Monitoring steps taken is only one of many ways to track physical activity and individuals may prefer to count minutes in activity rather than wear any type of step counting device. Step counting by definition is most relevant to ambulatory activity; however, this is not the only activity that can be performed at health-related intensities. Other examples include cycling and swimming. In addition, public health guidelines categorically recognize the importance of other types of non-ambulatory activity, including resistance training [3
]. Therefore, the estimates contained herein are limited to translations of physical activity guidelines only in terms of ambulatory activity. For those who swim and cycle (e.g., stationary or recumbent cycling), it may be possible to consider adding 'bonus steps' to daily totals to account for these extra non-ambulatory activities [71
]. For example, Miller et al. [71
] suggest adding 200 steps for every minute of non-ambulatory activities like cycling or swimming. De Greef et al. [72
] have instructed participants in pedometer-based interventions to add 150 steps to their daily total for every minute engaged in cycling and/or swimming.
On face value, a step is the fundamental component of walking; it represents the initiation of body weight transfer and a basic expression of human mobility. Cadence, or steps/minute, is a reasonable indicator of speed [73
] and is also related to the intensity of ambulation [41
], and can theoretically capture the "purposefulness" of ambulatory activity. As steps are accumulated more rapidly and continuously, an individual can be said to be walking purposefully, that is, to get somewhere and/or for exercise. Of course, running is represented at the highest cadences, but this is not likely applicable to many older adults or individuals living with disability or chronic illness. As mentioned above, 100 steps/minutes is a cadence that is growing in acceptance as a heuristic value indicative of walking at an absolutely-defined intensity of 3 MET intensity, at least in younger adults [41
]. This cadence may be unrealistic for many older adults (especially for those who are more frail) or for those living with disability or chronic illness. It may be useful to embrace a "something is better than nothing" approach [5
], or even a "better than usual" approach, in terms of setting relative goals for such special populations.
The correlation between age and preferred walking speed in a population study of older adults 60-86 years of age was -.34 (women) and -.41 (men) [74
]. Those living with disability or chronic illness may walk at even slower speeds [75
]. Overall, aging, disabled, and ill older adults may gradually lose their ability to walk at higher cadences and what remains is the "pottering" (i.e., random, unplanned movements) associated with activities of daily living that all ages appear to engage in to some extent [76
]. Slow walking speed in older adults is strongly associated with increased risk of cardiovascular mortality [77
]. Since public health guidelines for older adults continue to emphasize the importance of engagement in aerobic activities that are of at least moderate intensity, it follows that any step count translation also reflects this emphasis. Although pedometers have been widely criticized for not being sensitive to detecting slow walking, their ability to "censor" low force accelerations might actually be seen as a feature that permits a concerted focus on only those steps that are more likely to be beneficial to health [78
Regardless, the interest in detecting even very low force accelerations is evident from research studies focused on physical activity behaviours of older adults [13
] and especially of individuals living with disability and chronic illness [14
] that have been adopting the StepWatch Activity Monitor (SAM, CYMA Corporation, Mountlake Terrace, WA). The SAM is an ankle worn-accelerometer that detects a "stride" or "gait cycle." To be interpreted relative to more traditional waist-mounted instruments (both accelerometers and pedometers), its output needs to be doubled and expressed as steps. However, this instrument is designed to be exceptionally sensitive to slow gaits [80
] (and is also more likely to detect "fidgeting" activities [80
]) and therefore its output would appear higher than that of more traditional pedometers [17
]. For example, a sample of older adults (mean age 83 years) who wore the SAM for 6 consecutive days averaged approximately 10,000 steps/day [81
], or 'active' if directly (and inappropriately) interpreted against the graduated step index based on pedometer output [15
]. The SAM remains an important research tool, however, it is less practical for public health applications. No conversion factor exists at this time to assist in translation of SAM-detected steps to that of pedometers that have been more traditionally used in research and practice.
Another instrument, the ActiGraph accelerometer, is also known to be more sensitive to lower force accelerations ([82
]) and its output from earlier models needed to be manipulated in order to interpret it against existing pedometer-based scales [15
]. More recently, the manufacturers of this instrument have offered a 'low extension' option that can be selected, or deselected, depending on sensitivity requirements. Since pedometers are more likely to be adopted by a range of users including researchers, practitioners, and the general public, and since public health guidelines specifically emphasize MVPA (and not lighter intensity activities), the step-based translations presented in this article are intentionally more reflective of what would be expected from the use of good quality pedometers. Although the need to detect less forceful steps, especially in some clinical populations can be justified, it remains a concern that comparisons between datasets collected with different devices are hampered unless acceptable conversion factors to facilitate such interpretation can be determined.
Regardless of the choice of instrumentation, normative step values for older adults and special populations span a very wide range. Although the graduated step index described above offers a definite improvement over evaluation using any single step value (e.g., 10,000 steps/day), even smaller increments would provide additional "rungs on the ladder" and represent a more continuous and fully expanded steps/day scale. Specifically, 1,000 step increments [41
] are congruent with the concept of 10-minute bouts taken at 100 steps/min or minimally moderate intensity [3
], and three 10-minutes bouts (i.e., 3 × 1,000 steps = 3,000 steps) are congruent with a daily 30-minute minimally moderate intensity physical activity recommendation. Figure presents the fully expanded steps/day scale. The scale begins at zero and continues to 18,000+ steps/day, representing the single highest average value reported for a sample at this time in Amish men [85
]. Although all age groups are represented, the one-way arrows identify step-based translations of population-specific public health guidelines contained herein (and separately reviewed in companion papers) but also suggest that more is better. For example, the range for healthy older adults is 7,000-10,000 steps/day, at least 3,000 of which should be accumulated at a brisk pace. For individuals living with disability or chronic illness the range is 6,500-8,500 steps/day (although this is based on limited evidence at this time). The difference between thresholds for adults 20-65 years of age and healthy older adults 65+ years of age is nominal (i.e., approximately 300 steps), but it is based on the empirical evidence assembled, and suggests that apparently healthy older adults are capable of achieving minimum steps/day for improving health. However, quite clearly there is a larger gap at the upper end, which reflects decreasing capacity with age (and disease and disability) to achieve upper-end targets. Again, it is important to emphasize, that the oldest-old, especially those compromised by frailty, are more likely to be described as a special population where a clinical approach to increasing physical activity will more appropriately supersede a public health approach. Regardless, adoption of this fully expanded steps/day scale applied across the lifespan would facilitate communication, evaluation, and research. As evidence accumulates, it may be possible to locate population-specific likelihoods of achieving valued health-related outcomes along the scale.
Steps/day scale schematic linked to time spent in MVPA.
An important limitation must be emphasized. It is well known that the measurement mechanism of accelerometers is more sensitive to lower force accelerations (e.g., slow walking) and therefore this type of instrumentation will detect more steps than simple pedometers. However, there are no data at this time to inform us about the health value of steps taken at very low intensity steps independent of higher intensity steps. Indeed, perhaps one contributory factor to age-related decline is the decrease in intensity of daily movement and the progressive loss of higher intensity movements. This is speculative. Regardless, the difference in instrument sensitivity makes it so that the output of accelerometers should generally not be directly interpreted against the scaling presented herein. A direct conversion factor between instruments is not known at this time, but would certainly be useful. The continued use of BMI as a useful, albeit imperfect, indicator of body fatness is an appropriate analogy to the use of a pedometer as an indicator of healthful levels of physical activity. Regardless, any step-based translation of current physical activity guidelines should clearly convey the importance of making an appropriate portion of daily steps congruent with undertaking recommended amounts and bouts of MVPA [86