RT3 Accelerometer Research Articles

Calorie Expenditure As Function Of Age-gender And Lesson Length-content Interaction In Physical Education

Physical education is where all school-age children can receive benefits from physical activities that are planned for them. Calorie expenditure in physical education lessons is an important indicator of the benefits received by children. It is influenced, however, by lesson factors and children personal factors. PURPOSE: To identify personal (gender, age, BMI) and lesson factors (length, content, grade level) that influence children calorie expenditure in elementary and middle school physical education. METHODS: Activity calorie expenditure of 658 children (age 8-14, 49.5% girls) in randomly selected 14 elementary and 15 middle schools was measured in 267 lessons in three years using RT3 accelerometers. RESULTS: Factorial ANOVA with lesson as the unit of analysis revealed a length-by-content interaction: children in 30-45min and 46-70 min. sport or fitness lessons had a higher calorie expenditure rate than those did in 71-90 min. game or multi-activity lessons (2.76 - 2.97/min. vs. 1.21-2.19/min., p=.04, effect size: eta-squared =.07). At the personal-factor level, a hierarchical linear analysis identified an age-by-BMI interaction: younger, heavier children spent more calories than older, normal-weight and super-thin children (p=.02, effect size: eta-squared =.02); and an age-by-gender interaction: older boys expended more calories than younger boys and girls (p=.008, effect size: eta-squared =.02). At the lesson level, the analysis confirmed the lesson length-by-content interaction found in the ANOVA. CONCLUSION: Calorie expenditure in physical education is influenced by both personal and lesson factors. While personal factors (age, gender, BMI) are difficult to change at any given time, offering sport and fitness content in intermediate length lessons (45-70 min.) can provide optimal opportunities for children to expend more calories in physical education.

Using fitness devices and GPS (global positioning systems) technology in measuring energy expenditure and distance walked over flat and incline surfaces

The purpose of this study is to evaluate the accuracy of five fitness devices (one GPS watch, two types of pedometers, and two types of accelerometers) in estimating distance and energy expenditure (EE), as compared to criterion values, while traversing two different surfaces: flat and inclined. All five devices are worn by each participant for each trial. For the flat surface, participants walked at two different speeds (5 km/hr, 3 km/hr) on a 400‐m outdoor track. For each speed, participants completed three 6‐minute trials. For the incline surface, participants climbed stadium stairs at 5 km/hr for approximately one minute and at 3 km/hr for approximately two minutes. To determine how much each device varies from the criterions (measuring tape for distance and RT3 accelerometer for EE) the difference between the participants’ mean scores and the criterion was calculated. Seven females and seven males (mean ± SD; age 22.1 ± 2.1 yr, mass 71.40 ± 15.91 kg, height 171.27 ± 12.47 cm, BMI 23.57 ± 2.84) participated in the study. All devices underestimated EE below the RT3 estimate (14.6 kcal to 49.4 kcal). There was more variability estimating distance, with a range of overestimating by 44.1‐m and underestimating by 6.7‐m. Both pedometers generated similar findings for EE and distance. To help people lose or maintain weight, it is important to consider when fitness devices over‐ or under‐estimate EE and/or distance.Grant Funding Source: APS David S. Bruce Awards for Excellence in Undergraduate Research

Comparison of methods used to predict energy requirements in a whole room calorimeter

Studies examining diet-induced thermogenesis and substrate oxidation in a whole room calorimeter (WRC) benefit from a state of energy balance in the measurement period. We found reports on four approaches to assessing energy needs in this context, and they vary considerably. This study assessed the utility of three simple alternatives for predicting energy requirements for calorimeter studies. Energy expenditure (EE) data on 37 males and 104 females was obtained from the baseline measurements of three weight-loss trials. The EE data was from 3-d RT3 accelerometer measurements in a free-living environment, and 24-h WRC measurements. A linear regression model was developed from Study 1 and Study 2 (N = 97), using mean 3-d EE as the independent variable. Twenty-four hours WRC EE (N = 29) was compared with three prediction methods: (a) Schofield equation, (b) regression model, and (c) free-living EE × 85%. Energy expenditure measured by accelerometers was 2454.1 ± 491.9 kcal/d in the free-living condition and 2022.7 ± 295.8 kcal/d during the 24-h calorimeter stay (83.8% ± 10.6% of free-living). Energy requirements in the whole room calorimeter was estimated as 0.405 × mean [3-d RT3 energy expenditure] + 1009.6 kcal/d (N = 97, R(2) = 0.479, P < 0.001). Predicted energy requirements were not significantly different from the WRC EE but the Schofield method produced the lowest mean bias and standard deviation. Schofield equations are an inexpensive and convenient alternative for predicting energy requirements in WRC studies.

Calibration of the RT3 accelerometer for various patterns of physical activity in children and adolescents

The aim of this study was to determine thresholds for various intensities of physical activity in children and adolescents using the RT3 accelerometer. Forty healthy participants aged 10–16 years were recruited to the study. To validate the RT3 accelerometer data, an independent sample of 20 children and adolescents aged 10–16 years performed the same activities. Accelerometer data, heart rate, and oxygen consumption were measured at nine levels of physical activity, which varied in intensity: sedentary, light, moderate, and vigorous. Age and sex did not affect thresholds. The activity categories and accelerometer counts were: sedentary activity, 0–40 counts · min−1; light activity, 41–950 counts · min−1; moderate activity, 951–3410 counts · min−1; and vigorous activity, >3410 counts · min−1, respectively. These thresholds were considered valid as the difference between threshold values obtained using two independent groups of children was not significant. This study has established threshold values for various physical activities and enables the RT3 accelerometer to be used to quantify the duration of various levels of activity in adolescents under free-living conditions.

Reliability of the RT3 accelerometer for measurement of physical activity in adolescents

The aim of this study was to assess the reliability of the RT3 accelerometer under conditions of normal physical activity. Sixty healthy individuals (30 boys, 30 girls) aged 10–16 years wore two accelerometers while performing different structured physical activities. The accelerometers were synchronized and data were recorded every minute during nine 15-min sessions of physical activity that varied in intensity from sedentary (watching television, playing video games) to vigorous (running on a treadmill at different speeds). Intra-instrument coefficients of variation (CV) were assessed using the formula CV = standard deviation of the measure × 100/mean of the measure. The intra-instrument coefficient of variation was higher for sedentary (17%) and light activity (16.2%) than moderate (9.3%) and vigorous activity (6.6%). These results confirmed the poor reliability of the RT3 for activity of low magnitude and frequency that was demonstrated in studies using a shaker.

Estimates of energy expenditure using the RT3 accelerometer in patients with systemic lupus erythematosus

This study aimed to characterize energy expenditure patterns using the triaxial accelerometer and to identify the association of energy expenditure with clinical parameters in patients with systemic lupus erythematosus (SLE). Estimates of energy expenditures represented by total activity calorie (TA), physical activity calorie (PA), total activity calorie per body weight (TABW), and physical activity calorie per body weight (PABW) of 49 female SLE patients were assessed using the RT3 triaxial accelerometer (StayHealthy, Monrovia, CA) in a sevenday period. SLE patients in the highest body mass index (BMI) tertile showed significantly lower values of TABW compared to those in the lowest tertile, while SLE patients in the lowest TABW tertile showed significantly higher body weight, waist circumference, BMI, SLE disease activity index (SLEDAI), dosage of prednisone, and blood pressure. There was a high prevalence of metabolic syndrome and SLE patients with metabolic syndrome showed significantly lower TABW. In addition, both TABW and PABW significantly but negatively correlated with SLEDAI. In conclusion, the RT3 accelerometer is suitable for evaluating total and physical activity-related energy expenditure in patients with SLE. TABW measured by the triaxial accelerometer is inversely related with body weight status and disease activity in SLE patients. This suggests that estimates of energy expenditure by the tri-axial accelerometer may be applied in the management of SLE.

Construct validity of RT3 accelerometer: A comparison of level-ground and treadmill walking at self-selected speeds

This study examined differences in accelerometer output when subjects walked on level ground and on a treadmill. We asked 25 nondisabled participants to wear an RT3 triaxial accelerometer (StayHealthy, Inc; Monrovia, California) and walk at their "normal" and "brisk" walking speeds for 10 minutes. These activities were repeated on a treadmill using the individual speeds from level-ground walking on two occasions 1 week apart. Paired t-tests found a difference in RT3 accelerometer vector magnitude (VM) counts/min between the two walking speeds on both surfaces on days 1 and 2 (p < 0.001). Although we found no significant differences between VM counts/min on the two surfaces at normal and brisk speeds on days 1 and 2 (p > 0.05), we found wide limits of agreement between level ground and treadmill walking at both speeds. Measurement and discrimination of walking intensity employing RT3 accelerometer VM counts/min on the treadmill demonstrated reasonable validity and stability over two time points compared with level-ground walking.

Influence of a symptom management telehealth intervention on older adults' early recovery outcomes after coronary artery bypass surgery

The study objective was to examine the effect of a symptom management (SM) telehealth intervention on physical activity and functioning and to describe the health care use of older adult patients (aged > 65 years) after coronary artery bypass surgery (CABS) by group (SM intervention group and usual care group). A randomized clinical trial design was used. The study was conducted in 4 Midwestern tertiary hospitals. The 6-week SM telehealth intervention was delivered by the Health Buddy (Health Hero Network, Palo Alto, CA). Measures included Modified 7-Day Activity Interview, RT3 accelerometer (Stayhealthy, Inc, Monrovia, CA), physical activity and exercise diary, Medical Outcomes Study Short-Form 36, and subjects' self-report and provider records of health care use. Follow-up times were 3 and 6 weeks and 3 and 6 months after CABS. Subjects (N = 232) had a mean age of 71.2 (+4.7) years. There were no significant interactions using repeated-measures analyses of covariance. There was a significant group effect for average kilocalories/kilogram/day of estimated energy expenditure as measured by the RT3 accelerometer, with the usual care group having a higher estimated energy expenditure. Both groups had significant improvements over time for role-physical, vitality, and mental functioning. Both groups had similar health care use. Subjects were able to return to preoperative levels of functioning between 3 and 6 months after CABS and to increase their physical activity over reported preoperative levels of activity. Further study of those patients undergoing CABS who could derive the most benefit from the SM intervention is warranted.

Can accelerometry be used to discriminate levels of activity?

The aims of this study were to investigate the associations between an activity logbook and the RT3 accelerometer and to assess whether the RT3 can discriminate activity levels in healthy adults. Ten participants completed two trials wearing an RT3 accelerometer over a 4–6 h period and completed a detailed activity log. Results showed a poor correlation between the RT3 in moderate activities (r = 0.22) in comparison to low (r = 0.52) and hard (r = 0.70) from the logbook. A significant difference was found in average RT3 vector magnitude (VM) counts/min in each activity level (p < 0.0001). Discriminant analysis demonstrated that an RT3VM counts/min value of approximately 500 was found to have high sensitivity (88%), and specificity (88%) for discriminating between low and moderate activity levels from the logbook. This study found that accelerometry has the potential to discriminate activity levels in free living. This study is the first to investigate whether tri-axial accelerometry can discriminate different levels of free-living activity recorded in an activity logbook. The RT3 accelerometer can discriminate between low and moderate physical activities and offers a methodology that may be applicable to future research in occupational settings.

Effects of Exercise Training Amount on Physical Activity Energy Expenditure

We examined the effects of three exercise training interventions on total physical activity energy expenditure (PAEE) or nonexercise PAEE in a randomized controlled trial where sedentary, overweight, and obese men and women were assigned to inactive control, low-amount/moderate-intensity, low-amount/vigorous-intensity, or high-amount/vigorous-intensity aerobic exercise. To measure PAEE, triaxial RT3 accelerometers were worn by subjects for 7 d at the beginning and end of an 8-month exercise intervention. In total, 50 subjects (control, n = 8; two low-amount groups, n = 28; high-amount group, n = 14) had usable PAEE data collected at both time points. At baseline, subjects had an average age of 53.2 yr, had a body mass index of 29.7 kg x m(-2), and a relative peak VO2 of 28.7 mL x kg(-1) x min(-1). There were no significant differences between groups at baseline. After the intervention, average change in total PAEE was 8.4 +/- 20.9 kJ x h(-1) for controls, 58.6 +/- 20.9 kJ x h(-1) for the two low-amount groups, and 138.1 +/- 33.5 kJ x h(-1) for the high-amount group (means +/- SE). The high-amount group experienced a significantly greater increase in total PAEE compared with the controls (P = 0.02). As expected, total PAEE increased with increasing exercise volume. Average change in nonexercise PAEE was 8.4 +/- 20.9 kJ x h(-1) for control, 25.1 +/- 20.9 kJ x h(-1) for the low-amount groups combined, and 62.8 +/- 29.3 kJ x h(-1) for the high-amount group. There was no statistically significant difference in change of nonexercise PAEE among groups. We conclude that in middle-aged overweight or obese subjects participating in an extended exercise intervention, total PAEE increased, and there was no compensatory decrease in nonexercise PAEE.

Equivalence of accelerometer data for walking and running: Treadmill versus on land

The aim of this study was to compare equivalence and agreement of physical activity output data collected by a Research Tri-axial accelerometer (R3T) during walking and running on a treadmill versus on land. Fifty healthy volunteers, 35 males (age 21.9 ± 1.8 years) and 15 females (age 21.6 ± 0.7 years), underwent a series of tests on a treadmill and on land with the order of testing administered randomly. Each participant walked for 10 min at 4 km · h−1 and 6 km · h−1, and ran at 8 km · h−1 and 10 km · h−1, with the same accelerometer. Analysis of output data was assessed by two statistical tests: the equivalence test and Bland and Altman method. Mean differences for walking were 41.2 ± 129.8 counts per minute and −68.8 ± 173.15 counts per minute at 4 km · h−1 and km · h−1, respectively. Mean differences for running were 19.1 ± 253.20 counts per minute and 38.9 ± 270.2 counts per minute at 8 km · h−1 and 10 km · h−1, respectively. The physical activity output data from the treadmill were higher by an average of 3.5% than the data collected on land. The differences obtained between the treadmill and on land were small and non-significant. The equivalence test showed that output data from the treadmill versus on land were equivalent (P < 0.05). The Bland and Altman method showed good agreement between the counts obtained on the treadmill and on land (P < 0.05). In conclusion, physical activity output data were similar as measured by the RT3 accelerometer on a treadmill and on land. The findings suggest that the RT3 may be used in a laboratory and extrapolated to data obtained on land.

Reliability of RT3 Accelerometers among Overweight and Obese Adults

Accurate and reliable measurement of physical activity plays an important role in assessing effective lifestyle interventions for obesity. This study examined reliability of accelerometer-based estimates of physical activity levels of overweight and obese adults before and after a lifestyle weight loss program. Participants were overweight and obese (body mass index = 25-45 kg x m) members (n = 1592; 67% female, 42% African American) of the multicenter weight loss maintenance trial. They wore RT3 accelerometers during waking hours for 7 d at baseline and after a 6-month weight loss intervention that included diet and physical activity recommendations. Moderate-to-vigorous physical activity (MVPA) and MVPA occurring in bouts >or=10 min (bout MVPA) were assessed. At baseline, wear time minimums of 10 and 6 h.d resulted in similar average minutes per day of MVPA (18.3 and 18.0 min) and MVPA bout minutes per day (6.9 and 6.7 min). Similar wear times occurred after the weight loss intervention for MVPA (27.0 and 26.8 min) and bout MVPA (15.1 and 15.0 min). Reliability measurements by intraclass correlation (ICC) were larger for 4 versus 2 d x wk minimum wear time for both MVPA and bout MVPA (4-d ICC = 0.27-0.44 and 2-d ICC = 0.19-0.38), but there was little increase in ICC comparing 4 (ICC = 0.27-0.44) and 7 d x wk (ICC = 0.30-0.46). Longer wear time requirements did not result in significant increases in reliability. Using 4 d of data with >or=6 h x d of wear time optimized the balance between ICC and participant burden in overweight and obese adults before and after a weight loss intervention. Future investigations using accelerometers to estimate MVPA in overweight and obese samples can consider requiring less monitor wear time.

Weight Regain Is Related to Decreases in Physical Activity during Weight Loss

To examine whether adaptations in physical activity energy expenditure (PAEE) and resting metabolic rate (RMR) during weight loss were associated with future weight regain in overweight/obese, older women. Thirty-four overweight/obese (BMI = 25-40 kg x m(-2)), postmenopausal women underwent a 20-wk weight loss intervention of hypocaloric diet with (low- or high-intensity) or without treadmill walking (weekly caloric deficit was approximately 11,760 kJ), with a subsequent 12-month follow-up. RMR (via indirect calorimetry), PAEE (by RT3 accelerometer), and body composition (by dual-energy x-ray absorptiometry) were measured before and after intervention. Body weight and self-reported information on physical activity were collected after intervention and at 6 and 12 months after intervention. The intervention resulted in decreases in body weight, lean mass, fat mass, percent body fat, RMR, and PAEE (P < 0.001 for all). Weight regain was 2.9 +/- 3.3 kg (-3.1 to +9.2 kg) at 6 months and 5.2 +/- 5.0 kg (-2.3 to +21.7 kg) at 12 months after intervention. The amount of weight regained after 6 and 12 months was inversely associated with decreases in PAEE during the weight loss intervention (r = -0.521, P = 0.002 and r = -0.404, P = 0.018, respectively), such that women with larger declines in PAEE during weight loss experienced greater weight regain during follow-up. Weight regain was not associated with changes in RMR during intervention or with self-reported physical activity during follow-up. This study demonstrates that although both RMR and PAEE decreased during weight loss in postmenopausal women, maintaining high levels of daily physical activity during weight loss may be important to mitigate weight regain after weight loss.

Measuring Free-Living Physical Activity in Adults With and Without Neurologic Dysfunction With a Triaxial Accelerometer

Hale LA, Pal J, Becker I. Measuring free-living physical activity in adults with and without neurologic dysfunction with a triaxial accelerometer. Objective To investigate the reliability, validity, and utility of a triaxial accelerometer to measure physical activity in the free-living environment in adults with and without neurologic dysfunction. Design Repeated-measures design. Setting General community. Participants Volunteer sample of 17 men and 30 women (age range, 28−91y) living in the community with stroke of greater than 6 months in duration (n=20), Parkinson disease (n=7), or multiple sclerosis (n=11), and healthy but sedentary controls (n=9). Interventions Not applicable. Main Outcome Measures Physical activity measured with the TriTrac RT3 accelerometer, 7-day recall questionnaire, and activity diary. Results The accelerometer reliably measured free-living physical activity (intraclass correlation coefficient, .85; 95% confidence interval, .74−.91; P=.000). The standard error of measurement indicated that a second test would differ from a baseline test by ±23%. Mean daily RT3 data collected in the first 3 days differed significantly from that of the mean daily RT3 data collected over 7 days. The RT3 appeared to distinguish level of mobility better than the 7-day recall questionnaire, and participants found the RT3 to be a user-friendly and acceptable measure of physical activity. Conclusions The triaxial accelerometer provided a stable measure of free-living physical activity, was found to distinguish between people with varying levels of mobility, and was well tolerated by participants. The results indicate that collecting data for 3 days was not reflective of data collected over 7 days.

Validity of Physical Activity Intensity Predictions by ActiGraph, Actical, and RT3 Accelerometers

Accelerometers are promising tools for characterizing physical activity (PA) patterns in free-living persons. To date, validation of energy expenditure (EE) predictions from accelerometers has been restricted to short laboratory or simulated free-living protocols. This study seeks to determine the capabilities of eight previously published regression equations for three commercially available accelerometers to predict summary measures of daily EE. Study participants were outfitted with ActiGraph, Actical, and RT3 accelerometers, while measurements were simultaneously made during overnight stays in a room calorimeter, which provided minute-by-minute EE measurements, in a diverse subject population (n = 85). Regression equations for each device were used to predict the minute-by-minute metabolic equivalents (METs) along with the daily PA level (PAL). Two RT3 regressions and one ActiGraph regression were not significantly different from calorimeter measured PAL. When data from the entire visit were divided into four intensity categories-sedentary, light, moderate, and vigorous-significant (P < 0.001) over- and underpredictions were detected in numerous regression equations and intensity categories. Most EE prediction equations showed differences of <2% in the moderate and vigorous intensity categories. These differences, though small in magnitude, may limit the ability of these regressions to accurately characterize whether specific PA goals have been met in the field setting. New regression equations should be developed if more accurate prediction of the daily PAL or higher precision in determining the time spent in specific PA intensity categories is desired.

Relationships between fatigue and early postoperative recovery outcomes over time in elderly patients undergoing coronary artery bypass graft surgery

Despite successful coronary artery bypass graft (CABG) surgery, some patients continue to experience fatigue after their surgery. The purpose of this secondary analysis study was to examine the relationships of fatigue and early recovery outcomes (psychosocial and physiologic functioning, and physical activity) over time (6 weeks and 3 months) among older adult subjects, age 65 years and older, after CABG surgery. Comparison groups were those subjects who had fatigue at 3 weeks after surgery and nonfatigued subjects. A prospective, comparative design was used for this secondary analysis study. Subjects in this study were drawn from the control group of subjects enrolled in the larger parent study. Subjects (N = 119) were dichotomized into fatigue (n = 66) and nonfatigued (n = 53) groups on the basis of their 3-week self-reports of postoperative fatigue. At 6 weeks after surgery, fatigued subjects had significantly (P < .05) more impaired psychosocial functioning (role-emotional [t = 1.9], social [t = 2.6], and mental [t = 1.9] functioning) on the basis of the Medical Outcome Study Short Form 36. They had significantly (P < .005) higher mean hospital anxiety (t = -3.6) and depression (t = -2.9) subscale scores, respectively. Anxiety (t = -2.3, P < .05) remained significantly (P < .05) impaired at 3 months. At 6 weeks, role physical functioning, measured by the Medical Outcome Study Short Form 36, was significantly impaired (t = 2.4, P < .01). There were no significant differences in physical activity variables as measured by an RT3 accelerometer (Stayhealthy, Inc., Monrovia, CA) and self-report diary. Persistent fatigue can hamper early recovery after CABG surgery. Tailored interventions are needed to address fatigue management and improve patient outcomes.

Assessment of energy expenditure in children using the RT3 accelerometer

The aim of this study was to evaluate the utility of the RT3 accelerometer in young children, compare its accuracy with heart rate monitoring, and develop an equation to predict energy expenditure from RT3 output. Forty-two volunteers (mean age 12.2 years, s = 1.1) exercised at two horizontal and graded walking speeds (4 and 6 km · h−1, 0% grade and 6% grade), and one horizontal running speed (8 km · h−1, 0% grade), on a treadmill. Energy expenditure and oxygen consumption ([Vdot]O2) served as the criterion measures. Comparison of RT3 estimates (counts and energy expenditure) demonstrated significant differences at 4, 6, and 8 km · h−1 on level ground (P < 0.01), while no significant differences were noted between horizontal and graded walking at 4 and 6 km · h−1. Correlation and regression analyses indicated no advantage of vector magnitude over the vertical plane (X) alone. A strong relationship between RT3 estimates and indirect calorimetry across all speeds was obtained (r = 0.633–0.850, P < 0.01). A child-specific prediction equation (adjusted R 2 = 0.753) was derived and cross-validated that offered a valid energy expenditure estimate for walking/running activities. Despite recognized limitations, the RT3 may be a useful tool for the assessment of children's physical activity during walking and running.

Validation of the RT3 Accelerometer for Measuring Physical Activity of Children in Simulated Free-Living Conditions

This is a validation study of the RT3 accelerometer for measuring physical activities of children in simulated free-living conditions. Twenty-five children age 12-14 years completed indoor testing, and 18 of them completed outdoor testing. Activity counts from the RT3 accelerometer estimated activity energy expenditure (AEE) and the Cosmed K4b2 analyzer measured oxygen uptake. Correlations were found between activity counts and metabolic cost (r = .95, p < .001), metabolic cost and RT3 estimated AEE (r = .96, p < .001) in the indoor test, activity counts and RT3 estimated AEE (r = .97, p < .001) in the outdoor test, and activity counts and metabolic cost when all activities were combined (r = .77, p < .001). Results indicate that the RT3 accelerometer might be used to provide acceptable estimates of free-living physical activity in children.

Interinstrument Reliability of RT3 Accelerometer at Different Levels Of Physical Activity.

Accelerometers are validated instrument for assessing physical activity. However their reliability could vary according to the level of physical activity (PA). PURPOSE: To evaluate the interinstrument reliability of RT3 accelerometer at different level of PA. METHODS: Sixty healthy subjects (thirty boys, thirty girls), aged 10-16 years, were recruited to participate in the study. Subjects were worn two accelerometer on the right hip. Accelerometers data were recorded, every minute, during 9 levels of 15-minute physical activity that varied in intensity from sedentary (i.e., TV watching, reading, playing video game) to vigorous (i.e., running on a treadmill at different speed level). Interinstrument coefficient of variation was assessed using the formula CV = standard deviation of the measure × 100/mean of the measure). RESULTS: Interinstrument coefficients of variation (CV) varied from 4%, to 74.1% according to the intensity of physical activity. Indeed, CV was 44% to 74 % in sedentary, 7% to 47% in light activity, 5% to 6% in moderate activity, and 4% for vigorous activity. CONCLUSIONS: The interinstrument reliability of RT3 accelerometers is poor specially for low level of PA and could lead to significant error in assessing PA in sedentary children in usual condition of life. This discrepancy could account for difference in measuring PA in usual condition of life in subject with low physical activity pattern. The poor reliability of the RT3 accelerometer may be explained by the fact that this device has a wide frequency range (2.0- 10.0 Hz), for detecting movement. However, some thresholds for detecting low PA movement could be different among RT3 devices. Some investigations are needed to characterise accurately these discrepancies.

Walking for Health in Pregnancy

The purpose of this study was to examine RT3 accelerometer activity counts and activity energy expenditure of 36 pregnant women at 20 and 32 weeks' gestation during treadmill walking and free-living conditions. During treadmill walking, oxygen consumption was collected, and activity energy expenditure was estimated for a 30-min walk at a self-selected walking pace. The number of min it would take a pregnant woman to meet exercise recommendations (i.e., kcal/week) were calculated. Preliminary activity count cut points at a self-selected walking pace were then estimated and applied in interpreting free-living data. For the treadmill walking condition, the self-selected walking pace significantly decreased from 20 to 32 weeks' gestation. Additionally, few women (< 12% each day) met physical activity guidelines in the free-living condition. Encouraging pregnant women to walk for 30–40 min per day at a self-selected walking pace may be an appropriate public health recommendation.