How many steps/day are enough? for children and adolescents

Normative data (expected values)

Normative steps/day data (or expected values) provide an indication of central tendency and variability and are useful for comparison purposes and interpreting change. Howeverthey should not imply what children or adolescents "should" be takingan index more appropriately described as a cut point or threshold value. Early work [7] that attempted to collate normative data (from studies published between 1980 and 2000) reportedbased on a single study [10] published at the timethat we can expect 8-10 year old children to take 12,000 to 16,000 steps/day (lower for girls than boys). No data were available at the time to inform the number of steps/day that adolescents take. Since thenhoweverstudies of young people's step data collected using pedometers and accelerometers have proliferated. In particulartwo reviews have published normative data for childrentogether covering each sex-age group from 5-19 years of age [11,12]. Among childrenboys average 12,000 to 16,000 steps/day and girls average 10,000 to 13,000 steps/day [11]. Although there are exceptions among countriesin generalpeak values of mean steps/day occur before 12 years of age and decrease through adolescence until mean values of approximately 8,000 and 9,000 steps/day are observed in 18-year olds [12]. Across studiesphysical education class participation generally contributes ≅9-24% of daily steps in boys and ≅11.4-17.2% in girlsand afterschool activity accounts for ≅47-56% and ≅47-59% (boys and girls respectively) of daily steps on school days [11]. Differences among countries are apparentwith children from North America (Canada and United States) showing lower values compared to other regions of the worldfor examplewhen compared to European countries (SwedenUnited KingdomBelgiumCzech RepublicFranceGreeceand Switzerland)but especially when compared to Western Pacific countries (Australia and New Zealand) [12].

Beyond these reviewsa few specific references relative to normative data in young people are noteworthy. Vincent and Pangrazi [13] reported normative data for a U.S. sample in 2002 and at that time suggested that the mean values of 13,000 for U.S boys and 11,000 for U.S. girls could be used as reasonable standards for evaluation purposes. The U.S. President's Challenge: Physical Activity and Fitness Awards Program [14] adopted these same values to recognize physically active U.S. children (ages 6-17 years). A number of researchers from around the world have used these same values as cut points to evaluate data [15-17] although they can only be traced back to mean values based on a single descriptive study [13] of weekday step values obtained by 711 children aged 6-12 years living in the Southwestern U.S. The National Health and Nutrition Examination Survey (NHANES) in the U.S. adopted an accelerometer to objectively monitor physical activity in the 2003-2004 and 2005-2006 cycles; step data for children and adolescents collected in 2005-2006 have been recently published [5]. Once adjusted (i.e.reduced to those steps taken above a specified intensity) to make these accelerometer-determined step data interpretable against common pedometer-based scalesthe results indicate that American young people aged 6-19 years take approximately 9,500 (boys) and 7,900 (girls) steps/day [5]. The 2005-2007 Canadian Physical Activity Levels Among Youth (CANPLAY) pedometer-determined physical activity data (based on a nationally representative sample of > 11,500 Canadian young people) are also just recently available [6,18]. The results indicate that Canadian young people aged 5-19 years of age take 12,000 (boys) and 11,000 (girls) steps/day [6]. To put these American and Canadian values in contextAmish young people 6-18 years of agewho purposefully refrain from adopting most technologies of modern livingaverage over 15,000 steps/day [19].

Tudor-Locke and Bassett [20] established pedometer-determined physical activity cut points for healthy adults: 1) < 5,000 steps/day (sedentary); 2) 5,000-7,499 steps/day (low active); 3) 7,500-9,999 steps/day (somewhat active); 4) ≥ 10,000-12,499 steps/day (active); and 5) ≥12,500 steps/day (highly active). These categories were reinforced in an updated review in 2008 [21] and in 2009 the original sedentary level was segmented into two additional levels: < 2,500 steps/day (basal activity) and 2,500 to 4,999 steps/day (limited activity) [22]. A similar (but sex-specific) graduated step index has been introduced for children (ages 6-12 years) [21]. Values for boys are: 1) < 10,000; 2) 10,000-12,499; 3) 12,500-14,999; 4) 15,000 - 17,499; and5) ≥ 17,500 steps/day. The corresponding values for girls are: 1) < 7,000; 2) 7,000-9,499; 3) 9,500-11,999; 4) 12,000 - 14,499 and5) ≥ 14,500 steps/day. The primary anchors for both of these sex-specific indices were based on a BMI-referenced criterion study of U.S.Australianand Swedish children 6-12 years of age [23]and the appropriateness and generalizability of these cut points have been questioned [24]. The increments in the children's graduated step index were selected to be congruent with the adult index. For both sexeseach escalating category can be interpreted as "sedentary""low active," "somewhat active," "active," and "highly active" similar to the labels used to define levels in the adult graduated step indexhoweverthey have also been given labels of "copper," "bronze," "silver," "gold"and "platinum," in keeping with a reflective of current physical activity and fitness award programs in the U.S. [14]. Another strategy might be to adopt existing graduated Canadian Physical ActivityFitness and Life Approach (CPAFLA) [25] labels: Needs ImprovementFairGoodVery Goodand Excellent. It may be difficult to avoid unintentional potential for stigmatization using any qualitative labelhowever [21]. Only a single study has used this index to describe distribution of child data at this time [5] and we know of no validation study with regards to any other health parameter. An additional criticism of this version of children's graduated index could be that there are not enough "rungs on the ladder" leading up to the identified floor values separating 'sedentary' from 'low active." As indicated abovetwo additional levels have been added to the adult version. There is very little step data to inform an adolescent-specific graduated step index at this time.

Seventeen studies were identified that have reported relative achievement of various step-defined cut points and these are presented in Table 1 by publication year. Three of these have used the Vincent and Pangrazi [13] and/or President's Active Life Award [14] values of 13,000 for boys and 11,000 for girls (based on normative values for American adolescents [13]). Six have used BMI-referenced values (15,000 for boys12,000 for girls) described above [23]. Four have examined both of theseone used the Rowlands and Eston [16] cut points of 13,000 (boys) and 12,000 (girls) based on accumulating > 60 minutes in accelerometer-determined MVPA within the course of daily activityone used the sex-specific children's graduated step index [23]and the remainder have used other variations. In general1) relatively more children than adolescents achieve a given cut point2) relatively more children and adolescents are able to achieve lower (rather than higher) cut pointsand 3) relatively fewer U.S. children and adolescents achieve the same cut points when compared to those from other countries. Not included in the table is a study by Beets et al. [24] which evaluated the BMI-referenced cut points (e.g.in terms of sensitivity and specificity) but did not report the actual percentage of the sample achieving them.

In summarythe updated normative data (i.e.expected values) based on international studies indicates that we can expect 1) among childrenboys to average 12,000 to 16,000 steps/day and girls to average 10,000 to 13,000 steps/day; and2) steps/day values in adolescents to steadily decrease until approximately 8,000-9,000 steps/day are observed in 18-year olds.

Interventions

A systematic review of studies that have used pedometers to promote physical activity in children and adolescents has been recently published [26]. Only 14 studies were identifiedand 12 of these documented increases in physical activity. The magnitude of the intervention effects was variable and could very well reflect differences in study participants (e.g.children vs. adolescentsobese vs. non-obese)program factorsstudy design (e.g.1-week to 6-month interventions)and/or assessment protocols. Limited evidence suggests that the intervention effects are greater in participants who are 'low active' to begin with. In particularadolescents who already take ≥13,000-15,000 steps/day do not appear to respond to goal-setting or activity monitoring strategies using pedometers. The magnitude or pattern of change that can be expected from pedometer-based interventions in children and adolescents is not known at this time. The authors of that review concluded that since there were so few intervention studies publishedyet the results were generally positivecontinued research should be encouraged to inform guidelines with regards to using pedometers to promote physical activity in children and adolescents. It is clear that this area of knowledge is lackingespecially when compared with what is known about pedometer-based interventions in adults [27-29].

Controlled studies

Cadence is the expression of steps taken per unit time (i.e.steps/minute) and it can be used to infer intensity of continuous ambulation [30,31]. Four controlled studies have been conducted with healthy young people [32-35]. The series of studies conducted by Scruggs and colleagues [36-41] were not considered here since they focus on steps detected specifically during physical education classeswhich would logically include at least some sedentary time (e.g.for instructionclass managementetc.)and this would effectively lower mean cadence values. In a similar mannera study by Beets et al. [42] focused on steps associated with time in MVPA detected during afterschool programs was not considered here.

Jago et al. [35] studied pedometer-determined steps taken by 78 11-15 year old USA-based Boy Scouts at externally-paced slow (10 minutes at 4.83 km/hr ≅ 3 METs or moderate intensity) and fast walks (10 minutes at 6.44 km/hr ≅ 5.0 METs or moderate-vigorous intensity) and running (5 minutes at 8 km/hr ≅ 8 METs or vigorous intensity) on a 200 m track. METs (metabolic equivalents) are often used to quantify physical activity intensity with respect to resting or basal metabolic rate (1 MET ≅ 3.5 ml O₂/kg/min or 1 kcal/kg/min for adults). In the Jago et al. [35] study MET level was not directly measured but rather was inferred from the Compendium of Physical Activities [43]. Although participants also wore a CSA accelerometer (an earlier version of the ActiGraph accelerometers) during these trialsthe output of that instrument was only used to assess pedometer (New Lifes Digiwalker SW-200) validity by correlation and was not otherwise used to inform "how many steps are enough?" Mean steps/minute overall for the slow and fast walks and the run were 117127and 163respectively. The authors focused on the results of the fast walk (taken at 5 METs) to extrapolate that approximately 4,000 steps in 30 minutes or 8,000 steps in 60 minutes was equivalent to adolescent-appropriate amounts of time in MVPA. Howeverif 3 METs is considered the floor of moderate intensity activity [44]it follows that 3,510 steps in 30 minutes or 7,020 steps in 60 minutes would be a more literal translation of the results of the slow 3 MET walk. It must be notedthat moderate intensity might be more correctly considered to be 4 METs in children [45]. Since cadences were only measured for 3 MET (slow) and 5 MET (fast) walks122 steps/min is a mid-way estimate for a 4 MET walk. This produces an estimate of 3,660 steps in 30 minutes and 7,320 steps in 60 minutes. Since Jago et al. [35] also reported that adolescents at risk of overweight (BMI > 85^th percentile) took somewhat fewer steps/minute (i.e.111123and 156 steps/min for each of the trials)111 steps/min is the cadence associated with 3 METS and 117 steps/min would be the cadence associated with 4 METs. Togetherthe floor of moderate intensity might be better captured by a range of approximately 3,300-3,500 steps in 30 minutes (or 6,600-7,000 steps in 60 minutes) of continuous walking at 3 METs or approximately 3,500-3,700 steps in 30 minutes (or 7,000-7,400 steps in 60 minutes) at 4 METs.

Graser et al. [33] asked 34 girls and 43 boys aged 10-12 years to wear a pedometer and walk on a treadmill at 33.5and 4 miles/hour. Intensity was not directly measured; howeverthe authors considered these speeds to represent a range of MVPA walking intensities. The boys' and girls' cadence values were similar across the walking speeds and the researchers concluded thatin general120-140 steps/minute represented a reasonable cadence range associated with MVPA. Intensity-related translations based on taking 120 steps/minute at 3 miles/hour correspond to 3,600 steps in 30 minutesor 7,200 steps in 60 minutes. Graser et al. [33] studied a somewhat younger age group than the Jago et al. [35] study and this might have produced relatively higher cadence ranges. Taken togetherthe two studies indicate that continuous MVPA walking (assuming at least 3 METs) produces 3,300-3,600 steps in 30 minutes or 6,600-7,200 steps in 60 minutes in 10 - 15 year olds. It is important to emphasize that such a translation should only be applied to continuous ambulation performed over the specified amounts of time. It is most important to emphasize that definitions of MVPA differed between these two studies and neither used a direct measure of intensity.

Lubans et al. [34] studied 47 boys and 59 girls (all 14 years old) walking and running on a treadmill at 65-75% of maximum heart rate (confirmed by heart rate monitor). Twenty-seven participants repeated the test three times over the course of a month to determine reliability of results. The results were highly repeatable (ICC = .83-.87). Pedometer-determined cadence associated with the designated heart rate range was 147 steps/minute (range 125 to 149 steps/minute) for boys and 137 steps/minute (range 125 to 149 steps/minute) for girls. Cadence also differed by fitness level (assessed by the 3-min Queen's College Step Test): adolescents in the lowest quintile of cardiorespiratory fitness took 129 steps/minthose in the next two quintiles averaged 138 steps/minand those in the top two quintiles averaged 152 steps/min. It is difficult to use these cadence values to extrapolate to MVPA. The authors did not report when running vs. walking occurredbut it seems likely that the boys and girls with the top fitness levels were running at this higher cadence. Extrapolating from the adult data where the floor value (in absolute terms) of moderate and vigorous intensity is 100 and 130 steps/minute respectively [30]we would expect that a child/adolescent-specific vigorous intensity cadence is likewise at least 30 steps/minute (and likely even higher in children) more than the child/adolescent-specific moderate intensity cadenceor approximately 141 to 157 steps/minute. The Lubans et al. [34] study is grounded by a relative (vs. absolute) indicator of intensity (i.e.heart rate). Furtherthe heart rate range tested in this study is somewhat narrower than previously included in physical activity recommendations (i.e.55-90% of maximum heart rate) [46]. Public health guidelines issued by the American College of Sports Medicine and American Heart Association in 2007 do not provide explicit guidelines in terms of heart rate-determined intensity [47].

More recentlyGraser et al. [32] conducted another study of pedometer-determined cadence and heart-rate determined intensity in 12-14 year old adolescents. Treadmill speeds were set at 4.04.85.64and 6.42 km/hr after confirming that this age group could perform all speeds without breaking into a run. These researchers defined moderate intensity as 40-59% of maximum heart ratewhich may be considered low compared with physical activity recommendations (i.e.55-90% of maximum heart rate) [46]. The corresponding cadence averaged 122 (range 108-134) steps/minute in boys and 102 (range 80-123) steps/minute in girlssuggesting great individual variation in intensity-associated cadencea phenomenon that may reflect underlying variation in development as well as fitness. Limitations include the use of heart rate to define moderate intensity and the use of a target heart rate formula originally produced for adults. Heart rate reflects relative intensityunlike direct measures of intensity such as MET values. As in each of the controlled studies in children and adolescents described abovesteps were detected by a body-worn instrument instead of by direct observationwhich is arguably the more appropriate criterion for these types of lab-based studies.

In summaryno controlled studies of cadence have used a direct measure of absolutely-defined intensity at this time and none have counted steps taken using direct observation. The limited evidence at this time suggests thatin 10-15 year oldscontinuous MVPA walking produces 3,300-3,500 steps in 30 minutes or 6,600-7,000 steps in 60 minutes (assuming at least 3 METs). No studies were located that have attempted to intervene specifically on cadence. Hypotheticallyhoweversuch a practical approach might be useful for increasing time spent in MVPA.

Translating existing physical activity guidelines

As stated earlierpublic health physical activity guidelines are typically expressed in terms of frequencytimeand intensity. For examplea recent PHAC-commissioned systematic review [48] of physical activity and health concluded that "Children and youth 5-17 years of age should accumulate an average of at least 60 minutes per day and up to several hours of at least moderate intensity physical activity. Some of the health benefits can be achieved through an average of 30 minutes per day." It remains logically implicit (although not expressly stated) that these recommended minutes of at least moderate intensity be accumulated over and above such functional activities of daily life. There are no data at this time to inform a quantity of steps suggestive of these 'background' activities in children or adolescentsnecessary to compute an estimate of steps/day that will also include recommended amounts of time spent in MVPA. Howeverstudies of free-living behaviour present an opportunity to identify what total volume of steps/day also includes recommended amounts of activity that is of at least moderate intensity. Seven free-living studies were located that have attempted to provide such information. These studies are presented in Table 2 by year of publication. Two have focused on preschool samples [49,50]three with elementary/primary school children [15,16,51]one with adolescents recruited through primary care providers [52]and one of children and adolescents spanning 9-16 years of age recruited as part of a national survey [53].

Cardon et al. [49] reported that 13,874 pedometer-determined steps/day equated to a total volume of physical activity that included at least 60 minutes of accelerometer-determined time in MVPA in Belgian preschool children; only 8% of their sample actually achieved this level of steps/day. Tanaka and Tanaka [50] used a similar analytical approachbut collected accelerometer data using a triaxial accelerometer to conclude that 60100and 120 minutes of MVPA corresponded to 9,93412,893and 14,373 steps/dayrespectivelyin Japanese preschool children. Furthermore92.4%51.6%and 27.4% of the sample achieved these levels. Although a direct comparison between the Belgian and Japanese studies must be tempered by the fact that different instruments were used to collect step and MVPA datathe latter sample appears to have been much more active than the former; approximately 52% of the Japanese children achieved almost 13,000 steps/day and 100 minutes in MVPA while only 8% of the Belgian sample achieved a similar value of steps/day and only 60 minutes in MVPA.

In a separate studyCardon et al. [15] examined the relationship between 60 minutes of self-reported time in MVPA and pedometer-determined steps/day in Belgian elementary school children. Overall13,130 steps/day was equivalent to a total volume of daily physical activity that included 60 minutes of self-reported time in MVPA. Sex-specific values were 15,340 steps/day (boys) and 11,317 steps/day (girls). These results must be interpreted with caution; the correlation between pedometer-determined steps/day and self-reported time in MVPA was r=.39. In a another study comparing pedometer data with self-reported time in MVPA conducted with 9-16 year oldsthe correlations ranged from .44 to .50 [53]. Linear regression was used to determine that approximately 100 steps equated to about 1 minute of MVPA. By extrapolationthe authors suggested that at least 6,000 steps would be required to accumulate 60 min of MVPA (assumedly taken over and above life activities).

Rowlands and Eston [16] conducted a sensitivity/specificity analysis of various thresholds to ascertain likelihood of attaining 60 minutes of triaxial accelerometer-determined MVPA in Welsh primary school children. They concluded that 13,000 steps/day (boys) and 12,000 steps/day (girls) provided the most reasonable estimation of attainment of 60 minutes of MVPA by way of accumulating a total volume of daily steps. Beighle and Pangrazi [51] used a pedometer that had both a step counting function and an internal stopwatch that accumulates seconds of movement while the step counting lever arm is in motion. The resulting output is labeled "activity time" but also logically includes movement that is likely performed at less than MVPA. Although the outputs were dependent (obtained from the same counting mechanism)the researchers used regression to predict daily activity time from steps/day. They reported that 5,000 steps/day was equivalent to 64.5 minutes of activity10,000 steps/day equals 114.5 minutes12,000 steps/day equals 134.5 minutesand 15,000 steps/day equals 164.5 minutes. This study must be interpreted with due caution (and cannot be reasonably considered together with the other two studies of primary/elementary school children) since the activity time output from this instrument does not necessarily reflect time spent specifically in MVPAbut rather accumulated time associated with all detected movement.

Only a single study has attempted to translate time- and intensity-based physical activity guidelines into a steps/day value specific to adolescents [52]and this was specifically done in overweight 11-16 year olds recruited through their primary care providers. The authors used receiver operating characteristic (ROC) curves to determine a total volume of steps/day most likely related to also achieving 60 minutes of accelerometer-determined MVPA. Two definitions of moderate intensity were used (3 and 4 METs). Depending on the definitionbetween 10,000 (3 METs) and 11,700 (4 METs) steps/day produced the best sensitivity and specificity values for achieving at least 60 minutes of MVPA accumulated within the course of daily living.

In summarythe use of different approaches to measure steps and also time in MVPA hamper the ability to combine results and inform "how many steps are enough" in terms of attainment of recommended amounts of MVPA. Overalllimited evidence suggests that a total daily physical activity volume of 10,000-14,000 steps/day is associated with 60-100 minutes in MVPA for preschool children (≅4-6 years of age) [49,50]. Sixty minutes of MVPA in primary/elementary school children appears to be achievedon averagewithin a total volume of 13,000 to 15,000 steps/day in boys and 11,000 to 12,000 steps/day in girlsalthough these ranges reflect findings based on both self-report [15] and triaxial-determined time in MVPA [16]. For adolescents10,000 to 11,700 steps/day may be associated with 60 minutes of MVPAhowever there is only a single studyand it is based primarily on overweight adolescent girls [52].

Health outcome-related analyses

Besides a translation of time in intensitysteps/day recommendations could also be informed by studies that relate step-defined physical activity to desired health outcomes. Four studies (Table 3) were located that examined steps/day related to indicators of healthy vs. unhealthy body composition in young people. Tudor-Locke et al. [23] combined pedometer data collected in 6-12 year olds from three countries (AustraliaSwedenUSA) and used a contrasting groups method to identify criterion-referenced steps/day cut points related to BMI-defined normal weight vs. overweight/obese. The median value for 6-12 year olds was 15,000 steps/day for boys and 12,000 steps/day for girls. Duncan et al. [54] performed a similar analysis but using percent body fat obtained through bioelectric impedance in 5-12 year old New Zealanders. Overweight was defined as > 85^th percentile and compared with nonoverweight (< 85^th percentile). The authors reported that 16,000 steps/day (boys) and 13,000 steps/day (girls) were the best predictors of body fat percent-defined weight status. Laurson et al. [55] used ROC analysis to match sensitivity and specificity of various cut points and to identify the optimized cut point (which minimized misclassification error for normal weight vs overweight/obese children) in a sample of U.S. children. The optimized cut points approximated 13,500 steps/day (boys) and 10,000 steps/day (girls). Dollman et al. [56] also used ROC analysis in a sample of 2,071 5-16 year old Australian children. The optimized cut points for discriminating between normal weight and overweight/obese children were 12,000 steps/day for 5-12 year old boys10,000 steps/day for 5-12 year old girlsand 11,000 steps/day for 13-16 year old boys. The optimized cut point for 13-16 year old girls (14,000 steps) did not significantly discriminate between those who were classified as normal weight versus overweight.

In summarythe two studies that have applied the contrasting groups method applied to different weight status criteria (BMI and percent body fat) have produced consistently high values for steps/day: 15,000-16,000 steps/day for boys and 12,000-13,000 steps/day for girls [23,54]but these findings may be an artefact of the samples studied [24]. The ROC analyses conducted in the other two studies [55,56] demonstrate better sensitivity and specificity with much lower values of steps/day (approximately 10,000-13,500 steps/day). Although Eisenmann et al. [57] reported that children not meeting the BMI-reference cut points were more likely to be classified as overweightBeets et al. [24] also reported concerns about the sensitivity and specificity of the BMI-referenced cut pointsand in particular questioned their utility across countriesfor example in the U.S. where activity levels are lower (i.e.where even normal weight children have relatively lower activity levels). Across studiesthe lowest estimate has been 10,000 steps/dayand most can agree that even lower values are of increasing concernand higher values are increasingly desirable. Howeversince BMI is obviously influenced by more than just ambulatory activityit may be more appropriate to seek agreement on a step-based translation of public health guidelines than to pursue a more precise estimate associated with a healthy BMI in children and adolescents that is also universally applicable at this time.