Development of an aerobic capacity prediction model from one-mile run/walk performance in adolescents aged 13-16 years.

A popular algorithm to predict VO2Peak from the one-mile run/walk test (1MRW) includes body mass index (BMI), which manifests practical issues in school settings. The purpose of this study was to develop an aerobic capacity model from 1MRW in adolescents independent of BMI. Cardiorespiratory endurance data were collected on 90 adolescents aged 13-16 years. The 1MRW was administered on an outside track and a laboratory VO2Peak test was conducted using a maximal treadmill protocol. Multiple linear regression was employed to develop the prediction model. Results yielded the following algorithm: VO2Peak = 7.34 × (1MRW speed in m s(-1)) + 0.23 × (age × sex) + 17.75. The New Model displayed a multiple correlation and prediction error of R = 0.81, standard error of the estimate = 4.78 ml kg(-1) · min(-1), with measured VO2Peak and good criterion-referenced (CR) agreement into FITNESSGRAM's Healthy Fitness Zone (Kappa = 0.62; percentage agreement = 84.4%; Φ = 0.62). The New Model was validated using k-fold cross-validation and showed homoscedastic residuals across the range of predicted scores. The omission of BMI did not compromise accuracy of the model. In conclusion, the New Model displayed good predictive accuracy and good CR agreement with measured VO2Peak in adolescents aged 13-16 years.

Cross-Validation of Aerobic Capacity Prediction Models in Adolescents.

Cardiorespiratory endurance is a component of health-related fitness. FITNESSGRAM recommends the Progressive Aerobic Cardiovascular Endurance Run (PACER) or One mile Run/Walk (1MRW) to assess cardiorespiratory endurance by estimating VO2 Peak. No research has cross-validated prediction models from both PACER and 1MRW, including the New PACER Model and PACER-Mile Equivalent (PACER-MEQ) using current standards. The purpose of this study was to cross-validate prediction models from PACER and 1MRW against measured VO2 Peak in adolescents. Cardiorespiratory endurance data were collected on 90 adolescents aged 13-16 years (Mean = 14.7 ± 1.3 years; 32 girls, 52 boys) who completed the PACER and 1MRW in addition to a laboratory maximal treadmill test to measure VO2 Peak. Multiple correlations among various models with measured VO2 Peak were considered moderately strong (R = .74-0.78), and prediction error (RMSE) ranged from 5.95 ml·kg⁻¹,min⁻¹ to 8.27 ml·kg⁻¹.min⁻¹. Criterion-referenced agreement into FITNESSGRAM's Healthy Fitness Zones was considered fair-to-good among models (Kappa = 0.31-0.62; Agreement = 75.5-89.9%; F = 0.08-0.65). In conclusion, prediction models demonstrated moderately strong linear relationships with measured VO2 Peak, fair prediction error, and fair-to-good criterion referenced agreement with measured VO2 Peak into FITNESSGRAM's Healthy Fitness Zones.

Impact of short bouts of physical activity on attention-to-task in elementary school children.

OBJECTIVE: The study's objective was to describe the measurement of on-task behavior and review the research on the effects of short physical activity breaks on attention-to-task in elementary school students, with a particular focus on a promising approach to improving on-task behavior with short bouts of physical activity in the classroom setting. METHODS: Procedures to directly observe attention-to-task were detailed. Published studies that measured attention-to-task in elementary school students following physical activity breaks were reviewed. RESULTS: Direct measurement of attention-to-task is intensive and demanding on observers. Previous research on attention-to-task following physical activity breaks is sparse. The limited evidence suggests a small to moderate improvement on attention-to-task following physical activity breaks (Effect Sizes typically ranged from 0.13 to 0.60). Teachers can be trained in a relatively short time to effectively lead classroom-based physical activities. Students who participated in classroom-based physical activities that incorporate academic concepts demonstrated significantly better improvements (+8.3%) in attention-to-task than control group participants (-3.1%). CONCLUSIONS: Attention-to-task is a variable that directly relates to concerns of classroom teachers. The limited available research has demonstrated moderate to good evidence that physical activity during the school day improves attention-to-task in elementary school students. Because of the positive effects of physical activity on attention-to-task, it is recommended that elementary school teachers consider implementing physical activity sessions throughout the school day in the form of recess and classroom-based physical activities.

A randomized controlled trial of continuous activity, short bouts, and a 10,000 step guideline in inactive adults.

OBJECTIVE: Although several studies have examined the effect of accumulated bouts on health outcomes, the impact of recommending short bouts on activity-related behavior in health promotion efforts has received minimal investigation. METHOD: During this 5-week study in 2007-2008, 43 university employees (8 male, 35 female) in the Southeastern United States were randomly assigned to a group recommended to achieve (a) 10,000 steps (10K), (b) 30-minutes (30 min) of continuous physical activity, or (c) 30-minutes of activity in bouts of at least 10 minutes (bouts). RESULTS AND CONCLUSIONS: Repeated measures ANOVA revealed that the 10K group showed the largest increase in step counts whereas the bouts group showed the smallest change over the intervention period, p=0.01. Condition differences were most pronounced on days in which participants met their activity recommendation. Accelerometer results revealed that the 10K (d=1.1) and 30 min groups (d=0.89) showed large increases in minutes of moderate to vigorous activity (MVPA), whereas the bouts group showed minimal change (d=0.11). Although activity recommendations did not differentially affect self-efficacy, participants from all conditions showed decreased self-efficacy across the intervention (p=0.02), highlighting the need to develop strategies to increase self-efficacy in activity promotion efforts.

Shelter dogs, university employees, and lunchtime walks: A pilot study.

BACKGROUND: Workplace walking interventions can lead to positive physical and psychological outcomes for employees. For optimal success, however, innovative approaches that appeal to employees are needed. OBJECTIVE: The purpose of this study was to assess the physical activity levels and experiences of university staff members who walked shelter dogs during their lunch breaks. METHOD: Participants walked with a dog and a partner for 30 minutes during their lunch break one day a week for four weeks. Accelerometer data was collected during participant walks and interviews conducted post-intervention. RESULTS: Quantitative results indicated that participants averaged 24.9±7.4 minutes of moderate-to-vigorous physical activity (range 12- 37 min) during the walk. Qualitative findings suggested that the incorporation of shelter dogs into a walking intervention encouraged participants to take part in the study and continue each week. CONCLUSIONS: Both the quantitative and qualitative data from this pilot study support the notion that including shelter dogs into a university-based walking program encouraged physical activity engagement and adherence.

Walking and measurement.

Walking is an important form of physical activity. It is practiced by people of nearly all ages, throughout the world. Walking is an integral part of life, and there is accumulating evidence that it is essential to good health. There are many ways to measure walking including pedometers, accelerometers, trail counters, direct observation, physical activity questionnaires, and transportation surveys. When measuring walking, researchers must be prepared to demonstrate the validity of their instruments. A paradigm for validation in walking research consists of accumulating evidence at three levels or stages. First, the definitional stage involves investigation of prior theory and empirical evidence to describe the nature of walking. The confirmatory stage involves investigations that either confirm or disconfirm the definition of walking. The highest level of validation is at the theory-testing stage, where we examine theories of how walking is related to other constructs, including the outcomes and the determinants of walking. It is important that validation research in the latter two stages (confirmatory research and theory-testing research) is built on directly relevant research at the earlier stages. The articles presented at the conference on "Walking for Health: Measurement and Research Issues and Challenges" suggest future research directions that will increase our knowledge of walking and health outcomes and provide new approaches to get people walking.

Classroom-Based Physical Activity: Minimizing Disparities in School-Day Physical Activity Among Elementary School Students.

BACKGROUND: Evidence of the positive effects of school physical activity (PA) interventions, including classroom-based PA (CBPA), is rapidly growing. However, few studies examine how variations in scheduled PA opportunities and teacher-implemented CBPA affect students' PA outcomes. METHODS: Teachers at 5 elementary schools attended training on how to implement CBPA. Data on school-day PA opportunities [physical education (PE), recess, and CBPA] were obtained via calendar and teacher-recorded CBPA logs. Daily step counts were measured via accelerometry in 1346 students across 65 classrooms in first through fifth grades. RESULTS: PE, recess, and CBPA contributed significantly to students' daily steps. Males accrued more steps than females over the school day, during PE, and during recess. No gender disparity was seen in the amount of additional steps accrued during CBPA. Overall step counts were lower among fifth-grade students versus first-grade students, but CBPA attenuated this difference such that grade-level differences were not significant in fifth-grade students who received CBPA. CONCLUSIONS: Gender disparities in step totals were present on PE and recess days, but not on CBPA days. CBPA appears to provide equal PA benefits for both genders and to potentially minimize the decline in PA among older students.

Effects of a classroom-based program on physical activity and on-task behavior.

PURPOSE: This study evaluated the effects of a classroom-based physical activity program on children's in-school physical activity levels and on-task behavior during academic instruction. METHODS: Physical activity of 243 students was assessed during school hours. Intervention-group students (N = 135) received a classroom-based program (i.e., Energizers). The control group (N = 108) did not receive Energizers. On-task behavior during academic instruction time was observed for 62 third-grade (N = 37) and fourth-grade students (N = 25) before and after Energizers activities. An independent groups t-test compared in-school physical activity levels between intervention and control classes. A multiple-baseline across-classrooms design was used to evaluate the effectiveness of the Energizers on on-task behavior. Additionally, a two-way (time [pre- vs postobservation] x period [baseline vs intervention]) repeated-measures analysis of variance compared on-task behavior between observation periods. Magnitudes of mean differences were evaluated with Cohen's delta (ES). RESULTS: Students in the intervention group took significantly (P < 0.05) more in-school steps (5587 +/- 1633) than control-group students (4805 +/- 1543), and the size of this difference was moderate (ES = 0.49). The intervention was effective in improving on-task behavior; after the Energizers were systematically implemented, on-task behavior systematically improved. The improvement in on-task behavior of 8% between the pre-Energizers and post-Energizers observations was statistically significant (P < 0.017), and the difference was moderate (ES = 0.60). Likewise, the least on-task students improved on-task behavior by 20% after Energizers activities. This improvement was statistically significant (P < 0.001) and meaningful (ES = 2.20). CONCLUSION: A classroom-based physical activity program was effective for increasing daily in-school physical activity and improving on-task behavior during academic instruction.

The Invisible Employee: University Housekeeping Employees' Perceptions of Physical Activity.

BACKGROUND: A significant literature links race and socioeconomic status with physical inactivity and negative health outcomes. The aim of this study was to explore physical activity (PA) perceptions of an underserved, lower socioeconomic minority sector of the workforce. METHODS: Two focus groups were conducted to examine university housekeepers' perceptions of physical activity. Demographic and anthropometric data were also obtained. RESULTS: Participants (N = 12; 100% female, 100% African-American) overwhelmingly associated PA with traditional exercise (eg, going to a gym). The most important barrier to PA was the perception of being active on the job, thus not needing to do leisure time PA. The most important perceived benefit to PA was improvement of physical and mental health. Employees perceived that a university investment in employees' health might improve morale, especially within low-pay employee sectors where low levels of job satisfaction may be present. CONCLUSIONS: Although perceived benefits to PA in this population are consistent with other employee sectors, perceived barriers to PA may be unique to this sector of the workforce. PA promotion programs should focus on providing resources as well as guidelines that demonstrate the need for PA outside of the workplace setting. Such programs may improve employee health, morale, and productivity.

Before-school running/walking club: Effects on student on-task behavior.

Before-school programs provide a good opportunity for children to engage in physical activity (PA) as well as improve their readiness to learn. The purpose of this study was to examine the effect of a before-school running/walking club on elementary school children's on-task behavior. The study employed a two-phase experimental design with an initial baseline phase followed by an alternating treatments phase, and was first conducted at a private school (School A) and subsequently replicated at a public school (School B). Participants were third and fourth grade children from two schools in the Southwestern U.S. who participated in a before-school running/walking club that met two times each week (School A: 20 min; School B: 15 min) during the 2013/2014 academic year. Participation in the program was monitored using pedometers and on-task behavior was assessed through direct observation. Data analyses included visual analysis, Tau-U index, and multilevel modeling. Results from all analyses indicated that on-task behavior was significantly higher on days the children attended the before-school program than on days they did not. According to multilevel modeling results, mean differences and effect sizes were: School A = 15.78%, pseudo-R (2) = .34 [strong effect]; School B = 14.26%, pseudo-R (2) = .22 [moderate effect]. Results provide evidence for the positive impact of before-school PA programs on children's classroom behavior and readiness to learn. Such programs do not take time away from academics and may be an attractive option for schools. Results also have implications for the structure of children's school day and the scheduling of PA opportunities.

Influence of body composition on physical activity validation studies using doubly labeled water.

This study investigated the influence of two approaches (mathematical transformation and statistical procedures), used to account for body composition [body mass or fat-free mass (FFM)], on associations between two measures of physical activity and energy expenditure determined by doubly labeled water (DLW). Complete data for these analyses were available for 136 African American (44.1%) and Hispanic (55.9%) women (mean age 50 +/- 7.3 yr). Total energy expenditure (TEE) by DLW was measured over 14 days. Physical activity energy expenditure (PAEE) was computed as 0.90 x TEE - resting metabolic rate. During week 2, participants wore an accelerometer for 7 consecutive days and completed a 7-day diary. Pearson's product-moment correlations and three statistical procedures (multiple regressions, partial correlations, and allometric scaling) were used to assess the effect of body composition on associations. The methods-comparison analysis was used to study the effect of body composition on agreement. The statistical procedures demonstrated that associations improved when body composition was included in the model. The accelerometer explained a small but meaningful portion of the variance in TEE and PAEE after body mass was accounted for. The methods-comparison analysis confirmed that agreement with DLW was affected by the transformation. Agreement between the diary (transformed with body mass) and TEE reflected the association that exists between body mass and TEE. These results suggest that the accelerometer and diary accounted for a small portion of TEE and PAEE. Most of the variance in DLW-measured energy expenditure was explained by body mass or FFM.

Critical measurement issues/challenges in assessing aerobic capacity in youth.

We discuss current measurement issues related to tests of aerobic capacity in the FITNESSGRAM. Interpretation of tests of aerobic capacity is difficult because the criterion measure of aerobic capacity, maximal rate of oxygen uptake (VO2(max)) expressed relative to body weight, is inversely related to body fatness and body mass index (BMI). This association cannot be easily be eliminated in a way that maintains the units commonly used to express aerobic capacity (i.e., mL x kg(-1) x min(-1)) and is understandable to typical test users. Requiring the measurement of BMI to predict VO2(max) creates practical problems for users by: (a) uncoupling the relation of predicted VO2(max) to physical performance on the 1-mile run/walk (MRW) and the Progressive Aerobic Cardiovascular Endurance Run (PACER) tests, (b) making explicit the influence of body composition on the ability of children to achieve the aerobic capacity healthy fitness zone, and (c) creating a barrier for users who cannot measure height and weight. The use of test equating improved classification agreement between the MRW and PACER tests but required measurement of BMI to estimate aerobic capacity from the PACER. A new equation to predict aerobic capacity that does not require BMI was recently introduced to address user concerns. This change will improve ease of use of the Fitnessgram with little effect on prediction accuracy but will likely result in poorer classification agreement between the MRW and PACER tests. Although considerable progress has been made in addressing issues related to assessment of aerobic capacity in youth, future work is needed to carefully balance the issues of prediction accuracy, test feasibility, and test agreement.

Feasibility of retrofitting a university library with active workstations to reduce sedentary behavior.

BACKGROUND: Libraries are an inherently sedentary environment, but are an understudied setting for sedentary behavior interventions. PURPOSE: To investigate the feasibility of incorporating portable pedal machines in a university library to reduce sedentary behaviors. METHODS: The 11-week intervention targeted students at a university library. Thirteen portable pedal machines were placed in the library. Four forms of prompts (e-mail, library website, advertisement monitors, and poster) encouraging pedal machine use were employed during the first 4 weeks. Pedal machine use was measured via automatic timers on each machine and momentary time sampling. Daily library visits were measured using a gate counter. Individualized data were measured by survey. Data were collected in fall 2012 and analyzed in 2013. RESULTS: Mean (SD) cumulative pedal time per day was 95.5 (66.1) minutes. One or more pedal machines were observed being used 15% of the time (N=589). Pedal machines were used at least once by 7% of students (n=527). Controlled for gate count, no linear change of pedal machine use across days was found (b=-0.1 minutes, p=0.75) and the presence of the prompts did not change daily pedal time (p=0.63). Seven of eight items that assessed attitudes toward the intervention supported intervention feasibility (p<0.05). CONCLUSIONS: The unique non-individualized approach of retrofitting a library with pedal machines to reduce sedentary behavior seems feasible, but improvement of its effectiveness is needed. This study could inform future studies aimed at reshaping traditionally sedentary settings to improve public health.

Accuracy of intensity and inclinometer output of three activity monitors for identification of sedentary behavior and light-intensity activity.

Purpose. To examine the accuracy of intensity and inclinometer output of three physical activity monitors during various sedentary and light-intensity activities. Methods. Thirty-six participants wore three physical activity monitors (ActiGraph GT1M, ActiGraph GT3X+, and StepWatch) while completing sedentary (lying, sitting watching television, sitting using computer, and standing still) light (walking 1.0 mph, pedaling 7.0 mph, pedaling 15.0 mph) intensity activities under controlled settings. Accuracy for correctly categorizing intensity was assessed for each monitor and threshold. Accuracy of the GT3X+ inclinometer function (GT3X+Incl) for correctly identifying anatomical position was also assessed. Percentage agreement between direct observation and the monitor recorded time spent in sedentary behavior and light intensity was examined. Results. All monitors using all thresholds accurately identified over 80% of sedentary behaviors and 60% of light-intensity walking time based on intensity output. The StepWatch was the most accurate in detecting pedaling time but unable to detect pedal workload. The GT3X+Incl accurately identified anatomical position during 70% of all activities but demonstrated limitations in discriminating between activities of differing intensity. Conclusions. Our findings suggest that all three monitors accurately measure most sedentary and light-intensity activities although choice of monitors should be based on study-specific needs.

Estimation of aerobic fitness from 20-m multistage shuttle run test performance.

BACKGROUND: Aerobic fitness (VO(2)max) is a key component of youth fitness testing. Criterion-referenced (CR) assessments are used in FITNESSGRAM(®) to assess health risk. PURPOSE: The purpose of this study was to develop and cross-validate regression models to estimate VO(2)max from Progressive Aerobic Cardiovascular Endurance Run (PACER) 20-m shuttle run performance in boys and girls aged 10-16 years. Several previously published PACER models were also cross-validated. A secondary purpose was to examine the CR validity of the models. METHODS: PACER performance and VO(2)max were assessed in a sample of 244 participants. The sample was randomly split into validation (n=174) and cross-validation (n=70) samples. The validation sample was used to develop the regression models to estimate VO(2)max from PACER, BMI, gender, and age. CR validity was evaluated by comparing classification of the prediction models with classification by the criterion of measured VO(2)max. RESULTS: For the Quadratic Model, the multiple correlation between measured and estimated VO(2)max was 0.75, and the SE of estimate (SEE) was 6.17 mL/kg/min. Similar accuracy was found for Linear Model 2 (R=0.74; SEE=6.29 mL/kg/min). Accuracy of these models was confirmed on the cross-validation and total samples. Cross-validation demonstrated that the Quadratic Model and Linear Model 2 were slightly more accurate than previous PACER models. Evidence of CR validity for the newly developed models was of moderate levels. CONCLUSIONS: The Quadratic Model and Linear Model 2 provide valid estimates of VO(2)max and compare favorably to previous models. The CR validity evidence for the Quadratic Model and Linear Models developed in this study was slightly better than for the other models examined.

Cross-validation of an equating method linking aerobic FITNESSGRAM® field tests.

BACKGROUND: Field tests measuring the same construct, in this case, aerobic capacity, use different scales, which makes fitness assessment of children and youth potentially confusing. The Primary Field Test Centered Equating Method has been developed to set tests on the same scale, as illustrated by the conversion of Progressive Aerobic Capacity Endurance Run (PACER) scores to 1-mile run/walk times to estimate VO(2)max. PURPOSE: The purpose of this study was to cross-validate the Primary Field Test Centered Equating Method by using a data set of middle school students to assess its effectiveness. METHODS: PACER scores of 135 middle school students were converted to 1-mile run/walk times (Mile PEQ) using the proposed method. Several estimates of VO(2)max using PACER scores were then compared to estimated VO(2)max using Mile PEQ and measured VO(2)max. The obtained measures were classified according to the healthy fitness zone (HFZ; FITNESSGRAM(®), version 9) and compared to measured VO(2)max. BMI estimates based on the sample data and the national average also were considered to assess the method's flexibility. RESULTS: Agreement levels with actual values were similar for VO(2)max predicted using Mile PEQ and predictions using PACER laps and speed (73%-75%). The t-tests showed no significant difference between actual VO(2)max (M=44.43, SD= 8.36) and VO(2)max predicted using Mile PEQ (M=44.33, SD=5.88). Using BMI averages from sample data and the national data to estimate VO(2)max using Mile PEQ also yields high agreement levels, 70% and 73%, respectively. CONCLUSIONS: The Primary Field Test Centered Equating Method performs as well or better in estimating VO(2)max as several other models using PACER scores, especially for boys, and thus may be successfully used in practice. More research is needed to understand the relatively low prediction and classification accuracy in girls.

The Bland-Altman method should not be used in regression cross-validation studies.

The purpose of this study was to demonstrate the bias in the Bland-Altman (BA) limits of agreement method when it is used to validate regression models. Data from 1,158 men were used to develop three regression equations to estimate maximum oxygen uptake (R2 = .40, .61, and .82, respectively). The equations were evaluated in a cross-validation sample of 581 men. The BA means and differences were correlated (p < .001) in the cross-validation sample for each model (r = .55, .39, and .26, respectively), thus demonstrating bias. The BA method is inappropriate for validation of regression models. Validation of regression equations is properly conducted by plotting the residuals against the estimated values and examining the magnitude of the estimation error.

Stride rate recommendations for moderate-intensity walking.

UNLABELLED: Current physical activity guidelines recommend physical activity of at least moderate intensity to gain health benefits. Previous studies have recommended a moderate-intensity walking cadence of 100 steps per minute for adults, but the influence of height or stride length has not been investigated. PURPOSE: the purpose of the current study was to determine the role of height and stride length in moderate-intensity walking cadence in adults. METHODS: seventy-five adults completed three treadmill walking trials and three overground walking trials at slow, medium, and fast walking speeds while V˙O2 was measured using indirect calorimetry. Five stride length-related variables were also measured. RESULTS: mixed model regression analysis demonstrated that height explained as much variability in walking intensity at a given cadence as did two different measures of leg length and two different stride length tests. CONCLUSIONS: the previous general recommendations of 100 steps per minute were supported for use where a simple public health message is needed. Depending on height, moderate-intensity walking cadence can vary by more than 20 steps per minute, from 90 to 113 steps per minute for adults 198 to 152 cm tall, respectively. Height should therefore be taken into consideration for more precise evaluation or prescription of walking cadence in adults to provide health benefits.

Individual information-centered approach for handling physical activity missing data.

The purpose of this study was to validate individual information (II)-centered methods for handling missing data, using data samples of 118. We used a semisimulation approach to create six data sets: three physical activity outcome measurements (i.e., step counts, activity counts, and minutes of moderate to vigorous physical activity) for both groups (i:e., middle-aged adults and older adults). After analyzing each data set separately, we replaced missing values with two II-centered and two group information (GI)-centered methods. Root mean square difference (RMSD), mean signed difference, paired t tests, and Pearson correlations were used to determine the effectiveness of the various recovery methods. Overall, the II-centered methods showed smaller RMSDs than the GI-centered methods for each data set in both groups. We found no significant mean differences between the known values and the replacement values in all conditions. The II-centered methods produced better results than GI-centered methods. We determined substituting missing data points using the average of days remaining to be an accurate missing data recovery method for middle-aged adults' and older adults'pedometer and accelerometer data.

Energy expenditure of obese, overweight, and normal weight females during lifestyle physical activities.

OBJECTIVE: To quantify energy expenditure of various lifestyle physical activities of obese, overweight, and normal-weight girls. METHODS: In total, fifty-five girls participated in six activities: a treadmill walk at 4.0 km x hr(-1), run, football throw, walk in open area, cycle, and riding a scooter. Intensities for all activities except the treadmill walk were self-selected. Energy expenditure was measured using the COSMED K4b(2) portable metabolic system. Analyses of variance were used to compare the three groups (obese n = 11, overweight n = 16, and normal weight n = 28) on relative VO2 (ml x kg(-1) x min(-1) and ml x FFM(-1) x min(-1)), and absolute energy expenditure (kJ x min(-1)). Magnitudes of the mean differences were examined using Cohen's delta (ES). RESULTS: Relative VO2 (ml x FFM(-1) x min(-1)) was not significantly different (p > 0.05) among the groups for any activity. Obese girls expended more energy (p < 0.05) than normal-weight girls on all weight bearing activities. These differences were large (ES > or = 0.91). The differences in kJ x min(-1) between the obese and normal weight groups for the bicycle and scooter activities were moderate to large (ES > or = 0.56), although not statistically significant. The overweight group expended more energy than the normal weight group and less energy than the obese group on all activities (ES = 0.17 to 1.82), although these differences were generally not statistically significant. CONCLUSIONS: The oxygen costs of various activities are similar among obese, overweight, and normal-weight girls when expressed relative to fat-free mass. When engaging in self-selected levels of activity, obese girls have a higher absolute energy expenditure than normal-weight girls.