assumed that there is a common left-right asymmetry in the movement on the frontal plane during gait. The first objective of this study is to confirm whether there is a common left-right asymmetry in the maximum lateral movement of the trunk and center of mass (COM) during gait, the peak value of the vertical component of the ground reaction force (vGRF), and the lateral position of the center of pressure (COP).
In addition, Perry et al. state that the passenger, which consists of the head and neck, trunk, pelvis, and upper limbs, accounts for approximately 70% of the mass of the whole body and the amount of muscle activity of the lower limbs, which are locomotor unit, during gait is determined by the posture of the passenger7). Since gait is a periodic continuous movement, a gait in which the long axis relationship of each body segment is disrupted can cause mechanical stress on the load-bearing joints. When the difference between the left and right lateral movements of the COM during gait is large, adjustment of the direction of travel is required at the lower limbs, which are the weight-bearing joints. In fact, Komuro et al., in two studies, have reported that people with left thoracic deviation use different ankle strategies when gait, and that this asymmetry is common to many participants2, 8). In addition, it has been reported that there is a difference between the left and right movements of the lower limb joints in the gait of patients with scoliosis9) and between the left and right trajectories of the GRF application point relative to the direction of travel10), suggesting that the deviation in spinal alignment on the frontal plane may place an abnormal load on the locomotor unit during everyday gait. In clinical practice, when the deviation in posture on the frontal plane is corrected, the left and right asymmetry of trunk movement during gait improves, and forward propulsion is improved. Therefore, we suggest that clarifying the relationship between the magnitude of deviation in trunk posture during resting standing and the left and right asymmetry of movement on the frontal plane during gait will be helpful for observing posture and gait in physical therapy intervention situations. Based on the above, the purpose of this study was to group participants based on the direction of lateral deviation of the thorax relative to the pelvis and clarify the relationship between the degree of deviation in trunk posture when standing at rest and the degree of left-right asymmetry in gait.
PARTICIPANTS AND METHODS
The participants were 25 healthy adult males (mean ± standard deviation; age: 25.0 ± 3.4 years, height: 170.1 ± 5.3 cm, weight: 64.4 ± 9.2 kg, body mass index: 22.2 ± 2.4 kg/m2) without surgical history. The participants were recruited through poster advertisements on campus. Since marked locomotor changes due to development or aging could affect posture and gait, the target age range for recruitment was set to 20–39 years, based on previous studies11, 12) indicating stable gait speed within this age range. The purpose of this study was fully explained to all participants; the study was conducted with their consent. This study was approved by the Bunkyo Gakuin University Ethics Committee (approval number: 2023-0013).
A three-dimensional motion analyzer, the VICON-MX (Vicon Nexus 2, Vicon Motion Systems Ltd., Oxford, UK), and six force plates (Advanced Mechanical Technology, Inc., Watertown, MA, USA) were used. Eight infrared cameras and 9.5 mm-diameter infrared reflective markers were used, and the data were captured using a computer at a sampling frequency of 100 Hz. Markers were applied to 28 points to calculate the COM (front of head, back of head, acromion, lateral epicondyle of humerus, medial epicondyle of humerus, radial styloid processes, ulnar styloid processes, hip joint, medial and lateral cleft of knee joint, medial and lateral malleolus, and first and fifth metatarsal heads, all on the left and right sides), 4 points to calculate the center of the thorax (jugular notch [JN], xiphoid process [XP], spinous process of the second thoracic vertebra [Th2], and spinous process of the tenth thoracic vertebra [Th10]), 4 points to calculate the center of the pelvis (left and right superior anterior iliac spines [ASIS], and left and right superior posterior iliac spines [PSIS]), and 8 points to calculate the long axis of the foot (left and right heels, left and right first metatarsal heads, left and right second metatarsal heads, and left and right fifth metatarsal heads), totaling 44 points. Except for the head and hip joint markers, all reflective markers were directly attached to the skin to minimize skin-clothing artifacts and ensure accuracy in detecting small thoracic and pelvic motions. Measurements were taken during resting standing position and spontaneous gait.
In the resting standing posture measurement, the participants were placed in a stationary standing position with the upper limbs drooped, and the amount of lateral deviation of the thorax from the pelvis was calculated. To exclude the influence of postural changes caused by breathing, the participants were instructed to maintain a resting expiratory position for at least 5 s, and measurements were performed three times. The average of the three measurements was used as the representative value for each individual. The center of the thorax was calculated from the midpoints of the JN, XP, Th2, and Th10, and the center of the pelvis was calculated from the midpoints of the left and right ASIS and PSIS. From the three-dimensional coordinates obtained, the difference in each X-axis coordinate (center of thorax-center of pelvis) was normalized by height and defined as the amount of lateral deviation of the thorax relative to the pelvis (%BH) (Fig. 1). Positive values were defined as rightward deviation of the thorax and negative values as leftward deviation of the thorax. Furthermore, the participants were divided into the rightward and leftward deviation groups. In addition, the vertical components of GRF for each side were calculated in a resting standing position and normalized to body weight (%BW).
Fig. 1.
The amount of lateral deviation of the thorax relative to the pelvis in the standing position was defined as the difference in the X-axis coordinates between the center of thorax and the center of pelvis normalized by height (unit: %BH).
ASIS: superior anterior iliac spines; PSIS: superior posterior iliac spines; JN: jugular notch; XP: xiphoid process; Th2: spinous process of the second thoracic vertebra; Th10: spinous process of the tenth thoracic vertebra.
Regarding gait measurement, the starting point was adjusted for each participant such that the fifth step or later passed over the force plates. The participants were instructed to gait toward a landmark in front of the starting point. The vGRF was extracted from the left and right stance phases, and three measurements were averaged to obtain the representative values for each individual after normalizing the time to 100%. The positions of the COM, center of the thorax, center of the pelvis, and their respective coordinates were obtained from the body surface markers. The COM was calculated from 3D coordinate data using a rigid body link model that divided the body into 12 segments based on Japanese body data: head, trunk, right and left upper arms, right and left forearms, right and left thighs, right and left lower legs, and left and right feet11). The maximum lateral shifts in the COM, center of the thorax, and center of the pelvis in the frontal plane (X-axis coordinates) during the left and right stance phases were calculated based on the initial contact position for each trial and normalized by height (%BH). The polarity was set to “+” for a lateral shift to the stance leg and “−” for a lateral shift to the swinging leg (Fig. 2). The plantar coordinates were defined by the heel, first metatarsal head, second metatarsal head, and fifth metatarsal head, and the straight line from the heel as the origin to the second metatarsal head was defined as the long axis of the foot (Y-axis). The lateral position of the COP relative to the foot axis at the first peak of vGRF (mm) was calculated, and polarity was expressed as + for movement outside (stance side) the foot axis and − for movement inside (swing side) the foot axis (Fig. 3). The maximum lateral movement of the COM, center of the thorax, and center of the pelvis, and the difference between the left and right lateral positions of the COP (right stance phase − left stance phase) were calculated. The obtained GRF data were normalized to body weight, and the first and second peak values of the vGRF were calculated (%BW). All data were analyzed using Body Builder software Version 3.6.4 (Vicon Motion Systems, Ltd., Oxford, UK).
Fig. 2.
The calculation method of the maximum lateral shift of the center of mass (COM), center of the thorax, and center of the pelvis (unit: %BH) during gait. Maximum lateral shift is calculated based on the initial contact position. The left-right asymmetry index is calculated as the right stance phase minus the left stance phase.
Fig. 3.
The calculation method of the lateral position of center of mass (COM) at the first vertical ground reaction force (vGRF) peak (unit: mm) during gait. The lateral position of the COP was calculated relative to the foot longitudinal axis (heel – second metatarsal head), with positive values indicating a more lateral position.
Statistical analysis was performed after confirming normality using the Shapiro–Wilk test. The mean and 95% confidence interval (95% CI) of the lateral deviation of the thorax from the pelvis in the standing position were used. Asymmetry in the load in the standing position was investigated by comparing the left and right vGRF using a paired t-test. The maximum lateral shifts in the COM, center of the thorax, center of the pelvis and the first and second peak value of vGRF and the lateral COP position at the first peak of vGRF during gait were compared between the right and left stance phases using a paired t-tests or Wilcoxon signed rank-sum tests. The relationship between the amount of lateral thoracic deviation during quiet standing and the left-right asymmetry index of gait was examined using Pearson’s product-moment correlation coefficient. All analyses were performed on all participants (n=25) and the group with left thoracic deviation (n=21). The right thoracic deviation group (n=4) was not evaluated as a separate group due to the small number of participants. SPSS Statistics 30 software for Windows (IBM Corp., Armonk, NY, USA) was used for the analysis, with significance set at 0.05.
RESULTS
Table 1 shows information on the participants and their left-right asymmetry in the standing position. The mean deviation of the thorax from the pelvis in the standing position was −0.3 ± 0.4%, 95% CI −0.5 to −0.1%, indicating that the thorax was deviated to the left relative to the pelvis. The vGRF was significantly larger on the left side than on the right (p<0.01).
Table 1. The participants information and left-right asymmetry in the standing position.
| All participants | Left lateral deviation group | Right lateral deviation group | ||||
| (n=25) | (n=21) | (n=4) | ||||
| Mean ± SD | 95% CI | Mean ± SD | 95% CI | Mean ± SD | 95% CI | |
| Age (years) | 25.0 ± 3.4 | 23.6 to 26.4 | 25.0 ± 3.5 | 23.4 to 26.6 | 25.0 ± 2.9 | 20.3 to 29.7 |
| Body height (cm) | 170.1 ± 5.3 | 167.9 to 172.3 | 170.2 ± 5.1 | 167.8 to 172.5 | 169.6 ± 7.3 | 158.0 to 181.2 |
| Body weight (kg) | 64.4 ± 9.2 | 60.6 to 68.2 | 64.2 ± 9.3 | 59.9 to 68.4 | 65.6 ± 9.7 | 50.2 to 81.0 |
| Body Mass Index (kg/m2) | 22.2 ± 2.4 | 21.2 to 23.2 | 22.1 ± 2.5 | 21.0 to 23.2 | 22.7 ± 2.2 | 19.2 to 26.3 |
| Lateral deviation of the thorax (mm) | −5.2 ± 6.9 | −8.1 to −2.4 | −7.1 ± 5.7 | −9.7 to −4.5 | 4.4 ± 3.3 | −0.9 to 9.7 |
| Lateral deviation of the thorax (%BH) | −0.3 ± 0.4 | −0.5 to −0.1 | −0.4 ± 0.3 | −0.6 to −0.3 | 0.3 ± 0.2 | 0.0 to 0.6 |
| Left vertical GRF (%BW) | 50.0 ± 2.7 | 48.8 to 51.1 | 50.4 ± 2.5 | 49.3 to 51.6 | 47.6 ± 3.0 | 42.8 to 52.4 |
| Right vertical GRF (%BW) | 46.2 ± 2.7** | 45.1 to 47.3 | 45.9 ± 2.8** | 44.7 to 47.2 | 47.6 ± 2.3 | 44.0 to 51.2 |
**Significantly different (p<0.01) from left vertical GRF.
SD: standard deviation; CI: confidence interval; GRF: ground reaction force; BH: body height; BW: body weight.
Table 2 shows the maximum lateral shifts in the COM, center of the thorax, and center of the pelvis during the left and right stance phases, as well as the lateral COP position, and vGRF peak value. The mean lateral shift in the COM was significantly greater in the left stance phase than in the right for all participants and in the left lateral deviation group (p<0.05). No significant differences were observed in the lateral shift in the centers of the thorax and pelvis; however, the results showed a possible trend toward greater leftward shift during the left stance phase in both groups. The p-values for the thorax center were 0.104 in all participants and 0.068 in the left lateral deviation group; for the pelvis center, they were 0.089 and 0.074, respectively. The lateral COP position at the first peak of vGRF was significantly more lateral in the left stance phase, and the first peak of vGRF was significantly higher in the left stance phase (p<0.01).
Table 2. Left-right comparison of maximum lateral shift, value of GRF and COP position during the stance phase.
| All participants | Left lateral deviation group | Right lateral deviation group | |||
| (n=25) | (n=21) | (n=4) | |||
| Mean ± SD | Mean ± SD | Mean ± SD | |||
| Maximum lateral shift in COM | Left stance phase | 1.3 ± 0.5 | 1.4 ± 0.5 | 1.1 ± 0.5 | |
| (%BH) | Right stance phase | 1.1 ± 0.4* | 1.1 ± 0.4* | 1.0 ± 0.4 | - |
| Left-right difference | −0.3 ± 0.6 | −0.3 ± 0.6 | |||
| Maximum lateral shift in the center of | Left stance phase | 1.7 ± 0.6 | 1.7 ± 0.6 | 1.7 ± 0.5 | |
| the thorax (%BH) | Right stance phase | 1.5 ± 0.5 | 1.4 ± 0.5 | 1.7 ± 0.5 | - |
| Left-right difference | −0.2 ± 0.7 | −0.3 ± 0.7 | |||
| Maximum lateral shift in the center of | Left stance phase | 1.6 ± 0.6 | 1.7 ± 0.6 | 1.3 ± 0.4 | |
| the pelvis (%BH) | Right stance phase | 1.3 ± 0.5 | 1.4 ± 0.5 | 1.1 ± 0.6 | - |
| Left-right difference | −0.3 ± 0.7 | −0.3 ± 0.7 | |||
| COP position at the first vertical GRF peak | Left stance phase | 2.7 ± 4.7 | 2.1 ± 4.5 | 5.8 ± 4.7 | |
| (mm) | Right stance phase | −1.8 ± 4.7** | −1.9 ± 4.2** | −0.8 ± 7.5 | - |
| Left-right difference | −4.4 ± 4.6 | −4.0 ± 4.8 | −6.6 ± 3.3 | ||
| First peak value of the vertical GRF | Left stance phase | 113.8 ± 8.0 | 113.8 ± 8.5 | 113.5 ± 4.6 | |
| (%BW) | Right stance phase | 111.5 ± 8.0** | 111.2 ± 8.7** | 112.6 ± 3.1 | - |
| Second peak value of the vertical GRF | Left stance phase | 106.9 ± 6.1 | 106.6 ± 6.5 | 108.9 ± 3.1 | |
| (%BW) | Right stance phase | 106.5 ± 5.5 | 106.1 ± 5.7 | 108.3 ± 5.2 | - |
*Significantly different (p<0.05) from left stance phase, **Significantly different (p<0.01) from left stance phase.
Mean ± SD, BH: body height; BW: body weight; COM: center of mass; COP: center of pressure; GRF: ground reaction force; SD: standard deviation.
Table 3 shows the relationship between the lateral deviation of the thorax in the standing position and the asymmetry index of gait in the left lateral deviation group and all participants. In particular, in the group with left thoracic deviation, there was a positive correlation, in which the larger the left deviation of the thorax, the greater the asymmetry (left stance phase>right stance phase) in the lateral shift in the COM, center of the thorax, and center of the pelvis (p<0.05).
Table 3. Correlation coefficients between the lateral deviation of the thorax in the standing position and the asymmetry index during gait.
| All participants | Left lateral deviation group | ||
| (n=25) | (n=21) | ||
| Lateral deviation of the thorax (%BH) | |||
| Maximum lateral shift in COM (%BH) | Left stance phase | −0.38 | −0.37 |
| Right stance phase | 0.06 | 0.22 | |
| Left-right difference | 0.36 | 0.47* | |
| Maximum lateral shift in the center of the thorax (%BH) | Left stance phase | −0.31 | −0.45* |
| Right stance phase | 0.21 | 0.15 | |
| Left-right difference | 0.40* | 0.52* | |
| Maximum lateral shift in the center of the pelvis (%BH) | Left stance phase | −0.46* | −0.42 |
| Right stance phase | 0.03 | 0.23 | |
| Left-right difference | 0.38 | 0.51* | |
| COP position at the first vertical GRF peak (mm) | Left stance phase | 0.31 | 0.27 |
| Right stance phase | 0.29 | 0.34 | |
| Left-right difference | −0.02 | 0.14 | |
| First peak value of the vertical GRF (%BW) | Left stance phase | 0.27 | 0.38 |
| Right stance phase | 0.29 | 0.32 | |
| Second peak value of the vertical GRF (%BW) | Left stance phase | 0.14 | 0.09 |
| Right stance phase | 0.10 | 0.07 | |
*Significant correlation (p<0.05); BH: body height; BW: body weight; COM: center of mass; COP: center of pressure; GRF: ground reaction force.
DISCUSSION
In total, 84% of our participants had leftward deviation of the thorax from the pelvis in the standing position. Furthermore, vGRF was significantly higher on the left side. These results and those of previous studies1, 2) confirm that many healthy adults have a bias in trunk posture in the frontal plane. Furthermore, we examined whether there was asymmetry in the lateral shift in the COM during gait and found that the maximum shift to the stance side was larger in the left stance phase than in the right. In this study, the lateral shift in the COM was calculated as the amount of shift in the X-axis coordinates in absolute space based on the position at the initial contact. In other words, the magnitude of lateral shift (left stance phase>right stance phase) indicated that the COM tended to shift slightly to the left relative to the direction of movement throughout the left and right stance phases. Furthermore, a significant difference was found in the first vGRF peak value and the lateral COP position at that time, with the left stance phase being greater than the right stance phase. The first peak of vGRF is said to occur between the load response phase and the mid-stance phase in order to fulfill the purpose of load acceptance, shock absorption, and response to single-leg support in the early stance phase7, 13). Because the load at this time is greater on the left side, and the COP relative to the foot’s long axis is also in the lateral position, it is possible that in most people, the left load is dominant not only when standing at rest, but also during the first half of the stance phase, and that the left foot may land in a relatively supinated position. This suggests that the mechanisms of shock absorption and load response differ between the left and right sides.
In addition, the results of an investigation into the relationship between the magnitude of trunk posture deviation and the left-right difference in movement in the frontal plane during gait showed that, particularly in the group with left lateral thoracic deviation, the greater the amount of left lateral deviation of the thorax during standing at rest, the greater the left-right difference in the amount of lateral movement of COM, the center of the thorax, and pelvic center, with left stance phase being greater than right stance phase (p<0.05). Based on the correlation coefficients in Table 3, this is thought to be a result that particularly reflects the characteristics of trunk movement during the left stance phase. This explains that the greater the amount of left lateral deviation of the thorax relative to the pelvis during resting standing was, the greater the amount of leftward movement of the center of the thorax (p=0.043) and center of the pelvis (p=0.059) during gait. Excessive left lateral deviation of the thorax is thought to tend to accentuate the movement of the trunk and COM to the left, which is the side of the upper body mass deviation. In this way, to propel oneself towards a destination while having a deviation in the frontal plane of the upper body mass, steering with trunk movement and lower limb joint movement during the left and right stance phases becomes necessary, which might result in inefficient gait. Regarding the first vGRF peak value and lateral COP position, which did not show a significant correlation with the amount of lateral thoracic deviation relative to the pelvis, it has been reported that vGRF is affected by foot morphology14) and the range of motion of the subtalar joint15), and that lateral COP position is affected by foot morphology16) and the left-right asymmetry of the lower thoracic shape8). Therefore, we suggest that no direct relationship was found with the deviation of trunk posture in the frontal plane. The common causes of left-right asymmetry will require further verification in the future. Although limb dominance was not assessed in this study, future research should investigate how dominant hand or leg may influence left-right gait asymmetry.
The limitations and future challenges of this study include the small number of participants in the right lateral thoracic deviation group, which did not allow for further investigation or analysis. The inclination angle of the pelvis and leg length difference were not taken into account when calculating the amount of lateral thoracic deviation relative to the pelvis. In addition, the lateral bending and inclination of the trunk were not taken into account in the frontal plane movement of gait. Furthermore, this study clarified the relationship between bias in trunk posture when standing at rest and left-right asymmetry indexes in gait. In the future, further verifying the left-right asymmetry of trunk posture and trunk movement during gait through quantitative and qualitative evaluations will be necessary. Additionally, examining, in more details, the relationship between left-right characteristics of gait and propulsive force from the perspective of kinetics, such as muscle activity and joint moment will also be necessary.
In summary, the results of this study revealed that a high proportion of healthy adults exhibited consistent left-right asymmetry between trunk posture in the standing position and frontal plane movements during gait. Furthermore, in the group with leftward thoracic deviation, a greater degree of leftward thoracic deviation in the standing position was associated with a greater left-right asymmetry in the lateral movement of the trunk and COM. Clinically, the assessment of trunk posture deviations in the standing position may serve as an indicator of left-right asymmetry in frontal plane movements during gait.
Preprint publication
Mohara A, Homma Y, Komuro N, et al.: Relationship between lateral deviation of the thorax in the standing position and asymmetry in lateral shift in the body center of gravity and propulsive force during gait. SSRN, Preprint posted online on August 21, 2024. Doi: https://doi.org/10.2139/ssrn.4918456
Funding
This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
Conflict of interest
None.
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