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Comparison of Mean VO2 max in normal Weight, Overweight and Obese Students of a Local Medical College Using Analysis of Variance.

Byline: Naila Parveen, Riaz Ahmed Shahid, Lubna Riaz, Shahwar and Ahmed Safiullah Shaikh

Key words: VO2 max, body mass index, bruce protocol, exercise.

Introduction

Cardiovascular disease burden is on the rise and a leading cause of mortality worldwide. Increase in the body mass index i.e; overweight and obesity pose a major risk for developing cardiorespiratory illness.1

According to recent studies, morbid illness in both healthy and non-healthy persons can be predicted by the maximal oxygen consumption that determines the cardiorespiratory endurance.2

Related to the various functional mechanisms of the body, cardiorespiratory refers to the uptake and transport of oxygen, while the musculoskeletal system is involved in the maximum utilization of oxygen. Therefore, physical exercise by treadmill or ergometry is an indirect measure of VO2 max.3,4

While performing an exercise, oxygen deficit limits its performance and it is the VO2 max that measures the aerobic endurance of an individual to offset that limitation. Multiple factors influencing the VO2 max include the physical activity, gender, cardiorespiratory and skeletal muscle functions.5 Due to increased amount of fat mass, there is less uptake of oxygen by the musculoskeletal system during incremental exercise. However, with the reduction of weight, improvement in VO2 max was found. This is due to the fact that, in obesity there are reduced numbers of type I muscle fibers compared to type II muscle fibers leading to less uptake of oxygen in these individuals.6-8 It has been reported that physiologically, males have 20-25% greater VO2 max compared to females due to their increased lean body mass and reduced total fat mass.9

In this study, VO2 max is measured following the Bruce Protocol in which the individual performs the exercise test on the treadmill and both its speed and incline is made to increase after every three minutes. The length of time on the treadmill is the test score and can be used to estimate the VO2 max value.10 The main aim of this study was to compare the means of VO2 max among normal weight, overweight and obese individuals.

Subjects and Methods

A total of one hundred and two medical students were included in this cross-sectional study by purposive sampling. The study was conducted in the department of Physiology of a local medical college in Karachi from 25th November 2016 to 31st July 2017 after research committee approval of Liaquat National Hospital and Medical College.

Total sample size was estimated as 180 using the open epi sample size calculator with prevalence rate of obesity reported in Pakistan as 25% 11 and CI=95%. Written informed consent was taken from each participant prior to the start of the study.

Inclusion criteria: Both healthy male and female undergraduate medical students, between 19-23 years.

Exclusion criteria: Past history of cardiorespiratory illness such as congenital heart disease, known asthmatics and females on any hormonal medications.

The World Health Organisation (WHO) defines weight status according to body mass index (BMI), the ratio of weight (in kilograms) divided by height (in meters square).12

Weight and height of each student was measured using the standard stadiometer. The body mass index was calculated, from an individual's weight in kg divided by the square of the height in meters 5 using the following formula:

Body mass Index (BMI) = weight (Kg)/Height (m2).

According to WHO BMI classification for Asian population,12 students were divided into normal (18.5-22.9 kg/m2), overweight (23-24.9 kg/m2) and obese ([greater than or equal to]25 kg/m2) groups.

The selected students were instructed to prevent from any exertion 24 hours prior to the treadmill test. They were also asked to refrain from coffee intake four hours before the Bruce test.

To assess 2 max, the participants completed a continuous incremental exercise test to voluntary exhaustion on a calibrated treadmill. The participants started exercising on a calibrated treadmill (Ranker Model; RT-18400) at a speed of 2.7 km/h and an incline of 10% gradient for 3 minutes according to Bruce Protocol. Speed and inclination were subsequently increased after every three minutes until voluntary exhaustion was reached.10,13

The Bruce Protocol Formula for estimating VO2 max:

Males

Men: VO2 max (ml/kg/min) = 2.94 x T + 7.65

Females

Women: VO2 max (ml/kg/min) = 2.94 x T + 3.74

T = Total time on the treadmill measured as a fraction of a minute (ie: A test time of 9 minutes 30 seconds would be written as T=9.5).13

Statistical analysis of the data was done on SPSS version 21 software. Continuous data were expressed as means and standard deviation. Mean values for age, body mass index and VO2 max were calculated through descriptive statistics. One way analysis of variance (ANOVA) was done to compare the means of VO2 max in normal, overweight and obese groups. Post-hoc analysis by ukey's test was done to evaluate the significant difference between the three groups. p-value at less than 0.05 was considered as statistically significant.

Results

A total of 102 gender and age matched, undergraduate medical students were recruited to participate in the study for VO2 max estimation using the Bruce test. Mean age depicted was 20+-1.23 years and mean BMI of normal, overweight and obese individual was reported as 21.05+-1.01 kg/m2 and 24.10+-1.06 kg/m2 and 28.43+-0.06 respectively. Mean VO2 max for individuals with normal weight was found to be 55.29+-9.27 ml/kg/min., overweight and obese groups had mean values of 49.35+-5.24 ml/kg/min and 46.24+-6.34 ml/kg/min respectively.

Table 1: Descriptive statistics of continuous variables.

Variables###Mean+-SD

###Normal###Overweight###Obese

###Weight (n=40)###(n=32)###(n=30)

BMI(kg/m2)###21.05+-2.01###24.10+-1.06###28.43+-0.06

VO2 max###55.29+-9.27###49.35+- 5.24###46.24+-6.34

(ml/kg/min)

ANOVA and Post-hoc analysis showed significant mean differences of VO2 max with the body mass index in all the three groups (p <0.05) as in Table-2. Gender differences of VO2 max showed remarkable difference with increased maximal oxygen consumption reported in males compared to females as shown in Table-3.

Table 2: Comparison of means of VO2 max and BMI groups using ANOVA.

BMI Groups###N=102###VO2 max###S.E###p-value

###Mean+-SD

###(ml/kg/min)

Normal weight###40###55.29+-9.27###4.20

(18.5-22.9

kg/m2)

Overweight###32###49.35+-5.24###3.83###0.0001

(23-24.9 kg/m2)

Obese###30###46.24+-6.34###3.21

(25 kg/m2)

Table 3: Gender differences of mean VO2 max.

Groups###Mean +-SD###p-value

N=102###(VO2 max)

###ml/kg/min

Male (52)###57.25+-6.30

###0.0001

Female(50)###42.24+-2.22

Discussion

In the present study, mean VO2 max was estimated and compared with the body mass index in normal weight, overweight and obese students. Lack of regular physical activity and sedentary behavior leads to increased risk of cardiovascular ailments, obesity, diabetes mellitus, cancer, and early death. Recent studies have predicted a lethal association of prolonged total sedentary time with multiple chronic diseases and mortality outcomes.14,15 Lee et al has reported that among the various factors that pose a major risk for cardiovascular co-morbidities, VO2 max has been established as one of the independent risk factor leading to cardiovascular mortality.16

In the present study, mean VO 2 max was compared in normal weight, overweight and obese individuals. Students with increased fat mass or body mass index (overweight and obese), were reported to have decreased VO 2 max leading to reduced levels of physical fitness compared to normal weight participants. This was in agreement with the study conducted by Bandyopadhyay et al in which females with body mass index [greater than or equal to]25 kg/m2 had reduced VO 2 max.8

According to the researcher, decreased cardiorespiratory fitness was reported due to the fact that exceess deposition of fat had imposed a hindering effect in obese girls.8 Furthermore, a study conducted by Mondal et al, was also consistent with our study stating that an increase in BMI and body fat percentage has led to diminished levels of VO 2 max in young adults.17 The present study showed significant mean differences of VO 2 max between male and female participants. This was in agreement with the Perez- Gomez, Rodriguez et al. study who found that muscle consumes the greatest amount of oxygen during an endurance activity and since males have greater muscle mass compared to females, increased VO 2 max has been reported in them. According to a study by Nindl et al, the percentage of total fat in women is higher and the percentage of total lean tissue in men is greater. All these factors contribute to the inherent decreased muscle mass in females compared to males and thus the VO 2 max.18,19

Several limitations regarding this study were lack of measurement of clinical cardiorespiratory correlates such as heart rate, blood pressure, respiratory rate, etc and their association with VO2 max. More large scale studies are needed to elucidate the effect of aerobic endurance on VO2 max and create awareness about the importance of physical exercise among the young population.

In conclusion, results from this study indicate that body weight has a great impact on VO2 max of an individual. Thus, reduction in body weight can lead to marked improvement in aerobic endurance of overweight and obese students.

Acknowledgement

We sincerely thank all our students who participated voluntarily in this study. We also thank Shahwar and Ahmed Safiullah for their prompt and valuable contribution in this study.

Conflict of interest: None declared.

References

1. Lee CD, Blair SN. Cardiorespiratory fitness and stroke mortality in men. Med Sci Sports Exerc 2002; 34: 592-5.

2. Hamlin MJ, Draper N, Blackwell G, Shearman JP, Kimber NE. Determination of Maximal Oxygen Uptake Using the Bruce or a Novel Athlete-Led Protocol in a Mixed Population. J Hum Kineti 2012; 31: 97-104.

3. Poole DC, Wilkerson DP, Jones AM. Validity of criteria for establishing maximal O2 uptake during ramp exercise tests. Eur J Appl Physiol 2008; 102: 403-10.

4. Smirmaul BPC, Bertucci DR, Teixeira IP. Is the VO2 max that we measure really maximal? Frontiers in Physiol 2013; 4: 203.

5. Noakes TD, Peltonen JE, Rusko HK. Exercise performance during acute hypoxia and hyperoxia. The Journal of Experimental Biology 2001; 204: 3225-34.

6. Chatterjee S, Chatterjee P, Bandyopadhyay A. Cardiorespiratory fitness of obese boys. Indian J Physiol Pharmacol 2005; 49: 353-7.

7. Bandyopadhyay A, Chatterjee S. Body composition, morphological characteristics and their relationship with cardiorespiratory fitness. Ergonomis SA 2003; 1: 19-27.

8. Bandyopadhyay A. Cardiorespiratory fitness in obese girls. Ind J Physiol Pharmacol 2012; 56(4): 393-5.

9. Dabney U, Butler M. The predictive ability of the YMCA Test and Bruce Test for triathletes with different training backgrounds. Emporia State Res Stud 2006; 43(1): 38-44.

10. Cooper KH. A means of assessing maximal oxygen uptake. JPMA 1968; 203(3): 201-4.

11. Jafar TH, Chaturvedi N, Pappas G. Prevalence of overweight and obesity and their association with hypertension and diabetes mellitus in an Indo-Asian population. CMAJ; 175(9): 1071-7.

12. WHO Expert Consultation. Appropriate body-mass index for Asian populations and its implications for policy and intervention strategies. Lancet 2004; 363(9403): 157-63.

13. Mackenzie B. Bruce Treadmill Test, 2002. (Accessed on 4th October 2016) Available from URL: https://www.brianmac.co.uk/bruce.htm

14. Held C1, Iqbal R, Lear SA, Rosengren A, Islam S, Mathew J, et al.. Physical activity levels, ownership of goods promoting sedentary behavior and risk of myocardial infarction: results of the INTERHEART study. Eur Heart J 2012; 33(4): 452-66.

15. Dunstan DW, Thorp AA, Healy GN. Prolonged sitting: is it a distinct coronary heart disease risk factor? Curr Opin Cardiol 2011; 26(5): 412-9.

16. Lee DC, Artero EG, Sui X, Blair SN. Mortality trends in the general population: the importance of cardiorespiratory fitness. J Psychopharmacol 2010; 24: 27-35.

17. Mondal H, Mishra SP. Effect of BMI, Body Fat Percentage and Fat Free Mass on Maximal Oxygen Consumption in Healthy Young Adults. Journal of Clinical and Diagnostic Research: JCDR 2017; 11(6): 17-20.

18. Perez-Gomez J, Rodriguez GV, Ara I, Olmedillas H, Chavarren J, Gonzalez-Henriquez JJ, et al. Role of muscle mass on sprint performance: gender differences? Eur J Appl Physiol 2008; 102(6): 685-94.

19. Nindl BC, Scoville CR, Sheehan KM, Leone CD, Mello RP. Gender differences in regional body composition and somatotrophic influences of IGF-I and leptin. J Appl Physiol 2002; 92(4): 1611-8.
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Publication:Pakistan Journal of Medical Research
Article Type:Report
Geographic Code:9PAKI
Date:Mar 31, 2019
Words:2313
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