The mean (±SD) steps/day of 6,574 ± 3,541 suggests that our sample group fell below the lower end of 7,000-13,000 steps/day for healthy, younger adults . Our data were, nevertheless, consistent with the previous observation that individuals accumulating <5,000 steps/day are more likely to be classified as obese . Significant differences were also found between some biometric (percentage body fat, waist circumference) and clinical (blood glucose) outcomes in those participants in the <5,000 steps/day category, when compared with the other steps/day categories. As recently confirmed , total daily values less than 5,000 steps/day may be an appropriate index for inactivity and its associated risk with health consequences, such as obesity.
Additional findings were that 102 participants (32.7%) accumulated aerobic steps (≥100 steps/min for a minimum duration of 10-minutes/day). Only 34 participants (11.0%), however, accumulated aerobic steps for an average of at least 21 minutes/day, as a proxy for current PA guidelines that make reference to moderate intensity PA. This suggests that only approximately one-third of our study group accumulated some moderate intensity PA relevant to the current PA in respect to ambulatory PA .
The most notable finding was that most participants accumulating more than 10,000 steps/day were also accumulating “aerobic” steps. A direct and independent association of intensity-based steps was, however, only found in percentage body fat and diastolic blood pressure. The contribution of intensity-based steps towards achieving 10,000 steps/day however, highlights the value of intensity-based steps as a contributor towards achieving volume-based recommendations. Our research, therefore, emphasizes and supports emerging literature that exercise prescription and/or steps/day recommendations be framed within the context of volume, intensity and duration of intensity-based steps rather than volume alone [35,36].
Recent studies have shown that 30 minutes of moderate-to-vigorous walking corresponds to a total of between 3,000 and 4,000 steps [22,27,34,40]. In support of our additional findings, reference to 3,000 steps in 30 minutes was, therefore made as an overall guideline that incorporates volume, duration and intensity of steps/day. The use of 3,000 steps in 30 minutes is, however suggested as a heuristic value and taken over and above habitual activity levels. This recommendation therefore still supports the accumulation of volume-based steps and the 10,000 steps/day recommendation.
Whilst our study group may not be truly representative of the South African adult population, the results do support the viewpoint that globally, most adults are currently not meeting PA guidelines .
Association between steps per day and body composition
Research has shown that people meeting the 10,000 steps/day target are more frequently classified as normal weight and those individuals with values less than 5,000 steps/day are more frequently classified as obese . In addition, a distinct relationship between steps/day and body composition variables in the expected direction [39,42-47] has been previously reported.
In general, we did not find significant differences in body composition between participants accumulating more than 10,000 steps/day versus those accumulating 7,500-9,999 steps/day or even 5,000-7,499 steps/day. There was, however, significance between the <5,000 steps/day group and the other three groups in percentage body fat and waist circumference (adjusted for age, gender and aerobic steps, so as to establish the true effect of volume of steps/day). Similarly, there was a significant difference between the “no aerobic time” group and the other two groups in percentage body fat (adjusted for age, gender and total steps/day, so as to establish the independent effect of intensity based steps), suggesting that “some” intensity-based steps is better than “none”.
Steps per day in relation to moderate intensity physical activity and current physical activity guidelines
The categorization of our pedometer data into intensity-based steps categories described in the methodology so as to relate to current PA guidelines, showed conflicting findings. After adjusting for age, gender and total steps/day (to establish the independent effect of intensity-based steps), only percentage body fat and diastolic blood pressure were significantly different between the “no aerobic activity” and the “low aerobic activity” groups. A similar finding was observed when comparisons between the “no aerobic activity” and the “high aerobic activity” groups were made. No other between-group effects were noted. This may direct us to the notion that “some physical activity is better than none” .
Furthermore, the observation that most people accumulating 10,000 steps also accumulated intensity-based steps directs us to the viewpoint that intensity-based steps contributes to improved outcomes by increasing total volume of steps/day.
Tudor-Locke et al, in a recent paper , identifies the gap in current literature on the impact of intensity-based walking programs and on clinical outcomes, within the context of pedometry. Whilst pedometer-based walking programs have shown increased walking behavior and varying levels of improvement in clinical outcomes, research on the impact of intensity-based walking programs and their effect on clinical outcomes, is of emerging importance. Our study, in exploring the interplay between volume and intensity-based steps/day, supports this recommendation.
Mediation effect of waist circumference, percentage body fat and body mass index in the association between steps per day and clinical outcomes
Mediation analysis has emerged as a statistical technique for providing insights into the mechanisms of change, particularly in behavioral interventions. As such, in the area of PA and health, mediation analysis has been used to determine which behaviors contribute to weight loss. The notion that regular physical activity is associated with lower body fat composition (body mass index, percentage body fat and waist circumference) and improved clinical measures is well documented. Resting Energy Expenditure and the variation thereof is, however, largely due to differences in the extent of lean body mass and fat mass of an individual . Consequently, all associations between body size and other outcomes (such as cardiovascular risk factors) are partially confounded by the association with resting energy expenditure . Increased levels of PA are seen to increase energy expenditure and improve clinical measures, such as reducing blood pressure .
After accounting for PA, the positive correlation between increased resting energy expenditure and blood pressure, for example  may direct us to the viewpoint that the association between PA and clinical outcomes might be mediated by factors relating to body fat.
From our mediation analysis, it is evident that the relationship between steps/day (both total steps/day and aerobic time) and clinical outcomes (blood pressure, blood cholesterol and blood glucose) were influenced (mediated) by body composition estimates. In our study, percentage body fat emerged as the strongest and significant mediator in this association, and may, therefore be a useful consideration in the associations between PA measures and clinical outcomes, particularly as a criterion measure for body composition.
Whilst our results have clearly shown that body composition mediates the association between PA and health outcomes, the loss of significance of nearly all the outcome variables when adjusted for the mediator, further highlights that body composition (and most notably, percentage body fat) “completely”, rather than “partially”, mediates the association between PA and health outcomes.
Although such a finding has valuable and far-reaching implications on PA and health, the information presented may not, however, be able to draw inferences to causality, due to the cross-sectional nature of the data.
Strengths of the study
The research undertaken is, to our knowledge, among the first pedometer-based studies conducted in the Republic of South Africa, within an urban context, that establishes the association between ambulatory PA and health measures in an adult, employed population group.
The study was useful in establishing associations between volume, intensity (in terms of aerobic steps/day accumulated) and duration (total time spent in aerobic activity) of ambulatory PA and health measures.
A number of studies that have directly measured moderate intensity as 3 METs have concluded that 100 steps/minute is a reasonable heuristic value, indicative of moderate intensity PA [14,34,50]. The application of the 100 steps/minute criterion within our data analyses provides a unique presentation of cross-sectional pedometer data that relates to a combination of intensity and volume-based steps/day rather than volume alone.
The study, by way of the mediation analysis, provides an interesting finding on the role of physical activity in improving health through improved body composition.
The cross-sectional nature of the study provided information on the association between ambulatory PA and clinical outcomes. No causal inference could therefore be drawn.
The study was limited to those employees attending the health screening event and/or willing to participate in the study. This presents a selection bias, as the group agreeing to participate may be different from the non-participating employees. We were also not able to obtain data on the response rate of those invited to participate, and those that were excluded in the analysis.
Pedometers measure ambulatory PA. Our study was, therefore, limited to participants performing activities more specific to ambulation and did not include activities such as swimming, cycling and weight training.
The low steps/day volume noted in our study (6,574 + 3,541) may be related to the paucity of the data obtained (i.e. three consecutive days of pedometer-wear, minimum wear-time of ten hours). The wearing time is in keeping with documented literature that make reference to such criteria as a reasonable estimate of daily ambulatory PA [51,28,29].
The categorization of manufacturer-defined “aerobic” steps, from the hourly display into a more representative estimate of moderate intensity PA (i.e. 100 steps/minute in bouts of at least ten minutes), can be seen as a limitation due to the manual method by which this re-categorization of the data was performed.
Consequently, the sub-grouping of the data according to intensity-based categories using 21 minutes/day of aerobic activity, as a proxy for current PA guidelines, may be viewed as a further limitation, as this sub-grouping is similarly based on the manual tallying of data. This criterion has, however, allowed us to provide some level of differentiation of PA according to total volume of steps/day and aerobic time.