Speed, the Grim Reaper, and Stroke Rehabilitation
June 2014 Issue
"How Fast Does the Grim Reaper Walk?"
This was the title of an academic article published in the British Medical Journal in 2011, and sent to me by a good friend and colleague.1 The article stands as a strong witness for those of us who maintain that both personality and a sense of humor can be found in the minds of most academic researchers if one searches hard enough.
The premise of the article is a reasonable one: Preferred walking velocity has long demonstrated a relationship with mortality. That is, faster walkers tend to outlive slower walkers. So it follows that the Grim Reaper must also have both a preferred and maximum walking speed such that those who routinely outpace him are more likely to remain with us a little longer.
The article is informative and entertaining. Having slogged through countless manuscripts in the peer-reviewed literature (including several of my own), it was refreshing to encounter the following paragraph in the introduction section of the paper:
"The Grim Reaper, the personification of death, is a well-known mythological and literary figure. [Here the authors reference such works as the novels Reaper Man and the more familiar Harry Potter and the Deathly Hallows.] Reported characteristics include a black cloak with cowl, a scythe, and cachexia. High-quality scientific research linking the Grim Reaper to mortality has been scarce, despite extensive anecdotes."1
The introduction then explains the authors' hypothesis that by monitoring baseline walking speeds of older men along with their five-year survival rates, "we would be able to determine the walking speed of the Grim Reaper-information of importance to public health."1
The study cohort consisted of 1,705 men over the age of 70 living in several inner-city suburbs of Sydney, Australia. The authors clarified that "as 'living' in the study area was a criterion for entry to the study, we were unable to obtain Death's participation in clinic assessments."1 Rather, his speeds were deduced from the collected data.
After recording six-minute walk test (6MWT) results for the men at the initiation of the study, following the cohort over a five-year period, and recording the 266 deaths that occurred, the authors concluded that the Grim Reaper's self-selected walking speed was 0.82 meters per second (m/s). That is, older men who walked at a velocity greater than 0.82 m/s were 1.23 times less likely to encounter Death. Further, no mortalities occurred among those men capable of walking speeds in excess of 1.36 m/s (or about three miles per hour), suggesting this to be the Grim Reaper's maximum walking speed.
Besides reaffirming my belief that if humor is to survive in this world, it will largely be the work of Australians, the article underscores the simple premise that walking speed matters. The remainder of this article outlines the relationship between one of the O&P profession's most commonly encountered populations, individuals with cerebral vascular accident (CVA), and walking speed.
Establishing and Expanding Functional Thresholds
In 1995, Perry et al. established walking speed as a valid predictor of community walking status.2 Using a fairly broad classification, they made the following assertions: Walking speed below 0.4 m/s predicts household walking. Walking speed between 0.4 and 0.8 m/s predicts limited community walking. Walking speed in excess of 0.8 m/s predicts unlimited community walking and coincidentally, roughly approximates the walking speed of the Grim Reaper cited earlier (Table 1).
More recently, an effort was undertaken to expand these definitions and determine if walking velocity remained an accurate predictor of walking ability. In the study, a cohort of 130 stroke survivors was recruited from a New Zealand community setting. Of these, 15 subjects recovered fully from the effects of their stroke such that they were discharged into the community with no need for outpatient physical therapy (PT). The remaining 115 subjects retained sufficient disability that they required PT upon discharge.
A questionnaire was administered to all participants to better determine the extent of their unsupervised ambulatory abilities. For those subjects not requiring PT, this occurred two weeks after they returned home. For the rest of the subjects, this occurred one week following discharge from outpatient PT. In both instances, researchers felt that the timing of the survey would reflect the patients' peak mobility and outcomes. Using the self-report data, four levels of ambulation and community participation materialized: 1) unable to ambulate outside the home; 2) able to ambulate as far as the mailbox; 3) able to ambulate in the immediate environment; and 4) able to ambulate in a shopping center and/or places of special interest.
With these categories established, several outcome measures were assessed to see which would prove most predictive of community engagement. These included a standardized ten-meter walk test (10MWT) (walking velocity); the Functional Ambulation Categories (indoor and outdoor walking ability); the Rivermead Mobility Index (functional mobility); and a treadmill test (walking endurance). While relationships were observed between each outcome measure and the four functional groups, it was gait velocity-the simplest assessment-that appeared to be the most discriminatory measure. Thus, even with an expanded range of community ambulation levels, the simple metric of short distance walking velocity appears to be largely predictive of both ambulatory engagement and community participation. The average walking velocities observed in each group are shown in Table 2.
Do Changes in Gait Velocity Lead to Improvements in Mobility and Participation?
Having established that walking velocities appear to predict community engagement following a stroke, a natural question is whether or not subsequent changes in an individual's walking velocity will lead to changes in his or her community engagement. This question was addressed in a 2007 study funded through the U.S. Department of Veterans Affairs.4
In the study, assessments were performed before and after a 12 to 14 week home-based, structured, and progressive exercise intervention. The assessments included walking velocity, as measured with a standardized 10MWT, and function and quality of life, as measured with the activity and participation constructs of the Stroke Impact Scale (SIS).
To determine whether or not a patient experienced substantial improvement in his or her walking velocity during the course of the trial, the authors used the classifications of Perry et al. Thus, patients with initial walking velocities below 0.4 m/s (household walker) were "successful" if their walking velocities improved to 0.4 to 0.8 m/s (limited community walker). Similarly, patients with initial walking velocities between 0.4 and 0.8 m/s were considered "successful" if their new walking speeds exceeded 0.8 m/s (community walker). These results were then compared against changes in SIS scores to determine if improvements in walking velocities were associated with improvements in social activities and participation.
Among the 19 subjects initially presenting as household walkers, 12 (68 percent) became limited community walkers and seven (32 percent) stayed in their original ambulatory class. Compared to those who failed to move up to the next level of ambulatory velocity, the "graduates" presented with higher SIS scores in the domains of activities of daily living, mobility, and participation. Similarly, among the 45 subjects initially presenting as limited community walkers, only 17 (38 percent) moved up to a community walking speed while 28 subjects (62 percent) remained within the velocity range of limited community walkers. Though not as striking as the differentials observed in the original household walker cohort, the SIS scores for both mobility and participation were higher among the limited community graduates.
Importantly, if the entire study cohort is broken down into those who succeeded and those who failed to advance to the next walking class, the two groups presented with nearly identical mean gait velocities at the initiation of the trial. Thus, the improvements in mobility and participation were not a product of differences in initial gait speed, but rather improvements in gait speed. In summary, an increase in walking speed sufficient enough to represent a transition to a higher ambulation category appears to result in better function and quality of life. This was especially the case for initial household ambulators.4
Does Walking Velocity Predict Actual Activity?
The two previous studies have suggested two important points. First, gait velocity appears to be predictive of community engagement and participation. Second, enhancements to community mobility and participation appear to be associated with improvements in speed. The final study under consideration seeks to objectively quantify the extent to which walking velocity is associated with actual day-to-day activity.5
Fifty-nine subjects averaging four years since their strokes participated in the study. Using Perry et al.'s classifications, they consisted of household (n=13), limited community (n=23), and community (n=23) walkers. These subjects were asked to wear an Orthocare Innovations StepWatch™ Activity Monitor during waking hours for at least five consecutive days. Step count data was then cross-referenced to gait speeds, summarized in Table 3.
Gait velocity also appears to be largely predictive of daily activity. The transition from household to limited community ambulation is accompanied by an 87 percent increase in average daily step count. Further, the average daily step count of those with a gait velocity above 0.8 m/s (community ambulators), is 37 percent higher than those with a velocity between 0.4 and 0.8 m/s and 159 percent higher than those with a gait velocity slower than 0.4 m/s. Simply put, those who walk faster appear to take more steps.
As healthcare trends continue to focus on the concept of outcome assessment, there is value in recognizing the fundamental importance of one of our more easily assessed outcomes-changes in gait velocity. The simple metric of gait speed has been correlated to both basic and more discrete levels of community participation. Similarly, increases in gait speed appear to be associated with increases in both community mobility and participation, especially among more limited walkers. Finally, walking velocity appears to be largely predictive of activity level measures in the form of daily step counts. All of these factors are related to the principles used to open this article: Gait velocity is at least loosely correlated to mortality. The Grim Reaper continues his daily march with a hypothetically steady pace of 0.82 m/s. Perhaps because of their increased community participation and activity levels, those who are able to outpace the Grim Reaper are more likely to live longer, more fulfilling lives.
Phil Stevens, MEd, CPO, FAAOP, is in clinical practice with Hanger Clinic, Salt Lake City, Utah. He can be reached at
- Stanaway, F. F., D. Gnjidic, F. M. Blyth, et al. 2011. How fast does the Grim Reaper walk: Receiver operating characteristics curve analysis in healthy men aged 70 and over. British Medical Journal 343:d7679.
- Perry, J., M. Gerrett, J. K. Gronley, and S. J. Mulroy. 1995. Classification of walking handicap in the stroke population. Stroke 26(6):982-9.
- Lord, S. E., K. McPherson, H. K. McNaughton, L. Rochester, and M. Weatherall. 2004. Community ambulation after stroke: How important and obtainable is it and what measures appear predictive? Archives of Physical Medicine and Rehabilitation 85 (2):234-9.
- Schmid, A., P. W. Duncan, S. Studenski, et al. 2007. Improvements in speed-based gait classifications are meaningful. Stroke 38(7):2096-2100.
- Bowden, M. G., C. K. Balasubramanian, A. L. Behrman, and S. A. Kautz. 2008. Validation of a speed-based classification system using quantitative measures of walking performance poststroke. Neurorehabilitation and Neural Repair 22(6):672-5.