Spatiotemporal Gait Asymmetry Across the Lifespan: A Cross-Sectional Study in Adults

Introduction

Walking is defined as a method of locomotion involving the use of two legs alternately to provide both support and propulsion. The pattern of how a person walks is called gait. Normal gait is described as a series of rhythmical, alternating movements of the trunk and limbs which result in the forward progression of the centre of gravity and the body. Gait cycle has been defined as “The time interval between two successive occurrences of one of the repetitive events of walking” (heel strike to toe off).^1,2

The first mention of the manner of walking was made by Aristotle in 384-322 BCE and further progress in 1608-1679 was made by Giovanni Borelli, an Italian physiologist, physicist and mathematician who introduced a mathematical and experimental method of analysing human walking.³ Gait analysis is a method for identifying biomechanical abnormalities in the gait cycle. Gait analysis plays a pivotal role in assessing and diagnosing various musculoskeletal and neurological conditions. It provides clinicians and researchers with quantitative data on an individual's walking patterns.³

Walking is a fundamental human motor skill that involves a complex interplay of neuromuscular and biomechanical factors. The definition of gait indicates an important characteristic of gait i.e., rhythmicity (symmetry). Achieving a harmonious and symmetrical gait pattern is essential for efficient and stable locomotion.

Gait symmetry is considered as an indicator of normal gait. Symmetry is defined as “correspondence of body parts in size, shape, and relative position, on opposite sides of a dividing line”.^4,5 In this context, gait symmetry means identical movement of right side of the body to the left side in both space and time.^6,7 Whereas gait asymmetry means that movement of right side of the body is different to the left side with respect to both space (Spatial) and time (Temporal). This asymmetry in healthy individuals was attributed to the natural functional differences between the lower extremities. These functional differences were assumed to be due to contribution of each extremity in carrying out the tasks of propulsion and control during walking in healthy individuals.^4,8

Understanding the normal variations in gait asymmetry across the lifespan is crucial for distinguishing between typical age-related changes and pathological gait patterns. Asymmetry in gait can be influenced by various factors, including musculoskeletal structure, neuromuscular control, and aging. Therefore, establishing normative values for spatiotemporal gait asymmetry in healthy individuals spanning a wide age range is significant. The aim of the current study was to determine normative values for spatiotemporal gait asymmetry in a heterogeneous population of asymptomatic people between the ages of 20 and 79 years. This study attempted to explain how these patterns evolve over the course of the lifespan by systematically analysing gait patterns across various age groups.

The results of this study may deepen our grasp of the normal variations in gait asymmetry and serve as a benchmark for evaluating disordered gait. This study aids in the development of normative values, assisting health care professionals in making well-informed clinical decisions and helping the early identification of gait disorders in people of all ages.

Materials and Methods

Sample size was calculated based on the study by Yogev et al. (2007)⁹ that revealed the mean swing time amongst the normal to be 0.40 (SD= 0.04). Based on the above findings of the study, assuming population mean to be 0.417 and keeping the power of the study at 95% and with an alpha error of 5%, it was estimated that 72 normal healthy individuals need to be included in the study for Phase 1. This 72-sample size was divided into six groups (20-29 years, 30-39 years, 40-49 years, 50-59 years, 60-69 years, 70-79 years) having 12 subjects in each group.

Small sample 100(1−α)%100(1−α)% confidence interval for a population mean:

This formula deduced n= 12

Total sample size = n x (no of class intervals)

                                      = 12 x 6

                                      = 72

The inclusion criteria were community-dwelling subjects who were independently ambulatory, falling within the age range and having Mini Mental Status Examination (MMSE) scores > 24 were included in the study.

The exclusion criteria used were, neurological deficits that affect the gait (stroke, multiple sclerosis, etc.), known cases of ischemic heart disease or any cardiovascular disease which might alter the gait, moderate and severe language/cognitive deficits that might limit the informed consent and affect the gait (MMSE> 24) and orthopaedic disorders like an acute episode of OA knee, or hip which might alter gait, painful conditions of lower limbs such as neuralgia, diabetic neuropathies, etc.

The study received institutional ethical clearance, and voluntary participation was ensured through informed written consent from each participant, as outlined in Annexure 1 (supplementary files). The consent forms detailed the study's objectives, procedures, potential risks, and participant rights

Procedure

Subjects were categorized into six groups by decades, each comprising 12 individuals. Screening involved the John Hopkins fall risk questionnaire, clinical frailty scale, Mini Mental Status Examination (MMSE), and medical history. Vital signs (blood pressure, SpO2, pulse) were assessed in lying, sitting, and standing positions, as depicted in Figure 1. Gait assessment was done using GaitRite (A portable single layer pressure sensitive walkway measuring gait parameters). Subjects walked a designated path three meters forward and two meters afterward to consider acceleration and deceleration. After a non-recorded familiarization walk, participants performed three recorded walks at their preferred speed for spatial and temporal parameter analysis (Figure 2).

Data Processing

Central Tendency

All the parameters were continuous in nature, and were processed in terms of mean and standard deviation.

Asymmetry

For the purpose of this study, asymmetry was divided into:

Limb asymmetry: It was defined as the difference between the variables of the right and left limbs.

Gait asymmetry: The average of the differences between the two sides across the three trials was considered for quantification of gait asymmetry.

Identifying symmetric and asymmetric parameters consisted of three steps:

1. The difference between the right and left limbs for all the parameters was calculated for identifying consistency across three trials.
2. If the differences between the parameters in all three trials were zero, then those parameters were considered symmetric.
3. If the differences between the left and right limb parameters were different across all three trials, then they were considered asymmetric.

Temporal parameters: A total of six temporal parameters were measured.

Symmetrical: Step time, Cycle time

Asymmetrical parameters: Single support, Double support, Swing, and Stance all in % of gait cycle.

Results

Table 1 indicates more females in the 30-39 and 50-59 years age groups, while males dominated the 70-79 years age group. The 20-29, 40-49, and 60-69 years age groups showed an equal gender distribution. Overall, the study comprised a greater number of female subjects (38) than males (34). Younger mean age for each category, with a declining trend observed in height, weight, and limb length across age groups, suggest reductions in these measures as age increases in the sample population.

Spatial parameters: All the three parameters were asymmetrical across the age groups. The three spatial parameters measured in this study were step length, stride length and base of support measured in centimetre

Table 2 establishes asymmetry (normative data) for spatial parameters across all the age groups in all the three parameters from 20-79 years. In the younger age groups (20-49 years), step length difference increased until 40-49 years, plateaued at 50-59 years, and decreased thereafter. Stride length and H-H base of support differences consistently increased across all age groups from 20 to 79 years, with a reduction observed after 59 years. Table 3 establishes asymmetry (normative data) for temporal parameters across all the age groups from 20-79 years. Symmetry was noted in mean differences between left and right step time and cycle time, both measuring 0, indicating temporal symmetry. From 20 to 49 years, a reduction in single support, swing, and stance (% of Gait Cycle) implies a decrease with age. In contrast, double support exhibited a plateau from 50 to 79 years, remaining asymmetrical across age groups, with maximum asymmetry observed in the 50-59 and 60-69 age groups.

Table 4 reveals a decrease in the distance covered until the age of 50-59 years, followed by a linear increase in the 60-69 and 70-79 years age groups. Ambulation time exhibited a linear increase. Velocity generally decreased, except for a rise at 70-79 years. Mean normalized velocity remained consistent across age groups. Cadence remained constant until 49 years, decreasing thereafter with a slight increase at 70-79 years.

Discussion

Human walk is considered as cyclical and symmetric. Symmetry in this context means identical movements of right side of the body to the left side of the body in both space and time. But it is established that there is natural asymmetry present in normal healthy individuals due to natural functional differences between the lower extremities.⁴

The aim of the current study was to establish the normative values of spatiotemporal asymmetry in ambulatory individuals aged 20 to 79 years.

Spatial Parameters

It was observed in the results that for each age group, there was an average difference in step length between the left and right legs. The values differed between age groups, indicating that as people become older, this asymmetry increases. The mean difference was 1.42 units (with a standard deviation of 0.97) in the 20-29 years age group and 2.10 units (with a standard deviation of 1.3) in the 70-79 years age group.

This indicates that there was increase in asymmetry as age increased. This increase in asymmetry among older adults could be because, as people age, they tend to experience muscle atrophy (loss of muscle mass) and weakness. This can affect the ability to generate equal force and power with both legs, leading to differences in step lengths. Weaker muscles may result in compensatory movements to maintain balance during walking.¹⁰ Aging often leads to joint degeneration, including conditions like osteoarthritis. Degenerated joints can limit the range of motion and create discomfort or pain during movement. Individuals may alter their gait patterns to accommodate joint issues, leading to step length discrepancies and stride length discrepancy.¹¹

The study findings revealed a trend of increasing stride length asymmetry with age, but a subtle reduction in this asymmetry was observed in individuals aged 30- 39 and 40-49 years. Similar trends were observed in the heel-to-heel base of support, with a reduction in asymmetry observed during the 30-39 age group. These observations suggest a potential transition phase from young adulthood to middle age, which may impart subtle changes in an individual's gait pattern.

This transitional phase could be characterized by increased caution during walking, potentially contributing to the observed reduction in asymmetry. It signifies a period of gait and motor control maturation, where individuals refine and optimize their walking patterns. This maturation process may play a pivotal role in mitigating asymmetry during the 30-39 years age range, enhancing overall gait stability and consistency. These findings offer valuable insights into the dynamic nature of gait patterns across different stages of adulthood and underscore the significance of considering the transitional phase in understanding gait asymmetry dynamics.¹²

Temporal Parameters

In this study, it was observed that cycle time and step time were consistently symmetric parameters, not affected by age, speed of walking, etc. This suggests that to maintain the cyclicity of the gait, the body tends to adjust and adapt its step time and cycle time. Step time and cycle time are independent parameters and are indicative of gait being normal. Since there was no difference between the age groups, it could be an index of symmetry. An altered cycle time could potentially cause fall risk as the cyclicity of gait which is a fundamental feature of gait is compromised. In this study, it was observed that step time was consistently symmetrical and this could be to reduce the energy cost of walking since asymmetric step time increases the energy cost of walking. Stenum et al., conducted a study assessing the energy cost of asymmetric step time and observed that step time asymmetry is adaptable and can be changed volitionally according to the demands of the body.¹³

Ellis et al., conducted a study to evaluate the metabolic cost of asymmetric step time and observed that when the step time becomes asymmetric, there is an increase in metabolic cost compared to when the step time remains symmetric.¹⁴ The body tries to keep the step time symmetric to maintain the cyclicity of the gait and reduce the metabolic cost.

The study revealed a reduction in asymmetry in the mean difference between single support and swing phases of gait. These findings could be attributed to the Hemispheric Asymmetry Reduction in Older Adults (HAROLDS) model, which suggests that older adults may exhibit reduced motor asymmetry by engaging bilateral networks in their brains.¹⁵ This reduced asymmetry might serve as a compensatory mechanism during motor tasks such as walking.

The study observed a decrease in the stance phase duration as a percentage of the gait cycle, indicating that older individuals tended to adopt a faster walking velocity and cadence.¹⁶ However, it is important to consider that this increased pace may be influenced by a performance effect, as the elderly participants appeared to be enthusiastic about performing well.

In terms of double support, the data showed a plateau in this parameter after the age of 50 and up to 79 years. Given that the study focused on a healthy elderly population with no comorbidities, we can infer that the sample was composed of individuals who were in good health and not significantly concerned about the risk of falling.

The highest degree of asymmetry in all temporal parameters was observed in the age groups of 50-59 and 60-69 years. This suggests that these age groups are in a transitional phase where motor control strategies and patterns are undergoing modifications, leading to more pronounced left-to-right differences.

In summary, the study's findings indicate that older individuals tend to adopt a faster walking pace, with a potential influence of a performance effect. The plateau in double support suggests a lack of fear of falling among the healthy elderly participants. The increased asymmetry observed in the transitional age groups highlights changes in motor control strategies during this phase of aging.

The primary objective of this study was to assess the extent of asymmetry present in various spatiotemporal parameters across different age groups within a population of healthy individuals. This asymmetry index value serves as a valuable tool for distinguishing normal gait from pathological gait. Specifically, if the calculated asymmetry index surpasses the established threshold value, it signifies the presence of pathological gait. Furthermore, this index aids in pinpointing the specific parameters affected, providing essential information for extrapolating the underlying causes of the observed pathology.

Conclusion

This study explored the quantification of asymmetry among the spatiotemporal parameters across the age groups ranging 20-79 years. All the three spatial parameters were asymmetrical and among temporal parameters, step time and cycle time were symmetrical and the other four were asymmetrical. This study shows the interaction of asymmetry and other parameters during normal walk and pilot’s the values of asymmetry that could be as considered normal.

Sources of support

None

Conflict of Interest

None