A STUDY OF A TWELVE- MINUTE RUN TEST FOR THE INDIRECT ASSESSMENT OF MAXIMUM OXYGEN UPTAKE IN WOMEN

Transcription

1 .I a,~i~i_: _ T _, s i, E,,, i 77 _7,7,, Tiff iivii,i, T;_,:_* In. 0:02 J {Nd l I : ": A STUDY OF A TWELVE- MINUTE RUN TEST FOR THE INDIRECT ASSESSMENT OF MAXIMUM OXYGEN UPTAKE IN WOMEN Thesis for the Degree of M. A MICHIGAN STATE UNIVERSITY KATHLEEN EDINGTON BADGLEY V v 1977

2 IIII III IIIIIIIIIIIIIIIIII IIIIIIIIIIIIZI II i

3 A STUDY OF A TWELVE-MINUTE RUN TEST FOR THE INDIRECT ASSESSMENT OF MAXIMUM OXYGEN UPTAKE IN WOMEN By 9. Kathleen Edington Badgley A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of MASTER OF ARTS Department of Health, Physical Education and Recreation 1977

4 ACKNOWLEDGMENT The author gratefully acknowledges Dr. Wm. Heusner and Dr. Wayne Van Huss for their guidance and assistance. ii

5 TABLE OF CONTENTS Page LIST OF TABLES. iv LIST OF FIGURES Chapter I. II. III. IV. OVERVIEW OF THE STUDY Need for the Study Purpose of the Study Research Hypothesis. Research Plan... Rationale for Research Plan Limitations.. Significance of the Study. REVIEW OF RELATED LITERATURE. Factors Affecting Aerobic Capacity. Sex Differences. Habitual Activity.. Measurement of Aerobic Capacity. Direct Measures.. Indirect Measures.. Assessment of Aerobic Capacity in women METHODS AND PROCEDURES. Treadmill Test lz Min Run Test Data Analysis. RESULTS. DISCUSSION AND CONCLUSIONS l O CDNOSU IU'I-b-h REFERENCES

6 LIST OF TABLES Table Page Levels of cardiovascular fitness based on 12-min performance and maximum oxygen consumption. Levels of cardiovascular fitness for women based on the distance walked and run in l2 minutes Distances for the l2-min run performance and maximum oxygen intake values (ml/kg/min) measured on the treadmill, projected for women from distance run, and projected for men from distance run. Predicted maximal oxygen consumption on the basis of l2-minute performance iv

7 LIST OF FIGURES Figure Page I. Measured V0 max plotted against measured distance run in l2 min (r=.732)

8 CHAPTER I OVERVIEW OF THE STUDY The physiological measurement of aerobic capacity (maximum oxygen uptake) reflects the functional quality of the respiratory and circulatory systems and is the single most objective index of cardio-respiratory fitness (l,l0). As maximum oxygen consumption is a quantitative indicator of an individual's capacity to sustain hard muscular work, it is a prime factor in total physical fitness (lo,l5). Numerous techniques for assessing aerobic capacity have been described in the literature. Most of the procedures are clinical in nature and, therefore, are limited in application. The laboratory measurement of maximum oxygen uptake is determined during exhaustive work and requires trained administrators and sophisticated equipment. It is both time consuming and costly. Consequently, a search for simpler and shorter methods of evaluation has ensued. Field tests requiring neither trained personnel nor special equipment have been developed. Breath holding (29), step testing (7,28), motor fitness tests (18), a 600-yard run (l5), a 2-mile run (6), a 12-min run (10), and a l5-min run (16) all have been used in an attempt to fulfill the need for an indirect measurement reflecting cardio-respiratory fitness.

9 Cooper's test (10) uses the distance covered during 12 min of running (and/or walking) to predict maximum aerobic capacity. At present, this test may be the most reliable and valid indirect indicator of cardio respiratory fitness available for men. Doolittle and Bigbee (15) report a test-retest reliability coefficient of r=.94. Correlations of r=.897 (10), r=.94 (38), r= (8), and r=.90 (15) have been reported between maximum oxygen uptake and the 12-min run test. However, two investigators, who obtained correlation coefficients of r=.22 to.53 (35) and r=.66 (20) (both unpublished), have questioned the validity of Cooper's test. A review of literature revealed only two studies of field tests in which women were used as subjects. Cooper (12) reports a correlation for women of r=.57 between distance run in 12 min and maximum oxygen uptake (Vozmax). A higher value of r=.745 was reported for college women in an unpublished study by Burris (8). Wyndham (39) suggests that Cooper's predicted values of maximum oxygen uptake for men (10) should be reduced by 10% when women are assessed. As no supporting data were given by Wyndham, it may be this 10% correction factor is based upon the well-known observation of Astrand (1) that the mean value of maximum oxygen uptake per liter of blood is about 10% lower in women than in men. Problems arise when the sexes are'compared on any measure of cardio-respiratory fitness because the quantitative values of a large number of pertinent physiological women (l,3,13,l6,l7,21,24,25,26,34,39). parameters are lower in The possible implications of sex-related differences are beyond the scope of this discussion,

10 but two observations deserve comment. Mcnab (25) believes that a 10% differential in hemoglobin concentration may account for most of the difference in maximum oxygen consumption between men and women. The female's smaller lean body mass must also be considered. The between-sex variance in oxygen consumption is reduced significantly by expressing the data in terms of oxygen per kilogram of body weight (l,3,6,21,25,26). Cooper and Cooper (13) have advocated a self-evaluation technique for women that parallels Cooper's 12-min run test for men (10) (see Tables 1 and 2). Five subjective fitness categories (ranging from very poor to excellent) correspond to various distances run in 12 min. These subjective ratings provide a useful frame of reference for the laywoman who is attempting to improve her physical fitness, but they are of little value to the exercise scientist because the supporting physiological data are not presented. TABLE l.--levels of cardiovascular fitness based on 12-min performance and maximum oxygen consumption. Data from men 17 to 52 years (mean 22 years).a Distance Max. 02 Intake. (miles) (ml/kg/min) Fitness Level Very Poor 1.00 to to 33.7 Poor 1.24 to to 42.5 Fair 1 50 to to 51.5 Good 1 75 or more 51.6 or more Excellent ataken from Kenneth H. Cooper, "A Means of Assessing Maximum Oxygen Intake," J.A.M.A. 203(3): , 1968.

11 TABLE 2.--Levels of cardiovascular fitness for women based on the distance walked and run in 12 minutes. Data from women under 30 years of age.a Distance (miles) Fitness Level.95 Very Poor.95 to 1.14 Poor 1.15 to 1.34 Fair 1.35 to 1.64 Good 1.65 or more Excellent afrom Kenneth and Mildred Cooper, Aerobics for Women, p. 52. Need for the Study A reliable, valid and simple method of predicting maximum aerobic capacity in women is needed. Cooper's 12-min run test for men (10) may be efficacious, or some modification of that basic technique may be appropriate. The present descriptive fitness categories (very poor to excellent) that have been assigned to 1 distances run by women in a 12 min period are interesting; however, they cannot be evaluated objectively as no corresponding oxygen uptake values are available. Purpose of the Study The primary purpose of this investigation was to determine if a 12-min run test can be used to evaluate aerobic capacity in women who are between 17 and 28 years of age. Specifically, the study was designed: (a) to obtain bivariate data on Vozmax (ml/kg/min) and distance covered in 12 min of running using a selected group of young women as subjects, (b) to test the validity

12 of the cardio-respiratory fitness levels proposed for women by Cooper and Cooper (13) using Vozmax as the criterion measure, (c) to evaluate Wyndham's (39) suggested -10% correction factor for predicting values of Vozmax in women when Cooper's (10) protocol for men is used, and (d) to establish a preliminary regression equation for predicting V0 max in women from performance on a 2 test. 12-min run Research Hypothesis This investigation was conducted to test the premise that a 12-min run test can be used to evaluate maximum oxygen uptake in young women. Acceptance of this hypothesis was recognized to be contingent upon obtaining a correlation similar to those reported by Cooper (10) and Wyndham (38) for men and that reported by Doolittle and Bigbee (15) for adolescent boys. Given such a correlation: (a) the descriptive fitness categories established by COOper and Cooper (13) for women should correspond to ranges of Vozmax that are nearly mutually exclusive, and (b) a valid regression equation should exist for the prediction of aerobic capacity from 12 minutes of running performance. No initial hypothesis was generated regarding the appropriateness of Wyndham's (39) -10% correction factor for predicting maximum oxygen uptake in women from Cooper's (10) test for men. Research Plan Twenty-two available young women between 17 and 28 years of age were used as subjects for this investigation. All were

13 accustomed to leading active lives as instructors of physical education, college physical education majors, or participants in organized athletic programs. The tests were administered to each subject: (a) a treadmill test of maximum oxygen uptake, and (b) a 12-min run for distance on a 440-yard track. The tests were administered at the subject's convenience with a recovery interval of one to three days between. Each subject wore the same shoes and similar clothing for both tests. Although the environmental temperature for the 12-min run test ranged from 60 to 88 F, all subjects appeared to tolerate the test without difficulty. The 12-min run test requires a high level of activity for a prolonged period of time. Therefore, Wyndham's suggested check for motivation (39) was included in the protocol. All subjects met the criterion for satisfactory effort by having heart rates higher than 159 beats/min immediately after the test. The data were analyzed by standard correlation and regression techniques. In addition, the mean difference between measured maximum oxygen uptake and Cooper's predicted maximum oxyben uptake (10) was evaluated by the use of the t-test for dependent samples. Rationale for Research Plan The present study on women was patterned after Cooper's investigation of the relationship between distance covered in a 12- min run test and Vozmax in men (10). The selection of habitually active women as subjects was dictated by the fact that Cooper's data

14 were obtained from officers in the United States Air Force. It is assumed that such military men are moderately active to active individuals. Additional subjects would have been desirable, but restrictions on time and the equipment needed for maximum oxygen uptake determinations prohibited the use of a larger sample. The choice of tests and methods of analysis were determined by the nature of the investigation. Limitations 1. The Pearson product-moment coefficient of correlation is known to be quite sensitive to sample size. Therefore, the use of only 22 subjects may have had some undetermined effect on the results of this study. 2. The selection of a relatively homogeneous group of subjects undoubtedly tended to depress the obtained correlations. Conversely, the fact that the subjects were all habitually active probably decreased the random variability due to motivation. The degree to which these two effects were compensatory is unknown. 3. The Wyndham check for motivation acts only as a terminal criterion for satisfactory effort. No control of motivation was possible during most of the 12-min run test. 4. This investigation was not designed to evaluate the descriptive titles (very poor to excellent) assigned to fitness categories by Cooper and Cooper (13). Given a high correlation between maximum oxygen uptake and performance on the lz min run test, one could expect each fitness level to correspond to an identifiable

15 range of maximum oxygen uptake values. However, even if the descriptive categories could be shown to be distinct, there would be no assurance that they have been labeled correctly. Normative data on a large random sample would be needed to make that value judgment. 5. The nature of the study precluded any attempt to control the behavioral patterns of the subjects prior to and between the two test periods. Factors such as alterations in sleep and diet may have introduced random variability into the data. Significance of the Study The existence of the widely accepted self-evaluation program of Cooper and Cooper (13) is essentially encouraging to exercise scientists. However, there appears to be little research evidence to either support or refute the 12-min performance test as a valid method of assigning an individual woman to a given cardio-respiratory fitness category. If the program proposed by Cooper and Cooper is physiologically sound, it should be promoted; if not, it should be modified or discontinued. The present study has been undertaken to help solve one small part of this current problem.

16 CHAPTER II REVIEW OF RELATED LITERATURE The degree of adaptation of the circulatory and respiratory systems to the demands of strenuous exercise is a good criterion of one's capacity for physical work. Lung volumes and ventilation (3,29), diffusion rates and transport of 02 and CO2 by the blood (1,29), the total quantity of hemoglobin and blood volume (1,31), cardiac function (21,29), the physical condition of the involved muscles (19), body weight (9), muscle mass (17), age (1,3) and motivation (38) all contribute to the general ability of the body to perform sustained work. But, when the cardiovascular and respiratory systems are placed under real stress, maximum oxygen uptake (Vozmax) may provide more information than any other single measure as it reflects a basic physiological limit for prolonged physical activity (l,l4,l9,22,39). Many techniques have been developed to assess Vozmax, and considerable research has been conducted to identify physiological parameters which may influence aerobic working capacity. Factors Affecting Aerobic Capacity A comprehensive review of the factors affecting Vozmax is well beyond the scope and intent of this thesis. The interested reader is referred to Astrand (1,3). A few preliminary comments are 9

17 10 in order, however, as the present study is concerned with the validity of using procedures developed for men in the indirect assessment of the aerobic capacity of women. Maximum oxygen uptake can be expressed in liters per minute (l/min), milliliters per kilogram of total body weight per minute (ml/kg/min), and in milliliters per kilogram of lean body mass per minute (ml/kg LBM/min). Though the last technique is the most discriminatory, it also is technically the most difficult. Sex Differences The percentage of body weight due to fat is greater in women than it is in men (3,32). In a discussion of vondobeln's (34) computation to equalize this factor, Astrand (3) confirms a sex difference in aerobic capacity connected with the differing amounts of adipose and active tissue. The very necessity of a correction factor indicates that men have greater working capacities than do women. Disagreeing with the validity of vondobeln's computation, MacNab (25) studied the differences in maximal and submaximal work capacities of men and women and found that, though the differences were reduced (23% to 11%) when expressed in fat-free body weight, the mens' scores exceeded those of women in all tests. A good basis for comparing the sexes would be the use of maximal oxygen uptake per kg of muscle tissue. However, this measure cannot be determined directly as it is related to lean muscle mass. The relationships between muscular mass and heart force, extracellular fluid, blood volume, and total hemoglobin are not fully

18 ll understood, but Astrand (1) observed that the sex difference found in aerobic capacity per kg of body weight is reflected by a similar difference in total hemoglobin. Oxygen consumption depends not only upon cardio-respiratory function but also upon delivery of oxygen from the lungs to the tissues via hemoglobin. Astrand reports that hemoglobin concentration attains an optimal value which is different for men, women, and children. He further reports that the oxygen capacity of the blood is 12% lower and the maximum oxygen uptake per liter of blood volume is about 10% lower in females than in males. The hemoglobin concentration also is about 10% lower. Holmgren (23) and MacNab (25) consider the concentration of hemoglobin to be a major factor in the sex-related difference in V0 max values. 2 Habitual Activity Astrand's active female subjects had the same aerobic Capacity as male subjects (1). Astrand proposes that the more physically active an individual is, the more muscular mass will influence the total amount of hemoglobin. Other factors probably predominate in sedentary persons (1). Buskirk (9) also noted that the activity level of the individual may be of paramount importance. Studying Vozmax and its relationship to body composition in men, he has shown that there is no difference in maximum oxygen uptake per kg of fat-free weight when groups of similar fitness levels are compared. A significant difference does exist when sedentary versus active groups of individuals are contrasted. He concluded that when V0 max is used 2 to assess the capacity to perform exhaustive work, the values should

19 12 be expressed per kg of body weight; but when assessing the performance of the cardio-respiratory system, the values should be expressed per kg of fat-free weight. Buskirk further reported that the effects of physical conditioning on maximum 02 uptake values are independent of the mass of active tissue and that obesity per se has no effect on the maximum performance of the respiratory-cardiovascular system in men. It should be noted that training does indeed increase maximum 02 consumption. Astrand (l) proposes that the capacity of the vascular bed in the working muscles is the most influential limiting factor in aerobic capacity for individuals in good physical condition. Too frequently, well-trained men are compared with women in poorer physical condition. Little representative information is gained from such comparisons as it is impossible to ascertain whether the differences noted are conditioned by heredity or by training (24,25,26). The studies of Hermansen (21) and Astrand (1,3) appear sensitive to the problem of false comparison which permeates so much of the literature. Hermansen, studying aerobic capacities in young Norwegian men and women, reports an average of 71 ml/kg/min for successful male athletes as compared to 55 ml/kg/min for successful female athletes. Values of 44 ml/kg/min and 38 m1/kg/min were obtained for sedentary men and women respectively. Astrand found average values of maximum 02 intake in ml/kg/min of 58.6 :_.07 for adult men ages and 48.4 :_.05 for adult women ages

20 13 Measurement of Aerobic Capacity, Many procedures have been porposed to measure maximum oxygen consumption. The techniques can be categorized as: (a) laboratory or direct measures, and (b) field or indirect measures. Direct Measures The two most common laboratory methods of measuring Vozmax make use of either a bicycle ergometer or a motor-driven treadmill. Wyndham (37), Hermansen (21), and Glassford (19) all report lower obtained values with use of an ergometer. Furthermore, as cycling presumes specific muscle development and a degree of learning, both Cooper (10) and Wyndham (37) recommend use of a treadmill. Maximum oxygen uptake is most accurately determined during exhaustive work (1,10,39). Prolonged and strenuous effort is necessary as differences between fit and unfit subjects are smaller and less regular with easier work (7,10). Measurement procedures include tests of intermittent work and tests of continuous and increasing workloads until exhaustion is reached. Some employ an increase in the speed of work at a increase the intensity of work at a constant workload, whereas others constant speed. The criterion for the attainment of Vozmax is most frequently the leveling off of oxygen consumption despite an increase in workload. However, this phenomenon does not always occur when unfit subjects are tested or when the continuous work procedure is used (39). Taylor (33) proposes that maximum oxygen uptake has been realized on a treadmill when two consecutive determinations,

21 l4 separated by a grade of 2.5%, differ by less than 150cc/min or 2.1 cc/kg. Astrand (1) reported that some of his subjects never displayed a plateau of oxygen consumption and, therefore, suggested a blood lactic acid level of 100mg/100ml of blood as being indicative of maximal effort. To satisfy his assumption that oxygen consumption does indeed level off, Wyndham (39) introduced an expontial equation of oxygen consumption as a function of workload to estimate the "true" maximum value. Because this procedure requires a number of observations and is not practical in most experimental situations, he further proposed that if the three highest oxygen consumptions occur at successive workloads and do not differ by more than 200ml/min, the mean of the three values could be deemed a valid index of V0 max. 2 Indirect Measures As all direct measurements of maximum oxygen uptake are time consuming, costly, and impractical for large groups, many indirect alternative procedures have been suggested. The Astrand-Rhyming nomogram (2) which employs heart rate responses to submaximal workloads is one such procedure. Wyndham (39) and Glassford (l9) confirm its use as a good estimator of Vozmax in populations accustomed to cycling. However, trained personnel and a bicycle are necessary, and it is inappropriate for the quick evaluation of large numbers of subjects.

22 l5 Timed breath holding, as a measure of physical fitness, was explored and rejected by Montoye (29). He concluded that the test has relatively poor reproducability and that there is little evidence of any correlation between the various indices of physical fitness and breath-holding ability. The Harvard step test has been used widely as a measure of the capacity for sustained work. This test is based upon recovery heart rate, and it may be useful in differentiating fitness levels between individuals for the purpose of homogeneous grouping. It is not correlated with maximum 02 uptake, and it provides only comparative information as to the general fitness of an individual (7). Falls (18) administered the AAHPER youth fitness test to 87 adult males and concluded, from a multiple regression analysis, that V02 The 600-yard walkmax (kg/body weight) can be estimated with reasonable validity using four of the motor fitness items. run was found to be the best single predictor. Doolittle (15), dissatisfied with the 600-yard walk-run as an indicator of cardiorespiratory fitness, compared this measure with the lz-min run suggested by Cooper (10). Actual oxygen uptake values were obtained from a bicycle ergometer test. Maximum oxygen uptake correlated more highly with the 12-min run (r=.90) than with the 600-yard run (r=.62). Doolittle found that the distance covered during the 12-min test was a highly reliable measure and a more valid indicator of cardio-respiratory fitness than was the time of the 600-yard walk-run test.

23 l6 Cooper's 12-min field test is a modification of Balke's (6) 15-min best-effort run test. Based upon Henry's (22) work in which oxygen requirements were estimated for various running velocities, Balke (6) found that maximum oxygen uptake values established on a treadmill could be matched with distances covered in runs of approximately 10- to 20-min duration. Considering the aerobic and anaerobic phases of work capacity, he concluded work periods of 12- to ls-min duration could be used to provide realistic measures of aerobic capacity. The criterion measure in the Cooper field test is the distance an individual can walk or run on a level, hard-surface track in 12-min. Using 115 U.S. Air Force officers (male) as subjects, Cooper (10) obtained a correlation of.897 between performance on the field test and the results of a laboratory treadmill test for maximum oxygen uptake. The advantages of this type of test are: (a) it uses a well-known activity involving large muscle groups, (b) it elicits functional responses up to the limits of the individual's capacity, (c) it is adaptable to large groups of people, and (d) it requires no special equipment. These advantages were recognized by Wyndham (38) who replicated Cooper's study on a sample of 25 adult men and obtained a correlation of r=.94. (This remarkable value may be due partially to the relatively high altitude of Wyndham's laboratory.) Being interested in the clinical applications of an indirect test to the prescription of exercise programs and recognizing that an all-out run may not be prudent for some patients, Wyndham (38) compared the results of the 12-min run test

24 17 with those obtained from a submaximal step test. A correlation of.88 was reported between Vozmax and the step test results. The Cooper test was found to consistently overestimate maximum oxygen uptake values measured on a treadmill, whereas the step test tended to underestimate the laboratory-test results. Though the differences were small, the variability of prediction for the 12-min run test was slightly less than that for the step test. Assessment of Aerobic Capacity in Women Cooper (10,11,12) has established descriptive levels of cardio-respiratory fitness for men based upon the lz-min field test and maximum oxygen uptake (Table 1). Similar categories have been established for women (Table 2), but the corresponding maximum oxygen uptake values were not reported (13). The only published correlation between 12-min test results and Vozmax in women is r=.57 (12). However, Burris (8) in an unpublished account, reports an average correlation of r=.745 for college women. Wyndham (39) notes that Cooper did not consider the effects of altitude or age in his fitness classifications. He suggests 10% be subtracted from the predicted values as a tentative adjustment for women. Substantiation for this particular correction factor is not reported (38,39).

25 CHAPTER III METHODS AND PROCEDURES The present investigation on women was patterned after Cooper's (10) correlational study of field and treatmill testing as a means of assessing maximum oxygen uptake in men. Assuming Cooper's subjects (officers in the U.S. Air Force) were moderately active to active individuals, physically active women were sought as subjects for this study. A total of thirty physical education majors, physical education teachers, and participants in organized athletic programs were asked to serve as subjects for a treadmill 02 consumption test and a 12-min run test. Twenty-two of the women agreed to partiéipate. The average subject age was years (range 17 to 28), the average height was inches (range 61 to 69), and the average weight was kg (range 52.3 to 79.8). No subject ran both tests on the same day. The time interval between the treadmill run and the 12-min performance test was, as in Cooper's study (10), no longer than three days. Similar attire and the same shoes were worn for both tests. No attempt was made to randomize tests or to control test times. The tests were scheduled at the subjects' convenience. l8

26 19 Treadmill Test The Taylor-Henschel test for the determination of maximum oxygen uptake on a motor-driven treadmill was employed but modified to meet the fitness needs of the individual subjects (33). All subjects not familiar with the treadmill were given preliminary instructions and one trial which consisted of getting on, running at 5 mph until they could do so without holding stationary supports, and getting off. Sufficient time for recovery was given between the trial and the test. A return to resting heart rate was achieved before the recorded run began. All subjects were started at 5 mph, 0% grade. At 5 min the speed was increased by 1 mph and the grade by 1%. An additional increase of 1% grade was made for each additional minute run. Two exceptions were made in the standard protocol: (a) two subjects were tested at 5 mph throughout with no increase in grade, and (b) the speed was increased to 6 mph at 5 min without any grade increase for one other subject. These modifications were necessary to achieve treadmill runs long enough for sufficient gas collection. The time of the runs ranged between 4.5 and 9.0 min. Exercise 02 and C02 values were measured using open-circuit (Douglas Bag) procedures in an Otis-McKerrow1 low resistance system (less than 20mm H20 at flow rates up to 225 l/min). Heart rate was monitored by an exercise electrocardiogram on a Gilson recorder. 1Obtained from Warren Collins Inc., Boston, Mass. 535 Huntington Ave.,

27 20 Collection of expired gas began as the subject's heart rate approached 180. Gas was collected in 30-sec bags. Beckman analyzers (E-2 and LB-15)2 were used for gas analysis, and gas volumes were measured by pumping at a constant rate of flow through a calibrated dry gas meter. 12-Min Run Test The 12-min performance test was administered on an outdoor 440 yard track. The distance run was measured to the nearest yard. All subjects were instructed to cover as much distance as possible in 12 min. The subjects were told the elapsed time at 6, 9, and 11 min so they could adjust pace. motivation was employed, and all Wyndham's suggested check for subjects were considered to have exerted maximal effort as each had a heart rate greater than 159 immediately after completion of the 12-min run. Although environmental temperatures ranged from 60 to 88 F, all subjects appeared to tolerate the test without difficulty. Data Analysis The data were analyzed by correlational techniques. Three Pearson product-moment correlations were run between: (a) the actual Vozmax obtained on the treadmill and the projected Vozmax from Cooper's study (10), (b) the actual run distance and the predicted run distance from Cooper's study, and (c) the actual V0 max 2 2Obtained from Beckman Instruments Inc., Schiller Park, Illinois, River Road,

28 21 obtained on the treadmill and the actual run distance on the 12-min performance test. A regression equation for predicting Vozmax from the run data was computed as was a corrected regression equation for women utilizing Cooper's data. The mean difference between the measured Vozmax and Cooper's projected Vozmax was evaluated by the use of a t-test for dependent samples.

29 CHAPTER IV RESULTS Maximum oxygen uptakes in ml/kg/min for 22 female subjects were determined through direct measurement on a motor-driven treadmill. 0n the basis of distance covered in a 12-min run, a projected value of maximum oxygen uptake was obtained for each subject. These values were correlated with predicted values from Cooper's (10) regression equation for men. A correlation coefficient of.732 was obtained between actual measured maximum oxygen uptake and the distance run in 12 min. Though a significant relationship is indicated, the correlation is not as high as the value of r=.897 reported by Cooper (10) or that of r=.94 reported by Wyndham (38) for men. It is similar to the value of r=.745 found by Burris (8) for women. The correlation coefficient between maximum oxygen uptake values predicted by Cooper's method from the 12-min run and those obtained on the treadmill is.731. A correlation coefficient of.713 was obtained between the actual run distance by the female subjects and the run distance predicted by Cooper on the basis of the laboratorymeasured maximum oxygen uptake. Wyndham reports that the maximum oxygen uptakes predicted from the l2-min run are consistantly higher than those obtained by direct measurement on the treadmill (mean difference ml/kg/min). 22

30 23 This difference for men is significant at the.05 level. The maximum oxygen uptake values predicted for women were more extreme (mean difference ml/kg/min). This difference is significant at the.01 level. The regression equation from the present study for predicting maximum oxygen uptake for women on the basis of distance run in 12 min is: 0 max = (distance run) 2 standard error of estimate: ml/kg/min. Regression equations for predicting distance run in 12 min on the basis of measured V0 max for men are: 2 (Cooper): Distance = standard error of estimate: miles, (Wyndham): Distance = standard error of estimate: miles. The regression equation for predicting distance run in 12 min on the basis of measured V0 max for women is: 2 (present study): Distance = standard error of estimate: +.l362 miles. It is evident that the performance on a 12-min run is not as good an indicator of maximum oxygen consumption for women as it may

31 I 24 be for men. Furthermore, the variability of prediction is very large for women as is demonstrated by the standard error of estimate. Cooper indicated that more variability exists at distances of less than 1.4 miles as a result of the motivational component but that this increased variability does not appreciably alter the slope of the regression line. Linearity also was demonstrated in the analysis of data from the present study (see Figure l) but some physiological parameter other than motivation alone must account for the greater distances run by men. Fourteen of the 22 female subjects ran less than 1.4 miles. Table 3 provides a summary of the obtained data and includes projected maximum oxygen uptake values for women based on the distance run in 12 min. A regression correction equation was computed for women to be used with Cooper's projected values for men (Table 4): - =,, g Vozmax (o Vozmax).

32 «I- db co *0 6 V (Ulm/fixllW) Q? Q N Q O G xemzoa ['043V J I b 1 I CD l 1 uhuh A l l l l l I 7' W ' 6 I I I o/h.01xm 1:11J51.2 Actual Distance Run in 12 min (miles) Figure l.-measured V0 max plotted against measured distance run in 12 min (r=.g32).

33 26 TABLE 3.--Distances for the l2-min run performance and maximum oxygen intake values (ml/kg/min) measured on the treadmill, projected for women from distance run, and projected for men from distance run.,actual Q srojected Oflprojected Distance 9 V02 max. 02max. from vozmax. from (m1les) (treadmill) distance run distance runa afrom Table 4.

34 27 TABLE 4.--Predicted maximal oxygen consumption on the basis of 12- minute performancea. Distance Laps Max. 02 Consumption (miles) (1/4 mile track) (ml/kg/min) <l.0 <4 <25,o* * * /4 27.0* / / , / / , / / , / / / / / *Insufficient data at these distances to make reliable comparisons. ataken from "A Means of Assessing Maximal Oxygen Intake," J.A.M.A., 203(3):203 (1968).

35 CHAPTER V DISCUSSION AND CONCLUSIONS The performance on a 12-min run does not appear to be as accurate a method of assessing maximum oxygen uptake for women as it does for men. Though the obtained correlation of r=.732 between performance and Vozmax is significantly higher than the value of r=.57 previously published for women (13), it is not as high as the values of r=.897 and r=.94 reported for men (10,38). To insure completion of the 12-min run, the female subjects of this study were selected to be physically active individuals accustomed to exerting sustained effort of high intensity over prolonged periods of time. The observed correlation may have approached the relationship found for men as the functional capacity of moderately fit females probably overlaps that of the population of sedentary males. Cooper (10) suggests that the validity of the indirect assessment of Vozmax from running performance is directly related to the motivation of the subjects. However, the motivational component alone does not appear to account for either the wide variability in the observed data or the relatively short distances attained by these young well motivated female subjects. 28

36 29 The variability in the data may be due to any number of physiological parameters peculiar to women. In particular, the literature suggests low Hb levels (1) and a low proportion of lean body mass (3). These factors also may have influenced both: (a) the females' attainment of less distance than that covered by men possessing the same maximum oxygen uptake, and (b) the females' higher measured values of Vozmax on the treadmill for corresponding distances covered in 12 min. Certainly the effort of running 12 min represented a relatively high percentage of the females' physical working capacity (P.W.C.). Because of this high percentage of P.W.C. required to sustain the 12-min run, the possibility of this measure being injurious may be greater for the average population of unfit women than it is for sedentary men (38). Correcting for lean body mass, to minimize the physiological differences between men and women, would inherently refute the test's ease of applicability and its desirability as a quick and inexpensive indirect measure of maximum oxygen uptake. Meaningful information was revealed relevant to the validity of the fitness categories proposed by Cooper (Tables 1 and 2). The ranges of actual performance data corresponding to these levels were varied and inconsistant. The results clearly demonstrate the inadvisability of using these subjective fitness categories for women. The data do not support Wyndham's (39) suggested minus 10% correction for women.

37 30 The use of a 12-min run test as an indirect measure of maximum oxygen uptake for women was not substantiated by this study. The test may be appropriate for physically active men and women as an indicator of fitness and for monitoring changes in fitness, but predictions of maximum oxygen uptake for individual women are inappropriate.

38 REFERENCES 31

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