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APPLIED SCIENCES

Increasing Our Understanding of Reactivity to Pedometers in Adults

CLEMES, STACY A.; PARKER, RICHARD A.A.

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Medicine & Science in Sports & Exercise: March 2009 - Volume 41 - Issue 3 - p 674-680
doi: 10.1249/MSS.0b013e31818cae32
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Abstract

Walking is reported as the most popular form of leisure time physical activity in both the United Kingdom (16) and United States (30), yet walking, or ambulatory activity, is typically under reported in questionnaire-based surveys of physical activity (1,25,37). Owing to the high levels of physical inactivity reported in the United Kingdom (15,18) and United States (23), coupled with the increasing public health burden of obesity (20) and other diseases related to physical inactivity (2), valid and reliable objective measures of habitual free-living activity are necessary to address these current public health concerns (2,21,33).

Pedometers are increasingly being used as a surveillance tool to objectively assess ambulatory activity levels and patterns in different populations (5,8,10,11,19,22,31,32,36,40). They provide an inexpensive, accurate, and reliable objective measure of ambulatory activity by counting the number of steps taken per day, enabling the accumulative measurement of occupational, leisure time, and household activity, along with activity required for everyday transportation (19). In addition to their use as a surveillance tool, pedometers are also a popular motivational device. The ability of the individual to receive immediate feedback on their accumulated step count is an important feature of the motivational aspect of the pedometer (21,26).

When used as a measurement tool, researchers often provide participants with unsealed pedometers (no restriction on participants viewing their step count) and request that they record their daily step count in an activity diary/step log. The impact of wearing a pedometer, and recording daily step counts, on participants' activity level (i.e., daily step count) has received little attention, however. If activity changes as a result of wearing the pedometer, defined as reactivity (39), this could affect the validity of pedometer-determined activity data.

To date, little research has investigated whether reactivity exists in adult populations when participants wear an unsealed pedometer and record daily step counts (7,12,17,21). Matevey et al. (21) and Eastep et al. (17) both reported minimal differences between unsealed and sealed (when the visible display of the pedometer is restricted) step counts, whereas Behrens and Dinger (7) reported no evidence of reactivity occurring in response to wearing an accelerometer and an unsealed pedometer. Similar findings have been reported when pedometer reactivity has been assessed in children (24,27,38).

In the research outlined above (7,21,24,27,38), in the sealed condition, participants have all been aware that they were wearing a pedometer or a device that measures physical activity (17), which in itself may elicit some degree of reactivity. Only when participants are unaware that their activity levels are being monitored (termed covert monitoring) can a true investigation into reactivity be undertaken (6).

In the only study to date using covert monitoring, Clemes et al. (12) reported an increase in mean daily step counts of 1845 steps per day when participants wore an unsealed pedometer and recorded their daily steps in an activity log, relative to the covert condition. Many mechanisms could account for this observed increase in activity. These include the following: 1) the participants' knowledge that they were wearing a pedometer and that their daily step counts were being measured; 2) the feedback obtained from the pedometer's visible display-it has been suggested that the pedometers' ability to provide individuals with immediate feedback may serve as a behavioral modification tool (26); and 3) the requirement for participants to complete a daily step log, which may have further heightened the participants' awareness of their daily step count. It was unclear from this study, however, which of the above mechanisms caused the observed increase in daily step counts. The aim of the current study, therefore, was to increase our understanding of pedometer reactivity in adults by investigating the presence, if any, of pedometer reactivity in response to the three mechanisms proposed above, by assessing reactivity in response to wearing sealed and unsealed pedometers, with and without step count recording.

METHODS

Participants

A convenience sample of 63 adult participants, blinded to the study aim, volunteered to participate. Participants were recruited from the staff and student population at Loughborough University. A health screen completed before enrollment into the study confirmed that participants were all in good general health, and none had any physical illnesses or disabilities that might affect their normal daily routine. The study received ethical approval from the Loughborough University Ethical Advisory Committee, and participants provided written informed consent. At the study outset, body mass (kg) and height (cm) were directly measured without shoes using electronic weighing scales (Tanita UK Ltd., Middlesex, UK) and a wall-mounted stadiometer (Seca UK, Birmingham, UK). Body mass index (BMI) was calculated as kilograms per meter squared.

Pedometer

The New Lifestyles NL-1000 pedometer (New Lifestyles, Inc, Lees Summit, MO) was used in this study. This pedometer uses the same piezo-electric mechanism as the NL-2000 pedometer that has been shown to accurately detect steps taken in both laboratory (13,14,29) and free-living conditions (28). The NL pedometer range all have internal memory chips and are capable of storing up to 7 d of data, in 1-d epochs. Their internal clock resets the step count at midnight.

Procedure

During the first visit to the laboratory, participants were issued with a sealed pedometer and informed that the device was a "new body posture monitor that measures time spent in horizontal, seated, and standing postures" (covert condition). The tape used to seal the pedometer would tear if removed; therefore, noncompliance would be obvious when participants returned to the laboratory. Participants were shown the correct position to wear the device, that is, above the midline of the thigh, and were requested to wear it throughout waking hours for 7 d, only removing when bathing, showering, or swimming.

During the second visit to the laboratory, daily step counts measured from the past 7 d were recorded into an activity log by an experimenter using the NL-1000's memory function. Participants were informed that the device was actually a pedometer, and they were invited to participate in a further three study conditions, each condition having a duration of 1 wk. All participants took part in each of the three remaining conditions. These conditions comprised a sealed condition whereby the pedometer was resealed and worn throughout waking hours for 7 d. As in the covert condition, in the sealed condition, the pedometer's visible display was restricted. However, unlike the covert condition, participants were aware that they were wearing a pedometer and that their step counts would be retrieved by the experimenter at the end of the condition. An unsealed condition involved participants wearing the pedometer unsealed, whereby there was no restriction on the participants' viewing their step counts, and a diary condition involved participants wearing the pedometer unsealed, with the additional task of recording their daily step counts in an activity log provided, on going to bed each night. For the two unsealed conditions, participants were shown how to use the pedometer's memory function. After each condition, participants returned to the laboratory where the step counts were recorded by the experimenter using the memory function. The order of the three conditions that followed the covert condition were balanced across participants, with 21 participants commencing the remainder of the study in the sealed condition (followed by the unsealed and diary conditions), 21 commencing with the unsealed condition (followed by the diary and sealed conditions), and 21 starting with the diary condition (followed by the sealed and unsealed conditions). In addition to balancing the order of the three conditions, because step counts have been shown to vary between weekdays and weekend days (4,7,10,11,34,35), the day of the week that participants commenced the covert condition, and the remaining three conditions, were also balanced across participants with nine participants beginning the study on each day of the week, i.e., nine participants commenced each condition on a Monday, nine participants commended each condition on a Tuesday, nine on a Wednesday, and so on.

Statistical analyses

Statistical analyses were conducted using SPSS for Windows version 15 (SPSS Inc., Chicago, IL). Participants' mean daily step counts from each condition (covert, sealed, unsealed, and diary) were calculated and compared using a repeated-measures ANOVA, with gender as a between-subjects factor. Bonferroni-adjusted pairwise comparisons were performed in the event of an overall significant effect of condition. Within each condition, to investigate any changes in step counts with the study day (i.e., sealed day 1, sealed day 2, etc.), daily step counts recorded during each condition were compared using a repeated-measures ANOVA, with gender as a between-subjects factor. Daily step counts from each condition were also organized according to the day of the week and compared using a repeated-measures ANOVA, with gender as a between-subjects factor, to test whether mean step counts differed between days. In the event of a significant study day order, or day-of-the-week effect, Bonferroni-corrected post hoc comparisons were performed. Statistical significance was set at P < 0.05.

RESULTS

Participants

Demographic characteristics of the sample are summarized in Table 1. There were no significant gender differences in age and BMI.

T1-24
TABLE 1:
Participants' demographic characteristics.

Overall effects of condition

After the covert and sealed conditions, there was no evidence of any tampering with the pedometer seal, confirming that all participants were blinded to their step counts in these conditions and to the fact that they were wearing a pedometer in the covert condition. Furthermore, after the covert condition, when asked by an experimenter if they knew what the device that they had been wearing during the past 7 d actually was, 46 participants responded that it was a body posture monitor, whereas 17 said that they were not sure what the device actually was. Mean step counts recorded from each condition are shown in Table 2. There was a statistically significant difference between mean step counts recorded in each condition (F = 7.0, P < 0.001), with post hoc analyses revealing that mean step counts recorded in the diary condition were significantly higher than those recorded in both the covert (t = 5.2, P < 0.001) and the sealed (t = 3.3, P = 0.002) conditions. There was no significant gender interaction, or main effect, indicating that males and females responded similarly to the four study conditions.

T2-24
TABLE 2:
Mean daily step counts recorded in each study condition for the sample as a whole and for males and females separately.

Influence of study day order in each condition

Although mean step counts recorded in the sealed and unsealed conditions did not differ significantly to those recorded in the covert condition, there was a tendency for mean step counts to be higher during the first few days of monitoring in these conditions. Decreases in mean daily step counts are particularly evident in these conditions across the 7 d of monitoring, suggesting that reactivity was present to some degree during the first 3-4 d of the sealed and unsealed conditions (Fig. 1). Significant differences between the step counts recorded in both the sealed (F = 3.1, P = 0.006) and unsealed (F = 2.2, P = 0.04) conditions were observed across the monitoring frame with post hoc analyses, revealing that, in the sealed condition, step counts recorded on day 1 were significantly higher than those recorded on days 5 and 6 (both P < 0.002), and in the unsealed condition, step counts recorded on day 1 were significantly higher than those recorded on days 5 and 7. There were no significant overall effects of study day order in both the covert and diary conditions. In addition, within each condition, there were no significant gender interactions, or main effects, indicating that males and females responded similarly to all conditions. It can be observed from Figure 1 that, whereas in the diary condition there is a tendency for mean daily step counts to decrease slightly during the 7-d monitoring period, the step counts recorded in this condition do not return to the levels observed in the covert condition.

F1-24
FIGURE 1:
Mean daily step counts recorded during each study day within each condition along with SE bars.

Day-of-the-week effects

A significant day-of-the-week effect was evident in each condition (all P < 0.05), with post hoc analyses revealing that mean step counts reported on a Sunday were significantly lower than those reported on all other days (all P < 0.002; Fig. 2). Within each condition, there were no significant gender interactions, or main effects, indicating that males and females had similar activity levels and patterns during the different days of the week.

F2-24
FIGURE 2:
Mean daily step counts recorded on each day of the week in each condition along with SE bars.

DISCUSSION

The aim of the current study was to add to the understanding of pedometer reactivity in adults by investigating the presence of reactivity, if any, in response to wearing sealed and unsealed pedometers, with and without step count recording. This study is one of few that have used covert monitoring to investigate the true presence of pedometer reactivity in an adult sample (12). In the participants surveyed, the greatest increases in daily step counts were observed in the diary condition, with mean step counts recorded in this condition being significantly higher thanthose observed in both the covert (+1273 steps per day, SD = 1963) and sealed (+803 steps per day, SD = 1954) conditions.

The increase in daily step counts observed in the diary condition in the current study supports the findings of an earlier study using covert monitoring to investigate the presence of pedometer reactivity in an adult sample (12). Clemes et al. (12) reported a significant increase in mean daily step counts when participants wore an unsealed pedometer and recorded their daily step counts in an activity log, relative to a covert monitoring condition. It was unclear, however, from this study what mechanisms caused the increase in daily step counts, and three potential contributory factors were highlighted, including 1) the participants' knowledge that they were wearing a pedometer, 2) the feedback obtained from the pedometer's visible display, and 3) the requirement for participants to complete a daily step log. The current study aimed to increase our understanding of pedometer reactivity in adults by investigating the presence, if any, of pedometer reactivity in response to the three factors proposed above. The current findings suggest that the requirement of participants to record their daily step counts into an activity log elicits the greatest degree of reactivity. It is speculated that the act of recording daily step counts into an activity log heightens participant's awareness of their overall activity levels, which may lead to personal goal setting, and/or a greater self-efficacy (confidence) for walking (3), resulting in increases in daily activity. For example, in a minimal contact pedometer intervention study, Rooney et al. (26) observed that women who chose to make a note of their daily step count were more aware of their general activity levels and, as a result, were more likely to set challenging activity goals.

The duration of this reactivity effect in response to step count recording has yet to be determined. When assessing mean daily step counts in the diary condition according to study day order, it is evident from Figure 1 that although there was a tendency for step counts to be higher during the first 2 d of this condition followed by a slight decrease and leveling off during days 3 to 7, the step counts recorded during days 3 to 7 do not return to the levels observed in the covert condition. These findings suggest that reactivity to wearing a pedometer and recording daily step counts may last for slightly longer than 1 wk. In addition, there were no significant overall effects of study day order in the diary condition, supporting the suggestion that in this condition daily step counts remained elevated throughout the 7-d monitoring period and that systematic reductions in daily step counts during this period were negligible. These findings support observations made by Clemes et al. (12) in their study investigating pedometer reactivity, who also reported no effects of study day order in their diary condition. The current findings also support earlier suggestions made by Eastep et al. (17) in relation to the potential duration of pedometer reactivity after the comparison of sealed and unsealed step counts from 21 participants enrolled in a "Walking for Fitness" class. Although no differences in mean step counts were observed between the two study conditions, Eastep et al. (17) did observe that walking behavior decreased in a linear fashion throughout the two 3-wk conditions, suggesting that some degree of reactivity was present in both. It was concluded from this research that a pedometer "feedback effect" may be present, but it may only last between 1 and 2 wk (17).

Although overall mean step counts recorded in the sealed and unsealed conditions were slightly higher than those recorded in the covert condition, these differences between conditions were not statistically significant, indicating at first glance that reactivity to both sealed and unsealed (without step count recording) pedometers is minimal. However, when assessing mean step counts within each condition according to study day order, it is evident from Figure 1 that step counts seem to be highest during the first day of monitoring in the sealed and unsealed conditions followed by a gradual reduction in mean daily steps for the remainder of the two 7-d monitoring frames. In both the sealed and unsealed conditions, mean step counts from approximately day 4 onward approach a level comparable with mean daily step counts recorded in the covert condition (Fig. 1). It is suggested, therefore, that in the sample studied, reactivity was present at the beginning of both the sealed and unsealed conditions; however, it seemed to be relatively short-lived in these conditions. This finding has methodological considerations for researchers wishing to use sealed and/or unsealed pedometers in adults for ambulatory activity surveillance purposes, and it is recommended that the first 3 d of monitoring be treated as a familiarization period only, with the step counts recorded on the subsequent days being used as the primary data. Further research is required, however, to determine the duration of reactivity associated with wearing unsealed pedometers and recording daily step counts in an activity diary/step log.

It has recently been suggested that 7 d of pedometer monitoring are sufficient to reliably estimate monthly habitual activity (9). In line with the current findings, however, it is suggested that, until the duration of the reactivity effect in response to step count recording has been established, researchers wishing to use unsealed pedometers with stepcount recording for activity surveillance purposes should provide participants with a suitable familiarization period (>1 wk) with the pedometer and diary prior to this 7-d monitoring phase.

As widely reported elsewhere (4,7,10,11,34,35), a significant day-of-the-week effect was observed across all conditions in the current study, with step counts recorded on a Sunday being significantly lower than those recorded on all other days. To counterbalance the anticipated day-of-the-week effect, allowing for the true observation of any reactivity in terms of study day order to be observed, a counterbalanced repeated-measures study design was used. Equal numbers of participants (n = 9) began each condition on each day of the week, therefore the changes in step counts that occurred during the 7 d of monitoring within each condition, shown in Figure 1, represent changes caused by study day order, and they are not confounded by any day-of-the-week effects.

A limitation of the current study is the fact that participants were all volunteers, recruited from the staff and student population at Loughborough University. As participants responded to advertisements for volunteers to take part in a study "evaluating a novel body posture monitor," it is unlikely that the sample was biased toward those with an interest in their physical activity levels; however, the participants studied comprised a healthy, relatively young, normal-weight adult sample, and it is recommended that the current findings are confirmed in different population groups. For example, it would be interesting to investigate whether similar responses to wearing a pedometer and recording daily step counts are seen in children or in overweight and obese adults.

In conclusion, in the sample surveyed, the greatest increases in daily step counts occurred in response to wearing a pedometer and recording daily step counts in an activity log, with mean step counts recorded in the diary condition being significantly higher than those observed in both the covert and sealed conditions. The duration of this reactivity effect has yet to be determined; however, the results of the current study suggest that this effect may last for longer than 1 wk. This has validity implications for short-term pedometer studies investigating habitual activity levels. Although mean step counts recorded in the sealed and unsealed conditions were slightly higher than those recorded in the covert condition, these differences were not statistically significant. However, in these conditions, there was a tendency for step counts to be higher during the first couple of days of monitoring, suggesting that a certain degree of reactivity was present initially. The step counts recorded during the remainder of the sealed condition (days 4 to 7) were similar to those recorded during the covert condition, suggesting that the use of sealed pedometers (with the first 3 d treated as a familiarization period) provides a suitable measure of habitual ambulatory activity when covert monitoring is not appropriate or feasible. The findings from the current study increase our understanding of pedometer reactivity in an adult sample and have important implications to both researchers and practitioners interested in the use of pedometers for the assessment of habitual ambulatory activity.

There are no perceived conflicts of interest associated with this research. The results of the present study do not constitute endorsement by ACSM.

No external funding supported the work outlined in the article; the study was conducted using resources already available within the Department of Human Sciences.

The authors thank Professor Stuart Biddle for reading through and commenting on the manuscript before its submission.

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Keywords:

HABITUAL ACTIVITY; OBJECTIVE ASSESSMENT; SEALED PEDOMETERS; UNSEALED PEDOMETERS; ACTIVITY DIARY; COVERT MONITORING

©2009The American College of Sports Medicine