Evaluation of methods to assess physical activity in free-living conditions

Using three objective criteria to examine pedometer guidelines for free-living individuals

The purpose was to examine in free-living individuals from a high-density city (1) the objectively determined physical activity levels across quartiles derived from pedometer step counts, (2) the pedometer steps day(-1) required to meet health-enhancing guidelines of accruing 30 min day(-1) of moderate physical activity and (3) the agreement between three objective criteria for the pedometer guidelines. Over 7 days 49 Hong Kong Chinese aged 15-55 years (n = 30 males) wore a polar heart rate monitor (HRM), an MTI and Tritrac accelerometer, plus a Yamax pedometer for >or=600 min day(-1). Participants averaged 9,839 +/- 3,088 steps day(-1), whilst accumulating 44.5 +/- 22.6, 43.1 +/- 21.7, and 24.7 +/- 19.3 min day(-1) of moderate physical activity by the Tritrac, MTI and HRM, respectively. Significant differences between quartiles of pedometer-determined activity were predominantly seen in the accelerometry data, especially during moderate and moderate-to-vigorous intensity activity (effect sizes >1.5 between upper and lower quartiles), but not seen in the HRM data. Using both criterion accelerometer datasets, a threshold of 8,000 steps day(-1) accurately categorized approximately 90% of those achieving, and approximately 80% of those not achieving, 30 min day(-1) of appropriate activity. They also produced a screening sensitivity of approximately 95% and a specificity of approximately 70%, which were considerably higher than those from the HRM data. Overall, the agreement between the three criterion measures suggests 8,000 steps day(-1) might be a valid screening tool as a proxy for classifying those meeting public health physical activity recommendations of 30 min day(-1) of moderate activity.

The Impact of Body-Mass Index and Steps per Day on Blood Pressure and Fasting Glucose in Older Adults

The purpose of this study was to investigate the combined impact of obesity and physical activity (PA) on the health of older adults. Pedometer-determined steps/d, body-mass index (BMI), resting blood pressure, and fasting glucose (FG) were assessed in 137 older adults (69.0 ± 8.9 yr). The active group (>4,227 steps/d) had lower systolic blood pressure (SBP;p= .001), diastolic blood pressure (DBP;p= .028), and FG (p< .001) than the inactive group (≤4,227 steps/d). The normal-BMI group (18.5-24.9 kg/m2) had lower SBP (p< .001) and DBP (p= .01) than the obese group (≤30 kg/m2). There were no differences in SBP (p= .963) or DBP (p= 1.0) between active obese and inactive normal-BMI groups. The active obese group, however, had a more favorable FG than the inactive normal-BMI group (χ2= 18.9,df= 3,p= .001). Efforts to increase PA of older adults should receive the same priority as reducing obesity to improve BP and FG levels.

Physical activity in the United States measured by accelerometer

PURPOSE

To describe physical activity levels of children (6-11 yr), adolescents (12-19 yr), and adults (20+ yr), using objective data obtained with accelerometers from a representative sample of the U.S. population.

METHODS

These results were obtained from the 2003-2004 National Health and Nutritional Examination Survey (NHANES), a cross-sectional study of a complex, multistage probability sample of the civilian, noninstitutionalized U.S. population in the United States. Data are described from 6329 participants who provided at least 1 d of accelerometer data and from 4867 participants who provided four or more days of accelerometer data.

RESULTS

Males are more physically active than females. Physical activity declines dramatically across age groups between childhood and adolescence and continues to decline with age. For example, 42% of children ages 6-11 yr obtain the recommended 60 min x d(-1) of physical activity, whereas only 8% of adolescents achieve this goal. Among adults, adherence to the recommendation to obtain 30 min x d(-1) of physical activity is less than 5%.

CONCLUSIONS

Objective and subjective measures of physical activity give qualitatively similar results regarding gender and age patterns of activity. However, adherence to physical activity recommendations according to accelerometer-measured activity is substantially lower than according to self-report. Great care must be taken when interpreting self-reported physical activity in clinical practice, public health program design and evaluation, and epidemiological research.

Concurrent validity of the PAM accelerometer relative to the MTI Actigraph using oxygen consumption as a reference

The purpose of this study was to examine the concurrent validity of the Personal Activity Monitor (PAM) accelerometer relative to the Actigraph accelerometer using oxygen consumption as a reference, and to assess the test-retest reliability of the PAM. Thirty-two fit, normal weight adults (aged 21-54) performed two activities, treadmill walking and stair walking, while wearing the PAM, the Actigraph and the Cosmed K4b(2). Correlation coefficients and agreement in absolute energy expenditure (EE) levels between PAM, Actigraph and Cosmed were calculated. The test-retest reliability was examined among 296 PAM's using a laboratory shaker. Intraclass correlation coefficients (ICC) and coefficient of variation (CV) were determined. Correlations for treadmill walking and stair walking, respectively, were r(2)=0.95 and r(2)=0.65 for PAM with Actigraph, r(2)=0.82 and r(2)=0.93 for PAM with VO(2) and r(2)=0.64 and 0.74 for Actigraph with VO(2). Both the PAM and Actigraph underestimated EE during treadmill and stair walking by a substantial amount. The test-retest reliability of the PAM was high [ICC=0.80; 95% confidence interval (CI) (0.28;0.92) and intra-CV=1.5%]. The PAM and Actigraph accelerometer are comparable in assessing bodily movement during treadmill and stair walking. The PAM is a valid device to rank subjects in EE and can be useful in collecting objective data to monitor habitual physical activity.

Estimating activity energy expenditure: how valid are physical activity questionnaires?

Activity energy expenditure (AEE) is the modifiable component of total energy expenditure (TEE) derived from all activities, both volitional and nonvolitional. Because AEE may affect health, there is interest in its estimation in free-living people. Physical activity questionnaires (PAQs) could be a feasible approach to AEE estimation in large populations, but it is unclear whether or not any PAQ is valid for this purpose. Our aim was to explore the validity of existing PAQs for estimating usual AEE in adults, using doubly labeled water (DLW) as a criterion measure. We reviewed 20 publications that described PAQ-to-DLW comparisons, summarized study design factors, and appraised criterion validity using mean differences (AEE(PAQ) - AEE(DLW), or TEE(PAQ) - TEE(DLW)), 95% limits of agreement, and correlation coefficients (AEE(PAQ) versus AEE(DLW) or TEE(PAQ) versus TEE(DLW)). Only 2 of 23 PAQs assessed most types of activity over the past year and indicated acceptable criterion validity, with mean differences (TEE(PAQ) - TEE(DLW)) of 10% and 2% and correlation coefficients of 0.62 and 0.63, respectively. At the group level, neither overreporting nor underreporting was more prevalent across studies. We speculate that, aside from reporting error, discrepancies between PAQ and DLW estimates may be partly attributable to 1) PAQs not including key activities related to AEE, 2) PAQs and DLW ascertaining different time periods, or 3) inaccurate assignment of metabolic equivalents to self-reported activities. Small sample sizes, use of correlation coefficients, and limited information on individual validity were problematic. Future research should address these issues to clarify the true validity of PAQs for estimating AEE.

Empirical evaluation of physical activity recommendations for weight control in women

PURPOSE

Recent recommendations advise 30-60 min of physical activity per day to prevent weight gain and 60-90 min to prevent weight regain. No studies have used objective measures of physical activity to verify these public health recommendations. The purpose of this study was to use objective measures to quantify the amount and intensity of physical activity in a weight-loss-maintainer group and an always-normal-weight group, and, thus,empirically evaluate the recommendations for prevention of weight gain versus regain.

METHODS

The weight-loss-maintainer group (N = 135) lost >or= 30.6 kg, maintained >or= 10% weight loss for 14.2 yr, and had a BMI of 22.0 kg.m(-2). The always-normal-weight group (N = 102) had a BMI of 21.1 kg.m(-2) and no history of overweight. Accelerometry was used to assess the amount and intensity of physical activity.

RESULTS

The weight-loss-maintainer group spent significantly more minutes per day than the always-normal-weight group in physical activity (58.6 vs 52.1; P = 0.0001), largely because of more time spent in higher-intensity activities (24.4 vs 16.9; P = 0.02). The majority of individuals in the always-normal-weight group engaged in 30-60 min.d(-1) of physical activity, whereas a greater proportion of individuals in the weight-loss-maintainer group engaged in > 60 min (P = 0.002).

CONCLUSIONS

Findings support current recommendations that more activity may be needed to prevent weight regain than to prevent weight gain. Including some higher-intensity activity may also be advisable for weight-loss maintenance.

Extrapulmonary effects of chronic obstructive pulmonary disease on physical activity: a cross-sectional study

RATIONALE

Physical activity is reduced in patients with chronic obstructive pulmonary disease (COPD). COPD has a systemic component that includes significant extrapulmonary effects that may contribute to its severity in individual patients.

OBJECTIVES

To investigate the association of extrapulmonary effects of the disease and its comorbidities with reduced physical activity in patients with COPD.

METHODS

In a cross-sectional study, 170 outpatients with COPD (GOLD [Global Initiative for Chronic Obstructive Lung Disease] stages I-IV; BODE [body mass index, airway obstruction, dyspnea, and exercise capacity] score 0-10) underwent a series of tests. Physical activity was assessed over 5 to 6 consecutive days by using a multisensor accelerometer armband that records steps per day and the physical activity level (total daily energy expenditure divided by whole-night sleeping energy expenditure). Cardiovascular status was assessed by echocardiography, vascular Doppler sonography, and levels of N-terminal pro-B-type natriuretic peptide. Mental status, metabolic/muscular status, systemic inflammation, and anemia were assessed by Beck Depression Inventory, bioelectrical impedance analysis, handgrip strength, high-sensitivity C-reactive protein/fibrinogen, and hemoglobin, respectively.

MEASUREMENTS AND MAIN RESULTS

In a multivariate linear regression analysis using either steps per day or physical activity level as a dependent variable, the extrapulmonary parameters that were associated with reduced physical activity in patients with COPD independently of GOLD stages or BODE score were N-terminal pro-B-type natriuretic peptide levels, echocardiographically measured left ventricular diastolic function, and systemic inflammation.

CONCLUSIONS

Higher values of systemic inflammation and left cardiac dysfunction are associated with reduced physical activity in patients with COPD.

Physical activity assessment with accelerometers: an evaluation against doubly labeled water

This review focuses on the ability of different accelerometers to assess daily physical activity as compared with the doubly labeled water (DLW) technique, which is considered the gold standard for measuring energy expenditure under free-living conditions. The PubMed Central database (U.S. NIH free digital archive of biomedical and life sciences journal literature) was searched using the following key words: doubly or double labeled or labeled water in combination with accelerometer, accelerometry, motion sensor, or activity monitor. In total, 41 articles were identified, and screening the articles' references resulted in one extra article. Of these, 28 contained sufficient and new data. Eight different accelerometers were identified: 3 uniaxial (the Lifecorder, the Caltrac, and the CSA/MTI/Actigraph), one biaxial (the Actiwatch AW16), 2 triaxial (the Tritrac-R3D and the Tracmor), one device based on two position sensors and two motion sensors (ActiReg), and the foot-ground contact pedometer. Many studies showed poor results. Only a few mentioned partial correlations for accelerometer counts or the increase in R(2) caused by the accelerometer. The correlation between the two methods was often driven by subject characteristics such as body weight. In addition, standard errors or limits of agreement were often large or not presented. The CSA/MTI/Actigraph and the Tracmor were the two most extensively validated accelerometers. The best results were found for the Tracmor; however, this accelerometer is not yet commercially available. Of those commercially available, only the CSA/MTI/Actigraph has been proven to correlate reasonably with DLW-derived energy expenditure.

Accelerometers and pedometers: methodology and clinical application

PURPOSE OF REVIEW

The relationship between physical activity and health varies considerably, partly due to the difficulty of assessing physical activity accurately. This review examines recent literature on the validation of movement sensors to assess habitual physical activity. Recommendations are given for the use of movement sensors during free-living conditions and methods of data analysis and interpretation are discussed.

RECENT FINDINGS

Recent progress in physical-activity research includes detailed comparative studies of different monitor brands. The move away from using linear-regression equations and the use of novel data-analysis strategies is increasing the accuracy with which energy expenditure can be estimated from accelerometry. New technologies, including the combination of accelerometry with the measurement of physiological parameters, have great potential for the increased accuracy of physical-activity assessment.

SUMMARY

Accelerometry is able to adequately assess physical activity and its association with health outcomes but currently methods have limited accuracy for the estimation of free-living energy expenditure. Pedometers provide an inexpensive overall measure of physical activity but are unable to assess intensity, frequency and duration of activity or to estimate energy expenditure. Interpretation of monitor output is best kept as close to the measurement domain as possible.

Physical activity-related energy expenditure with the RT3 and TriTrac accelerometers in overweight adults

OBJECTIVE

The objective was to evaluate two accelerometers, the RT3 and the TriTrac-R3D for their ability to produce estimates of physical activity-related energy expenditure (PAEE) in overweight/obese adults.

RESEARCH METHODS AND PROCEDURES

PAEE estimates from both accelerometers were obtained in two experiments. In Experiment 1, 13 overweight/obese subjects (BMI 34.2+/-6.4 kg/m2) were monitored over 2 weeks in everyday life, PAEE being simultaneously measured by the doubly labeled water method (DLW). In Experiment 2, 8 overweight/obese subjects (BMI 34.3+/-5.0 kg/m2) and 10 normal-weight subjects (BMI 20.8+/-2.1 kg/m2) were monitored during a treadmill walking protocol, PAEE being simultaneously measured by indirect calorimetry.

RESULTS

In Experiment 1, there was no significant difference between methods in mean PAEE (DLW: 704+/-223 kcal/d, RT3: 656+/-140 kcal/d, TriTrac-R3D 624+/-419 kcal/d). The relative difference between methods (accelerometer vs. DLW) was -17.1%+/-16.7% for the RT3 and -20.0+/-44.6% for the TriTrac-R3D. Correlation for PAEE between RT3 and DLW was higher than between TriTrac-R3D and DLW (r=0.67, p<0.05 and r=0.36, p=0.25, respectively). The 95% confidence interval (CI) (kcal/d) of the mean difference between methods was large, amounting to -385 to 145 for the RT3 and -887 to 590 for the TriTrac-R3D. In Experiment 2, both accelerometers were sensitive to the changes in treadmill speed, with no significant difference in mean PAEE between methods in overweight/obese subjects.

CONCLUSIONS

Although both accelerometers did not provide accurate estimates of PAEE at individual levels, the data suggest that RT3 has the potential to assess PAEE at group levels in overweight/obese subjects.

Comparing different measures of energy expenditure in human subjects resident in a metabolic facility

OBJECTIVE

To compare energy expenditure (EE) measured by doubly labeled water (DLW) with other measures, both physical and based on subjective questionnaires.

DESIGN

A comparison of methods in a stratified sample of adult volunteers.

SETTING

The feeding behaviour suite (FBS) at the Rowett Research Institute, Aberdeen.

SUBJECTS

A total of 59 subjects, stratified for age, sex and body mass index (BMI).

INTERVENTIONS

EE was assessed by DLW (validated using measurements of energy balance), heart rate monitor (HRM), activity monitor (Caltrac), 24-h physical activity diary (PAD) and 7-day physical activity recall. Energy intake was assessed using covert (investigator-weighed) food intake (EI). Data were collected over a 12-day period of residence in the Rowett's FBS.

RESULTS

No methods correlated highly with physical activity assessed by DLW. Physical methods correlated more closely than did subjective recording. All methods (except EI) significantly underestimated EE, estimated by DLW. There were no significant differences in association between methods and sex, age, BMI or fat-free mass.

CONCLUSION

EE is difficult to measure precisely or accurately with current approaches but physical methods are slightly better than subjective accounts.

Criterion-related validity of the last 7-day, short form of the International Physical Activity Questionnaire in Swedish adults

Objective

To examine the validity of the short, last 7-day, self-administered form of the International Physical Activity Questionnaire (IPAQ).

Design

All subjects wore an accelerometer for seven consecutive days and completed the IPAQ questionnaire on the eighth day. Criterion validity was assessed by linear regression analysis and by modified Bland–Altman analysis. Specificity and sensitivity were calculated for classifying respondents according to the physical activity guidelines of the American College of Sports Medicine/Centers for Disease Control and Prevention.

Setting

Workplaces in Uppsala, Sweden.

Subjects

One hundred and eighty-five (87 males) participants, aged 20 to 69 years.

Results

Total self-reported physical activity (PA) (MET-min day−1) was significantly correlated with average intensity of activity (counts min−1) from accelerometry (r=0.34, P<0.001). Gender, age, education and body mass index did not affect this relationship. Further, subcomponents of self-reported PA (time spent sitting, time in PA, time in moderate and vigorous activity (MVPA)) were significantly correlated with objectively measured PA (P<0.05). Self-reported time in PA was significantly different from time measured by accelerometry (mean difference: −25.9 min day−1; 95% limits of agreement: −172 to 120 min day−1; P<0.001). IPAQ identified 77% (specificity) of those who met the current PA guidelines of accumulating more than 30 min day−1 in MVPA as determined by accelerometry, whereas only 45% (sensitivity) of those not meeting the guidelines were classified correctly.

Conclusions

Our results indicate that the short, last 7-days version of the IPAQ has acceptable criterion validity for use in Swedish adults. However, the IPAQ instrument significantly overestimated self-reported time spent in PA. The specificity to correctly classify people achieving current PA guidelines was acceptable, whereas the sensitivity was low.

Energy Expenditure Estimated by Accelerometry and Doubly Labeled Water

PURPOSE

The purpose of this study was to compare energy expenditure derived from regression equations determined from accelerometry with energy expenditure obtained from the doubly labeled water method (DLW).

METHODS

Thirteen subjects participated in a 7-d protocol during which total daily energy expenditure (TDEE) was measured with DLW. Simultaneously, during the 7 d, subjects wore a Tritrac-R3D and an Actigraph (ACT). Pearson and concordance correlations and one-sample t-tests were used to determine the agreement of six Tritrac and eight ACT regression equations that convert body acceleration to energy expenditure with the DLW measurements.

RESULTS

Tritrac TDEE determined from the different Tritrac regression equations under- and overestimated TDEE determined with DLW that ranged from -10 to +101%. For ACT, the percent difference between DLW and ACT-TDEE determined with the regression equation developed by Hendelman and Swartz were not statistically significantly different from zero. The mean of the difference was -2 and -4%, but the range of the difference was large for both equations, -29 to +24%. TDEE determined with the six other ACT equations were significantly different compared with DLW.

CONCLUSION

Of the 14 different regression equations from the literature, only two developed for ACT compared favorably with DLW; however, the difference in TDEE between these two methods was variable and rather large. These results reemphasize the difficulty in converting body movement into energy expenditure on an individual basis from accelerometry. These results imply that researchers may want to avoid using accelerometers to predict energy expenditure in free-living conditions, instead using these instruments only to measure patterns of physical activity.

Using the Actigraph to measure physical activity of people with disabilities: an investigation into measurement issues

This study investigates measurement issues when using the Actigraph motion sensor to measure the physical activity of people with disabilities. Four volunteers with rheumatoid arthritis participated in the study. Activity levels were measured using the Actigraph over four consecutive weekdays. Activity counts were determined using Actigraph Standard Software. The daily percent of waking time spent at each intensity level was calculated and a weighted average calculated to determine a single daily measure of activity. The variability of measurement, over 1, 2, 3 and 4 days, was examined using these weighted and rolling averages. Activity counts were very low, with over 50% of waking time spent in the 'very low' intensity category, demonstrating a marked floor effect. Little variability (+/-0.11 counts/min) in the level of physical activity was found across 1-4 days. The limited variability (consistency across days) in combination with the floor effect indicates that a 1-day data collection period is adequate. The limitations of the Actigraph are thus related to the existing software options, which have been designed for people without rheumatoid arthritis. The Actigraph does not appear to be a sensitive measure in people performing very low physical activity.

Estimating energy expenditure using accelerometers

The purpose of this study was to examine the validity of published regression equations designed to predict energy expenditure (EE) from accelerometers (Actigraph, Actical, and AMP-331) compared to indirect calorimetry, over a wide range of activities. Forty-eight participants (age: 35 +/- 11.4 years) performed various activities that ranged from sedentary behaviors (lying, sitting) to vigorous exercise. The activities were split into three routines of six activities, and each participant performed at least one routine. The participants wore three devices (Actigraph, Actical, and AMP-331) and simultaneously, EE was measured with a portable metabolic system. For the Actigraph, 15 previously published equations were used to estimate EE from the accelerometer counts. For the Actical, two published equations were used to estimate EE from the accelerometer counts. For the AMP-331 we used the manufacturer's equation to estimate EE. The Actigraph and Actical regressions tended to overestimate walking and sedentary activities and underestimate most other activities. The AMP-331 gave a close estimate of EE during walking, but overestimated sedentary/light activities and underestimated all other activities. The only equation not significantly different from actual time spent in both light and moderate physical activity was the Actigraph Freedson kcal equation. All equations significantly underestimated time spent in vigorous physical activity (P < 0.05). In conclusion, no single regression equation works well across a wide range of activities for the prediction of EE or time spent in light, moderate, and vigorous physical activity.

Convergent validity of six methods to assess physical activity in daily life

The purpose was to examine the agreement (convergent validity) between six common measures of habitual physical activity to estimate durations of light, moderate, vigorous, and total activity in a range of free-living individuals. Over 7 consecutive days, 49 ethnic Chinese (30 men, 19 women), aged 15-55 yr, wore a Polar heart rate monitor, a uniaxial MTI, and triaxial Tritrac accelerometer, plus a Yamax pedometer for > or = 600 min/day. They also completed a daily physical activity log and on day 8 a Chinese version of the 7-day International Physical Activity Questionnaire. At each level of activity, there was good agreement between the two questionnaire-derived instruments and the two accelerometry-derived instruments, but wide variation across different instruments, with two- to fourfold differences in mean durations often seen. The heart rate monitor overestimated light activity and underestimated moderate activity compared with all other measures. Spearman correlation coefficients were low to moderate (0.2-0.5) across most measures of activity, with the pedometer showing correlations with total activity that were often superior to the other movement sensors. We conclude that, with the use of commonly accepted cut points for defining light, moderate, vigorous, and total activity, little convergent validity across the instruments was evident, suggesting these measures are sampling different levels of habitual physical activity and care is needed when comparing their results. To provide a more stable comparison of activity among different people, across studies, or against accepted physical activity promotion guidelines, further work is needed to fine tune the different cut points across a range of common activity monitors to provide more consistent results during free-living conditions.

Concurrent validation of the Bouchard Diary with an accelerometry-based monitor

PURPOSE

This study was conducted to examine the relationships between the Bouchard activity diary and a temporally matched objective measure: the Tritrac-R3D (Professional Products, Reining International, Madison, WI) accelerometer. A secondary purpose was to examine the intraindividual variability in correlation coefficients between the two temporally matched measures.

METHODS

A total of 70 participants (ages 18-23 yr) wore a Tritrac monitor and completed the Bouchard activity diary during a 24-h period. Estimates of activity energy expenditure (AEE) and total energy expenditure (TEE) were compared using correlations, t-tests, and Bland-Altman graphical procedures.

RESULTS

A strong linear relationship was found between the Tritrac and the Bouchard measure for both AEE (r = 0.72) and TEE (r = 0.86). Large and significant differences were seen in the estimates of AEE (576 +/- 381 kcal) and TEE (645 +/- 494) from the two instruments. The Bouchard diary yielded higher estimates of TEE than the Tritrac for nearly all participants (97%) and the Bland-Altman plots revealed a systematic bias in the relationships (smaller bias for lower energy expenditure levels and higher bias for higher energy expenditure estimates). Intraindividual correlations between estimated TEE from the Tritrac and Bouchard diary ranged from 0.34 to 0.93 (mean r = 0.74).

CONCLUSION

The overall response indicates that individuals are able to provide reasonable self-reported estimates of their activity levels across a day.

Accelerometry combined with heart rate telemetry in the assessment of total energy expenditure

The aim of the present study was: (1) to develop a new method for total energy expenditure (TEE) assessment, using accelerometry (ACC) and heart rate (HR) telemetry in combination; (2) to validate the new method against the criterion measure (DLW) and to compare with two of the most common methods, FLEX-HR and ACC alone. In the first part of the study VO(2), HR and ACC counts were measured in twenty-seven subjects during walking and running on a treadmill. Considering the advantages and disadvantages of the HR and ACC methods an analysis model was developed, using ACC at intensities of low and medium levels and HR at higher intensities. During periods of inactivity, RMR is used. A formula for determining TEE from ACC, HR and RMR was developed: TEE = 1.1x(EQ(HR) x TT(HR) + EQ(ACC1) x TT(ACC1) + EQ(ACC2) x TTACC2 + RMR x TT(RMR)). In the validation part of the study a sub-sample of eight subjects wore an accelerometer, HR was logged and TEE was measured for 14 d with the DLW method. Analysis of the Bland-Altman plots with 95 % CI indicates that there are no significant differences in TEE estimated with HR-ACC and ACC alone compared with TEE measured with DLW. It is concluded that the HR-ACC combination as well as ACC alone has potential as a method for assessment of TEE during free-living activities as compared with DLW.

Comparative validation of the IPAQ and the 7-Day PAR among women diagnosed with breast cancer

BACKGROUND

The criterion-related validity and measurement bias of the long form of the International Physical Activity Questionnaire (IPAQ) was compared to the 7-Day Physical Activity Recall (PAR).

METHODS

Participants were women who have been diagnosed with breast cancer and enrolled in the ongoing Women's Healthy Eating and Living Study. Women (N = 159, average age 57 years) wore an accelerometer for one week and then completed the IPAQ or the PAR.

RESULTS

The validity correlation of the PAR was significantly higher (p < 0.001) than the IPAQ (0.73 vs. 0.33, respectively). The PAR and IPAQ overestimated total physical activity by 13% vs. 247%, respectively. The PAR had better sensitivity (p = 0.14) and specificity (p < .01) than the IPAQ (100% vs. 71% and 84% vs. 59%, respectively) in predicting attainment of the ACSM physical activity guideline.

CONCLUSION

The PAR was superior to the IPAQ in terms of validity, measurement bias, and screening statistics.

Integration of physiological and accelerometer data to improve physical activity assessment

PURPOSE

Accurate measurement of physical activity (PA) is a prerequisite to determine dose-response relationships between activity and health. The combination of HR and accelerometers (ACC) holds promise for improving the accuracy of PA assessment, but it is unclear how currently proposed modeling techniques compare and to what extent different levels of individual calibration (IC) of HR influence monitoring accuracy.

METHODS

A total of 10 men and women (25.8 +/- 3.4 yr, 1.70 +/- 0.1 m, 71.7 +/- 11.8 kg, 24.4 +/- 5.0 kg.m-2) were recruited for this study, in which IC of HR to PA energy expenditure (PAEE) during both arm crank and treadmill activity were available. Participants completed 6 h of free-living activity, during which PAEE (obtained with indirect calorimetry), HR, hip ACC, arm ACC, and leg ACC were collected. PAEE was then modeled from two different methods of combining HR and ACC (arm-leg HR+M and branched model), both with IC and group-level calibration (GC) of HR, and also from hip ACC estimates alone. Estimates of PAEE were compared with criterion values for PAEE.

RESULTS

Combined estimates of PAEE from the arm-leg HR+M and the branched model were similar when IC was used (R2 = 0.81, SEE = 0.55 METs and R2 = 0.75, SEE = 0.61 METs, respectively). When using GC, all estimates of PAEE had larger error, but the performance of the branched model suffered less than the arm-leg HR+M model (R2 = 0.75, SEE = 0.67 METs and R2 = 0.67, SEE = 0.88 METs, respectively). Both combination modeling techniques were more precise than single-measure hip ACC estimates (R2 = 0.41, SEE = 0.96 METs).

CONCLUSION

The combination of HR and ACC improves the accuracy of PAEE estimates and could be applied in large-scale epidemiological studies.

Validation of the Spanish version of the physical activity questionnaire used in the Nurses' Health Study and the Health Professionals' Follow-up Study

OBJECTIVE

The objective of this analysis was to test the validity of the estimates of energy expenditure and sedentary lifestyle obtained through a self-administered questionnaire of physical activity for Spanish-speaking people adapted from US questionnaires (Nurses' Health Study and Health Professionals' Follow-up Study) using a triaxial accelerometer (RT3 Triaxial Research Tracker) as the reference.

DESIGN AND SETTING

Validation study, calculating the non-parametric correlation coefficients between the level of physical activity and sedentary lifestyle collected by the self-administered questionnaire and the triaxial accelerometer measurements. Percentage of misclassification and kappa coefficients were also calculated.

SUBJECTS

The study population consisted of a sample of 40 obese women who were participants of the SUN (Seguimiento Universidad de Navarra) project (a prospective cohort study among Spanish university alumni). They were selected because of their peculiar metabolic characteristics, in the search for a sub-optimal scenario for validity.

RESULTS

Physical activity during leisure time (estimated as MET-h week(-1)) derived from the self-administered questionnaire moderately correlated with kcal day(-1) assessed through the accelerometer (Spearman's rho = 0.507, 95% confidence interval (CI) 0.232, 0.707). The Spearman correlation between the ratio of sedentary lifestyle to physical activity obtained through the questionnaire and the direct estimation (RT3) was -0.578 (95% CI -0.754, -0.325). The kappa index was 0.25 (P = 0.002) when assessing the cross-classification into quintiles and 0.41 for the dichotomous estimation of a sedentary lifestyle. Only 2.5% of participants were misclassified by the questionnaire more than two quintiles apart from the estimates of the RT3.

CONCLUSIONS

The moderate values obtained for correlation in a sub-optimal scenario for validity and the low percentage of extreme misclassification suggest the validity of the questionnaire to assess physical activity in Spanish-speaking women aged 20-50 years.

The Technology of Accelerometry-Based Activity Monitors: Current and Future

PURPOSE

This paper reviews accelerometry-based activity monitors, including single-site first-generation devices, emerging technologies, and analytical approaches to predict energy expenditure, with suggestions for further research and development.

METHODS

The physics and measurement principles of the accelerometer are described, including the sensor properties, data collections, filtering, and integration analyses. The paper also compares these properties in several commonly used single-site accelerometers. The emerging accelerometry technologies introduced include the multisensor arrays and the combination of accelerometers with physiological sensors. The outputs of accelerometers are compared with criterion measures of energy expenditure (indirect calorimeters and double-labeled water) to develop mathematical models (linear, nonlinear, and variability approaches).

RESULTS

The technologies of the sensor and data processing directly influence the results of the outcome measurement (activity counts and energy expenditure predictions). Multisite assessment and combining accelerometers with physiological measures may offer additional advantages. Nonlinear approaches to predict energy expenditure using accelerometer outputs from multiple sites and orientation can enhance accuracy.

CONCLUSIONS

The development of portable accelerometers has made objective assessments of physical activity possible. Future technological improvements will include examining raw acceleration signals and developing advanced models for accurate energy expenditure predictions.

Conducting Accelerometer-Based Activity Assessments in Field-Based Research

PURPOSE

The purpose of this review is to address important methodological issues related to conducting accelerometer-based assessments of physical activity in free-living individuals.

METHODS

We review the extant scientific literature for empirical information related to the following issues: product selection, number of accelerometers needed, placement of accelerometers, epoch length, and days of monitoring required to estimate habitual physical activity. We also discuss the various options related to distributing and collecting monitors and strategies to enhance compliance with the monitoring protocol.

RESULTS

No definitive evidence exists currently to indicate that one make and model of accelerometer is more valid and reliable than another. Selection of accelerometer therefore remains primarily an issue of practicality, technical support, and comparability with other studies. Studies employing multiple accelerometers to estimate energy expenditure report only marginal improvements in explanatory power. Accelerometers are best placed on hip or the lower back. Although the issue of epoch length has not been studied in adults, the use of count cut points based on 1-min time intervals maybe inappropriate in children and may result in underestimation of physical activity. Among adults, 3-5 d of monitoring is required to reliably estimate habitual physical activity. Among children and adolescents, the number of monitoring days required ranges from 4 to 9 d, making it difficult to draw a definitive conclusion for this population. Face-to-face distribution and collection of accelerometers is probably the best option in field-based research, but delivery and return by express carrier or registered mail is a viable option.

CONCLUSION

Accelerometer-based activity assessments requires careful planning and the use of appropriate strategies to increase compliance.

Metabolic equivalent: one size does not fit all

The metabolic equivalent (MET) is a widely used physiological concept that represents a simple procedure for expressing energy cost of physical activities as multiples of resting metabolic rate (RMR). The value equating 1 MET (3.5 ml O2·kg−1·min−1 or 1 kcal·kg−1·h−1) was first derived from the resting O2 consumption (V̇o2) of one person, a 70-kg, 40-yr-old man. Given the extensive use of MET levels to quantify physical activity level or work output, we investigated the adequacy of this scientific convention. Subjects consisted of 642 women and 127 men, 18–74 yr of age, 35–186 kg in weight, who were weight stable and healthy, albeit obese in some cases. RMR was measured by indirect calorimetry using a ventilated hood system, and the energy cost of walking on a treadmill at 5.6 km/h was measured in a subsample of 49 men and 49 women (26–45 kg/m2; 29–47 yr). Average V̇o2 and energy cost corresponding with rest (2.6 ± 0.4 ml O2·kg−1·min−1 and 0.84 ± 0.16 kcal·kg−1·h−1, respectively) were significantly lower than the commonly accepted 1-MET values of 3.5 ml O2·kg−1·min−1 and 1 kcal·kg−1·h−1, respectively. Body composition (fat mass and fat-free mass) accounted for 62% of the variance in resting V̇o2 compared with age, which accounted for only 14%. For a large heterogeneous sample, the 1-MET value of 3.5 ml O2·kg−1·min−1 overestimates the actual resting V̇o2 value on average by 35%, and the 1-MET of 1 kcal/h overestimates resting energy expenditure by 20%. Using measured or predicted RMR (ml O2·kg−1·min−1 or kcal·kg−1·h−1) as a correction factor can appropriately adjust for individual differences when estimating the energy cost of moderate intensity walking (5.6 km/h).

Position-sensing technologies for movement analysis in stroke rehabilitation

Research has focused on improvement of the quality of life of stroke patients. Gait detection, kinematics and kinetics analysis, home-based rehabilitation and telerehabilitation are the areas where there has been increasing research interest. The paper reviews position-sensing technologies and their application for human movement tracking and stroke rehabilitation. The review suggests that it is feasible to build a home-based telerehabilitation system for sensing and tracking the motion of stroke patients.

Food habits and nutritional status assessment of adolescent soccer players. A necessary and accurate approach

The aim of this study was to assess the food habits and nutritional status of high level adolescent soccer players (N = 33; ages 14-16 yrs) living in their home environment. Body composition (height, mass, skinfolds), biochemical and hematological parameters, performance in soccer-specific tests (sprinting, jumping, intermittent endurance), and dietary intake (weighed food intake method) and related behaviors (nutrient supplement use, daily activity profile) were assessed. Daily energy expenditure and energy intake were 12.5 MJ and 12.6 MJ, respectively. Protein (16% of energy intake; 1.9 g/kg of body mass), lipid (38%), and cholesterol (385 mg) intake were above recommendations, while carbohydrates (45%) were below. The food intake of these adolescents was based on cereals and derivates; meat, fish, and eggs; milk and dairy products; biscuits and confectionery; and oil, butter and margarine, which provided 78% of total energy intake, 85% of proteins, 64% of carbohydrates, 90% of lipids, and 47% of fiber. Although diet provided sufficient iron, 48% of individuals showed iron deficiency without anemia. Based on these results, a well designed nutrition intervention would be advisable for optimizing performance, and especially for promoting healthy eating habits in adolescent soccer players.

Comparison of two approaches to structured physical activity surveys for adolescents

PURPOSE

To compare the test-retest reliability, convergent validity, and overall feasibility/ usability of activity-based (AB) and time-based (TB) approaches for obtaining self-reported moderate-to-vigorous physical activity (MVPA) from adolescents.

METHODS

Adolescents (206 females and 114 males) completed two 3-d physical activity recalls using the AB and TB surveys, which contained identical lists of physical activities. The participants wore an MTI Actigraph accelerometer for the same period.

RESULTS

The TB instrument took about 3 min longer to complete (P = 0.022). Overall 2-d test-retest correlations for MVPA were similar for the two surveys (r = 0.676 and 0.667), but the girls had higher reliability on the AB survey than the boys (girls: r = 0.713; boys: r = 0.568). The overall 3-d correlations for MVPA surveys and Actigraph counts varied by gender (girls: AB = 0.265 vs TB = 0.314; boys: AB = 0.340 vs TB = 0.277). Correlations for vigorous physical activity and Actigraph counts were higher for the AB than for the TB (r = 0.281 vs 0.162). As the interval between completing the surveys and the days being recalled increased, reliability and validity were lower, especially for the AB survey.

CONCLUSION

For both genders, either approach is acceptable for obtaining MVPA information on a single day, but the TB approach appears to be slightly favored over the AB approach for obtaining multiple days of MVPA. A 3-d recall period appears to be too long for accurate recall of MVPA information from either instrument. For both genders, the surveys overestimated activity levels; thus, self-reports should be supplemented with objective data.

Description and validation of the ActiReg: a novel instrument to measure physical activity and energy expenditure

The ActiReg (PreMed AS, Oslo, Norway) system is unique in using combined recordings of body position and motion alone or combined with heart rate (HR) to calculate energy expenditure (EE) and express physical activity (PA). The ActiReg has two pairs of position and motion sensors connected by cables to a battery-operated storage unit fixed to a waist belt. Each pair of sensors was attached by medical tape to the chest and to the front of the right thigh respectively. The collected data were transferred to a personal computer and processed by a dedicated program ActiCalc. Calculation models for EE with and without HR are presented. The models were based on literature values for the energy costs of different activities and therefore require no calibration experiments. The ActiReg system was validated against doubly labelled water (DLW) and indirect calorimetry. The DLW validation demonstrated that neither EE calculated from ActiReg data alone (EEAR) nor from combined ActiReg and HR data (EEAR-HR) were statistically different from DLW results. The EEAR procedure causes some underestimation of EE >11 MJ corresponding to a PA level >2.0. This underestimation is reduced by the EEAR-HR procedure. The objective recording of the time spent in different body positions and at different levels of PA may be useful in studies of PA in different groups and in studies of whether recommendations for PA are being met. The comparative ease of data collection and calculation should make ActiReg a useful instrument to measure habitual PA level and EE.

Long-period accelerometer monitoring shows the role of physical activity in overweight and obesity

CONTEXT

Physical activity (PA) plays an important role in obesity. A new accelerometer has been developed to assess total energy expenditure as well as PA.

OBJECTIVE

To investigate the association of PA with overweight and obesity in Japanese men and women, a large cross-sectional study was performed using a single-axis accelerometer.

DESIGN, SETTING AND PARTICIPANTS

Population-based cross-sectional study of Japanese 18-84 y of age. Height, body weight and PA were measured in 400 male and 388 female Japanese volunteers from 1999 to 2000. The outcome measurements were overweight and obesity, which are defined as a body mass index >/=25 kg/m(2). PA was measured for 1 to 4 weeks and was then categorized into three activity levels, which were defined as light, moderate and vigorous PA.

RESULTS

Prevalence of overweight and obesity was 22.3%. Number of steps and time spent in moderate and vigorous PA per day were lower in overweight and obese individuals. No difference was found in time spent in light PA. Individuals who are in the 4th and 5th quintile of moderate and vigorous PA showed a significantly lower body mass index. When odd ratios (ORs) of overweight and obesity estimated by logistic regression were used as effect measures, overweight and obesity were negatively associated with vigorous PA (ORs=0.91).

CONCLUSION

These results indicate that overweight and obese individuals have a lower step rate and are spending less time for moderate to vigorous PA. Participation in vigorous PA is an important predictor of overweight and obesity.

Validation of a simplified physical activity record by doubly labeled water technique

INTRODUCTION

For obtaining reliable information about physical activity in epidemiological studies, validated and easy-to-use instruments are required. Therefore, a new simplified physical activity record based on 15-min recording intervals was developed and validated.

SUBJECTS

Nonobese volunteers (n = 31).

MEASUREMENTS

Physical activity was recorded over a 7-day period without detailed instructions. Energy expenditure was calculated (EE(sPAR)) and compared to energy expenditure measured by doubly labelled water technique (EE(DLW)).

RESULTS

A good agreement between EE(sPAR) (12.1+/-3.0) and EE(DLW) (11.7+/-3.3) with a mean difference of 0.33+/-1.55 MJ (r = 0.880, P < 0.001) was observed. The absolute difference between EE(sPAR) and EE(DLW) was < 10% in 65% of the subjects. The difference between EE(sPAR) and EE(DLW) was independent of gender, age, body weight, and body mass index. A weak positive association between the difference and total body fat was observed (r = 0.618, P < 0.001), suggesting a slight tendency to overestimate EE(sPAR) with increasing total body fat.

CONCLUSION

The new simplified physical activity protocol needs no detailed instructions, provides valid estimates of physical activity in nonobese free-living adults and can be used in epidemiological studies to assess total daily energy expenditure and physical activity level.

Physical activity and human energy expenditure

PURPOSE OF REVIEW

This is a review on the measurement of physical activity under daily life conditions. The focus is on the doubly labelled water method and accelerometry. Doubly labelled water is a gold standard and the reference for the validation of field methods to assess physical activity. Accelerometry is the most objective and precise technique to assess activity patterns in terms of frequency, duration and intensity. Applications of the two techniques are illustrated with the limits of physical activity and energy expenditure and with activity intensity as a determinant of the physical activity level.

RECENT FINDINGS

The upper limit of the physical activity index (total energy expenditure as a multiple of basal metabolic rate) of 2.5, as derived from cross-sectional data, is confirmed by training intervention studies. Exercise training, in which total energy expenditure was measured before and at the end of the training programme, showed no increase in physical activity index when training was combined with an energy restricted diet and in elderly subjects. In children, the distribution of time spent at activities with low and high intensity determines the physical activity index while in adults moderate-intensity activities are the main determinant.

SUMMARY

In adults, within the normal physical activity index range, the distribution of time spent at activities with low and moderate intensity determines the physical activity level. High-intensity activity does not have much impact on daily energy expenditure. High-intensity activity is not required to increase the activity energy expenditure.

The Effects of Health and Environment on Exercise-Class Participation in Older, Urban Women

This research investigated the effects of health and environmental factors on the dropout and intermittent nonattendance of an exercise program designed specifically for older, female, primary-care patients living in the inner city. Class-attendance records (n = 21,538) from a cohort 110 women were analyzed. Women who dropped out early had poorer perceived health and were more likely to report pain as an exercise barrier at baseline. Those who lived in a census tract where a larger percentage of workers walk to work were less likely to drop out early. Intermittent nonattendance was associated with adverse weather conditions including heat index above 90 degrees F, wind-chill index below 20 degrees F, overcast sky, and snow. Better attendance was associated with greater atmospheric pressure, as well as lower number of sunlight hours per day. This research highlights the need to better understand environmental barriers when promoting physical activities in older women.

Validity of a multi-sensor armband in estimating rest and exercise energy expenditure

The SenseWear Armband (SWA; BodyMedia, Inc.), using multiple sensors, was designed to estimate energy expenditure (EE) in free-living individuals.

PURPOSE

To examine the reliability and validity of the SWA during rest and exercise compared with indirect calorimetry (IC).

METHODS

EE was assessed with SWA and IC in 13 males during two resting and one cycle ergometry (40 min at 60% VO2peak) sessions. In a second experiment, 20 adults walked on a treadmill for 30 min at three intensities (80.5 m x min, 0% grade; 107.3 m x min, 0% grade; 107.3 m x min, 5% grade) while IC and SWA measured EE.

RESULTS

At rest, no significant differences were found between EE measurements from the SWA (1.3 +/- 0.1 kcal x min) and IC (1.3 +/- 0.1 kcal x min), and the two methods were highly correlated (r = 0.76; P < 0.004). The SWA EE estimation was reliable when comparing the two resting visits (r = 0.93; P < 0.001). For the ergometer protocol, no significant differences were found between the SWA and IC measurements of EE early, mid, or late in exercise or for the total bout, although the measurements were poorly correlated (r = 0.03-0.12). The SWA EE estimate of walking increased with treadmill speed but not with incline. The SWA significantly overestimated (13-27%) the EE of walking with no grade (P < 0.02) and significantly underestimated (22%) EE on the 5% grade (P < 0.002). The SWA estimation of EE correlated moderately with IC (r = 0.47-0.69).

CONCLUSION

The SWA provided valid and reliable estimates of EE at rest and generated similar mean estimates of EE as IC on the ergometer; however, individual error was large. The SWA overestimated the EE of flat walking and underestimated inclined walking EE.

Physical activity in low-income postpartum women

PURPOSE

To validate the 7-day physical activity recall (PAR), including alternative PAR scoring algorithms, using pedometer readings with low-income postpartum women, and to describe physical activity patterns of a low-income population of postpartum women.

METHODS

Forty-four women (13 African American, 19 Hispanic, and 12 White) from the Austin New Mothers Study (ANMS) were interviewed at 3 months postpartum. Data were scored alternatively according to the Blair (sitting treated as light activity) and Welk (sitting excluded from light activity and treated as rest) algorithms. Step counts based on 3 days of wearing pedometers served as the validation measure.

FINDINGS

Using the Welk algorithm, PAR components significantly correlated with step counts were: minutes spent in light activity, total activity (sum of light to very hard activity), and energy expenditure. Minutes spent in sitting were negatively correlated with step counts. No PAR component activities derived with the Blair algorithm were significantly related to step counts. The largest amount of active time was spent in light activity: 384.4 minutes with the Welk algorithm. Mothers averaged fewer than 16 minutes per day in moderate or high intensity activity. Step counts measured by pedometers averaged 6,262 (SD = 2,712) per day.

CONCLUSIONS

The findings indicate support for the validity of the PAR as a measure of physical activity with low-income postpartum mothers when scored according to the Welk algorithm. On average, low-income postpartum women in this study did not meet recommendations for amount of moderate or high intensity physical activity.

Comparison of Activity Monitors to Estimate Energy Cost of Treadmill Exercise

PURPOSE

To evaluate the validity of five physical activity monitors available for research: the CSA, the TriTrac-R3D, the RT3, the SenseWear Armband, and the BioTrainer-Pro.

METHODS

A total of 10 healthy men and 11 healthy women performed 10 min of treadmill walking at 54, 80, and 107 mxmin and treadmill running at 134, 161, 188, and 214 mxmin. The CSA, TriTrac-R3D, RT3, and BioTrainer-Pro accelerometers were placed side by side bilaterally at the waist in the axillary position, and the SenseWear Armband monitors were placed bilaterally on the posterior portion of each arm in the mid-humeral position. Simultaneous measurements of body motion and indirect calorimetry were continuously recorded during all exercise. Data were analyzed with repeated measures ANOVA and pairwise Bonferroni-adjusted estimated marginal means.

RESULTS

: There was no significant difference in the mean energy expenditure (EE) recorded bilaterally by any of the monitors (P < 0.05) at any treadmill speed. The SenseWear Armband, the TriTrac-R3D, and the RT3 had significant increases in mean EE across all walking and running speeds (P < 0.05). Below 161 mxmin, the mean EE recorded by the BioTrainer-Pro and the CSA increased significantly (P < 0.001); however, there was no significant difference (P > 0.10) in mean EE recorded by either monitor for speeds above 161 mxmin. In general, all monitors overestimated EE at most treadmill speeds when compared with indirect calorimetry (P < 0.001), except for the CSA which underestimated EE at the lowest and highest speeds.

CONCLUSION

The CSA was the best estimate of total EE at walking and jogging speeds, the TriTrac-R3D was the best estimate of total EE at running speeds, and the SenseWear Armband was the best estimate of total EE at most speeds.

Assessment of physical activity by telephone interview versus objective monitoring

PURPOSE

To compare different methods of quantifying time in physical activity (PA).

METHODS

Twenty-five participants (12 male, 13 female) volunteered to be monitored for seven consecutive days, during which different PA patterns were measured by the simultaneous heart-rate motion sensor technique (HR+M). At the end of the 7th day, participants completed questions taken from the 2001 Behavioral Risk Factor Surveillance System (BRFSS) PA module telephone survey, in which they recalled the amount of time spent walking, and in moderate and vigorous activities. The results of the BRFSS PA module were then compared with those of the HR+M.

RESULTS

No significant group differences were found in the amount of time spent in moderate and vigorous activities between methods. However, individual differences were greater for time spent in moderate activities (SE +/- 7.36 min x d(-1); range -70 to 77 min x d(-1)) than for time spent in vigorous activities (SE +/- 3.57 min x d(-1); range -39 to 33 min x d(-1). Spearman correlation coefficients between the HR+M and the BRFSS were significant for vigorous activities (r = 0.54, P < 0.01). There was 80% agreement between the two methods of classifying individuals who either: (a) met the recommendations (through moderate and/or vigorous PA) or (b) did not meet the recommendations.

CONCLUSION

The BRFSS and HR+M methods yielded similar group estimates of PA, but individual assessments of moderate activity differed more than those of vigorous activity. BRFSS estimations of group compliance with national PA recommendations were similar to those of the HR+M.

Controlled outcome evaluation of the First Step Program: a daily physical activity intervention for individuals with type II diabetes

OBJECTIVE

To conduct a randomised trial of a physical activity (PA) intervention, The First Step Program (FSP) for adults with type II diabetes.

DESIGN

A 16-week intervention study and 24-week follow-up assessment.

PARTICIPANTS

A total of 47 overweight/obese, sedentary individuals (age=52.7 +/- 5.2 y; BMI=33.3 +/- 5.6 kg/m2) recruited through a diabetes education centre.

MEASUREMENTS

PRIMARY OUTCOME

daily PA assessed by pedometer (steps/day).

SECONDARY OUTCOMES

anthropometric measures (weight, BMI, waist girth, hip girth); indicators of cardiovascular health (resting heart rate and blood pressure); glycemic control (fasting glucose, insulin, HbA1c, glucose concentration 120 min postglucose load); plasma lipid status (total cholesterol, HDL cholesterol, LDL cholesterol, and triglycerides).

RESULTS

Relative to the CONTROL group, FSP participants increased their PA >3000 steps/day (approximately 30 min/day) during the intervention (P<0.0001). Waist and hip girth decreased (approximately 2-3 cm), but did not differ significantly between groups. Significant changes did not emerge for any of the other variables.

CONCLUSIONS

The FSP is a practical intervention that elicits an immediate and profound change in walking behaviour. Such change is an important 'first step' towards increasing the volume and/or intensity of PA necessary to improve long-term health outcomes in this largely sedentary and overweight or obese population. Relapse by 24 weeks indicates that other strategies such as booster sessions are needed to maintain lifestyle change. Further research must determine realistic and responsive health outcomes for this population that are achievable through practical, real-world programming.

Total energy expenditure estimated using foot-ground contact pedometry

Routine walking and running, by increasing daily total energy expenditure (TEE), can play a significant role in reducing the likelihood of obesity. The objective of this field study was to compare TEE estimated using foot-ground contact time (Tc)-pedometry (TEE(PEDO)) with that measured by the criterion doubly labeled water (DLW) method. Eight male U.S. Marine test volunteers [27 +/- 4 years of age (mean +/- SD); weight = 83.2 +/- 10.7 kg; height = 182.2 +/- 4.5 cm; body fat = 17.0 +/- 2.9%] engaged in a field training exercise were studied over 2 days. TEE(PEDO) was defined as (calculated resting energy expenditure + estimated thermic effect of food + metabolic cost of physical activity), where physical activity was estimated by Tc-pedometry. Tc-pedometry was used to differentiate inactivity, activity other than exercise (i.e., non-exercise activity thermogenesis, or NEAT), and the metabolic cost of locomotion (M(LOCO)), where M(LOCO) was derived from total weight (body weight + load weight) and accelerometric measurements of Tc. TEE(PEDO) data were compared with TEEs measured by the DLW (2H2(18)O) method (TEE(DLW)): TEE(DLW) = 15.27 +/- 1.65 MJ/day and TEE(PEDO) = 15.29 +/- 0.83 MJ/day. Mean bias (i.e., TEE(PEDO) - TEE(DLW)) was 0.02 MJ, and mean error (SD of individual differences between TEE(PEDO) and TEE(DLW)) was 1.83 MJ. The Tc-pedometry method provided a valid estimate of the average TEE of a small group of physically active subjects where walking was the dominant activity.

Estimating human energy expenditure: a review of techniques with particular reference to doubly labelled water

This review includes an historical overview of the techniques for measuring energy expenditure (EE). Following this overview, the "gold standard" method of measuring EE, the doubly labelled water (DLW) method, is emphasised. Other methods, such as direct calorimetry, indirect calorimetry systems, heart rate and EE relationships, questionnaires and activity recall, motion sensors, combined heart rate and motion sensors for the estimation of EE are then highlighted in relation to their validation against the DLW method. The major advantages and disadvantages for each method are then considered. The preferred method to determine EE is likely to depend principally on factors such as the number of study participants to be monitored, the time period of measurements and the finances available. Small study participant numbers over a short period may be measured accurately by means of indirect calorimetric methods (stationary and portable systems). For periods over 3-4 days, EE should ideally be measured using the DLW method. However, the use of motion sensors is very promising in the measurement of EE, and has a number of advantages over the DLW method. Furthermore, if used correctly, both heart rate and questionnaire methods may provide valuable estimates of EE. Additional studies are needed to examine the possibility of improving the accuracy of measurement by combining two or more techniques. Such information, if confirmed by scientific rigour, may lead to an improvement in the estimation of EE and population-based physical activity levels. The accurate measurement of physical activity and EE is critical from both a research and health prospective. A consideration of the relevant techniques used for the estimation of EE may also help improve the quality of these frequently reported measurements.

Amount and bouts of physical activity in a sample of African-American women

PURPOSE

To describe physical activity (PA) patterns in a sample of African-American women in comparison with the national recommendation for moderate PA.

METHODS

Volunteers (N=55; ages 25-55 yr (mean +/- SD 39.6 +/- 8.7); body mass index [BMI] 17.9-56.4 kg.m(-2) (31.3 +/- 7.9 kg.m(-2))) were recruited by word of mouth. PA was measured using accelerometers, pedometers, and PA records for two 4-d periods.

RESULTS

Participants accumulated 31.9 +/- 18.0 min.d(-1) in moderate-to-vigorous PA (MVPA), primarily through short bouts lasting 1-4 (median 11.9 bouts.d(-1)) and 5-7 min (median 0.6 bouts.d(-1)) but only on 3.1 +/- 2.4 d.wk(-1). Women with BMI<25.0 kg.m(-2) accumulated more daily PA than those with BMI 25.0-29.9 kg.m(-2) or > or =30 kg.m(-2) (50.3, 32.0, and 25.3 min.d(-1), respectively; P<0.001) and on more days per week (5.8, 3.0, 2.3 d, respectively; P<0.001). Of 42 women who completed both PA data collection periods, 17 achieved > or =30 min of MVPA on > or =5 of 8 d; however, only two achieved the PA in the recommended pattern (one 30-min bout or several 8-10 min bouts).

CONCLUSION

The current study showed that, although this sample was not sedentary, few participants met the activity level recommended for health benefits because activity was performed on too few days per week, particularly among overweight and obese participants. In addition, the bout pattern for most participants was not at the recommended length of at least 8-10 min. This suggests that additional emphasis on the recommended days per week and bout length may be necessary when counseling individuals about physical activity.

Physical activity level measured by doubly labeled water and accelerometry in children

The present study investigated the use of a tri-axial accelerometer, Tracmor2, for the measurement of physical activity in children. Eleven children [age 6.9 (2.2) years, body mass 19.5 (5.3) kg and height 112.3 (14.4) cm] were studied. Total daily energy expenditure (TDEE) was measured using the doubly labeled water method over a 2-week period. In addition, basal metabolic rate (BMR) was determined by the ventilated hood system. Physical activity level (PAL) was defined as TDEE/BMR. Tracmor2 was worn during the same 2-week period throughout waking hours after which average counts per day were calculated. The average counts per day were shown to be highly correlated to PAL values measured by doubly labeled water: PAL = 1.156 x 10(-5) x Tracmor2 average counts day(-1) + 0.978 (r=0.79, P<0.01). In conclusion, Tracmor2 is a valid instrument to measure physical activity in children under free-living conditions.

Is the ArteACC index a valid indicator of free-living physical activity in adolescents?

OBJECTIVE

The principal aim of this study was to validate a proposed new index of physical activity, the activity-related time equivalent based on accelerometry (ArteACC), in adolescents. A secondary aim was to develop regression equations for prediction of total energy expenditure (TEE) and activity energy expenditure [AEE = 0.9 x TEE - resting metabolic rate (RMR)].

RESEARCH METHODS AND PROCEDURES

RMR and energy expenditure (EE) under standardized exercises were measured by indirect calorimetry in 36 adolescents (14 to 19 years old). TEE was measured by the doubly labeled water method, and physical activity was assessed simultaneously with an accelerometer for 14 days. AEE, AEE in relation to body weight (AEE per kilogram), and activity-related time equivalent based on energy expenditure (ArteEE = AEE/[EE reference activity - RMR]) were calculated from laboratory and free-living EE data. ArteACC was calculated as total activity counts/activity counts of reference activity.

RESULTS

ArteACC was significantly related to AEE per kilogram (r = 0.57; p < 0.0001) and ArteEE (r = 0.68; p < 0.001). The absolute amount of time (minutes per day) spent in physical activity was significantly lower when calculated from ArteACC than from ArteEE (p < 0.001). TEE was significantly influenced by RMR, sex, and ArteACC (r(2) = 0.89). AEE was significantly influenced by sex and ArteACC (r(2) = 0.59).

DISCUSSION

Despite an absolute difference between the two indexes, ArteEE and ArteACC, ArteACC seems to be a valid indicator of free-living physical activity. It contributed significantly, by 3.3% and 12.5%, to the explained variations in TEE and AEE, respectively.

Utility of pedometers for assessing physical activity: convergent validity

Valid assessment of physical activity is important to researchers and practitioners interested in surveillance, screening, programme evaluation and intervention. The validity of an assessment instrument is commonly considered its most important attribute. Convergent validity is the extent to which an instrument's output is associated with that of other instruments intended to measure the same exposure of interest. A systematic review of the literature produced 25 articles directly relevant to the question of convergent validity of pedometers against accelerometers, observation, and self-reported measures of physical activity. Reported correlations were pooled and a median r-value was computed. Pedometers correlate strongly (median r = 0.86) with different accelerometers (specifically uniaxial accelerometers) depending on the specific instruments used, monitoring frame and conditions implemented, and the manner in which the outputs are expressed. Pedometers also correlate strongly (median r = 0.82) with time in observed activity. Time in observed inactivity correlated negatively with pedometer outputs (median r = -0.44). The relationship with observed steps taken depended upon monitoring conditions and speed of walking. The highest agreement was apparent during ambulatory activity (running, walking) or during sitting (when both observation and pedometers would register few steps taken). There was consistent evidence of reduced accuracy during slow walking. Pedometers correlate moderately with different measures of energy expenditure (median r = 0.68). The relationship between pedometer outputs and energy expenditure is complicated by the use of many different direct and indirect measures of energy expenditure and population samples. Concordance with self-reported physical activity (median r = 0.33) varied depending upon the self-report instrument used, individuals assessed, and how pedometer outputs are expressed (e.g. steps, distance travelled, energy expenditure). Pedometer output has an inverse relationship with reported time spent sitting (r = -0.38). The accumulated evidence herein provides ample support that the simple and inexpensive pedometer is a valid option for assessing physical activity in research and practice.

Factors affecting levels of physical activity in adults

A large proportion of adults in Western cultures are physically inactive, despite several decades of warnings about the potentially negative health consequences of a sedentary lifestyle. Efforts to promote physical activity have focused on identifying its determinants and designing interventions that might effectively promote regular physical activity. The multitude of factors that induce adults to initiate and maintain programmes of physical activity have been divided into those that are invariable (age, gender, race, ethnicity) and those that are presumed to be modifiable (behavioural and personality characteristics, environmental circumstances and community settings). The lack of consistency in the design, analysis and reporting of interventions in the lives of inactive or sedentary individuals has produced equivocal results. However, several social and environmental factors have systematically emerged as determinants of physical activity in adults. In ethnic minorities, the removal of barriers such as unaffordable facilities and unavailable childcare, high crime rates, fear for personal safety and culturally inappropriate activities are of primary importance. Social support from family, peers, communities and healthcare providers has resulted in modest improvements across cultures, ages and genders in selected settings, but the definition of specific interventions and their outcomes deserve additional attention. Longitudinal studies indicate that components of physical fitness are relatively transitory, with low to modest correlations between physical activity and measures of physical fitness in childhood and adolescence and in adulthood. Attempts to explain the activity behaviour of adults by applying various theories in programmes of intervention have also produced mixed results. Successful interventions tailor programmes to individual needs, account for personal levels of fitness, allow for personal control of the activity and its outcomes, and provide for social support by family, peers and communities. The initiation and maintenance of regular physical activity in adults depends on a multitude of biological and sociocultural variables that demand attention across the lifespan.