Cooper’s 12 min run test: Its validity in Indian swimmers and volleyball players

INTRODUCTION

Maximum oxygen uptake or VO_2max is one’s ability to transport maximum amount of oxygen to the exercising muscles during exhaustive work. It is globally considered as the gold standard of an individual’s cardiorespiratory fitness. It is also an important parameter to judge an athlete’s performance ability. Direct estimation of VO_2max involves complicated experimental protocol that is exhaustive and time consuming.^[1] It is also expensive and involves skilled personnel and several equipments. Thus, it is not possible to apply the procedure of direct estimation of VO_2max outside the well-equipped laboratory infrastructure.^[2] Therefore, it acts as a hindrance when large number of samples needs to be evaluated, especially in the field-based studies. Direct measurement of VO_2max is also influenced by the motivation of the individual.^[3] Therefore, it will be a good alternative to choose indirect simple procedure(s) for the evaluation of VO_2max, especially in case of sportspersons to evaluate their cardiorespiratory fitness in the field and also in absence of favorable laboratory set up.^[1,2]

The previous studies enumerated the validity of prediction of VO_2max using non-exercise based models in Indian college students.^[3,4] A study on Japanese adult population standardized 3 min walking distance for prediction of VO_2max with respect to gender, age, and body composition.^[5] Huntsman et al.^[6] restricted the use of equipment by enumerating the applicability of a field test in rowers. Marsh^[7] tried to assess the validity of the American College of Sports Medicine’s submaximal treadmill running test in predicting VO_2max in moderately well-trained men of 18–34 years of age. Lima et al.^[8] also standardized the 3200 m field test in Brazilian indoor soccer players. Klusiewicz et al.^[9] have standardized another indirect protocol based on 2000 m trial that reflected the physical work capacity in terms of heart rate and that was further extrapolated with suitable regression norm in Polish rowers. All these studies emphasized that indirect protocols for VO_2max prediction should be validated in the specific population before its implementation to enable the measurement of VO_2max using simple methods with least instrumentation.

Cooper’s 12 min run test (CRT) is one of the popular indirect field tests for prediction of VO_2max.^[10] One measuring tape is required to measure the distance covered in 12 min. Application of this test in Indian sportspersons requires proper inventory of the validity of the test since it was originally enumerated in Western population.

Therefore, the present study was aimed to assess the suitability for application of the CRT to predict VO_2max in male and female swimmers and volleyball players of Kolkata, West Bengal, India.

MATERIALS AND METHODS

RESULTS

Both the physical and physiological parameters of the subjects belonging to the two athletic populations of swimmers and volleyball players are shown in Table 1. Significant difference was found in body height, body weight, and distance covered in CRT when compared between the groups of same genders.

For the study groups of swimmers and volleyball players of both genders, Bland and Altman approach for limit of agreement analysis is plotted in Figures 1-4, respectively.

Close

Figure 1:

Plotting of difference between PVO2max and VO2max values against the average of directly and indirectly measured values of VO2max in the study group of male swimmers.

Export to PPT

Close

Figure 2:

Plotting of difference between PVO_2max and VO_2max values against the average of directly and indirectly measured values of VO2max in the study group of female swimmers.

Export to PPT

Close

Figure 3:

Plotting of difference between PVO2max and VO2max values against the average of directly and indirectly measured values of VO₂max in the study group of male volleyball players.

Export to PPT

Close

Figure 4:

Plotting of difference between PVO₂max and VO₂max values against the average of directly and indirectly measured values of VO2max in the study group of female volleyball players.

Export to PPT

Based on the existence of significant correlation between VO_2max and distance covered in CRT for the study groups of swimmers and volleyball players of both genders, regression equations have been computed and plotted in [Figures 5-8], respectively.

Close

Figure 5:

Relationship between VO₂max and distance covered in CRT in the study group of male swimmers.

Export to PPT

Close

Figure 6:

Relationship between VO2max and distance covered in CRT in the study group of female swimmers.

Export to PPT

Close

Figure 7:

Relationship between VO2max and distance covered in CRT in the study group of male volleyball players.

Export to PPT

Close

Figure 8:

Relationship between VO2max and distance covered in CRT in the study group of female volleyball players.

Export to PPT

DISCUSSION

PVO_2max (60.47 ± 4.20 ml.kg^-1.min^-1 in males and 55.70 ± 4.13 ml.kg^-1.min^-1 in females) of swimmers showed significant difference with VO_2max (52.57 ± 4.53 ml.kg^-1.min^-1 in males and 48.40 ± 4.30 ml.kg^-1.min^-1 in females) in the study group. Bland and Altman^[15] analysis revealed that the limits of agreement between PVO_2max and VO_2max were large enough (2.17–13.61 ml.kg^-1.min^-1 in males and 2.91–11.67 ml.kg^-1.min^-1 in females) with poor confidence intervals [Figures 1 and 2]. This finding indicated the inapplicability of current protocol of CRT for indirect prediction of VO_2max in swimmers of Kolkata, India. Moreover, significant (P < 0.001) difference between PVO_2max and VO_2max indicated that application of the Cooper’s protocol^[10] does not accurately predict maximum oxygen uptake in the studied population. However, the distance covered in CRT exhibited significant correlation (r = 0.79 in males and r = 0.86 in females, P < 0.001) with directly measured VO_2max. Accordingly, prediction equations were computed in male (Y = 18.99 X – 8.41 [SEE = 2.84 ml.kg^-1.min^-1]) and female (Y = 20.16 X – 11.88 [SEE = 2.12 ml.kg^-1.min^-1]) swimmers from the data obtained in the study groups for precise assessment of VO_2max in the studied population [Figures 5 and 6].

In case of the volleyball players, PVO_2max (58.55 ±4.09 ml.kg^-1.min^-1 in males and 54.19 ± 4.01 ml.kg^-1.min^-1 in females) revealed significant difference with VO_2max (50.19 ± 3.47 ml.kg^-1.min^-1 in males and 45.49 ± 4.12 ml.kg^-1.min^-1 in females) in the study group. Bland and Altman (1986) method of limit of agreement analysis revealed that the limits of agreement between PVO_2max and VO_2max were large enough (4.34–12.36 ml.kg^-1.min^-1 in males and 4.04–13.36 ml.kg^-1.min^-1 in females) with poor confidence intervals [Figures 3 and 4], indicative of unsuitability of current protocol of CRT in this particular population. Moreover, significant (P < 0.001) difference between PVO_2max and VO_2max marked that it would not be justified in accepting the prediction of maximum oxygen uptake in the studied population through CRT application as suggested by Cooper.^[10] However, the distance covered in CRT depicted significant correlation (r = 0.87 in males and r = 0.83 in females, P < 0.001) with directly measured VO_2max in the study group of both genders, and accordingly, regression norms were computed in male (Y = 16.55 X – 1.49 [SEE = 1.724 ml.kg^-1.min^-1]) and female (Y = 19.30 X – 11.03 [SEE = 2.281 ml.kg^-1.min^-1]) volleyball players depending on the data obtained in the study groups for precise prediction of VO_2max in the studied population [Figures 7 and 8].

The newly derived equations were applied in the confirmatory group of both the genders of swimmers. This revealed insignificant difference between PVO_2max (53.12 ± 3.48 ml.kg^-1. min^-1 in males and 49.73 ± 3.73 ml.kg^-1.min^-1 in females) and VO_2max (52.71 ± 3.34 ml.kg^-1.min^-1 in males and 48.87 ± 3.87 ml.kg^-1.min^-1 in females). Moreover, the standard errors of estimate of these norms were substantially small (SEE = 2.84 ml.kg^-1.min^-1 and 2.12 ml.kg^-1.min^-1 in male and female groups, respectively). Prediction of VO_2max from this new equation showed a variation of <5% in 52 male and 55 female participants, 5–9% in 8 male and 11 female participants, 10–14% in 4 male and 3 female participants, and 15–19% in 2 male and 1 female participants from their respective directly measured value of VO_2max. Application of Bland and Altman’s analysis between directly measured VO_2max and indirectly predicted VO_2max from the newly derived equation revealed substantially small limits of agreement in male (–0.19–1.51 ml.kg^-1.min^-1) and female (–0.05–1.85 ml.kg^-1. min^-1) groups. The percentage of variation between VO_2max and PVO_2max reduced from 15.03% to 0.77% in male swimmers and from 15.08% to 1.76% in female swimmers following application of the revised population-specific equations.

Further, in case of the volleyball players, application of these newly derived equations in the confirmatory group indicated insignificant difference between PVO_2max (49.68 ± 3.73 ml.kg^-1.min^-1 in males and 47.72 ± 3.64 ml.kg^-1.min^-1 in females) and VO_2max (50.29 ± 4.03 ml.kg^-1.min^-1 in males and 46.57 ± 3.75 ml.kg^-1.min^-1 in females). Moreover, the standard errors of estimate of these norms were substantially small (SEE = 1.724 ml.kg^-1.min^-1 and 2.281 ml.kg^-1.min^-1 in male and female groups, respectively). Prediction of VO_2max from this new equation showed a variation of <5% in 62 male and 59 female participants, 5–9% in 18 male and 15 female participants, 10–14% in 5 male and 5 female participants, and 15–19% in 3 male and 2 female participants from their respective directly measured value of VO_2max. Application of Bland and Altman’s analysis between directly measured VO_2max and indirectly predicted VO_2max from the newly derived equation revealed substantially small limits of agreement in male (0.16–1.76 ml.kg^-1.min^-1) and female (0.06–1.06 ml.kg^-1.min^-1) groups. The percentage of variation between VO_2max and PVO_2max reduced from 16.65% to 1.21% in male volleyball players and from 19.12% to 0.24% in female volleyball players following application of the revised population-specific equations. This variation should be within a range of 7% for the acceptability of the modified norm.^[16] The criterion has been satisfied in the present investigation.

The exercise protocol of the modified method remains the same, but the regression equation has been modified in different genders of swimmers and volleyball players on the basis of proper statistical analyses. These are the population-specific corrections of the regression norm as also reported in the earlier studies dealing with standardization of indirect protocols for the valid prediction of VO_2max.^[1,2,12,13]

Variation of results between the original equation and presently modified equation was perhaps due to the fact that the original equation was proposed in sedentary Western population while the present study involved swimmers and volleyball players from Kolkata, West Bengal, India. There is a variation in the ethnicity as well as physical fitness level which might be potential reasons for the inapplicability of the existing protocol in the currently studied sportspersons of both genders.

Bland and Altman’s guideline^[15] was adopted to test the repeatability of the modified equations in the studied population. It has been observed that the mean difference between repeated measures of VO_2max (determined by both direct method and indirect modified method) was insignificantly different from zero in both the genders of swimmers. As per the definition of “Repeatability Coefficient,”^[17] it is expected that 95% of differences would be less than two SDs (±2SDs) which has been met in the present investigation. The SDs between repeated measures of each method separately were computed and the SDs of differences between the means for each method were also computed to determine the repeatability coefficients in both the genders for direct method and indirectly modified method. The mean differences of repeated measures were 0.0052 ml.kg^-1.min^-1 and 0.0061 ml.kg^-1.min^-1 for modified equations in males and females, respectively, whereas 0.0043 ml.kg^-1.min^-1 and 0.0049 ml.kg^-1.min^-1 for direct method in males and females, respectively. The corresponding values of repeatability coefficients were ±0.42 ml.kg^-1.min^-1, ±0.46 ml.kg^-1.min^-1, ±0.48 ml.kg^-1.min^-1, and ±0.43 ml.kg^-1.min^-1, respectively.

Further, for volleyball players, repeatability of the modified equations has also been tested according to the guideline of Bland and Altman.^[11] It has been observed that the mean difference between repeated measures of VO_2max (determined by both direct method and indirect modified method) was insignificantly different from zero in both the genders of volleyball players. According to the definition of “Repeatability Coefficient.”^[12] It is expected that 95% of differences would be ±2SDs which has been met in the present investigation. The SDs between repeated measures of each method separately were computed and the SDs of differences between the means for each method were also computed to determine the repeatability coefficients in both the genders for direct method and indirectly modified method. The mean differences of repeated measures were 0.0058 ml.kg^-1.min^-1 and 0.0065 ml.kg^-1.min^-1 for modified equations in males and females, respectively, whereas 0.0049 ml.kg^-1.min^-1 and 0.0054 ml.kg^-1.min^-1 for direct method in males and females, respectively. The corresponding values of repeatability coefficients were ±0.53 ml.kg^-1.min^-1, ±0.56 ml.kg^-1.min^-1, ±0.52 ml.kg^-1.min^-1, and ±0.58 ml.kg^-1.min^-1, respectively.

CONCLUSION

From the present observation, it may be concluded that the presently derived or modified equations will predict VO_2max in the studied populations more accurately. Therefore, these newly derived norms, validated against direct measurement of VO_2max using incremental cycle ergometer test, are recommended for the application of Cooper’s 12 min run test as a valid method for correct and precise evaluation of cardiorespiratory fitness in terms of VO_2max in swimmers and volleyball players of both genders of Kolkata, West Bengal, India.