A recess intervention to promote moderate-to-vigorous physical activity.

BACKGROUND: Schools provide a prime environment for interventions that attempt to increase physical activity and prevent obesity. OBJECTIVE: This study examined the effect of a 30-min, structured recess using 22 games of known energy expenditure on moderate-to-vigorous physical activity when compared to free play implemented with third graders from two elementary schools over 9 weeks. METHODS: Moderate-to-vigorous physical activity and other cardiovascular risk factors were assessed pre- and post-intervention in 27 children. RESULTS: Moderate-to-vigorous physical activity during recess increased significantly in intervention school children from 6.9 ± 0.8 to 14.9 ± 0.9 min pre- and post-intervention, respectively (adjusted mean change 8.0 ± 1.1; P < 0.0001), with no differences by gender or body mass index (BMI). In-school, moderate-to-vigorous physical activity also increased significantly more for intervention compared to control children (adjusted mean change 14 ± 4 min vs. 3 ± 3 min; P = 0.014, respectively). CONCLUSION: There was no significant difference in BMI and cardiovascular risk factors. A structured recess is feasible to implement and can significantly increase moderate-to-vigorous physical activity.

Calibrating a novel multi-sensor physical activity measurement system.

Advancing the field of physical activity (PA) monitoring requires the development of innovative multi-sensor measurement systems that are feasible in the free-living environment. The use of novel analytical techniques to combine and process these multiple sensor signals is equally important. This paper describes a novel multi-sensor 'integrated PA measurement system' (IMS), the lab-based methodology used to calibrate the IMS, techniques used to predict multiple variables from the sensor signals, and proposes design changes to improve the feasibility of deploying the IMS in the free-living environment. The IMS consists of hip and wrist acceleration sensors, two piezoelectric respiration sensors on the torso, and an ultraviolet radiation sensor to obtain contextual information (indoors versus outdoors) of PA. During lab-based calibration of the IMS, data were collected on participants performing a PA routine consisting of seven different ambulatory and free-living activities while wearing a portable metabolic unit (criterion measure) and the IMS. Data analyses on the first 50 adult participants are presented. These analyses were used to determine if the IMS can be used to predict the variables of interest. Finally, physical modifications for the IMS that could enhance the feasibility of free-living use are proposed and refinement of the prediction techniques is discussed.

The effect of endurance training on resting heart rate variability in sedentary adult males.

Eleven previously sedentary adult males, serving as the experimental (EXP) group [mean (SE) age 36.6 (1.7) years, body mass 87.2 (4.3) kg, body mass index, BMI, 28.4 (1.5) kgm(-2)] participated in a 16-week supervised exercise program (3 days x week(-1), 30 min day(-1), at approximately equal to 80% of heart rate reserve) to determine the temporal effects of a moderate-to-vigorous-intensity exercise program on heart rate variability (HRV). Five sedentary males [mean (SD) age 36.6 (4.2 )years, body mass 83.8 (6.6) kg, BMI 22.8 (1.7) kg x m(-2)] served as non-exercising controls (CON). HRV was measured every 4 weeks from a resting electrocardiogram obtained while subjects paced their breathing at 10 breaths x min(-1) (0.167 Hz). The time-domain measures of HRV recorded were the proportion of adjacent intervals differing by more than 50 ms (pNN50), the root mean square of successive differences (rMSSD), and the standard deviation of the resting interbeat interval. The frequency-domain measures recorded were high (HF) and low (LF) frequency oscillations, as determined using the fast Fourier transform technique. Aerobic capacity (i.e., peak oxygen uptake) increased by 13.8% in EXP (P < 0.001), but did not change in CON. Resting heart rate did not change in either EXP or CON. In EXP, pNN50 at week 12 (P<0.01), rMSSD at weeks 12 (P < 0.01) and 16 (P = 0.05), and HF power at weeks 12 (P < 0.01) and 16 (P = 0.05) were elevated above baseline. Time- and frequency-domain measures of HRV remained unchanged in CON. It is concluded that a moderate-to-vigorous-intensity exercise program produces increases in time- and frequency-domain measures of HRV within 12 weeks.

Sources of variance in daily physical activity levels in the seasonal variation of blood cholesterol study.

The authors examined sources of variance in self-reported physical activity in a cohort of healthy adults (n = 580) from Worcester, Massachusetts (the Seasonal Variation of Blood Cholesterol Study, 1994-1998). Fifteen 24-hour physical activity recalls of total, occupational, and nonoccupational activity (metabolic equivalent-hours/day) were obtained over 12 months. Random effects models were employed to estimate variance components for subject, season, day of the week, and residual error, from which the number of days of assessment required to achieve 80% reliability was estimated. The largest proportional source of variance in total and nonoccupational activity was within-subject variance (50-60% of the total). Differences between subjects accounted for 20-30% of the overall variance in total activity, and seasonal and day-of-the-week effects accounted for 6% and 15%, respectively. For total activity, 7-10 days of assessment in men and 14-21 days of assessment in women were required to achieve 80% reliability. For nonoccupational activity, 21-28 days of assessment were required. This study is among the first to have examined the sources of variance in daily physical activity levels in a large population of adults using 24-hour physical activity recall. These findings provide insight for understanding the strengths and limitations of short term and long term physical activity assessments employed in epidemiologic studies.

Seasonal variation in household, occupational, and leisure time physical activity: longitudinal analyses from the seasonal variation of blood cholesterol study.

The authors examined seasonal variation in physical activity in longitudinal analyses of 580 healthy adults from Worcester, Massachusetts (the Seasonal Variation of Blood Cholesterol Study, 1994-1998). Three 24-hour physical activity recalls administered five times during 12 months of follow-up were used to estimate household, occupational, leisure time, and total physical activity levels in metabolic equivalent (MET)-hours/day. Trigonometric models were used to estimate the peak-to-trough amplitude and phase of the peaks in activity during the year. Total activity increased by 1.4 MET-hours/day (121 kcal/day) in men and 1.0 MET-hours/day (70 kcal/day) in women during the summer in comparison with winter. Moderate intensity nonoccupational activity increased by 2.0-2.4 MET-hours/day in the summer. During the summer, objectively measured mean physical activity increased by 51 minutes/day (95% confidence interval: 20, 82) in men and by 16 minutes/day (95% confidence interval: -12, 45) in women. The authors observed complex patterns of seasonal change that varied in amplitude and phase by type and intensity of activity and by subject characteristics (i.e., age, obesity, and exercise). These findings have important implications for clinical research studies examining the health effects of physical activity and for health promotion efforts designed to increase population levels of physical activity.

Objective monitoring of physical activity using motion sensors and heart rate.

Although neither motion sensors nor heart rate are perfect markers of physical activity, they certainly eliminate subjectivity of obtaining physical activity information. The objective method of choice depends on how the measurement will be used. For example, if walking behavior is the desired outcome, then a pedometer may be sufficient. If patterns and intensity of activity over longer periods of times such as a week or longer are needed, then an accelerometer with large memory capacity should be selected. In the future, efforts should be directed towards developing an objective motion sensor as inexpensive as a pedometer but with the data acquisition capabilities of the CSA or Tritrac accelerometer. Providing simultaneous heart rate with motion is also recommended to further verify that elevated heart rate does in fact represent a physical activity response. As the cost of the electronic components continues to decrease, these activity monitor configurations may become possible.

Comparing physical activity assessment methods in the Seasonal Variation of Blood Cholesterol Study.

PURPOSE: This paper evaluated three measures of physical activity employed in the Seasonal Variation of Blood Cholesterol Study (Seasons), and it had two objectives: 1) To examine the laboratory validity of the Actillume activity monitor, and 2) To examine the relative validity of three 24-h physical activity recalls (24HR) in quantifying short-term physical activity behaviors. METHODS: Nineteen healthy middle-age adults completed seven activity trials (reading, typing, box moving, stepping, and walking (3.5, 4.25, 5.0 km x h(-1))) while oxygen consumption and Actillume measures were obtained. ANOVA, linear regression, and a scatter plot were employed to examine the validity of the Actillume. In relative validity analyses of the 24HR in the Seasons study, participants (N = 481) completed two or three 24HR (MET-h x d(-1)) and a modified Baecke Questionnaire. A subset of the cohort (N = 41) wore the Actillume for 3-8 d (counts x min(-1) x d(-1)). The relative validity of the 24HR method was examined by comparison to these criterion measures. RESULTS: In laboratory validation analyses, the monitor was found to discriminate between sedentary and moderate intensity activities, changes in walking speed, and to account for 79% of the variance in oxygen consumption across sedentary and walking trials. In relative validity analyses, correlations between the 24HR and the modified Baecke ranged from 0.29 to 0.52 (P < 0.01) across total, household, occupational, and leisure-time activities. CONCLUSIONS: In laboratory testing, the Actillume monitor discriminated between sedentary and moderate intensity activities and was highly correlated with oxygen consumption. Three 24HR of physical activity were observed to have a relative validity that was comparable to published data from other short-term activity assessments that also employed the Baecke Questionnaire and activity monitors as criterion measures.

Field evaluation of the Computer Science and Applications, Inc. physical activity monitor.

PURPOSE: The purpose of this study was to evaluate the Computer Science and Applications, Inc. (CSA) activity monitor to quantify physical activity in free living subjects using an activity diary as the criterion measure. METHODS: Subjects also completed a 7-d physical activity recall at the end of the monitoring period. Nine male and 10 female subjects (mean, SD) (25.0, 3.6 yr) wore the CSA monitor for 7 consecutive days. On 3 of those days, subjects completed an activity diary (2 weekdays and 1 weekend day). Total kcal per day (Dkcal(tot)) was calculated from the self-reported diary classifications of the subject's activities. For the 3 days that coincided with the diary, total number of counts accumulated per day (cnt(tot)) was obtained from the monitor. RESULTS: The amount of activity per day recorded by the CSA monitor followed the same pattern of change as the activity diary. The cnt(tot) and Dkcal(tot) were significantly (P < or = 0.05) correlated on day 1 (r = 0.65), day 2 (r = 0.49), day 3 (r = 0.55), and for the 3 days pooled (r = 0.51). Subjects were classified as low, moderate, or highly active based on tertiles of kcal from the diary and counts from the CSA monitor. The percentage agreement between the CSA and the activity diary was 68.4% (Kappa = 0.53, P < 0.01). The number of minutes spent in the various activity categories were compared between instruments using an ANOVA model. The results of these analyses suggest that the CSA overestimated light activity and underestimated vigorous activity compared with the diary. CONCLUSION: In conclusion, the CSA monitor may be useful in a field situation where total physical activity and patterns of physical activity are the desired outcomes.

Using objective physical activity measures with youth: how many days of monitoring are needed?

PURPOSE: The purpose of this study was to establish the minimal number of days of monitoring required for accelerometers to assess usual physical activity in children. METHODS: A total of 381 students (189 M, 192 F) wore a CSA 7164 uniaxial accelerometer for seven consecutive days. To examine age-related trends students were grouped as follows: Group I: grades 1-3 (N = 92); Group II: grades 4-6 (N = 98); Group III: grades 7-9 (N = 97); Group IV: grades 10-12 (N = 94). Average daily time spent in moderate-to-vigorous physical activity (MVPA) was calculated from minute-by-minute activity counts using the regression equation developed by Freedson et al. (1997). RESULTS: Compared with adolescents in grades 7 to 12, children in grades 1 to 6 exhibited less day-to-day variability in MVPA behavior. Spearman-Brown analyses indicated that between 4 and 5 d of monitoring would be necessary to a achieve a reliability of 0.80 in children, and between 8 and 9 d of monitoring would be necessary to achieve a reliability of 0.80 in adolescents. Within all grade levels, the 7-d monitoring protocol produced acceptable estimates of daily participation in MVPA (R = 0.76 (0.71-0.81) to 0.87 (0.84-0.90)). Compared with weekdays, children exhibited significantly higher levels of MVPA on weekends, whereas adolescents exhibited significantly lower levels of MVPA on weekends. Principal components analysis revealed two distinct time components for MVPA during the day for children (early morning, rest of the day), and three distinct time components for MVPA during the day for adolescents (morning, afternoon, early evening). CONCLUSIONS: These results indicate that a 7-d monitoring protocol provides reliable estimates of usual physical activity behavior in children and adolescents and accounts for potentially important differences in weekend versus weekday activity behavior as well as differences in activity patterns within a given day.

Classification of cardiorespiratory fitness without exercise testing.

PURPOSE: We examined the ability of a nonexercise based VO2max, prediction model to classify cardiorespiratory fitness (CRF) in a population of men and women aged 19-79 yr of age (N = 799). METHODS: A VO2max (mL.kg(-1).min(-1)) prediction model was developed in the study group using multiple linear regression from the independent variables age, age2, gender, physical activity status, height, and body mass. The classification accuracy of this model was examined by cross-tabulating age and gender specific quintiles of measured and predicted CRF. RESULTS: Overall classification accuracy of the model was modest (36%); however, 83% of all subjects were either classified correctly or within one quintile of measured CRF. Extreme misclassification (e.g., misclassifying a low fit individual as high fit) was only rarely observed (0.13%). CONCLUSIONS: The present results support the concept that CRF prediction models can be used to reasonably characterize the fitness level of a cohort using data that can be obtained from a questionnaire. Accordingly, predicted CRF values may be useful as an exposure variable in large epidemiologic studies in which exercise testing is not feasible.

Bone mineral density and body composition of the United States Olympic women's field hockey team.

OBJECTIVE: To evaluate total bone mineral density (BMD) and body composition (% fat) in world class women field hockey players, members of the 1996 United States Olympic team. METHODS: Whole body BMD (g/cm2) and relative body fatness (% fat) were assessed by dual energy x ray absorptiometry using a Lunar DPX-L unit with software version 1.3z. Body composition was also estimated by hydrostatic weighing and the sum of seven skinfolds. RESULTS: Mean (SD) BMD was 1.253 (0.048) g/cm2 which is 113.2 (4.0)% of age and weight adjusted norms. Estimates of body composition from the three methods were similar (statistically non-significant): 16.1 (4.4)% fat from dual energy x ray absorptiometry, 17.6 (3.2)% from hydrostatic weighing, and 16.9 (2.6)% from the sum of seven skinfolds. Mean fat free mass was approximately 50 kg. CONCLUSIONS: The mean whole body BMD value for members of the 1996 United States Olympic women's field hockey team is one of the highest reported for any women's sports team. Moreover, the mean fat free mass per unit height was quite high and % fat was low. In this group of world class sportswomen, low % fat was not associated with low BMD.

The reliability of lactate measurements during exercise.

The purpose of this study was to establish the reliability of lactate threshold (LT) measurement across days. Twelve endurance-trained males aged 21-44 years participated in the study. Blood lactate concentration in capillary whole blood was measured at rest and at completion of 5 minute stages on a treadmill at 60%, 65%, 71%, 77%, 83% and 89% of VO2max during 3 separate days of testing. Velocity at LT (LT(VEL)), oxygen consumption at LT (LT(VO2)), and heart rate at LT (LT(HR)) are determined using each of the following criteria: fixed lactate concentrations of 2.0 mmol, 2.5 mmol, and 4.0 mmol, the breakpoint of the lactate-intensity curve, 1 mmol above rest, and 1 mmol above exercise baseline. A one factor repeated measures ANOVA model was used to calculate intraclass reliability coefficients across the 3 testing sessions. Confidence intervals (95%) were calculated around the point estimates of reliability for each LT criterion. Intraclass correlation coefficients ranged from 0.98 to 0.99 LT(VEL) (SEM 0.06 to 0.14 km x hr(-1)), from 0.91 to 0.96 for LT(VO2) (SEM 0.34 to 0.72 ml x kg(-1) x min(-1)), and from 0.75 to 0.96 for LTHR (SEM 0.7 to 1.9 beats x min(-1)). These results support the reliability of LT(VEL), LT(VO2), and LT(HR) measurement.

Calibration of the Computer Science and Applications, Inc. accelerometer.

PURPOSE: We established accelerometer count ranges for the Computer Science and Applications, Inc. (CSA) activity monitor corresponding to commonly employed MET categories. METHODS: Data were obtained from 50 adults (25 males, 25 females) during treadmill exercise at three different speeds (4.8, 6.4, and 9.7 km x h(-1)). RESULTS: Activity counts and steady-state oxygen consumption were highly correlated (r = 0.88), and count ranges corresponding to light, moderate, hard, and very hard intensity levels were < or = 1951, 1952-5724, 5725-9498, > or = 9499 cnts x min(-1), respectively. A model to predict energy expenditure from activity counts and body mass was developed using data from a random sample of 35 subjects (r2 = 0.82, SEE = 1.40 kcal x min(-1)). Cross validation with data from the remaining 15 subjects revealed no significant differences between actual and predicted energy expenditure at any treadmill speed (SEE = 0.50-1.40 kcal x min(-1)). CONCLUSIONS: These data provide a template on which patterns of activity can be classified into intensity levels using the CSA accelerometer.

Preexercise feeding in untrained adolescent boys does not affect responses to endurance exercise or performance.

The effects of preexercise feeding on responses to endurance exercise and performance were investigated. Untrained adolescent boys (N = 13, age 14.9 +/- 0.5 years) completed three endurance test sessions separated by a minimum of 72 hr. Each session consisted of 75 min of cycling at 60% of VO2 max followed by a high-intensity performance test. Dietary conditions were a candy bar (C1: 280 kcal, 36 g CHO), fat-free fig bars (C2: 200 kcal, 44 g CHO), and a nonnutritive sweetened drink (C3: placebo), ingested 10 min prior to exercise. Respiratory gases, heart rate, blood glucose, and lactate concentrations were measured throughout the test. ANOVA results revealed significant time effects for all variables; however, no differences were seen among the conditions. Performance times, 311.9 +/- 38.5 s in C1, 316.2 +/- 37.3 s in C2, and 328.1 +/- 46.4 s in C3, were not significantly different among conditions. Thus, preexercise feeding did not affect responses to endurance exercise or performance in adolescent boys.

Intraindividual variation of running economy in highly trained and moderately trained males.

Previous studies of intraindividual variation in running economy have not compared within-subject variability between groups of runners differing in training level, nor have they considered the workload of the submaximal but relative to the lactate breakpoint. Therefore, the purpose of the present study was to assess intraindividual variation in submaximal oxygen consumption (VO2) during steady rate treadmill running below the lactate breakpoint in highly trained (n = 7) and moderately trained (n = 8) male runners. Subjects completed a discontinuous VO2 max protocol with blood sampling to determine the lactate breakpoint. Three 15 minute level treadmill bouts at approximately 88% of the lactate breakpoint were then performed. Time of day, day of the week, diet, and and footwear were controlled within each subject across the three tests. Statistically significant differences were found between groups in VO2 max, relative fat, training mileage, and 10 km race time (p < 0.01), while the lactate breakpoint was similar between groups (integral of 80% of VO2 max). The difference in treadmill speed between highly trained and moderately trained runners for the submaximal bouts was statistically significant (p < 0.01) and correlated with reported training paces (r = 0.82). Although the mean coefficient of variation for steady rate VO2 was smaller for the highly trained group, the difference was not statistically significant (highly trained = 1.77%, moderately trained = 2.00%; p > 0.05). The mean coefficient of variation for all 15 subjects was 1.90%. After accounting for technological error, biological variation was found to comprise approximately 94% of the intraindividual variation in running economy. In comparison to other studies, these results suggest that workloads below the lactate breakpoint may allow more stable measures of running economy to be obtained.

Changes in VO2max and maximal treadmill time after 9 wk of running or in-line skate training.

This study tested the hypothesis that running and in-line skating training elicit similar improvements in cardiorespiratory fitness. Changes in maximal oxygen consumption (VO2max) and maximal treadmill endurance time were compared in runners (N = 16), in-line skaters (N = 19), and controls who did no systematic training (N = 7). Training volumes were similar for runners and skaters (3 d.wk-1, 10-40 min/session, 80-90% of exercise specific maximal heart rate) and included both continuous and interval workouts. Pre- and post-training VO2max and maximal treadmill time were measured in all subjects using a running protocol and in skaters using an in-line skating protocol. The groups did not differ in pre-training running VO2max or maximal treadmill time. After 9 wk, significant increases in running VO2max and maximal treadmill time were observed in runners (mean +/- SE, 9.3 +/- 1.3%, 14.9 +/- 2.5%) and skaters (6.6 +/- 1.0%, 9.1 +/- 3.4%), but not controls. Skaters also significantly increased their skating VO2max and maximal treadmill time (8.6 +/- 1.8%, 7.9 +/- 2.9%). The magnitude of these increases was not different between the two training groups. In conclusion, in moderately active college-aged students, similar improvements in VO2max are achieved with running and in-line skating programs that are equivalent in training volume and intensity.

Physical activity assessment: a review of methods.

In order to determine the actual threshold level of habitual physical activity necessary to obtain protective effects against degenerative diseases, valid, reliable, nonreactive, and precise instruments are needed. Because regular, low-intensity exercise provides prophylactic effects, the ability to distinguish activity patterns should be a primary consideration when choosing an instrument to assess activity in the field. Although self-report methods in the form of questionnaires are the instruments of choice when large populations are to be assessed, they are somewhat limited in their objectivity. The doubly labeled water (DLW) technique is a highly accurate and objective technique for assessing total daily energy expenditure that should be utilized more as a criterion measure for validating questionnaires that assess energy expenditure. However, the DLW technique remains too costly to be considered practical for large-scale studies. Supplementing questionnaires with a personal interview does elicit more detailed data, but activity monitors provide a more objective measure of activity that can be used as an adjunct to questionnaires. Several models of activity monitors are capable of collecting and storing data for many days, weeks, or even months. More importantly, the internal real-time clocks of these monitors allow the discrimination of activity patterns. Future studies should combine the use of these monitors with a suitable questionnaire.

Reliability and validity of a portable metabolic measurement system.

The purpose of this study was to assess the reliability and validity of a portable metabolic system (TEEM 100) during submaximal and maximal (VO2max) exercise using a computer-based metabolic system as the reference system (REF). Between repeated trials of submaximal exercise at three constant loads, differences in ventilation (Ve) and oxygen consumption (VO2) were 0.2 +/- 4.9 L . min-1 and 0.03 +/- 0.10 L . min-1 for REF, and 1.9 +/- 0.7 L . min-1 and 0.00 +/- 0.17 L . min-1 for TEEM 100. Pooled intraclass reliability coefficients for Ve and VO2 calculated from the repeated submaximal trials were r = .89 and r = .94 for REF, and r = .86 and r = .94 for the TEEM 100. Respiratory exchange ratio (RER) measured by the TEEM 100 was significantly higher (p = .01) at only the lowest workload. At VO2max, the TEEM 100 recorded significantly higher values for FeO2 (p = .01) and RER (p < .001). These results suggest that the TEEM 100 provides reliable and valid measurements of VO2 during submaximal and maximal exercise.

Exercise responses to running and in-line skating at self-selected paces.

Exercise responses to running and in-line skating at self-selected paces. Med. Sci. Sports Exerc., Vol. 28, No. 2, pp. 247-250, 1996. The purpose of this investigation was to compare physiological responses to in-line skating and running at preferred levels of exertion. Ten males and ten females performed 15 min of in-line skating or running on two separate days. Subjects were instructed to exercise at an intensity that represented an effective cardiovascular workout. Heart rate (HR) and oxygen consumption (VO2) were monitored continuously using a portable, telemetric, open-circuit spirometry system. Subjects maintained steady rate VO2 over minutes 11-15 of in-line skating and running at speeds (mean +/- SD) of 21.7 +/- 2.4 and 12.2 +/- 2.3 km.h-1, respectively. A significantly higher (P = 0.03) VO2 (mean +/- SEM, 44.0 +/- 1.7 ml.kg-1.min-1) was observed during running compared with in-line skating (42.0 +/- 2.0 ml.kg-1.min-1), but there were no differences in ventilation, HR, or rating of perceived exertion. Consistent with the results of previous investigations, we conclude that in-line skating is an appropriate form of exercise for improving cardiorespiratory fitness. Future studies should compare the cardiovascular training effects of in-line skating and running in individuals of varying levels of fitness and skating ability.