Biomedical subjects

Gregory J Welk

Publications and source records attributed to Gregory J Welk.

9 recordsLinked to original sources

PubMed2006

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.

Acceleration↗

PubMed2005

Relationship between adolescent fitness and fatness and cardiovascular disease risk factors in adulthood: the Aerobics Center Longitudinal Study (ACLS).

PURPOSE: To examine the relationship between cardiorespiratory fitness and body fatness during adolescence and cardiovascular disease (CVD) risk factors in adulthood. METHODS: The sample was 48 participants from the Aerobics Center Longitudinal Study (ACLS) who had one clinical visit during adolescence (mean age = 15.8 years) and a follow-up visit during adulthood (mean age = 26.6 years). Values for treadmill time (TM), body fatness (body mass index [BMI], percent body fat [%BF], and waist circumference [WC]), traditional CVD risk factors (blood pressure [BP], fasting total cholesterol [TC], high-density lipoprotein cholesterol [HDL-C], triglycerides [TG], and glucose), and a composite metabolic syndrome risk factor score were adjusted for age and sex. The relationships between adolescent TM and body fatness variables and adult CVD risk factors were examined by partial correlations, controlling for length of follow-up (mean = 11 years). The correlation between changes in TM and body fatness (DeltaTM and Deltabody fatness, respectively) and changes in CVD risk factors between adolescence and adulthood (DeltaCVD risk factors) were also examined. Adolescent cardiorespiratory fitness and body fatness variables also were separated into 2 categories based on the median split: low (below median) and high (above median). RESULTS: TM and body fatness variables showed moderate stability between adolescence and adulthood ( r = 0.44-0.78). Adolescent TM and DeltaTM showed moderate correlations with adult body fatness indicators (BMI, WC, and %BF, r = -0.34 to -0.47) and Deltabody fatness ( r = -0.24 to -0.46), respectively. Adolescent TM was not significantly related to traditional CVD risk factors in adulthood. Adolescent WC was significantly related to adult BP ( r = 0.33 to 0.45), and body fatness variables during adolescence were significantly related to adult TM ( r = -0.32 to -0.44). The DeltaWC was significantly related to DeltaTM ( r = -0.46) and DeltaHDL-C ( r = -0.51), and DeltaBMI was significantly related to DeltaBP ( r = 0.45) and DeltaHDL-C ( r = -0.34). Subjects with a high TM during adolescence showed lower levels of body fatness as adults, and those with high levels of WC during adolescence showed higher BP during adulthood. CONCLUSIONS: The results indicate a significant relationship between adolescent cardiorespiratory fitness and adult body fatness and a lack of an association between adolescent cardiorespiratory fitness and adult cholesterol, BP, and glucose levels. Adolescent body fatness is moderately related to selected adult CVD risk factors.

Adolescent↗

PubMed2005

Principles of design and analyses for the calibration of accelerometry-based activity monitors.

The term "calibration" in accelerometry research has come to mean the conversion of counts into other established measurement units. In this article, two types of calibration research are described. Unit calibration (or interinstrument variability) is described as a reliability issue, whereas value calibration is described as more of a validity issue. Principles for design of accelerometry-based validation studies are described to provide a guide for future calibration research. The population must be representative of the intended population in terms of demographics and size, monitors must be representative of the population of monitors that would be available, and activities in the protocol must be representative of the types of activities performed by the intended population. It is also important to employ appropriate analytical strategies in this type of research. A case study employing the appropriate design principles is included to demonstrate how results can vary depending on the type of analyses that are used. Direct comparisons are made between a mixed model regression approach and an approach based on receiver operator characteristic curves.

Acceleration↗

PubMed2004

Assessing body composition among 3- to 8-year-old children: anthropometry, BIA, and DXA.

OBJECTIVE: To examine the inter-relationships of body composition variables derived from simple anthropometry [BMI and skinfolds (SFs)], bioelectrical impedance analysis (BIA), and dual energy x-ray (DXA) in young children. RESEARCH METHODS AND PROCEDURES: Seventy-five children (41 girls, 34 boys) 3 to 8 years of age were assessed for body composition by the following methods: BMI, SF thickness, BIA, and DXA. DXA served as the criterion measure. Predicted percentage body fat (%BF), fat-free mass (FFM; kilograms), and fat mass (FM; kilograms) were derived from SF equations [Slaughter (SL)1 and SL2, Deurenberg (D) and Dezenberg] and BIA. Indices of truncal fatness were also determined from anthropometry. RESULTS: Repeated measures ANOVA showed significant differences among the methods for %BF, FFM, and FM. All methods, except the D equation (p = 0.08), significantly underestimated measured %BF (p < 0.05). In general, correlations between the BMI and estimated %BF were moderate (r = 0.61 to 0.75). Estimated %BF from the SL2 also showed a high correlation with DXA %BF (r = 0.82). In contrast, estimated %BF derived from SFs showed a low correlation with estimated %BF derived from BIA (r = 0.38); likewise, the correlation between DXA %BF and BIA %BF was low (r = 0.30). Correlations among indicators of truncal fatness ranged from 0.43 to 0.98. DISCUSSION: The results suggest that BIA has limited utility in estimating body composition, whereas BMI and SFs seem to be more useful in estimating body composition during the adiposity rebound. However, all methods significantly underestimated body fatness as determined by DXA, and, overall, the various methods and prediction equations are not interchangeable.

Absorptiometry, Photon↗

PubMed2004

Comparison of the computerized ACTIVITYGRAM instrument and the previous day physical activity recall for assessing physical activity in children.

This study compared the validity of children's physical activity recall through a computerized assessment (ACTIVITYGRAM) and through a popular paper and pencil assessment (Previous Day Physical Activity Recall; PDPAR). A total of 147 sixth-grade children from two schools completed the two recall instruments. Data from both self-report instruments were obtained over the same 3 days, and these data were matched by time with data from a subsample of children who wore an accelerometry-based activity monitor (n = 28). To confirm previous validity research with the PDPAR, a larger sample (n = 128) with matched data on the PDPAR and the accelerometer were also used. Activity levels recorded from all three instruments were computed for three periods (afternoon: 3-6 pm, evening: 6-11 p.m. and afternoon/evening: 3-11 p.m.). Descriptive and correlational analyses were conducted across days and for the separate time periods to evaluate the two self-report instruments. There were no differences in mean activity bouts reported on the ACTIVITYGRAM and the PDPAR (p > .05). Correlations with the activity monitor were above .50 for both the PDPAR and the ACTIVITYGRAM, and the relationships were consistent across days and periods for both measures. The magnitude of the correlations varied widely in the two schools for the ACTIVITYGRAM comparisons (r = .80 vs. r = .20) but not for the PDPAR, suggesting differential administration or understanding of the ACTIVITYGRAM instrument. Direct correlations between the ACTIVITYGRAM and the PDPAR measures were high (r = .72), and classification agreement exceeded 80% for the school that provided adequate assistance and training on the ACTIVITYGRAM. Results were weaker in the school with less staff support. This study provides convergent and criterion evidence to support the validity of the computerized ACTIVITYGRAM assessment and suggests similar information as the paper and pencil PDPAR assessment in young children. The study also revealed no differences in PDPAR values or associations, when a simpler scoring procedure was used instead of the traditional more complex metabolic equivalent-based approach.

Adolescent↗

PubMed2004

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.

Adolescent↗

PubMed2004

Reliability of accelerometry-based activity monitors: a generalizability study.

INTRODUCTION: Numerous studies have examined the validity of accelerometry-based activity monitors but few studies have systematically studied the reliability of different accelerometer units for assessing a standardized bout of physical activity. Improving understanding of error in these devices is an important research objective because they are increasingly being used in large surveillance studies and intervention trials that require the use of multiple units over time. METHODS: Four samples of college-aged participants were recruited to collect reliability data on four different accelerometer types (CSA/MTI, Biotrainer Pro, Tritrac-R3D, and Actical). The participants completed three trials of treadmill walking (3 mph) while wearing multiple units of a specific monitor type. For each trial, the participant completed a series of 5-min bouts of walking (one for each monitoring unit) with 1-min of standing rest between each bout. Generalizability (G) theory was used to quantify variance components associated with individual monitor units, trials, and subjects as well as interactions between these terms. RESULTS: The overall G coefficients range from 0.43 to 0.64 for the four monitor types. Corresponding intraclass correlation coefficients (ICC) ranged from 0.62 to 0.80. The CSA/MTI was found to have the least variability across monitor units and trials and the highest overall reliability. The Actical was found to have the poorest reliability. CONCLUSION: The CSA/MTI appeared to have acceptable reliability for most research applications (G values above 0.60 and ICC values above 0.80), but values with the other devices indicate some possible concerns with reliability. Additional work is needed to better understand factors contributing to variability in accelerometry data and to determine appropriate calibration protocols to improve reliability of these measures for different research applications.

Adult↗

PubMed2003

Laboratory calibration and validation of the Biotrainer and Actitrac activity monitors.

PURPOSE: The Biotrainer and Actitrac activity monitors (IM Systems) offer potential research advantages over existing accelerometry-based activity monitors, but they have not been tested under controlled conditions. The purpose of this study was to develop and test laboratory-based prediction equations for both monitors to estimate energy expenditure (EE) for walking/running movements. METHODS: Participants in the study wore a Biotrainer and Actitrac monitor on both hips and completed three paced bouts on the treadmill (3, 4, and 6 mph for 6 min each). Metabolic data collected using an indirect calorimetry system were used as the criterion measure. Multiple regression techniques were performed to develop prediction equations, and these equations were then applied to data from a separate sample for cross-validation purposes. Reliability was also examined. RESULTS: The correlations between the raw counts from each monitor and the measured metabolic variables ranged from r = 0.74-0.88 for the Biotrainer and from r = 0.81-0.91 for the Actitrac. The equations predicting EE (kcal x min-1) from counts yielded strong validation results for both the Biotrainer (R2 = 0.88, SEE = 1.47) and the Actitrac (R2 = 0.91, SEE = 1.24). When used on the cross-validation sample, the correlations between measured and predicted EE were r = 0.93 (Biotrainer) and r = 0.94 (Actitrac). Intraclass reliability coefficients computed between the left and right monitors ranged from 0.60 to 0.71 (Biotrainer) and 0.80 to 0.87 (Actitrac). When the equation developed from one side was applied to data from the monitor on the other side, there were no significant differences in predicted and measured EE for most comparisons. CONCLUSION: The results support the validity of Biotrainer and Actitrac monitors for estimating energy expenditure under controlled conditions.

Adult↗

PubMedDate not supplied

Stability of variables associated with the metabolic syndrome from adolescence to adulthood: the Aerobics Center Longitudinal Study.

The purpose of the study was to examine the stability of variables associated with the metabolic syndrome from adolescence to adulthood. The sample included 48 subjects from the Aerobics Center Longitudinal Study who had one clinical visit during adolescence (mean age = 15.8 years) and a follow-up visit during adulthood (mean age = 26.6 years). The following variables were considered: treadmill time to exhaustion (TM), body mass index (BMI), waist circumference (WC), percent body fat (%BF), total cholesterol (TC), high-density lipoprotein cholesterol (HDL-C), TC:HDL-C, triglycerides (TG), glucose (GLU), and systolic (SBP), diastolic (DBP), and mean (MAP) blood pressure. A composite risk factor score using variables consistent with the WHO and ATP III definition of the metabolic syndrome (WC, HDL-C, TG, MAP, and GLU) was calculated. Tracking coefficients were computed as partial correlations, controlling for length of follow-up (mean = 11 years). Tracking coefficients (r values) were moderate for all variables (TM, 0.53; BMI, 0.64; WC; 0.79;%BF, 0.44; TC, 0.62; HDL-C, 0.60; TG, 0.54; TC:HDL-C, 0.78; SBP, 0.45; and MAP, 0.41), except GLU (0.26) and DBP (0.21). The composite risk factor score also tracked moderately well (0.56) from adolescence into adulthood. The results support previous findings that variables associated with the metabolic syndrome track moderately well from adolescence to adulthood. The findings support the prevention and treatment of obesity, atherosclerosis, type 2 diabetes, and the metabolic syndrome during childhood and adolescence.

Adolescent↗