One Step at a Time
December 2018 Issue
How would you describe the average activity level of your prosthetic patients? Active? Inactive? Sedentary? In an era of smartphone-based pedometry, daily step counts are available across a range of populations, with a well-established literature base that has defined the terms and objective step count ranges. This article introduces published observations on step counts among individuals with lower-limb amputations, places these observations in the broader context of observed human activity levels, and discusses those interventions that may or may not ultimately influence activity levels among users of lower-limb prostheses.
Activity Levels Among Individuals With Limb Loss
A recent narrative review summarized the current data related to step count in individuals with lower-limb amptuations.1 Reporting on 35 publications over a 21-year period (1995-2016), the authors concluded, "the majority of participants with lower extremity amputations were found to be sedentary, taking approximately 3,000-4,000 steps/day."1 That phrase, sedentary, will be placed in its broader context later in this article.
As might be expected, some variability was observed across the population of individuals with amputations, with some factors correlating with activity levels as might be reasonably expected and other factors falling short of anticipated relationships. Age, for example, largely failed to consistently correlate with activity levels with several studies reporting only "weak trends," "no statistically significant association," or "no relationship" between physical activity and age, with a single study countering with the observation that "physical activity was negatively correlated with age."1
The impact of amputation level on physical activity was quite variable. Some authors observed that "participants with transtibial amputations were more physically active than those with transfemoral amputations," while others found the relationship "not to be significant," or merely a "trend," and still other publications finding "no relationship between physical activity and level of amputation."1
By contrast, any correlations between body mass index (BMI) and activity levels were relatively limited, ranging from "weak relationships" and "trends towards a negative association between physical activity and BMI," to observations of "no relationship" or "non-significant odds of being physically active for different BMI or body weight."1
Walking capacity largely correlated to observed activity levels. For example, those "who normally walked outdoors without the support of a walking aid were more physically active that those who normally walked with an aid." Similarly, those "without a history of falling were more physically active in the community than those who experienced a fall at least once in the past 12 months." Physical activity was also reported to be associated with self-selected walking speed, six-minute walk distance, and performance on the two-minute walk test.1
The impact of amputation etiology was also variable. At one extreme, one publication reported an average difference of almost 3,000 steps per day among participants with amputations "free of peripheral vascular disease." At the opposite extreme, a separate publication found differences in the odds of being physically active by amputation etiology were not significant. A third publication observed greater physical activity among participants with amputations of non-vascular etiology, but at a more modest discrepancy, reporting an average of 3,300 steps following non-vascular amputation and 2,200 steps following vascular amputations.1
Variables outside of healthcare demographics were also found to influence activity. For example, one publication observed increased activity levels among individuals with lower-limb amputations in spring and summer months, while a second observed increased activity levels on weekdays compared to those observed on weekends.1
Established Activity Level Descriptors and Thresholds
Catherine Tudor-Locke, PhD, pioneer-ed the academic work on step count and activity level, defining a tiered set of descriptors with associated step count ranges.2 A physically active lifestyle was defined as a daily step count that exceeded 7,500 steps. Some readers may note that this is not the more arbitrary target of 10,000 daily steps, a target that appears to have originated in the run-up to the 1964 Tokyo Olympics when pedometers became popular in a country caught up in the excitement of the upcoming event. One pedometer manufacturing company came out with a device called the manpo-kei, or 10,000 step meter, and that number has largely stuck in the hearts and minds of fitness enthusiasts around the globe.
The target of 7,500 steps is more informed and nuanced. Larger rates of step accumulation occur during increasingly intense ambulatory activity with the highest rates occurring during the performance of moderate-to-vigorous physical activity (MVPA). Research has suggested that those who obtain 7,000-8,000 steps per day are also obtaining at least 30 minutes of daily MVPA. Restated, the target of 7,500 daily steps generally requires the daily performance of augmented physical activity (think exercise) to obtain.3
Within Tudor-Locke's widely accepted activity standards, people who fail to reach an average of 7,500 daily steps are labelled physically inactive,3 a somewhat accusatory tag that ultimately refers to those individuals who fail to reach ideal levels of MVPA (again, think exercise beyond the requirements of your daily routine).
Among the physically inactive, the highest tier is labelled at 5,000-7,499 steps per day, described as a low active lifestyle.3 Again, these are not sedentary individuals, but rather, those who are active throughout the day but not engaged in regular exercise.
A sedentary lifestyle is defined as step counts below 5,000 steps per day, characterized by a deficiency of not only exercise, but also non-exercise physical movement. This lifestyle has been further divided into limited activity, with 2,500-4,999 daily steps and rather descriptive basal activity at step counts beneath 2,500 daily steps.3
As with the 7,500-step threshold, the 5,000-step threshold that defines a sedentary lifestyle is bolstered by scientific observation. In defining a step-defined sedentary lifestyle index, Tudor-Locke and colleagues summarily observed, "Unfavorable indicators of body composition and cardiometabolic risk have been consistently associated with taking < 5,000 steps/day."3 More specifically, since that average daily step target was first identified in 2001, those that fail to reach it have been observed to exhibit higher body mass indices; higher prevalence of cardiometabolic risk factors including metabolic syndrome; and higher waist circumferences, systolic blood pressures and fasting glucose, triglycerides, and high density cholesterol values.3 Further, those individuals who increase their daily activity levels from less than 5,000 steps to more than 5,000 steps experience improved glucose tolerance, along with decreases in body weight, BMI, and resting heart rate.3
The population of individuals with lower-limb amputations are far from alone with average daily step counts that define them as sedentary. Other sedentary populations include individuals with heart and vascular disease, COPD, dialysis, arthritis, joint replacement, fibromyalgia, and according to some optimistic data sets, 36 percent of the adult population of the United States.3
Global Observations on Activity
Against this backdrop, it is clear that our patient population would benefit from interventions that increase current daily average step counts above the 5,000-step threshold. However, recent global activity data highlights the level of challenge associated with such a transition.4The study in question analyzed de-identified smartphone data from more than 700,000 individuals in 111 countries who used the smartphone app Argus to track physical activity. While the accelerometer derived step counts of such smartphone-based monitors may lack the sensitivity of research-grade activity trackers, the Argus data reported that the average human adult took 4,961 daily steps,4 a figure indicating that the average human adult is leading a sedentary lifestyle.
The inhabitants of some countries exceeded this threshold, led by Hong Kong with an average daily step count of 6,880 steps, followed by China and the Ukraine with 6,189 and 6,107 steps respectively.4 Other nations approximated the activity levels of individuals with lower-limb amputations, with Indonesia exhibiting the lowest average daily step count of 3,513 steps, followed by Saudi Arabia and Malaysia and 3,807 and 3,963 steps respectively.4
Among the 46 countries with at least 1,000 users, the United States ranked 30th, with an average daily step count of 4,774.4 Against this backdrop, the average step counts of prosthesis-users, reported at between 3,000-4,000 steps, while defined as sedentary, is not far behind the global adult population.
What Does Not Appear to Work
A recently published representative report of activity levels among individuals with lower-limb amputations used a cohort of Canadian adults rehabilitating from diabetes-related amputations.5 Reporting upon a cohort of 22 subjects with diabetes who had undergone a recent transtibial amputation, the authors reported an average daily step count of 3,213 steps three months after discharge from rehabilitation.5 This figure increased modestly to an average of 3,809 steps six months later, with an additional report of an average of 24 minutes of MVPA.5
Given the reported benefits for those who take more than 5,000 steps per day, this appears to be a population that would benefit from increased activity. The natural question is which interventions might prove effective in this effort. So far, collective observation has failed to support the idea that prosthetic component choices have much impact on activity. Adding features such as shock absorbing pylons, torsion adaptors, different feet, and microprocessor knees has failed to significantly increase observed activity levels.1
This is exemplified in the recent work of Wurdeman et al. who reported upon the observed activity levels of 28 subjects with transtibial amputations. These subjects were relatively high functioning (K3/K4) with a mixture of traumatic (n = 16) and vascular (n = 8) etiologies who were crossed-over after three-week periods wearing SACH and energy storage and return feet (ESAR).6 Consistent with those publications included in the narrative review cited earlier, despite the high-function capacity of the participants and very meaningful functional differences in the foot types, activity levels were largely unchanged, reported at 4,944 daily steps and 4,660 daily steps in the SACH and ESAR feet.6
What May Work
One likely explanation for the inability of prosthetic component choice to affect activity level may be that the activity level is more dependent on the requirements of daily routines and behavioral choices. The number of steps from the parking lot to the front door at the office, or from the home to the mail box is unchanged by prosthetic componentry. Yet, recent work from the University of Colorado suggests that behavioral changes may facilitate the change needed to increase daily activity levels.7
The randomized pilot trial recruited 38 subjects who had unilateral transtibial amputations. Nineteen of these subjects were assigned to a 12-week control condition, inclusive of a weekly 30-minute phone call with a study therapist in which the patient's health status was discussed, along with life activities planned for the upcoming week. The remaining 19 subjects were also assigned to a 12-week intervention that comprised weekly 30-minute phone calls, but the content of the calls was different. The calls included collaborative goal setting in the areas of home exercise, walking activity, and disease self-management. Initial goals were set in each of these three areas, with one to three additional goals made every week according to the individual's personal motivation.6
The impact of this pattern of weekly activity-based goal setting was readily apparent in the reported activity levels from both groups. The daily step counts of the control group were relatively static, increasing from an average of 1,369 to 1,510. In contrast, those engaged in the behavioral change interventions of goal setting and revision increased their daily step counts from a baseline of 1,305 steps to 2,294 steps, an increase of just over 75 percent.7 While the authors of this study were careful to characterize these initial observations as pilot-level work, their results suggest that, as with other sedentary populations, activity levels may be responsive to behavioral interventions.
While the daily activity levels of individuals with lower-limb amputations appear to fall well short of idealized targets, available data suggests that these levels are not too far behind those unaffected by limb amputation. The narrative labels surrounding step-based activity levels were originally proposed nearly two decades ago and describe the average activity levels of those with and without amputations as sedentary. As such, available data suggests that prosthesis users would likely benefit from increased daily activity. While component changes in isolation have failed to meet this objective, recent pilot data suggests that activity levels may be affected by behavioral intervention techniques such as joint goal setting with respect to daily exercise and activity.
1. Pepin, M. E., K. G. Akers, and S. S. Galen. 2018. Physical activity in individuals with lower extremity amputations: A narrative review. Physical Therapy Review 23(2):77-87.
2. Locke, C. T., and D. R. Basset. 2004. How many steps/day are enough: Preliminary pedometer indices for public health. Sports Medicine 34:1-8.
3. Tudor-Locke, C., C. L. Craig, J. P. Thyfault, and J. C. Spence. 2012. A step-defined sedentary lifestyle index: < 5000 steps/day. Applied Physiology, Nutrition, and Metabolism 38(2):100-14.
4. Althoff, T., J. L. Hicks, A. C. King, S. L. Delp, and J. Leskovec. 2017. Large-scale physical activity data reveal worldwide activity inequality. Nature 547(7663):336.
5. Desveaux, L., R. S. Goldstein, and S. Mathur, et al. 2016. Physical activity in adults with diabetes following prosthetic rehabilitation. Canadian Journal of Diabetes 40:336-41.
6. Wurdeman, S, R, K. K. Schmid, S. A. Myers, A. L. Jacobsen, and N. Stergiou. 2017. Step activity and 6-minute walk test outcomes when wearing low-activity or high-activity prosthetic feet. American Journal of Physical Medicine and Rehabilitation 96(5):294-300.
7. Christensen, C. L., M. J. Miller, and A. M. Murray et al. 2018. Behavior-change intervention targeting physical function, walking and disability after dysvascular amputation: A randomized controlled pilot trial. Archives of Physical Medicine and Rehabilitation [Epub ahead of print].
Phil Stevens, MEd, CPO, FAAOP, is a director with Hanger Clinic's Department of Clinical and Scientific Affairs. He can be contacted at email@example.com.