Ferraro, Richard A. MPT, PhD; Pinto-Zipp, Genevieve PT, EdD; Simpkins, Susan PT, EdD; Clark, MaryAnn EdD
Recent studies of population trends indicate a rising percentage of older adults in the United States with the greatest percentage of growth in the age group comprising people 65 years and older.1 Included in that growth are those older than 85 years who are expected to increase by 7.3 million by the year 2020.2 Despite this population trend, adults 65 years and older are maintaining higher levels of activity than previous generations.3
Although older adults are more active than ever, they remain susceptible to age-related declines that occur in the body. For example, overall strength decreases due to various age-related changes in the human body. At the cellular level, there is evidence that cross-sectional area of muscles decreases with age.4 Ultimately, changes at the microscopic level contribute to a progressive decline in isolated, maximum voluntary contractions as well as muscular endurance in the lower extremity. As a result, there is a progressive decrease in the efficiency of gait between the sixth and ninth decades of life.5
In addition to a decline in strength associated with advancing age, numerous studies have documented a progressive loss in overall joint range of motion (ROM) due to an increase in noncontractile tissue, decreased muscle length, and more dense capsular tissue around joints.6,7 Other causes of age-related loss of joint motion include less than optimal joint alignment and pain due to osteoarthritic changes.8
Age-related physiological changes are just one possible explanation for the differences in gait between younger and older adults. Researchers generally agree, however, that older adults prioritize stability whereas younger adults seek to optimize forward progression, mobility and efficiency while walking.9–11 Gait patterns of younger adults on level ground are characterized by phases of instability that allow for forward progression and lateral shifting of the body's center of mass with each step.12,13 When compared to younger adults on level ground, older adults increase their cadence, decrease their velocity, take shorter steps, and increase the percentage of the gait cycle in double support to increase stability while they walk.9,14 However, it is not clear whether this shift in priority is the cause or the result of the spatiotemporal and kinematic differences observed when older adults walk on level ground. Therefore, although results from previous studies on level ground walking are both informative and descriptive, these findings may not be generalized to gait patterns on alternate surfaces such as inclines.
In comparison to level ground walking, the ability to walk on inclines requires a different lower extremity motor pattern. This motor pattern requires increased force output by lower extremity musculature and increased range of motion particularly at the ankle.15,17 Relative to walking on level ground, motor patterns of younger healthy participants during incline walking show increased torque at the hip and ankle joints which act to simultaneously stabilize each of these joints and propel the mass of the body upward.18–20
Generally, as the slope of the incline increases a resultant decrease in cadence and velocity occurs, while both step length and stride length increase.21–23 Data also suggest that there is a larger excursion of movement of the center of mass (COM) while walking up and down inclines relative to level ground. This larger COM excursion is associated with greater balance requirements.17 Despite strong evidence to suggest the presence of different gait patterns among young healthy adults on incline surfaces when compared to level ground, there is no evidence to confirm that similar changes also occur in older adults.
More specifically there is a paucity of data describing how older adults negotiate inclines that are frequently encountered in the community making access into buildings and businesses such as banks, places of worship, and malls possible. On the basis of the rapid increase in the numbers of older adults in this country, the physiological decline that is associated with aging and evidence that suggests age-related changes in gait patterns on level ground, a closer analysis of older adults' walking patterns on common community surfaces such as inclines is merited. Understanding the influence of inclines on older adults walking patterns will assist clinicians in designing plans of care that incorporate effective training methods for community ambulators to meet the challenges associated with incline walking.
The purpose of this study is twofold: (1) to examine the effects of an incline surface on spatiotemporal gait parameters among older adults and (2) to identify any differences that exist between low and high fall risk participants' spatiotemporal gait parameters during level and incline walking.
A within-participant repeated-measures study design was employed.
Data collection was performed in one 40-minute session for each participant on the grounds of local adult communities and community centers in New Jersey.
Seventy-eight healthy older adults 70 years and older (mean age = 77.8, SD = 4.8, range = 70–93) without disabilities or musculoskeletal impairments were recruited for this study (Figure 1). Criteria for inclusion in this study required that participants be at least 70 years old and independent community ambulators. For the purposes of this study, an independent community ambulator was defined as anyone who could walk outside their own neighborhood but within their own town without use of an assistive device or aide from another person. Confirmation of eligibility was done via telephone call by the primary researcher before each participant was scheduled for a data collection session at one of the community centers. This phone screening included questions about age, general health, and well-being and community independence.
To determine each respondent's level of independence in the community, the University of Alabama Birmingham Life-Space Assessment Form (UAB-LSAF) was administered during this initial screening. The UAB-LSAF is a self-reported assessment tool which was read to the potential participants as their responses were noted on a coded intake form.26 The overall results from this self-reported assessment of community mobility provided a “snapshot” of a person's ability over a period of time and thus are different from many assessments that evaluate a person's maximum abilities being scored in one discreet session. The form is organized into various degrees of mobility or “life space” levels ranging from one's own bedroom (level 0) to places outside one's own town (level 5). For each life-space level, potential participants were asked how many days in a week they visited that life-space and whether they required an assistive device or aid from another person. A composite score of life-space combining components of life space attained, frequency (how many times per week they frequent these life spaces), and level of assistance (use of assistive device or aid from another) was obtained. It was determined that a minimum score of 24 on life-space level 4 (in their own town) was required to be eligible for the study. Pursuant to our study of healthy and active older adults the participants that obtained this score were generally those that traveled into their own town a minimum of 2 to 3 times per week with no assistance required. The LSAF has been validated showing high correlations with the Geriatric Depression Scale in activities of daily living, Instrumental Activities of Daily Living (IADLs), and physical and mental health performance categories.25 In addition, baseline strength and ROM measures confirmed that each participant possessed minimum physical requirements needed to perform basic everyday activities.
Participants were excluded if they (1) were diagnosed with any neurological or orthopedic condition that altered the normal observable gait sequence, (2) required assistance from another person or device during ambulation, (3) reported any visual or vestibular dysfunction that compromised balance during ambulation, and (4) scored lower than 24 on level 4 of the UAB-LSAF tool.
Before beginning data collection, the project was approved by the sponsoring university's institutional review board. Before data collection began, all participants were asked to sign the approved institutional review board informed consent form. Participants were also asked to wear comfortable walking shoes for the walking trials.
All participants were then screened by the same investigator to ensure that strength and ROM were within functional limits at the ankle and hip and thus would not impact task performance. Leg length measurements were then taken and included in each participant's GAITRite profile to normalize spatiotemporal data for leg length. Isometric strength measurements and ROM data were collected at hip and ankle joints bilaterally using the Lafayette Manual Muscle Test system using standardized testing methods.26 If limitations were noted in strength or ROM at the hip or ankle the participant was excluded from the study. Participants' knee strength and ROM were not specifically tested as the authors inferred from the participants required inclusion score on the UAB-LSAF that if limitations were present at the knee they did not hamper their functional mobility.27 Isometric strength of hip extensors and ankle dorsiflexors and plantarflexors were specifically targeted on the basis of earlier incline research that showed significant contributions from these muscle groups as participants walked on inclines similar to those used in this study.16,19
To gain an understanding of the participants' balance abilities, 2 functional balance measures, the Berg Balance Scale (BBS) and Dynamic Gait Index (DGI), were administered to each participant using protocols established in the literature.28 Alternating the initial balance test performed by each participant minimized practice and fatigue effects.
The final component of data collection consisted of 5 walking trials on both level and incline surfaces. To offset the effects of practice and fatigue the initial walking surface (level or incline) was alternated for each ensuing participant. One practice trial on each walking surface was given to each participant to allow participant accommodation to the surface and angle of incline. A second GAITRite (CIR Systems Inc, Havertown, Pennsylvania) was placed in front of the incline surface to determine if any preparatory stepping patterns existed prior to encountering the primary GAITRite that was placed on the ramp. Before each walking trial began, verbal instructions were given to each participant to walk at a “comfortable” pace over the entire electronic walkway.
Each participant started walking 2 m before recording began to ensure a steady state of walking speed.29 They were then asked to walk at a “comfortable” self-selected pace over the electronic walkway and continue beyond the end of the mat toward a visual cue placed on a 5 × 5 turn platform beyond the GAITRite recording surface.30,31 During the incline trials, the GAITRite mat was positioned approximately one meter beyond the start of the incline to avoid recording the initial accommodating footfalls that occur as the walking surface changed. This location was marked to ensure the same position of the GAITRite relative to the incline for all trials. Regardless of walking surface, participants were given a 30-second rest break after each trial. In addition, between each set of five trials and before they walked over the alternate surface (level or incline) each participant received a one minute rest break. These rest breaks and the allocation of random starting surfaces was designed to minimize the effects of learning and fatigue.
The BBS was used to assess static and dynamic balance. To ensure that each participant understood all BBS items, both verbal instructions and demonstration were provided before each test item as previously described.28 Items on the BBS range from simple mobility tasks (ie, transfers, standing unsupported) to more difficult tasks (ie, tandem stance and turning 360°). A maximum score on the BBS is a 56 with scores under 45 indicative of an increased fall risk.28 The BBS has high interrater, intrarater, and test-retest reliability with an Intraclass Coefficient (ICC) of 0.98 for all measures of consistency.28 It also has been shown to have moderate to high concurrent validity when compared to other functional measurement tests such as Fugyl-Meyer, DGI, Timed Up and Go, and the Tinnetti Balance Scale.28
Dynamic balance abilities during gait was further assessed by the DGI which was developed to document a patient's ability to modify gait in response to changing task demands in ambulatory patients with balance impairments.30 The DGI tests 8 different items including level ground walking, walking with head turns (both vertical and horizontal) and stair negotiation. Each item is scored from 0 to 3 on a Likert scale based on the level of impairment while completing the task. A maximum score is a 24 with scores under 19 indicative of increased fall risk.30 Previous studies have examined the reliability and validity of the total DGI and reported good interrater reliability (ICC = 0.98) and intrarater reliability (0.76–0.99).31 The DGI also compares favorably to the BBS with moderate but significant correlations (r = 0.71; P < .01) establishing its concurrent validity.32
The GAITRite computerized walkway system was used to collect data and measure spatial and temporal gait parameters. The walkway is portable, can be laid over any flat surface, requires minimal setup and test time, and does not require placement of any devices on the patient. As the participant walks, the system captures the geometry and the relative arrangement of each footfall as a function of time. The use of the GAITRite system is well established in the literature as a valid and reliable tool for collecting data on various aspects of gait.33–36 ICCs ranged from 0.92 to 0.99 for walking speed, cadence, step length, and step time, when comparing the GAITRite system to the Vicon system.37 Previous studies have also demonstrated good test-retest reliability among younger and older adults with ICCs between 0.82 and 0.92 for all spatial parameters, except for toe-out.35
After data collection was completed, a gait-stability ratio (GSR) was calculated by using the GAITRite values of cadence (steps/s) and dividing it by mean normalized gait velocity (m/s) to measure changes in walking velocity and step length.10 It should be noted that the GAITRite software requires bilateral leg lengths so that mean normalized gait velocity can be calculated. This is done to control for the effects of leg length on velocity. The resultant unit of measurement for GSR is steps/m and describes an individual's ability to adapt their walking pattern to perceived balance requirements.11 Recently, the GSR has been found to be a more sensitive measure of dynamic balance than either cadence or walking velocity alone. An increase in GSR represents an increased number of steps taken per unit of distance and more time spent in double support indicating less stability during an activity.10 Correlations were found to exist between GSR and the more dynamic items on the BBS, specifically items 12, 13 and 14. Item 12 (alternate stepping on a stool) was found to have a strong inverse relationship with GSR calculations (r2 = −0.54). Specifically, those who had fewer steps onto the stool had higher GSR indexes. Based on these results, researchers suggested that the weightshifting and alternate leg movement required in Item 12 strongly correlates to dynamic activities such as gait.10,11
The GAITRite system was placed on a portable modular ramp constructed out of commercial grade aluminum and met or exceeded all Occupational Safety and Health Administration's (OSHA) safety standards for wheelchair ramps (Express Ramps Inc, Dove Lane, Chattanooga, Tennessee). A 5′ × 5′ level “turn platform” was added to allow participants to comfortably turn around and ensure a constant gait speed while walking on the incline. The resultant 18-foot ramp length also met OSHA requirements rising to a sum of 3 feet. The resultant ramp was a realistic incline (averaged between residential and business requirements) often encountered by independent community ambulators in their community. The resultant 10° angle approximated the slope angles documented in previous incline studies and was above the critical threshold when gait parameters were verified to change.17,20 The ramp was constructed with handrails on both sides which were not used for support by any of the participants during the study.
To control for extraneous variables, a repeated measures design was used as each group of participants served as their own control. Data were analyzed using SPSS for Windows (version 16.0) (Statistical Package for the Social Sciences, Version 17.0, 2008: SPSS Inc, Chicago, Illinois). Mean scores were calculated for all gait parameters for each of the 5 trials for both walking surfaces. To compare differences on each walking surface, paired t tests were used to analyze means across conditions for all spatiotemporal variables. A 2 × 2 ANOVA was performed to determine differences in means among the high and low risk subgroups (as determined by the BBS and DGI) comparing their level and incline walking patterns. The level of significance was set at P = 0.05. A Tukey post hoc analysis was used to compare all possible pairwise comparisons.
A convenience sample of seventy-eight active, older adults participated in this study. Participant characteristics are presented for the entire sample in Table 1. A score of a 24 on level 4 of the UAB-LSAF describes a participant that generally frequents the town they live in on average at least one to three times per week without assistance. Demographic results for this study sample are comparable to United States census data for this age range as evidenced by females outnumbering males in this study 52 (67%) to 26 (33%).38
Step length, cadence, mean normalized velocity (MNV) and GSR values were compared for all participants between level and incline walking using paired t-tests. Results indicate significant changes in incline walking patterns for all four variables (Table 2).
On the basis of the scores obtained on the BBS and DGI, participants were then placed in subgroups. Those participants who scored below the fall risk threshold (<45) (n = 12) on the BBS were placed in the high-risk subgroup. The overall test for differences in means in the repeated-measures ANOVA was significant for step length (P = 0.01), cadence (P = ≤0.001), MNV (P = ≤0.001) and GSR (P = 0.004). When using BBS to define fall risk, the test for interaction was not significant for any of the dependent variables analyzed. In the DGI subgroup (those who scored ≤ 19) (n = 22) the overall test for differences in means was significant for step length, F1,75 = 10.98, P = 0.001, cadence, F1,75 = 4.21, P = 0.04 and MNV, F(1,75) = 5.50, P = 0.02 and GSR, F (1,75) = 1.02, P = 0.01 (Table 3). Further analysis revealed interaction effects for step length, P = 0.001, cadence, P = 0.05 and MNV, P = 0.03 (Figure 2).
It is well documented that healthy, young adults (ages 25–34) walk on inclines differently than level ground to progress the body's center of mass forward and upward against increased gravitational demands.16,37 In addition to kinematic evidence of gait changes on level ground, spatiotemporal aspects including cadence, step and stride length and velocity also change significantly on inclined surfaces.19,20 The results of this study serve to expand on the already existing incline data on younger adult participants by assessing the effects of inclines in a healthy older adult population.
Similar to studies with younger adults, cadence decreased on inclines relative to level ground walking. However, unlike younger adults who took longer strides, our results suggest that the main reason for the decrease in cadence was a change in the temporal component of each step. Therefore, as the slope increased, step time increased, and the number of steps taken in a fixed period decreased which is consistent with previous research.16,20
Older participants also decreased their step length on inclines. This adaptation suggests a shift toward increasing postural stability by ensuring the participant's center of mass remains within their base of support. Results of this study further support the notion that when balance or safety is a concern, older adults alter their walking pattern to prioritize stability.41,42 By taking smaller, more controlled steps older adults were able to compensate for reductions in dynamic balance control that naturally occurs while walking on inclines. This is a similar pattern that develops on level ground in older adults while walking on compliant surfaces or during vision-compromised gait trials.11
Older adults walked at slower speeds on inclines as compared to level ground. Decreases in step length and cadence resulted in this decrease in MNV during incline walking. Because of the vertical displacement of the body's center of mass and the increased work requirements, older adults required more time to cover the same distance when walking on an incline relative to level ground. As seen in younger adults on inclines, it is likely that the increased physiological demand and increased balance requirements contributed to an increased cycle time and slower speeds while walking on inclines.16,20 This finding is unlike the gait patterns of younger adults on inclines who were able to increase step lengths to maintain a velocity consistent with level ground.17
During incline walking, GSR increased relative to each participant's level ground stability. As a ratio of cadence and velocity measured in units of steps per meter, GSR was initially designed to provide an indication of the amount of adaptation an individual makes to increase gait stability.10 An increase in GSR reflects a decrease in step length, slower forward progression of the body's center of mass and subsequent increase in percentage of double-limb support time of the gait cycle.11 In this study, both cadence and velocity decreased but not in an equal ratio on inclines suggesting that the increase in GSR was most likely due to velocity decreasing proportionally more than cadence.
The adaptations that occurred in older adults suggest that increasing dynamic stability while walking on inclines was their primary goal. Paradoxically these changes that were made to improve stability may be less safe and efficient. By taking more steps and walking slower there is inherently more variability introduced into the gait cycle.43 In addition, by decreasing step length on an incline it may actually be more difficult to advance the weight of the body up an incline. Although, older adults were able to successfully negotiate this challenge, they may not be successful on inclines with higher grades, or less stable, more compliant walking surfaces (ie, grass, sand). Interestingly, regardless of their individual fall risk, healthy older adults' walking patterns changed significantly with very similar patterns developing on inclines relative to level ground walking.
This pattern was even more conclusive in those that were categorized as a high risk for falls. Between participants there was a main effect for fall risk for all gait parameters except for cadence. High-risk older adults, as defined by the 2 validated clinical balance measures, had shorter step lengths, walked slower and had decreased dynamic stability (higher GSRs) than the low risk subgroup on both level and incline surfaces. This is an interesting finding because all of the participants included in the study reported no falls or fear of falls and confirmed frequent and independent ambulation in and around their communities.
Several limitations in the present study have been identified. First, although the sample was large and culturally diverse, it was one of convenience. While this sample is certainly representative of a larger population of healthy and independent older adults caution should be used when generalizing these results. Second, because of the nature of the items on the BBS and the ceiling effect for higher functioning healthy adults the BBS proved to be less than ideal for measuring aspects of dynamic balance in this study. Also, once the total study sample was separated into subgroups of low and high fall risk the small group sizes decreased the power and conclusiveness of the results.
Although participants in this study reported no history of falls and ambulated regularly and independently in their communities, they adopted a stable gait pattern on inclines. This was accomplished primarily by limiting the amount of time spent in single support. By taking smaller and slower steps decreased velocity resulted and ultimately, an increase in stability while walking up inclines.10,38 While this gait pattern was successful on this incline surface it may not be an option when negotiating more challenging obstacles based on evidence in several studies suggesting an increased fall risk with decreased velocity.39,42,43
From a clinical viewpoint, when training active older adults, with or without reported gait or balance dysfunctions, progression toward more challenging and dynamic activities should be integrated into the plan of care. Challenges should include alternate terrain training, change of direction, dual task activities, and dynamic reaching outside the boundaries of their base of support. Practicing maintaining a steady velocity and reducing variability should also be considerations in dynamic balance training in healthy active older adults.
Despite the limitations of this study, the findings provide important information on the strategies used by healthy adults over the age of 70 when negotiating inclines. Surprisingly, there has been virtually no data published on this rapidly growing population with regard to walking and balance on incline surfaces. Data from this study on healthy older adults without pathologies as they walk over a common community barrier provide essential baseline data for comparative analyses in future studies. The clear differences in spatiotemporal parameters of gait between level and incline walking surfaces and the intriguing but less conclusive results comparing subgroups of adults based on higher and lower scorers on the BBS and DGI offers direction for future research. Overall, this study adds to the existing data on gait and balance while providing a framework for future studies on the rapidly expanding older adult population. Data may also assist therapists to minimize the incidence of falls and fall-related sequelae in the community.
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gait parameters; older adults; walking on inclines