Mallory R. Marshall

Development of a Prediction Model to Predict VO2peak in Adolescent Girls Using the Bruce Protocol to Exhaustion

Purpose: The purpose of this study was to develop a prediction model based on a submaximal workload during the Bruce treadmill protocol to estimate peak oxygen consumption (VO2peak) in adolescent girls. Method: Adolescent girls (N = 116, Mage = 13.2 ± 2.0 years) performed a Bruce Treadmill Test to exhaustion. Expired respiratory gases and heart rate (HR) were collected and measured continuously via indirect calorimetry and telemetry. To be included in the analysis, each participant met 2 of 3 criteria: attain 95% of age-predicted HRpeak, respiratory exchange ratio>1.05, or plateau of VO2. VO2 and HR at Stage 1 and Stage 2 of the Bruce test were entered into a regression model to predict VO2peak. Results: A regression model, constructed using the predicted sum of squares statistic, was developed using VO2 (VO22) and HR (HR2) attained at the 2nd 3-min stage of the Bruce treadmill protocol: VO2peak = 46.77 − (0.2854155 × HR2)+(1.46732912 × VO22). Actual average ( ± SD) VO2peak was 36.2 ± 6.9 ml·kg− 1·min− 1 (range = 22.9–55.9). Predicted VO2peak was 36.2 ± 5.5 ml·kg− 1·min− 1 (range = 24.3–56.2). The correlation between actual and predicted VO2peak was r = .80, standard error of estimate = 4.2 ml·kg− 1·min− 1, with no bias relative to participant aerobic fitness. Conclusion: Based on this model, the VO2peak of healthy adolescent girls can be predicted within 4.2 ml·kg− 1·min− 1 using submaximal Bruce data.

Physical Activity Device Reliability and Validity during Pregnancy and Postpartum

Current physical activity (PA) recommendations for women experiencing a normal pregnancy reflect recent research showing numerous health benefits for mother and offspring. However, few studies have evaluated PA devices’ reliability and validity during pregnancy, because anatomical and physiological changes throughout gestation could affect an instrument’s accuracy. PurposeThis study aimed to determine the reliability and validity of PA devices worn on the hip, ankle, and triceps during pregnancy and postpartum. MethodsThirty-three women performed six activities of daily living and one treadmill walk at approximately 21 and 32 wk of pregnancy, and 12 wk postpartum. There were two visits at each time period, 1 wk apart. Energy expenditure (oxygen consumption) was measured by using indirect calorimetry (IC; criterion measure), whereas PA was quantified by using accelerometers and pedometers placed at the right hip and ankle and left triceps. Interclass reliability and monitor validity compared with IC in relative (mL·kg−1·min−1) terms were calculated using Pearson correlation. Both multitrial and single-trial intraclass reliabilities (ICC) were estimated using ANOVA to assess monitor reliability at each time period. SEM values were calculated in relative terms for each time period. ResultsThe reliability of the devices was moderate/strong because 66% of the Pearson correlations were between 0.6 and 1.0. Multitrial ICC values were largely in the moderate/strong range because 38% of the ICC values were between 0.6 and 0.79 and 50% were between 0.8 and 1.0. The SEM values for each device between visits ranged from 7% to 23% of the mean values. Comparison between IC and devices showed that 40% and 46% of the validity coefficients were between 0.4 and 0.59 and between 0.6 and 0.79, respectively. ConclusionsPA devices show moderate/strong reliability and moderate validity for measuring PA during pregnancy and postpartum.

Perceived Exertion of Physical Activity During Pregnancy

BACKGROUND 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. METHODS 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. RESULTS 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. CONCLUSIONS 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.

Pregnancy walking cadence does not vary by trimester

BACKGROUND Pregnancy-related changes in walking speed, gait dynamics, and total physical activity have been reported in past research, but free-living step cadences and their rates of change across pregnancy have not been studied. RESEARCH QUESTION The purpose of this study was to describe free-living stepping cadence in pregnant women and examine differences between second and third trimester women. We hypothesized that physical activity walking cadences would be lower later in pregnancy. METHODS Fifty pregnant women were recruited for this study and n = 45 was the analytic sample size; 46.7% were in their second trimester (13-25 weeks) while 53.3% were third trimester (≥26 weeks). Participants completed a survey of demographic characteristics and wore an accelerometer on their non-dominant wrist for 7-8 days. These accelerometer data were downloaded in 60-sec epochs, allowing for determination of min-by-min walking cadence, defined as steps/min. Mean steps/day, mean cadence, peak cadence (average cadence over the 30 min of highest cadence in each day), mean time spent in moderate- to vigorous-intensity physical activity (MVPA, time spent with cadence ≥100 steps/min), and mean daily time spent in several cadence ranges were calculated for each participant. Between-trimester differences were determined using independent-samples t-tests. RESULTS Average daily steps were 11,060.1 ± 2,955.3; 66.7% of second trimester and 54.2% of third trimester women met daily step recommendations of 10,000 steps/day, but 0.0% of the sample accumulated the recommended 150 min/wk of MVPA. There were no differences by trimester for cadence at any step rates (p > 0.05). SIGNIFICANCE Overall, pregnant women accumulated high numbers of steps per day but at low cadences; neither daily steps nor cadence varied from second to third trimester. These data suggest that steps and MVPA recommendations are not equivalent and therefore should not be used interchangeably, especially during pregnancy.BACKGROUND Pregnancy-related changes in walking speed, gait dynamics, and total physical activity have been reported in past research, but free-living step cadences and their rates of change across pregnancy have not been studied. RESEARCH QUESTION The purpose of this study was to describe free-living stepping cadence in pregnant women and examine differences between second and third trimester women. We hypothesized that physical activity walking cadences would be lower later in pregnancy. METHODS Fifty pregnant women were recruited for this study and n = 45 was the analytic sample size; 46.7% were in their second trimester (13-25 weeks) while 53.3% were third trimester (≥26 weeks). Participants completed a survey of demographic characteristics and wore an accelerometer on their non-dominant wrist for 7-8 days. These accelerometer data were downloaded in 60-sec epochs, allowing for determination of min-by-min walking cadence, defined as steps/min. Mean steps/day, mean cadence, peak cadence (average cadence over the 30 min of highest cadence in each day), mean time spent in moderate- to vigorous-intensity physical activity (MVPA, time spent with cadence ≥100 steps/min), and mean daily time spent in several cadence ranges were calculated for each participant. Between-trimester differences were determined using independent-samples t-tests. RESULTS Average daily steps were 11,060.1 ± 2,955.3; 66.7% of second trimester and 54.2% of third trimester women met daily step recommendations of 10,000 steps/day, but 0.0% of the sample accumulated the recommended 150 min/wk of MVPA. There were no differences by trimester for cadence at any step rates (p > 0.05). SIGNIFICANCE Overall, pregnant women accumulated high numbers of steps per day but at low cadences; neither daily steps nor cadence varied from second to third trimester. These data suggest that steps and MVPA recommendations are not equivalent and therefore should not be used interchangeably, especially during pregnancy.