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Work 50 (2015) 205–211 DOI 10.3233/WOR-141824 IOS Press
Modification of Fox protocol for prediction of maximum oxygen uptake in male university students Amit Bandyopadhyay∗ and Sangita Pal Sports and Exercise Physiology Laboratory, Department of Physiology, University of Calcutta, University College of Science and Technology, Kolkata, India
Received 11 October 2012 Accepted 6 August 2013
Abstract. BACKGROUND: Direct estimation of VO2 max involves labourious, exhaustive, hazardous, time consuming and expensive experimental protocols. Hence, application of various indirect protocols for prediction of VO2 max has become popular, subject to proper population-specific standardisation of the indirect protocol. OBJECTIVES: Application of Fox (1973) protocol in male sedentary university students of Kolkata, India led to premature fatigue in their leg muscles that hindered the muscular activity leading to inability in completing the exercise. The present study was aimed at modifying and validating the Fox (1973) protocol with a convenient workload of 110 W (i.e., modified Fox test or MFT) in the said population. METHODS: Ninety (90) sedentary male students were recruited by simple random sampling from the University of Calcutta, India and they were randomly assigned into study group (n = 60) and confirmatory group (n = 30). VO2 max was directly estimated by Scholander micro-gas analysis after incremental bicycle exercise. Predicted VO2 max (PVO2 max) was computed from MFT by using the submaximal heart rate (HRsub ). RESULTS: In the Study Group VO2 max (2216.63 ± 316.77 mL.min−1 ) was significantly different (P < 0.001) from PVO2 max (3131.73 ± 234.32 mL.min−1 ) measured by using the equation of Fox (1973). Simple and multiple regression equations have been computed for prediction of VO2 max from HRsub and physical parameters. Application of these norms in the confirmatory group depicted insignificant difference between VO2 max and PVO2 max with substantially small limits of agreement and lower values of SEE. CONCLUSION: The modified regression norms are therefore recommended for use in MFT for accurate assessment of VO2 max in the studied population. Keywords: VO2 max, Indian males, sedentary, cycle ergometry
1. Introduction Maximum oxygen uptake (VO2 max) is the single most valid parameter to measure the functional capac∗ Corresponding author: Amit Bandyopadhyay, Sports and Exercise Physiology Laboratory, Department of Physiology, University of Calcutta, University College of Science and Technology, 92, A. P. C. Road, Kolkata: 700009, India. Tel.: +91 33 23508386 (Extension 221); Fax: +91 33 23519755; E-mail:
[email protected].
ity of the cardiorespiratory system. It is an internationally accepted parameter to denote one’s cardiorespiratory fitness and frequently measured to evaluate the efficiency of cardiovascular system as well as respiratory system not only in clinical settings but also in researches dealing with work physiology, sports and exercise science. The direct estimation of VO2 max involves exhaustive, laborious, hazardous, difficult and expensive experimental protocols [1]. The exercise test
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for the assessment of maximal oxygen uptake is unsuitable for screening tests in public heath examinations because of the potential risks of exercise exertion and time demands [2]. That is why heart rate was used as the alternate parameter to evaluate physical exertion level during various forms of working tasks [2– 5]. Moreover, it is not feasible to conduct the test in absence of well equipped laboratory, especially when a large number of subjects need to be evaluated. Due to such obstacles, researchers also fail to apply the direct estimation of VO2 max in field tests. Assessment of VO2 max for workers engaged in organised and unorganised sectors is very important because it has long been proposed that severity during the work shift should not exceed 50% of VO2 max [3]. Total Health Promotion Plan for industrial workers was instituted by WHO Ottawa Charter of 1986 including the determination of the maximal oxygen uptake (VO2 max) as an indication of whole body endurance that further helps to prevent the workers from potential risks of cardiovascular diseases [4]. To bypass the difficulties of conducting direct estimation method of VO2 max, Fox [1] validated a prediction method for indirect estimation of VO2 max in 87 healthy college males of Ohio State University, Columbus, from their submaximal heart rate recorded during the 5th min of bicycle exercise at 150 W. Attempts have been made to apply the test in male sedentary university students of Kolkata, India, but all of them felt that the workload was substantially high and reported some premature fatigue in their leg muscles. Consequently they failed to sustain the exercise up to the recommended duration of 5 min. This indicated a poorer stamina in the study population than that of college males of Ohio State University. Hence, similar test was conducted with lower workloads (140 W, 130 W, 120 W and 110 W) with at least 4 days’ gap in between the tests in the same subjects [5]. They satisfactorily performed the bicycle exercise for the stipulated duration of 5 min at the workload of 110 W which was therefore considered as the maximum sustainable workload in this population to complete the protocol successfully. In the present context, the research was focused to carry out the test on bicycle ergometer for 5 min at 110 W workload and to determine the peak heart rate that would enable us to predict their VO2 max value from the regression equation that has been originally proposed by Fox [1]. Such predicted value will be compared with the directly measured VO2 max. It was hypothesized that:
1. The VO2 max value predicted from this peak heart rate will have insignificant difference from the directly measured VO2 max. In that case the question of applicability of the originally proposed regression equation of Fox [1] does not arise. 2. The predicted VO2 max value will have significant variation from the directly measured VO2 max. If this will be the case, then separate regression equation needs to be developed and the applicability of that regression equation should be evaluated. Therefore the specific objective of the present study was to modify and validate the Fox [1] protocol with 110 W workload (i.e., modified Fox test or MFT) in the sedentary male university students of Kolkata, West Bengal, India.
2. Material and methods 2.1. Study population Ninety (90) healthy sedentary male students of same socio-economic background having mean age, body height and body mass of 22.8 ± 1.7 years, 167.7 ± 4.2 cm and 58.3 ± 4.0 kg, respectively were selected for the study by simple random sampling from the post-graduate section of the University of Calcutta, West Bengal, India. The sample size was calculated using PS-Power and Sample Size Calculation version 3.0.43 [7]. The power and the confidence interval were set at 80 and 95%, respectively. They were randomly assigned into two groups by simple random sampling from the selected subjects. The first group, i.e., “study group” (n = 60) on which the experiment was carried out to compute the new regression norm and the second group was termed as “confirmatory group” (n = 30) upon which the modified regression norm was validated. The entire experimental protocol was well explained to all the participants and written informed consent was also taken from them. They took light breakfast 2–3 hours before the test and refrained from any energetic physical activity for that period. The participants had no history of any major disease and received no physical conditioning programme except some recreational sports. The study was approved by the Human Ethical Committee, Department of Physiology, University of Calcutta. The study was conducted in the Sports and Exercise Physiology Laboratory, Department of Physi-
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ology, University of Calcutta from October 2010 to March 2011. The entire experiment was performed at a room temperature varying from 26–29◦C and at a relative humidity ranging between 72 to 83%. 2.2. Experimental design Each subject came to the laboratory for three days. On the first day they were familiarised with the experimental protocol. The direct evaluation of VO2 max and MFT were conducted on the second and third visit, respectively at an interval of at least 4 days in between the tests [6,8]. So, these two experiments were conducted by random sequencing or cross-over design in which direct estimation of VO2 max was followed by MFT in one half of the subjects whereas the MFT was followed by VO2 max determination in other half of the subjects to avoid any possibility of bias. Subjects were asked to take rest at least for half an hour prior to the exercise, so that pulmonary ventilation and pulse rate could come down to a steady state [6,8,9]. 2.3. Workload selection for MFT Fox [1] protocol predicted the VO2 max in college males from HRsub measured at the end of 5 min of bicycle exercise at 150 W by using the equation: Y = 6300–19.26 X. Application of the same protocol in the present population revealed onset of premature fatigue in the leg muscles. Therefore the subjects were asked to exercise in the bicycle ergometer at different submaximal work-load, i.e., 100 W, 110 W, 120 W, 130 W and 140 W. Out of these workloads, 120 W and higher workloads also led to onset of premature fatigue. 110 W was the mostly opted highest sustainable workload by the subjects and hence this was selected as the workload for the study. 2.4. Procedure of MFT Muller’s magnetic brake bicycle ergometer (Model of Max Plank Institute of Ergology, Germany) was used for the study. The subjects performed a warm up exercise at 50 W intensity for a duration of 5 min. Then the work load was increased to 110 W where they performed the exercise for 5 min. The peak heart rate at 5 min (HRsub ) was recorded manually from the time taken for ten carotid pulsations [6,8,10,11] immediately following the cessation of 5 min of exercise in the 110 W. The predicted value of VO2 max was computed from the equation of Fox [1] : PVO2 max = 6300– (HRsub x 19.26).
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2.5. Direct measurement of maximum oxygen uptake capacity The subjects at first performed a warm up exercise at 75 W intensity for a duration of 5 min in the Muller’s magnetic brake bicycle ergometer (Model of Max Plank Institute of Ergology, Germany). Immediately after performing the submaximal exercise, the intensity was increased to the first incremental intensity of 130 W and thereafter the intensity was increased by 25 W every 3 min until the subject stopped due to exhaustion. The oxygen uptake was considered maximum when the following factors set in [12]: i) A heart beat within 10 beats.min−1 of agepredicted maximum heart rate: 220 beats.min−1 – age ii) A respiratory exchange ratio of > 1.15 iii) Levelling off, i.e., when no further increase in oxygen uptake took place despite further increase in intensity, or the increase in oxygen uptake was less than 100 mL.min−1 in response to the next higher intensity for repeated tests followed at an interval of 4 days [6,8,9]. Low resistance high velocity Collin’s Triple “J Type” plastic valve was used for the collection of expired gas by open circuit method [6,8,9]. The valve was connected with the Douglas Bag (150 L) and the expired gas was collected at the last min of final intensity of exercise. Gas was also collected at the second min of the exhausting (final) work load if signs of severe exhaustion supervened. No gas collection was made in the first min of the work load. The volume of expired gas was measured in a wet gasometer (Toshniwal, Germany, CAT. No. CG05.10) and the aliquots of gas samples were analyzed in a Scholander microgas analysis apparatus following the standard procedure [13]. The peak heart rate was recorded manually from the time taken for ten carotid pulsations immediately following the cessation of exhaustive exercise [6, 8,10,11]. VO2 max values were corrected to standard temperature pressure dry (STPD) condition. 2.6. Statistical analysis Paired t-test was done to test the significance of difference between mean values of VO2 max and PVO2 max. Correlation statistic was conducted to test the significant relationship of physical parameters with VO2 max. Bland and Altman approach for limit of agreement [14] were adopted for testing the applicability of the modified protocol. Simple and multiple lin-
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Table 1 Values of correlation coefficient (r) of VO2 max with different physical parameters VO2 max Age Weight Height
VO2 max 1.000
Age 0.718 1.000
Weight 0.885 0.699 1.000
Height 0.767 0.688 0.666 1.000
All values of ‘r’ are significant at the level of p < 0.001.
ear regression analysis were also adopted to compute linear regression equation considering VO2 max as regressee variable and HRsub and physical parameters as regressor variables, respectively. The regressee variable is a normal variate and homocedastic (having the same variance) in the current study that in turn fulfils the assumption underlying linear regression analysis [15].
3. Results and discussion The pre-exercise heart rate recorded in the Study Group and Confirmatory Group were 70.32 ± 4.71 beats.min−1 and 71.16 ± 5.24 beats.min−1, respectively. The difference in the values of HRsub obtained in the study group and confirmatory group (164.5 ± 12.16 and 163.6 ± 18.73 beats.min−1, respectively) was statistically insignificant (p > 0.05). No significant difference (p > 0.05) was found in age, body mass, body height and pre-exercise heart rate between the study group and confirmatory group. The values of correlation coefficients of VO2 max with different physical parameters have been presented in Table 1. Oxygen uptake is also a reliable predictor of metabolic indices and use of heart rate to predict oxygen uptake and physical exertion has also been attempted in Japanese workers [5]. The study revealed that heart rate is more useful than oxygen uptake in evaluating the exertion level during physical labour in individual workers. Work related physical activity was identified as a good predictor of cardiorespiratory fitness in Korean workers by the use of a non-exercise regression model [2]. It has been further suggested that after adjustment for other factors in males, an ambulatory work form may be associated with an increase in maximum oxygen uptake in one year [16]. Hirai et al. [3] suggested that the physical work load, represented by the work form, contributes to increases in VO2 max in male Japanese workers. Besides working pattern, life style, addiction and exercise habit also influence the oxygen uptake in work-
ers [17–20]. Intensity, duration and posture of work vary in different industries and accordingly it affects the VO2 max among workers. Concomitant increase in VO2 max with increase in work load and changing posture has been well documented among workers [3,21]. In the context of the available literature, the present study is very much significant since it modifies an indirect protocol that predicts cardiorespiratory fitness from heart rate in terms of VO2 max among young Indian males. Application of this test will not only help to evaluate the VO2 max but also help to assess the physical exertion level among young Indian indutrial workers and help to prevent them from potential risks of cardiovascular diseases as well as to implement the health promotion plan. The mean value of VO2 max (2216.63 ± 316.77 mL. min−1 with a range of 1561.56–2747.58 mL.min−1) showed significant difference (p < 0.001) with the predicted VO2 max or PVO2 max (3131.73 ± 234.32 mL. min−1 with a range of 2717.64–3526.56 mL.min−1) that was predicted by using the equation of Fox [1] in the study group. HRsub exhibited significant negative correlation (r = −0.81, r2 = 0.6561, p < 0.001) with the directly measured VO2 max in the study group. However, Application of multiple correlation and multiple regression statistics revealed the following equation: VO2 max (ml.min−1 ) = 9.422 × Age + 2.95 × Height + 48.25 × Weight – 10.853 × HRsub + 479.4369 (R = 0.961, p < 0.001, R2 = 0.923, SEE = 91.1474 ml.min−1) The value of multiple correlation coefficient (R) was higher than the simple correlation coefficient (r) with lower value of standard error of estimate in case of multiple regression equation than that of simple regression equation. Application of the simple linear regression norm in the confirmatory group depicted insignificant difference (p > 0.05) between the VO2 max (2240.81 ± 198.57 mL.min−1) and PVO2 max (2310.57 ± 200.88 mL.min−1) measured from MFT. Bland and Altman [14] method of analysis (Fig. 2) revealed that the limits of agreement between PVO2 max and VO2 max were substantially small (51.96 to 87.56 mL. min−1 ). The standard error of estimate (SEE) of the norm was 187.86 mL.min−1. Prediction of VO2 max from this new equation showed a variation of less than 5% in 61 participants, 5–9% in 23 participants and 10–14% in 6 participants from their respective directly
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2800
2600
-1
VO2max (ml.min )
2400
2200
2000
1800
Y = 5670.35 – 20.995 X; r = -0.81 P 0.05) between the VO2 max (2240.81 ± 198.57 mL.min−1) and PVO2 max (2287. 416 ± 238.130 mL.min−1 ) measured from MFT. Bland and Altman [14] method of analysis (Fig. 3) revealed that the limits of agreement between PVO2 max and VO2 max were smaller (55.808 to 79.512 mL. min−1 ) than that of simple regression norm. The standard error of estimate (SEE) of the multiple regression norm is also much smaller (SEE = 91.1474 ml.min−1 ) than the simple regression norm. Prediction of VO2 max from the multiple regression equation showed a variation of less than 5% in 72 participants, 5–9% in 15 participants and 10–14% in 3 participants from their respective directly measured value of VO2 max. However, the standard errors of regression coefficients for age, height, weight and HRsub were
10.71, 4.45, 4.66 and 1.42, respectively. The standard error of constant was 814.59. Thus the comparative analysis regarding the application of computed simple and multiple regression equations revealed that the multiple regression equation would predict VO2max more precisely and accurately in the studied population than the simple regression equation. Therefore, from the present observations, the multiple regression equation obtained from the modified method of Fox [1] protocol or MFT is recommended as a valid method to evaluate cardiorespiratory fitness in terms of VO2 max in the young sedentary male university students of Kolkata, West Bengal, India. Application of this modified protocol will benefit the researchers working in the relevant field to predict VO2 max of their subject within 5 min involving a non-exhaustive simple exercise protocol without any financial obligation. However, the simple regression equation may also be used as another useful prediction norm to have a first hand impression about VO2max in the studied population.
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Acknowledgements The author acknowledges the financial assistance provided by the University of Calcutta under the “Research Contingency” grant. The wholehearted participation and cooperation of the subjects are also gratefully acknowledged.
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