David M. Pober

BEST PRACTICES FOR USING PHYSICAL ACTIVITY MONITORS IN POPULATION-BASED RESEARCH

The use of physical activity monitors in population-based research has increased dramatically in the past decade. In this report, we review the major purpose for using physical activity monitors in different types of population-based studies (i.e., surveillance, intervention, association studies) and discuss the strengths and weaknesses for the various behavioral outcomes derived from monitors for each study type. We also update and extend previous recommendations for use of these instruments in large-scale studies, particularly with respect to selecting monitor systems in the context of technological advances that have occurred in recent years. The current state of the science with respect to optimal measurement schedules for use of physical activity monitors is also discussed. A checklist and flowchart are provided so that investigators have more guidance when reporting key elements of monitor use in their studies.

An artificial neural network to estimate physical activity energy expenditure and identify physical activity type from an accelerometer

The aim of this investigation was to develop and test two artificial neural networks (ANN) to apply to physical activity data collected with a commonly used uniaxial accelerometer. The first ANN model estimated physical activity metabolic equivalents (METs), and the second ANN identified activity type. Subjects (n = 24 men and 24 women, mean age = 35 yr) completed a menu of activities that included sedentary, light, moderate, and vigorous intensities, and each activity was performed for 10 min. There were three different activity menus, and 20 participants completed each menu. Oxygen consumption (in ml x kg(-1) x min(-1)) was measured continuously, and the average of minutes 4-9 was used to represent the oxygen cost of each activity. To calculate METs, activity oxygen consumption was divided by 3.5 ml x kg(-1) x min(-1) (1 MET). Accelerometer data were collected second by second using the Actigraph model 7164. For the analysis, we used the distribution of counts (10th, 25th, 50th, 75th, and 90th percentiles of a minutes second-by-second counts) and temporal dynamics of counts (lag, one autocorrelation) as the accelerometer feature inputs to the ANN. To examine model performance, we used the leave-one-out cross-validation technique. The ANN prediction of METs root-mean-squared error was 1.22 METs (confidence interval: 1.14-1.30). For the prediction of activity type, the ANN correctly classified activity type 88.8% of the time (confidence interval: 86.4-91.2%). Activity types were low-level activities, locomotion, vigorous sports, and household activities/other activities. This novel approach of applying ANNs for processing Actigraph accelerometer data is promising and shows that we can successfully estimate activity METs and identify activity type using ANN analytic procedures.

Validity of the Omron HJ-112 Pedometer during Treadmill Walking

PURPOSE The purpose of this investigation was to examine the validity of step counts measured with the Omron HJ-112 pedometer and to assess the effect of pedometer placement. METHODS Ninety-two subjects (44 males and 48 females; 71 with body mass index [BMI] <30 kg.m and 21 with BMI >or=30 kg.m) completed three, 12-min bouts of treadmill walking at speeds of 1.12, 1.34, and 1.56 mxs. A subset (21 males and 23 females; 38 BMI <30 kg.m and 6 BMI >or=30 kg.m) completed a variable walking condition. For all conditions, participants wore an Omron HJ-112 pedometer on the hip, in the pants pocket, in the chest shirt pocket, and around the neck. Hip pedometer placement was alternated between right and left sides with the Yamax Digiwalker SW-701. During each walk, an investigator recorded actual steps with a manual hand counter. RESULTS There was no substantial bias with the Omron in any speed condition (-0.1% to 0.5%). Bias was larger with the Yamax (-3.6% to 2.0%). The largest random error for the Omron was 3.7% in the variable-speed condition for the BMI <30 kg.m group, whereas random errors for the Yamax were larger and up to 20%. None of the Omron placement positions produced statistically significant bias. Hip mounting produced the smallest random error (1.2%), followed by shirt pocket (1.7%), neck (2.2%), and pants pocket (5.8%). CONCLUSION The Omron HJ-112 pedometer validly assesses steps in different BMI groups during constant- and variable-speed walking; other than that in the pants pocket, placement of the pedometer has little effect on validity.

Effects of a single bout of exercise on resting heart rate variability.

PURPOSE Chronic exercise training has been shown to have a positive influence on cardiac autonomic function as assessed by measures of heart rate variability (HRV). Recent evidence indicates that several benefits associated with exercise training (e.g., improved insulin action, reduced blood pressure, improved blood lipid profile) may be realized transiently after a single bout of exercise. As many of these effects of recent exercise are linked to cardiovascular control systems, the purpose of this investigation was to test the hypothesis that a single bout of exercise would result in favorable changes in cardiac autonomic function as assessed by frequency-domain measures of HRV. METHODS Subjects were 11 healthy male volunteers ages 18-35 yr. Resting HRV measures were obtained during 5 min of paced breathing before and 1, 3, 6, and 22 h after a 60-min bout of cycling exercise at approximately 65% of peak oxygen uptake. Identical measures were obtained in a nonexercise condition based on a randomized crossover design. RESULTS Exercise resulted in increased high-frequency HRV, decreased low-frequency HRV, and consequently a decrease in the ratio of low-frequency to high-frequency HRV compared with the nonexercise condition. Additionally, a time-domain measure of HRV (pNN50) was markedly higher in the exercise condition as compared to nonexercise. CONCLUSION The changes in cardiac autonomic function observed are similar to those seen in investigations of long-term training. These changes indicate a shift in autonomic function toward increased parasympathetic nervous system activity and decreased sympathetic nervous system activity, suggesting a more stable autonomic environment for the heart. These results may provide further evidence of the cardioprotective effects of a single bout of submaximal exercise.

Exercise tolerance and thermoregulatory responses during cycling in boys and men.

PURPOSE Physiological responses to exercise in the heat differ between prepubertal children and young adults. Whether these maturity-related variations imply lower exercise tolerance, inferior thermoregulation, and greater risk for heat injury in the child is uncertain. This study directly compared thermoregulatory and cardiovascular responses as well as endurance performance between prepubertal boys and adult males during steady-load cycling in moderately hot and cool ambient conditions with moderate humidity. METHODS Eight prepubertal boys (age 11.7 +/- 0.4 yr) and eight adult men (age 31.8 +/- 2.0 yr) performed steady-load cycling to exhaustion at an intensity equivalent to approximately 65% peak V O2 in both hot (approximately 31 degrees C) and cool (approximately 19 degrees C) environments, with fluid intake ad libitum. RESULTS Exercise duration in the heat was shorter for both groups (hot: men 30.46 +/- 8.84 min, boys 29.30 +/- 6.19 min; cold: men 42.88 +/- 11.79 min, boys 41.38 +/- 6.30 min), with no significant difference between men and boys (P > 0.05). Increases in rectal temperature, heart rate, and cardiac index were similar between groups and conditions. Stroke index, mean arterial pressure, and arterial venous oxygen difference were stable and similar in both conditions, without group differences. No significant dehydration was observed in men or boys. CONCLUSIONS This study failed to reveal differences in exercise tolerance, thermoregulatory adaptation, or cardiovascular response to exercise in the heat between euhydrated prepubertal boys and adult men.