defense meghan phillips

Meghan Phillips

University of Northern Iowa

Spring 2009

UTILITY OF A NON-EXERCISE METHOD OF ESTIMATING AEROBIC

CAPACITY

Introduction Aerobic capacity is the ability to exercise

at relatively high intensities for extended periods of time.

Many exercise physiologists believe aerobic capacity is the best indicator of overall physical fitness in a person (Blair, 1995).

Maximal oxygen uptake (VO2max) is a direct measure of aerobic capacity

Background Heart rate is an indication of the amount of

work the heart must do to meet the demands of the body during work and exercise (Wilmore &

Costill, 2004).

It is well known that heart rate and oxygen consumption increase linearly with exercise intensity and that they are linearly related to each other (ACSM, 2000).

Physically trained individuals have a lower resting heart rates as compared to sedentary individuals (Dixon, Kamath, McCartney, & Fallen, 1992).

Background Maximum heart rate is defined as the

highest heart rate value attainable during an all-out effort to the point of exhaustion (Wilmore & Costill, 2004).

Maximum heart rate is largely associated with one’s age, steadily decreasing about one beat per year beginning in early adolescence.

It can be estimated by subtracting one’s

age (in years) from 220.

Heart Rate Variability

HRV is defined as the beat-to-beat alterations in heart rate and is based on the changes in R-R intervals from one beat to the next.

http://www.cbi.dongnocchi.it/glossary/RWave.html

Heart Rate Variability Some authors conclude that HRV increases

due to training (Dixon and colleagues, 1992).

Age is another factor that affects heart rate variability (HRV). With increasing age, HRV decreases. (Molgaard, Sorensen, & Bjerregaard, 1991).

This suggests the important role of long-term exercise and its effect in mitigating the loss of HRV in active people.

Measuring Aerobic Capacity Field test protocols include:

step tests, bicycle ergometer tests, distance run tests, walking tests, and shuttle run tests.

Distance run tests have been the test of choice for estimating aerobic capacity among children in a school setting. moderately high reliability and validity,

ranging from approximately .60 to .90 (Safrit, 1990)

The PACER Test “Progressive Aerobic Cardiovascular

Endurance Run”

The PACER is the recommended assessment for aerobic capacity in the FITNESSGRAM test battery and has become quite popular in recent years, particular in school settings (Meredith & Welk, 2005).

The PACER Test

The controlled nature of the workload (pace) serves to largely eliminate the problem with pacing that is a limitation of distance run tests.

The resultant score on the PACER is the

total number of laps completed. The longer a person continues, the higher the rate of estimated oxygen uptake.

The PACER Test

Reliability of the PACER among youth has consistently been reported as moderate or high, with reliability coefficients ranging from r = .64 to r = .96

(Legar, et al., 1982; Van Mechelen, Hlobil & Kemper, 1986; Liu, Plowman, & Looney, 1992; Mahar et al., 1997; Plowman & Liu, 1999; Beets & Pitetti, 2006)

The Pacer Test Validity of the PACER for predicting

aerobic capacity in children and adolescents ranges from approximately r = .55 to r = .90, depending upon the gender and age of the subject (Leger et al., 1988; Van Mechelen, Hlobil & Kemper, 1986; Boreham, Paliczka, & Nichols, 1990; Liu, Plowman, & Looney, 1992; Mahar et al., 1997; Mahar, Crotts, McCammon, & Rowe, 2002; McIver, Pfeiffer, Mahar, & Pate, 2004; Mahar, Welk, Rowe, Crotts, & McIver, 2006; Cureton & Plowman, 2006)

Non-Ex Techniques

According to Erdmann and colleagues (1999), non-exercise prediction of VO2max would be useful as a nontraditional method in estimating aerobic capacity in youth.

Such a prediction test could be used as a screening tool, particularly suited for those individuals with inconsistent pacing efforts during exercise field testing.

Non-Ex Techniques Studies have shown that N-EX

equations for predicting aerobic capacity are relatively accurate for an adult population R values ranging from .73 to .93(Jackson et al., 1990; Heil et. al, 1995; George et. al, 1997;

Matthews et. al, 1999; Bradshaw et al., 2005; Jurca et al., 2005)

Jackson and colleagues (1990) found that the accuracy of prediction is substantially lower among highly fit subjects

Polar Fitness Test The Polar F11 HRM measures 255 heart beats in a 3-

5 minute time period during which the subject relaxes in a supine position (Polar Electro Oy, 2006).

A 4-point scale, adapted from the 7-point NASA/JSC scale developed by Jackson et al. (1990), is used to assess physical activity level.

About half the variance of one’s OwnIndex score (i.e., VO2max) is explained by the combination of heart rate variability, resting heart rate, and physical activity assessment. The other half is explained by the demographic variables of gender, age, height, and weight.

Polar Fitness Test The general consensus is that the

Polar Fitness Test is a valid and reliable measure of maximal aerobic power in adult men and women. (Validity, R=.97) (Polar Electro Oy, 2006)

Current Study There appears to be sparse research on

the use of the Polar Fitness Test and its associated HRMs with children.

The present study was designed to test the utility of the Polar Fitness Test as a measure of aerobic capacity in an adolescent population by comparing estimates of VO2max by the Polar F11 HRM with VO2max predicted using the PACER test.

Participants

Participants in this study consisted 33 of high school students (18 males and 15 females)

Age ranged from 14 to 18 years

All were students of Grundy Center High school in Grundy Center, Iowa [USA] during Fall 2008.

PACER Protocol

The PACER was administered in accordance with recommended test procedures (Meredith &

Welk, 2005).

All students are required to take the test during the first part of the academic semester.

Testing took place inside the school gymnasium on a 20-meter shuttle run course.

PACER Protocol During the PACER testing, the students

were encouraged by their teachers to put forth maximum effort for as long as possible.

Students were instructed to aim for their heart rate to be as close to their predicted maximum heart rate (220 - participant’s age).

While performing the PACER test, all students wore heart rate monitors.

Polar Test Protocol The Polar Fitness Test was administered to

participating students within a few weeks of completing the PACER test.

All participating students were fitted with a Polar F11 HRM in order to calculate their OwnIndex score, the equivalent to VO2max.

The following variables were pre-loaded by the investigator into each student’s HRM: age, height, weight, sex, and activity level.

Activity Rating Activity level was based on self-reported

activity assessment using the 4-level scale prescribed for use with Polar heart rate monitors (Polar Electro Oy, 2006).

The activity levels were as follows: 1 – low (does not participate regularly in recreational sport or heavy physical activity);2 – middle (participates regularly in recreation sports);3 – high (participates regularly, at least 3 times a week, in heavy physical activity);4 – top (participates regularly in heavy physical exercise at least 5 times a week).

Polar Test Protocol Participants sat quietly for approximately 2

minutes in order to obtain their resting heart rate value.

To obtain the measures for heart rate and heart rate variability, participants were instructed to: limit body movement, refrain from talking, and lie

(sit) quietly for approximately 5 minutes.

During this time the Polar F11 HRM obtained measures on 255 heart beats (Polar Electro Oy, 2006).

Analysis Scores (laps completed) obtained

during the PACER test were converted to maximal oxygen consumption (VO2max) (Welk, 2008).

Means and standard deviations were calculated for all measured variables.

Analysis

An independent groups t-test was used to determine if there was a significant difference between males and females on the variables on interest.

The relationship between VO2max scores estimated using the PACER test and VO2max scores derived from the Polar Fitness Test was determined using the Pearson product-moment correlation.

Analysis A dependent groups (paired) t-test was used

to test for significant differences in mean VO2max estimated from the two tests.

Effect size was calculated to estimate the magnitude of the difference.

Participants were classified as to whether they met the age and gender specific Healthy Fitness Zone standards using VO2max estimates obtained from each test. Classification equivalency between the two

methods was calculated using the Kappa statistic.

Analysis A Bland-Altman analysis and plot was

used to assess the level of agreement between the PACER and the Polar Fitness Test (Bland & Altman, 1986)

The Bland-Altman technique is a graphical representation.

All statistical analyses were performed using the Statistical Package for the Social Sciences, version 11.0 (SPSS Inc.,

Chicago, IL). The significance level was set at = .05

for all statistical tests.

Results

Results

The Pearson product-moment correlation between PACER predicted VO2max and VO2max predicted from the Polar Fitness Test using the Polar F11 HRM was r = 0.62 (p < .05).

Scatter plot of relationship between PACER predicted VO2max and Polar Fitness Test predicted VO2max

Pearson-Correlation

POLAR Fitness Test Predicted VO2max

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Results

Results of a paired t-test indicated a significant difference between PACER predicted VO2max and Polar Fitness Test predicted VO2max

(t = 4.61, df = 32, p < .05).

Effect size was estimated by calculating Cohen’s d for repeated measures which resulted in a value of 1.61

a large effect according to Cohen (1988).

Results

The mean difference score ( SD) between PACER predicted VO2max and Polar Fitness Test predicted VO2max for the total sample was 6.69 4.64 ml· ۬۠kg-1·min-1

with the Polar Fitness Test yielding a lower VO2max

for 24 of the 33 research participants.

The Polar Fitness Test predicted higher VO2max values for six participants, while three participants had virtually the same estimated VO2max values using the two tests.

Results

Bland-Altman plot and 95% confidence limits which illustrate the degree of agreement between the two methods of estimating VO2max.

Bland Altman Plot

Results Coefficient kappa was used to determine

the criterion-referenced equivalence between the PACER and the Polar Fitness Test using the Polar F11 HRM.

The resultant kappa value of 0.16 was not statistically significant (p > .05) and constitutes “slight agreement.” (Landis and Koch, 1977)

This indicates that the adolescents in the present study were classified differently by the two tests.

Kappa Coefficient

Discussion This study was designed to investigate the utility of a non-

exercise procedure for predicting aerobic capacity in adolescent boys and girls.

Specifically, the study examined the equivalency of the Polar Fitness Test (i.e., Polar F11 HRM) and the PACER in predicting VO2max among a sample of high school students.

The results suggest that the Polar Fitness Test and the PACER do not provide similar information about the aerobic capacity among the study sample.

The environmental conditions in a typical school setting may not be conducive to the proper administration of the Polar Fitness Test.

Limitations Lack of a laboratory-based criterion measure

makes it impossible to judge whether the Polar Fitness Test or the PACER is the more valid test of aerobic capacity.

The inability to precisely follow the standardized directions for the Polar Fitness Test may have compromised the accuracy of the predicted aerobic capacity.

The study sample was very homogeneous in nature and included only one ethnic/racial minority student.

low generalizabilty

Conclusion the results of the current suggest that the Polar

Fitness Test and the PACER do not provide similar information about the aerobic capacity among adolescents.

The results indicate that, compared to the PACER, the Polar Fitness Test consistently underestimates the aerobic capacity of adolescent boys and girls.

The practical side of the study indicates that the environmental conditions and lack of control in a typical school setting may not be conducive to the proper administration of the Polar Fitness Test.

Suggestions for Future Studies Validation of Polar Test with children and

adolescents

Control internal validity, with a measurement of the Polar Test in “laboratory- like” settings.

Administer the Polar Test at the same time of day for all participants.

Have each participant during the Polar Test in a lying position.

Use true resting heart rate values for participants taken over a 24 hour period with a HRM.