We calculated individual heart rate–oxygen consumption (HR–V̇O2) regression lines for 49 sixth-grade girls based on a treadmill test. From these data, we determined V̇O2 at HRs of 140 and 160 b · min−1 and 50%, 60%, and 75% of maximal heart rate reserve (MHRR), and the relationship between V̇O2 and %fat at given heart rates. Results indicated traditional 140 and 160 b · min−1 HR cutpoints were at the low end of exercise intensity (46 and 63% V̇O2max) and were negatively correlated with %fat. Heart rates at 50%, 60%, and 75% MHRR corresponded to 52%, 62%, and 76% of V̇O2max. Although the best method for analyzing HR data to describe physical activity intensity is unknown, use of 140 and 160 cutpoints may not describe vigorous or very hard exercise in adolescent girls as well as 75% MHRR. Researchers should also consider the effects of adiposity when using specific heart rate cutpoints.
Use of Heart Rate Cutpoints to Assess Physical Activity Intensity in Sixth-Grade Girls
Karin M. Allor and James M. Pivarnik
Perceived Exertion of Physical Activity During Pregnancy
Mallory R. Marshall and James M. Pivarnik
Maternal physical activity declines across gestation, possibly due to changing perception of physical activity intensity. Our purpose was to a) determine whether rating of perceived exertion (RPE) during a treadmill exercise changes at a given energy expenditure, and b) identify the influence of prepregnancy physical activity behavior on this relationship.
Fifty-one subjects were classified as either exercisers (N = 26) or sedentary (N = 25). Participants visited our laboratory at 20 and 32 weeks gestation and at 12 weeks postpartum. At each visit, women performed 5 minutes of moderate and vigorous treadmill exercise; speed was self-selected. Heart rate (HR), oxygen consumption (VO2), and RPE were measured during the last minute at each treadmill intensity.
At moderate intensity, postpartum VO2 was higher compared with 20- or 32-week VO2, but there was no difference for HR or RPE. For vigorous intensity, postpartum HR and VO2 were higher than at 32 weeks, but RPE was not different at any time points.
RPE does not differ by pregnancy time point at either moderate or vigorous intensity. However, relative to energy cost, physical activity was perceived to be more difficult at 32 weeks compared with other time points. Pregnant women, then, may compensate for physiological changes during gestation by decreasing walking/running speeds.
Validation of the CSA Accelerometer in Adolescent Boys during Basketball Practice
Dawn Coe and James M. Pivarnik
Junior high school male basketball players (n = 10) were assessed during a 55-min practice to evaluate the validity of the Computer Science and Applications, Inc. (CSA) accelerometer for estimating physical activity (PA). Direct observation (Five-Level Children’s Activity Rating Scale [CARS]) and heart rate monitoring (HR) were used as criterion measures. CSA, CARS, and HR values were recorded during each minute of practice. Correlation using group data showed a moderate to good (r = 0.60; P < .001) relationship between CSA and HR. Individual participant analyses revealed a significant correlation (range 0.54–0.81; P < .001) between CSA and HR in nine of ten subjects. ANOVA revealed significant differences (P < .001) in CSA and HR in values associated with CARS levels 2–4. The CSA provides valid estimates of PA intensity (compared to CARS and HR) during basketball played by adolescent boys. It appears that CSA is sufficiently sensitive to quantify physical activity level as well as to discriminate between various intensity levels that exist during a typical basketball practice session.
Longitudinal Assessment of Aerobic Fitness in Middle School African-American Girls
James M. Pivarnik, Wendell C. Taylor, and Sharon S. Cummings
This study presents 3 years of data from a longitudinal study designed to follow changes in VO2max and treadmill (TM) exercise performance in African-American girls throughout middle school. Subjects (N = 19) were tested 6 months apart during grades 6-8. VO9 and heart rates (HR) were measured continuously while each subject performed an incremental TM test to volitional exhaustion. Absolute VO2max (ml • min1) increased with time, while relative (ml • kg 1 * min1) values declined significantly from 6th to 8th grade. Treadmill time to exhaustion improved after the first test, but showed a significant decline by the end of 8th grade. Correlations between fall 6th-grade and spring 8th-grade aerobic fitness measures ranged from .35 to .57, indicating moderate tracking of these variables throughout middle school. Aerobic fitness values are low (compared to Caucasians) in African-American adolescent girls and show significant declines throughout middle school. Future studies should investigate anatomical, physiological, and behavioral reasons for the apparently low aerobic fitness seen in African-American girls.
Overcoming Barriers to Physical Activity During Pregnancy and the Postpartum Period: The Potential Impact of Social Support
Christopher P. Connolly, Deborah L. Feltz, and James M. Pivarnik
Pregnant and postpartum women have reported a number of barriers that prevent them from being sufficiently physically active. Overcoming these barriers is critical to ensure the health benefits of physical activity to both mother and fetus. The primary focus of this review centers on the potential impact social support may have in overcoming each of the primary barriers to physical activity experienced during pregnancy and the postpartum period. A reasonable body of research exists regarding the relationships between social support and these barriers; however, few investigations have specifically attempted to mitigate the effects of these barriers via social support interventions. Within this review, the enabling influence of social support as it pertains to pregnant and postpartum women's physical activity is discussed. Recommendations are suggested for the application of social support in future research investigations involving physical activity during pregnancy and postpartum.
Reliability and Validity of the VmaxST Portable Metabolic Analyzer
Candace D. Perkins, James M. Pivarnik, and Matthew R. Green
The reliability and validity of the SensorMedics VmaxST was tested.
Thirty subjects (age = 24.5 ± 4.0 years, height = 174.8 ± 9.8 cm, weight = 70.3 ± 12.6 kg) performed treadmill exercise on three occasions, twice using the VmaxST and once using the SensorMedics 2900 system. Oxygen consumption (VO2; L/min) and heart rate (HR; beats/min) were measured continuously during three, 6- minute stages: 80 m/min, 0% grade; 94 m/min, 5% grade; and 160 m/min, 0% grade, and VO2max.
Reliability was high, and measurement error was low for VO2 (Rxx range = 0.97 - 0.99, CI = 0.94 - 1.00, SEM = 0.03 - 0.08 L/min) and HR (Rxx = 0.94 - 0.99, CI = 0.88 - 1.00, SEM = 1.8 - 3.2 beats/min). Validity was high for VO2 (Rxy range = 0.92 - 0.98, CI = 0.84 - 0.99, SEE = 0.08 - 0.21 L/min) and HR (Rxy = 0.97 - 0.99, CI = 0.94 - 1.00, SEE = 0.9 - 1.8 beats/min). Mean differences in VO2 between VmaxST and 2900 were small yet significant (P < 0.001).
The VmaxST demonstrated excellent reliability and validity for measuring VO2 and HR over several exercise intensities. Small overestimates in VO2 by the VmaxST are countered by low measurement error.
Ornithine Supplementation and Insulin Release in Bodybuilders
Luke R. Bucci, James F. Hickson Jr., Ira Wolinsky, and James M. Pivarnik
Ornithine supplementation has gained popularity with athletes because of its alleged potential to release anabolic hormones, factors governing skeletal muscle hypertrophy. Three female and nine male bodybuilders sewed as subjects in a study to test the effectiveness of oral ornithine in bringing about the release of insulin, an anabolic hormone. After an overnight fast, subjects were administered 40, 100, or 170 mg·kg−1 L-ornithine.HC1 by mouth in a random fashion on three consecutive Saturday mornings. Blood samples were drawn at baseline (T=O), 45, and 90 min afterward. Serum ornithine levels were elevated (p~0.01) at T=45 and 90 min for all three dosage levels. However, serum insulin did not change from baseline levels at any dose of ornithine. The present findings show that ornithine is not an insulin secretagogue.
Caltrac Validity for Estimating Caloric Expenditure with Children
Molly S. Bray, James R. Morrow Jr., James M. Pivarnik, and John T. Bricker
This study investigated the validity of the Caltrac accelerometer for estimating resting and exercise energy expenditure for children. Seventeen children 9 to 12 years of age participated in the study. Criterion values of energy expenditure were determined from measures of oxygen consumption (VO2) and respiratory exchange ratio (RER), and Caltrac estimates of energy expenditure were obtained concurrently for each experimental condition. Correlations were significant between Caltrac estimates and measured energy expenditure at rest (r = .53, p<.03) and at slow (r = .89, p<.001) and brisk (r = .85, p<.001) treadmill walking. The Caltrac overestimated caloric expenditure for rest (M = 7%; range = −8 to 36%) and also for both slow (M = 17%; range = −3 to 30%) and brisk (M = 25%; range = 5 to 46%) walking. However, because of the high validity coefficients during activity, and because of its practicality in field settings, the Caltrac may be useful in estimating daily resting and walking energy expenditure for groups of children.
Body Mass Index is Associated With Appropriateness of Weight Gain but not Leisure-Time Physical Activity During Pregnancy
Rebecca A. Schlaff, Claudia Holzman, Lanay M. Mudd, Karin A. Pfeiffer, and James M. Pivarnik
Little is known about how leisure-time physical activity (LTPA) influences gestational weight gain (GWG) among body mass index (BMI) categories. The purpose of this study was to examine the relationship between pregnancy LTPA and the proportion of normal, overweight, and obese women who meet GWG recommendations.
Participants included 449 subcohort women from the Pregnancy Outcomes and Community Health (POUCH) study. LTPA was collapsed into 3 categories [(None, < 7.5 kcal/kg/wk (low), ≥ 7.5 kcal/kg/wk (recommended)]. GWG was categorized according to IOM recommendations (low, recommended, or excess). Chi-square and logistic regression analyses were used to evaluate relationships among LTPA, BMI, and GWG.
Overweight women were more likely to have high GWG vs. normal weight women (OR = 2.3, 95% CI 1.3–4.0). Obese women were more likely to experience low GWG (OR = 7.3, 95% CI 3.6–15.1; vs. normal and overweight women) or excess GWG (OR = 3.5, 95% CI 1.9–6.5; vs. normal weight women). LTPA did not vary by prepregnancy BMI category (P = .55) and was not related to GWG in any prepregnancy BMI category (P = .78).
Regardless of prepregnancy BMI, LTPA did not affect a woman’s GWG according to IOM recommendations. Results may be due to LTPA not differing among BMI categories.
Validation of an Historical Physical Activity Recall Tool in Postpartum Women
Patricia W. Bauer, James M. Pivarnik, Deborah L. Feltz, Nigel Paneth, and Christopher J. Womack
Physical activity (PA) is an important component of a healthy pregnancy and postpartum period. Since prospective PA monitoring throughout gestation is difficult, a valid PA recall tool would be of significant benefit to researchers. The purpose of this study was to evaluate the ability of women to recall their physical activity performed during pregnancy and postpartum, 6 years later.
Thirty women participated in an historical PA recall study. Pregnancy PA was monitored carefully via assisted physical activity diary (PAD) 6 years before the current investigation. A Modifiable Activity Questionnaire (MAQ) was used to assess current and past pregnancy PA. The MAQ was administered for each time period in the order of most distant past to most current. Leisure time energy expenditure values (kcal/kg/day) calculated from the PAD and the MAQ were compared.
MAQ energy expenditure values showed good positive relationships with PAD measures at 20 weeks gestation (r = .57; P < .01), 32 weeks gestation (r = .85; P < .01), and 12 weeks postpartum (r = .86; P < .01). Correlations found were similar to those from previous PA recall and MAQ validation studies using nonpregnant populations.
The MAQ is an appropriate tool to assess pregnancy and postpartum PA in women 6 years postpartum.