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Applied Sciences: Physical Fitness and Performance

Pedometer Indices for Weekly Physical Activity Recommendations in Postmenopausal Women

JORDAN, ALEXANDER N.1; JURCA, GINA M.1; TUDOR-LOCKE, CATRINE2; CHURCH, TIMOTHY S.1; BLAIR, STEVEN N.1

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Medicine & Science in Sports & Exercise: September 2005 - Volume 37 - Issue 9 - p 1627-1632
doi: 10.1249/01.mss.0000177455.58960.aa
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Abstract

Approximately 38% of American women are postmenopausal and will spend about one third of their lives in a postmenopausal state (15). About 30% of women in the postmenopausal age range are considered sedentary, and the prevalence increases with age (20). A sedentary lifestyle increases cardiovascular disease risk factors (blood pressure, blood lipids, excessive weight gain, and hyperinsulinemia) and leads to low cardiorespiratory fitness levels (4). The high incidence of inactivity and elevated risk associated with this variable make sedentary behavior a major public health problem, especially in postmenopausal women. The most common form of physical activity for adults is walking, and therefore it may be useful to express physical activity recommendations in terms of this behavior. Pedometers or step counters are self-monitoring devices used to track healthful amounts of physical activity by quantifying doses of walking in steps per day (18,19).

Pedometers have demonstrated good validity for measuring moderate-intensity ambulatory activity under controlled laboratory conditions (1–3,5,14,18,21). Pedometers also are a reliable and cost-efficient way to monitor physical activity under free-living conditions in adult women (6,9). It is important to develop evidence-based pedometer recommendations congruent with current public health recommendations for weekly physical activity. The current public health recommendation states, “every U.S. adult should accumulate 30 min or more of moderate-intensity physical activity on most, preferably all, days of the week” (13). The public health recommendation is in addition to normal daily physical activity. Ten thousand steps per day, in total daily activity, has been recommended for obtaining health benefits (24). It is unclear whether these two recommendations are congruent or whether 10,000 total steps per day is more than 30 min of moderate-intensity physical activity. The 10,000 steps·d−1 recommendation was determined from young healthy Japanese males expending 300 and 400 kcal·d−1 as measured by V̇O2 gas exchange (5). The energy expenditure associated with 10,000 steps·d−1 is substantially greater than the suggested public health recommendation, which is about 150 kcal·d−1 accumulated through moderate-intensity physical activity (13,16,20). Therefore, it is uncertain whether this 10,000 steps·d−1 target is appropriate for other population subgroups, such as postmenopausal women.

It would be useful to examine the number of steps per day in moderate-intensity structured exercise needed to meet specific caloric increments of the public health recommendation for weekly physical activity. Thus, the purpose of this investigation was to examine the number of steps per day needed for sedentary postmenopausal women to meet 50, 100, and 150% of the current public health recommendation for weekly physical activity.

METHODS

Subjects

The data for the analyses presented here are derived from a sample of participants enrolled in a large clinical exercise trial (Dose Response to Exercise in Women (DREW)). Participants were postmenopausal women (age 45–75 yr), who were sedentary (≪8000 steps·d−1), had a body mass index of 25–40 kg·m−2, systolic blood pressure between 120 and 159 mm Hg (diastolic blood pressure <100 mm Hg), and stable hormone replacement therapy status for the previous 6 months. We selected individuals who did not self-report participation in regular bouts of exercise three or more times per week lasting longer than 20 min each time. Therefore, we rationalized that ≪8000 steps·d−1 would be an appropriate cut point for identifying individual baseline physical activity patterns, which excluded structured exercise. The detailed study design and rationale, description of participant recruitment, inclusion criteria, and laboratory and clinical testing procedures are available in a previous report (11).

Exercise Training Program

The Cooper Institute institutional review board approved this study annually. All DREW participants attended an orientation session in which they signed an informed consent, received instructions on proper use and placement of the pedometer (1), and had their height and weight measured. After completion of a 2-wk run-in period and baseline testing, we randomly assigned participants into one of three exercise groups. Then we issued an Accusplit Eagle 120 pedometer (Accusplit, Pleasanton, CA) and monthly pedometer logging forms to each woman. We asked participants to maintain their current physical activity habits for the next 6 months outside the planned exercise sessions. All exercise sessions took place in The Cooper Institute exercise training laboratory and occurred under strict control of the type, intensity, and amount of physical activity. Participants alternated exercise sessions between a treadmill and recumbent cycle ergometer (Life Fitness, Franklin Park, IL) for 6 months, and only treadmill data were used for the analyses reported here. Exercise intensity was kept within ±5 beats at a HR equivalent to 50% of their V̇O2peak by monitoring the entire exercise session with a HR transmitter (Polar Vantage, NV).

Participants in the exercise groups expended kcal·kg−1·wk−1 (KKW) equivalents of 4 KKW, 8 KKW, or 12 KKW, which we calculated as 50, 100, or 150% of the consensus public health recommendation for physical activity, as applied to sedentary women in the age range of this study. All women in each exercise group began exercising for approximately 60 min·wk−1 or equivalent to 4 KKW. Participants in the two higher exercise dose groups incrementally increased their energy expenditure by adding 15 min·wk−1, equivalent to 1 KKW, until they accumulated 120–150 min·wk−1 (8 KKW) or 210–240 min·wk−1 (12 KKW) of exercise each week. Justification for the gradual increase in energy expenditure was to prevent soreness, injuries, and fatigue and minimize dropouts. Participants were weighed each week, and their weight was multiplied by their exercise dose (4, 8, or 12 KKW) to determine the energy expenditure for the week. Power output was calculated at 3-min intervals by speed and grade combinations for the treadmill. When HR fell outside the prescribed training zone, power output was increased or decreased to keep HR within the desired intensity. On average, participants exercised three to four times per week for 6 months.

Pedometer Data

We selected a pedometer model similar to the Yamax SW-200 (YX 200) (Yamax Inc., Tokyo, Japan) called the Accusplit Eagle 120 (AE 120). Previous studies indicate the YX 200 is statistically valid and accurate under free-living and controlled conditions (1,7,14). To our knowledge, there are not any published data showing direct comparison of the YX 200 and the AE 120 under free-living conditions. Therefore, we randomly selected 19 participants to wear the YX 200 on their right hip and the AE 120 on the left hip during waking hours for two consecutive days. Participants then recorded their step counts from each pedometer at the end of the day. Our methodology was similar to a previous study comparing the Yamax SW-200 to 12 other various pedometer models (14). The average interclass correlation of the AE 120 compared to the YX 200 was 0.97. The average steps per day for the YX 200 and the AE 120 were 7482 ± 2611 and 7247 ± 2851, respectively. Delta was −235, which means the AE 120 underestimated 3.1% of the step counts compared to the YX 200. We found this to be acceptable measurement error for the AE 120, and these results justify our choice of pedometer for this study.

Baseline step counts.

Participants wore their pedometers during all waking hours and recorded their daily step count on a machine readable (Teleform™) logging form each night just before going to bed. The pedometer was reset the next day and baseline step counts were recorded over seven consecutive days after the initial study orientation.

Free-living step counts.

Women randomized into the trial continued to wear pedometers and record daily step values over the course of the study. These free-living pedometer data allowed us to monitor the women’s daily activity outside the planned exercise sessions. Participants returned completed log forms at the end of each month. Pedometer data were entered into our database and sorted by exercise group. We categorized pedometer data into months 1 through 6, organized into weeks 1 through 24, and calculated steps per week for each participant. For our study, we used only weeks that had ≫3 d reported and pedometer log compliance was determined by how many days were recorded from a 7-d week. On average, our participant sample completed 93% of their monthly pedometer logs over the 6-month training period.

Exercise step counts.

Participants removed their pedometer before each exercise session. Exercise step counts were collected using different pedometers specifically assigned to each treadmill, which ensured measurement consistency for exercise step count data. Immediately after completing each treadmill exercise session, participants removed the “exercise-specific” pedometers and laboratory staff recorded the value. We obtained exercise steps per day from treadmill sessions with no grade and slow to moderate speeds ranging from 1.8 to 3.6 mph or 48 to 97 m·min−1 with identical energy expenditures for each session. Because two of the exercise groups had gradual energy expenditure increases each week, we needed to ensure participants were achieving their assigned randomized dose of weekly energy expenditure. Therefore, we only used pedometer data for each group from weeks 1–24 (4 KKW), weeks 5–24 (8 KKW), and weeks 9–24 (12 KKW).

Statistical Analyses

Baseline and exercise characteristics for each study group are presented as means ± SD. We examined the average exercise time (minutes per session) and average number of exercise sessions (sessions per week) for each group. We determined baseline steps per week, free-living steps per week, exercise steps per visit, and treadmill speeds and distances for each exercise group. We used one-way ANOVA to evaluate differences between exercise groups for baseline steps per day, free-living steps per day, and exercise steps per visit, and repeated-measures ANOVA to evaluate differences between baseline and free-living pedometer data over the course of the study. Because each group differed in sample sizes, the statistical tests for mean differences in study variables were followed by Tukey’s post hoc tests for homogeneity of variance. Statistical significance for all tests was determined at P < 0.05. All statistical analyses were completed with SPSS 10.0 (Cary, NC) statistical software.

RESULTS

Baseline characteristics of study participants are shown in Table 1 for women in each of the three exercise doses. The women had low V̇O2peak, were obese, and had mildly elevated blood pressure, all of which were expected due to the study inclusion and exclusion criteria. At baseline, participants averaged 32,728 ± 13,127, 32,394 ± 10,598, and 30,301 ± 12,279 steps per week for the 4, 8, and 12 KKW groups, respectively. There were no significant differences among groups for baseline steps per week (P = 0.25) and steps per day (P = 0.49). During the 6-month exercise-training period, the average free-living (outside of the formal exercise sessions) steps per week were 35,904 ± 12,238 (4 KKW), 36,752 ± 12,854 (8 KKW), and 33,503 ± 8,846 (12 KKW). Pedometer data at baseline and free-living (6 months of exercise training) periods for each group did not differ significantly (4 KKW, P = 0.70; 8 KKW, P = 0.33; and 12 KKW, P = 0.41).

T1-25
TABLE 1:
Baseline study characteristics for each of the three exercise groups.

Exercise Training

There were 1590 exercise sessions performed by 111 participants who met criteria set to establish pedometer indices (i.e., treadmill speed and grade with identical energy expenditures, two or more visits per week, and meeting the assigned energy expenditure doses). Figure 1 presents the breakdown of exercise sessions used in these analyses. Average exercise session data are presented in Table 2. The women obtained their weekly exercise dose in three to four sessions per week. Mean total time spent exercising was 78 ± 21 min·wk−1 (4 KKW), 144 ± 25 min·wk−1 (8 KKW), and 240 ± 36 min·wk−1 (12 KKW). The average amount of weekly energy expenditure completed was 358.2 ± 74.5 kcal·wk−1 (4 KKW), 658.7 ± 108.0 kcal·wk−1 (8 KKW), and 975.7 ± 132.0 kcal·wk−1 (12 KKW). This closely matched the average amount of weekly energy expenditure prescribed at 337.3 ± 44.3 kcal·wk−1 (4 KKW), 630.7 ± 93.6 kcal·wk−1 (8 KKW), and 957.2 ± 164.1 kcal·wk−1 (12 KKW).

For each exercise group, the average weekly exercise step counts were 8313 ± 1774 steps·wk−1 (4 KKW), 16,370 ± 3955 steps·wk−1 (8 KKW), and 24,121 ± 3929 steps·wk−1 (12 KKW). As expected, there was a direct and significant linear trend from the lowest to highest exercise group for pedometer data (P = 0.001). Participants attended 3.0 sessions per week (4 KKW and 8 KKW) or 3.8 sessions per week (12 KKW), and the average exercise steps per session to meet the prescribed dose of energy expenditure is given in Table 2.

F1-25
FIGURE 1— Schematic outline of the distribution of exercise training sessions into exercise groups and the number of participants associated with each group.
T2-25
TABLE 2:
Description for average exercise session characteristics for each group.

DISCUSSION

The primary finding in this study is that postmenopausal women can meet 50% (4 KKW), 100% (8 KKW), and 150% (12 KKW) of the current public health recommendation of weekly energy expenditure through planned moderate-intensity walking 3–4 d·wk−1, averaging about 2800 steps per exercise session (50%), 5500 steps per exercise session (100%), and 6500 steps per exercise session (150%). On the remaining days of the week, participants maintained their sedentary behavior similar to baseline levels. Public health physical activity recommendations are usually expressed as distances walked, duration, and frequency of exercise. For example, Pate et al. (13) recommend walking approximately 30 min·d−1, most days of the week, in addition to normal daily physical activity. This recommendation does not give a clear definition of the routine physical activity level to which purposeful exercise walking needs to be added. Second, we do not know how many steps are needed to meet this public health recommendation as a way of quantifying the recommendation with objective monitoring. For instance, the 10,000 steps·d−1 recommendation does not indicate how much intentional exercise walking is needed over and above routine daily steps. Therefore, if we quantify the dose of exercise needed to meet the public health recommendation and define normal daily activity, we can get a better delineation of precise bouts of physical activity.

Currently, there is limited scientific literature using pedometers to define the consensus public health recommendation for weekly physical activity in postmenopausal women. Limitations in existing data underscore the need for additional information on pedometer values necessary to meet the consensus recommendation for weekly physical activity and total accumulated daily activity for postmenopausal women. Welk et al. (22) initially extrapolated a pedometer-driven guideline for meeting the current physical activity guidelines. Thus, they concluded 3800–4000 steps would be sufficient to meet the current activity guidelines of walking for 30 min at a moderate intensity (2 miles at approximately 4.0 mph). The average step counts for their participants on days with exercise were 11,603 steps·d−1. But Welk et al. did not measure baseline pedometer values; therefore, they were unable to adequately define daily activity absent of structured exercise. A study by Wilde et al. (23) determined baseline pedometer values and 30 min of brisk walking for sedentary women (33–55 yr). Their results showed women averaged 7439 steps·d−1 at baseline and 3104 steps in 30 min of brisk walking, but this investigation also showed that on days women walked for 30 min, almost half of them did not meet the 10,000 total steps-per-day target. In contrast, LeMasurier et al. (8) demonstrated that sedentary women accumulating 10,000 total steps per day were more likely to meet exercise bouts equivalent to the 30 min·d−1 public health recommendation. Another study that demonstrates 30 min·d−1 of walking in addition to normal physical activity can approximately achieve the 10,000 steps·d−1 recommendation was the investigation of Moreau et al. (10). They examined the effectiveness of the American College of Sports Medicine (ACSM) and Centers for Disease Control and Prevention (CDC) recommendations (13) for lowering blood pressure in postmenopausal women and indirectly quantified pedometer values needed to achieve the public health recommendation. The walking program was designed to increase daily walking distances (2–4 km·d−1), in addition to their total daily physical activity, equivalent to meeting the consensus public health recommendation. The exercise group averaged 5400 steps·d−1 at baseline, increased their walking by 4300 steps·d−1 (2.9 km·d−1), and averaged 9700 total steps per day.

No other investigators have used weekly energy expenditure, objectively determined in a laboratory setting, to quantify the public health recommendation. Our study design differs from the previous research because we administered the public health recommendation as weekly energy expenditure over 3–4 d rather than daily exercise time or walking distance. Due to the amount of travel time required to attend the supervised exercise sessions, our participants opted to spend more time exercising per day on fewer days of the week to meet their weekly dose of energy expenditure. Therefore, our results indicate the portion of steps per day that could be accumulated in bouts of purposeful walking at moderate intensity a few times a week rather than every day of the week. Simply put, these sedentary and overweight postmenopausal women met 100% of current public health recommendation of weekly energy expenditure through moderate-intensity walking at approximately 2.6 mph for approximately 48 min, producing approximately 5500 steps per exercise session, in addition to their normal daily activity, 3 d·wk−1. The pedometer data in the studies previously mentioned were self-reported and not rigorously controlled. We had each participant perform a V̇O2peak cycle ergometer test, and thus we were able to tightly control exercise intensity and energy expenditure according to HR in our exercise training.

On days that our participants exercised, the total daily step counts support both the initially published step count public health indices (17) of total daily activity and the highly publicized 10,000 steps·d−1 recommendation (5). Therefore, the current cumulative steps per day recommendation is plausible for sedentary postmenopausal women to achieve. Further emphasis of a pedometer recommendation should be put on the amount of planned moderate-intensity activity accomplished throughout the day in addition to normal free-living activity levels. For example, a goal for postmenopausal women would be to achieve somewhere between 5500 steps·d−1 (3 d·wk−1) or 6500 steps·d−1 (4 d·wk−1) of moderate-intensity walking over and above sedentary levels to meet 100 or 150% of the public health recommendation for weekly physical activity. Therefore 3–4 d of 10,000 steps·d−1 are necessary to meet energy expenditure guidelines for the week. Even though daily recommendations are consistent with the Surgeon General’s approach, Moreau et al. and others have also shown the daily goal of 10,000 steps to be achievable, even in postmenopausal women, in maintaining an exercise program for improving health.

Currently, we do not have evidence that performing fewer steps per day over an entire week will elicit similar health benefits as fewer days of more steps per day. However, it is likely that there are additional health benefits associated with exceeding the thresholds studied. The exercise doses were determined from weekly energy expenditure derived from the consensus recommendation for weekly physical activity, which has been shown to confer positive health benefits (12,13).

There are two limitations in this investigation that need to be addressed. The primary limitation is that participants alternated exercise modalities (treadmill and bicycle) throughout the week. This means participants did not experience an entire week of exercise dedicated exclusively to walking. Because the pedometer was not worn during bicycle exercise sessions, this has no bearing on our results. A second limitation is our inability to quantify intensity or duration in the free-living pedometer data accumulated outside of our laboratory. We used the free-living step data to determine whether significant changes occurred in normal daily physical activity patterns.

In summary, initially sedentary postmenopausal women who take <5400 steps·d−1 at baseline can meet 100% of the current public health recommendation of weekly physical activity through planned moderate-intensity walking, averaging at least 5500 steps per exercise session (3.5 km), 3 d·wk−1. Our investigation is in general agreement with preliminary pedometer indices for public health for sedentary postmenopausal women (17). Our research also provides clarity to previous research done in similar populations and pedometer values mentioned meeting the consensus recommendation for weekly energy expenditure. Additional research in this area is warranted for other age- and gender-specific populations. This would prove beneficial for determining appropriate step count recommendations for public health promotion initiatives. Further research from DREW will allow us to observe the health benefits derived from the different exercise doses in sedentary postmenopausal women.

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Keywords:

STEP COUNTERS; ENERGY EXPENDITURE; EXERCISE; WALKING; FEMALES

©2005The American College of Sports Medicine