International Journal of Sports Sciences and Fitness, Volume 5(1) 2015
A STEP TEST FOR ESTIMATING MAXIMAL OXYGEN CONSUMPTION (VO2max) IN MALE SECONDARY SCHOOL STUDENTS *Ibrahim Aminu, A. and **Nuhu Jibril, M. 1. Physiotherapy Department, Muhammad Abdullahi Wase Specialist Hospital, Kano, Kano State, NIGERIA. 2. Department of Physiotherapy, Faculty of Medicine, Bayero University, Kano, Kano State, NIGERIA. Email:
[email protected]
(Received November, 30, 2014, accepted December 12, 2014)
ABSTRACT
The objective of this study was to develop a regression equation to predict maximal oxygen consumption (VO2max) in apparently healthy male secondary school students using a step test. The 20 meter shuttle run test (MST) and the step test were administered on fifty eight 14 to 20 years old male secondary school untrained volunteers. Data (predictor variables) collected include age, gender, body mass index (BMI) and step test post-exercise heart rate (HRpe) were used to develop a regression equation to predict VO2max. VO2maxvalues generated from the 20MST were correlated with those obtained using the regression equation from the step test. A probability level of 0.05 or less was considered statistically significant. Multiple linear regressions generated the following prediction equation: VO2max (ml.kg-1.min -1) = 62.887 (0.439 × age) + (0.152 × BMI) – (0.116 × HRpe) and correlation between the 20MST and step testVO2max values were r = 0.52(p < 0.05; SEE = 3.67 ml.kg-1.min-1) which indicates a significant relationship. Also, cross-validation reveal minimal shrinkage of r = 1% (SEE = 3.55 ml.kg-1.min-1). Based on these findings, it was concluded that the step test developed was a valid and reliable predictor of maximal oxygen consumption in the sample studied. It was recommended that a study with a larger sample size be conducted among healthy untrained male secondary school students to corroborate the results of this study.
Key words: Maximal oxygen consumption, Step test, Healthy, Maximal, Sample.
INTRODUCTION
Maximal oxygen consumption or VO2max is the gold standard index of cardiorespiratory fitness (CRF) and has been defined as the highest rate of oxygen consumption attainable
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during maximal or exhaustive exercise (Wilmore and Costill, 2005). It is the best measure of CRF with high levels attributed to health benefits such as a lower risk of all-cause mortality (Kodama et al. 2009; Lee et al. 2011) and a high physical work capacity (Astrand 1956; Balke and Ware 1959). The assessment of VO2max is, therefore, of significance for the exercise specialist among both trained and untrained
individuals to determine
cardiorespiratory fitness levels which can also serve as guide for exercise prescription in different age groups in health and in disease. The direct testing or measurement requires a well-equipped laboratory, specialized and sophisticated technical equipment because of its exhausting and complicated experimental protocol. Consequently, this method is time consuming, expensive and not suitable for measuring large groups of untrained subjects (Astrand and Rhyming, 1954). Therefore a number of testing methods, using a variety of exercise modes, have been devised to predict VO2max indirectly from maximal or sub maximal tests which can be conducted in non-laboratory environments, offering the attractiveness of simplicity, low cost, safety and validity.
Step exercises have been used as a tool for conditioning the cardiorespiratory system and for estimating VO2max. The benefits of step exercise are that it is easy to administer, can be prescribed for all age groups, requires minimal equipment and space, stressing joints less than with such modes as running and jogging. A number of stepping protocols for estimating VO2max are available such as the Harvard step test (Keenen, 1958; Reedy, Sarger and Hoster, 1958), the Queens College step test (Mc Ardle et al, 1972), the Chester step test (Buckley, et al, 2004; Sykes and Robert, 2004) and so forth, which were developed mainly on Caucasians and may not be suitable for use in our environment due to environmental and lifestyle differences. Therefore we developed a sub maximal, non-progressive step test using some predictive variables and generated a regression model for estimating VO2max in male untrained black Africans of secondary school age.
METHODOLOGY
This study is a descriptive study with co-relational design in which maximal oxygen consumption estimated from a step test was correlated with maximal oxygen consumption estimated from 20 MST. Fifty eight apparently healthy, untrained male senior secondary 43
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students of the Federal Government College in Kano participated in the study. Subjects were included if they were living in the boarding house of the school, within the age range of 14 to 20 years and answered “No” to all the questions in the Physical Activity Readiness Questionnaire. Subjects suffering from any musculoskeletal disorder and those with a history of cardiovascular disease or other serious health concerns were not included.
Each exercise test session was preceded by a warm up and followed by a cool down. The procedure for the collection of data was carried out on a measured track in the Federal Government College, Kano. All participants read and signed the informed consent as well as the Physical Activity Readiness Questionnaire (PAR-Q). Prior to the administration of the Step and PACER tests, subjects' ages were recorded; their heights and weights were measured.
An interval of one-week (rest period) between any two test sessions was allowed to ensure there was no carryover in the subjects' fatigue from one test to the next. A pilot test was conducted on twenty students using 3 different bench heights (35cm, 40cm and 45cm) to determine the height that would elicit heart rate and hence the equation with the best correlation with the 20 MST. The same procedure (described below) was carried out for each bench at an interval of one week. The post-exercise HR from the 40cm bench resulted in equation with the best correlation with the 20 MST, i.e. VO2max = 64.126 - 0.242 × (Age) 0.525 × (BMI) + 0.29 × (HRpe), coefficient of correlation being r = 0.56(p< 0.05; SEE = 1.78 ml.kg-1.min-1).
The PACER Test The 20 MST was administered in the 58 subjects. The protocol for this test was identical to that described by Leger and Lambert (1982). The test was conducted on a flat surface measured track within the field in the college. Subjects ran in groups of ten to add an element of competition. Lining up behind the starting line, a partner was assigned to each of them to count the number of laps completed (a lap consists of a 20-meter distance). Subjects were verbally encouraged to perform maximally during each assessment. The tape gave a 5 second count down (5, 4, 3, 2, 1,) and instructs the participants to “Begin”. At the command “Start”,
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participants ran forth and back in a straight line between the restraining lines in accordance with the pace dictated by the audio signal emitted at set intervals from the PACER tape. Subjects continued to run in this manner until they were unable to maintain the rhythm of running. Any subject that was unable to catch up with the sound of the beep for two consecutive times was required to stop. The speed at the last completed running stage is termed the “Maximal Aerobic Speed” (MAS). The same procedure was then use for the second group of 5 participants. The result for each subject was expressed as a predicted VO2max (ml/kg/min) by cross referencing the final level and shuttle number (completed) at which the subject volitionally became exhausted. The speed obtained at an appropriate level, was used in the regression equation developed by Leger, Mercier, Gadoury and Lambert (1988) to compute VO2max in ml/kg/min.
The Step Test This comprised of the step test and its re-test. Subjects began by standing 20cm from the bench with steps being dictated by the sounds emitted by the metronome. The metronome was set to give a stepping rate of 35 steps cycle per minute. The right foot was placed with the first signal and the left foot with the second on the 40cm bench. The right foot was brought to the floor with the third sound while the left foot was placed on the floor with the fourth signal. Subjects carried on in this manner and the test was terminated after 3 minutes. Post exercise Heart Rate (HRpe) was noted and recorded within the 30 seconds after the test using a heart rate monitor (Polar Electro OY, Kempele, Finland). A regression equation was developed (VO2max (ml.kg-1.min-1) = 62.887 - (0.439 × age) + (0.152 × BMI) – (0.116 × HRpe) to compute VO2max. The result obtained was used to correlate with that obtained from the 20 MST (test of validity). The results of test and re-test were correlated to test the reliability of the step test. Cross-validation was also performed to by splitting the sample (N=58 subjects) into two groups A and B via random selection procedures (29 subjects in each group) with prediction (regression) equation being created in each group. Equation developed from group A was used to create predicted scores for members of the second group (i.e. group B) and vice versa. The predicted scores were correlated with the observed scores on the dependent variable (ryy') to determine the cross-validity coefficient and shrinkage was determined to determine the generalization capacity of the equation. Both
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samples were then combined so that a final prediction equation based on the larger sample was created.
The data were analyzed using descriptive (means and standard deviation) and inferential statistics (correlation and regression). Data from the step test were analyzed using multiple linear regressions to develop a regression model. Results obtained using the regression equations were correlated with those obtained from the PACER test prediction equation using the Pearson Product Moment Coefficient of Correlation. All statistical analyses were performed on an IBM compatible microcomputer using the Statistical Package for the Social Sciences (SPSS) (Windows version 21.0 Chicago IL, USA).
RESULTS AND DISCUSSION
Fifty eight secondary school boys aged 14 to 20 years participated in the study. All participants achieved a valid VO2max during the 20 MST (mean ± SD: 45.94 ±4.18 ml. kg-1 min-1). Participant’s height, weight and body mass index (BMI) ranged from 1.44-1.78m, 3264kg and 13.1-22.3 kgm-2 respectively (Table 1). There was statistically significant correlation between VO2max values obtained from 20MST and those obtained from the step test (p < 0.05; SEE = 3.67 ml.kg-1.min-1) (Table 2) suggesting that the step test was a valid predictor of VO2max. Table 1 Physical characteristics of the participant Variables
Mean
± SD
Age (years)
15.81
± 1.21
Weight(kg)
47.02
± 8.14
Height(m)
1.624
±0.09
BMI (kg/m2)
17.85
±2.14
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Table 2 Correlation between 20MST and step testVO2maxvalues
Variables (Tests)
VO2max ( ml.kg-1.min-1)
Mean
±SD
df
r
p
________________________________________________
20 MST
45.94
±4.18 56
Step Test
45.89
0.520
0.001*
±2.18
Data are presented as means± standard deviation (SD). P values are from the results of Pearson correlation tests for defining the relationship between VO2max values obtained from 20MST and those obtained from the step test. * indicates statistical significance.
Maximal oxygen consumption obtained from the step test (values for test versus re-test) was correlated. A high and significant correlation was found (r = 0.822, p < 0.05; SEE = 3.82 ml.kg-1.min-1) which indicates that the step test was reliable in predicting VO2max (Table 3). Cross validation was also performed and shrinkage was determined and found to be very minimal (r = 1%; SEE = 3.55 ml.kg-1.min-1) suggesting good generalization capacity of the equation.
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International Journal of Sports Sciences and Fitness, Volume 5(1) 2015
Table 3 Correlation between test and re-test VO2max values of the step test Variables (Tests)
VO2max ( ml.kg-1.min-1)
Mean
±SD
df
r
p
________________________________________________________
Test
45.94
±4.18 56
Re-test
45.96
0.822
0.006*
±1.89
Data are presented as means± standard deviation (SD). P values are from the results of Pearson correlation tests for the relationship between VO2max values obtained from test and those obtained from the re-test of the step test. * indicates statistical significance.
This study developed a step test with a regression model for estimating maximal oxygen consumption (VO2max) in male secondary school students. Multiple linear regressions generated a prediction equation that produced VO2max values with significant correlation between the 20MST and the step test as well as high test-retest reliability. The 20MST has been established as a good predictor of VO2max (Ramsbottom, Brewer and Williams, 1988; Paliczka, Nicholas and Boreham, 1987). Therefore, we used it for correlation in lieu of a direct protocol. Researchers have shown the 20MST to be good tool for correlation with other tests. For example, the work of Naughton, Cooley, Kearney and Smith (1996) sought to determine whether there was a significant difference between the 20MST used to estimate VO2max, and a European version (ET) of the test. The 20MST was used to compare and to
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determine how valid the European version was. A relationship between the two sets of shuttle run data indicated that there was a significant correlation between the 20MST and the ET, (r= 0.834, p < 0.0001).
The work of Sharkey (1979) is in line with present study, the author developed a step test using a 40cm bench to estimate the maximal aerobic power of United States Forestry workers. The participants’ age, BMI and post-exercise heart rate were used to calculate the maximal aerobic power using a published table and the test was found to provide a good estimate of maximal oxygen consumption. Also consistent with our finding is that of McArdle (1972) who developed the Queen’s college step test to assess the maximal oxygen consumption of male and female athletes using heart rate recovery after stepping a 41.3cm bench at the rate of 22 steps per minute for females and 24 steps per minute for males. The test re-test reliability for recovery heart rate was measured as r = 0.92 and the author concluded that the test could provide a measure of cardiorespiratory or endurance fitness. A study conducted by Francis and Brasher (1992) is also in agreement with the present study. The authors validated a model of VO2max estimated from the recovery heart rate of 15 seconds in thirty-three men aged 18 to 47 following a single-stage height adjusted step at stepping frequencies of 22, 26 and 30 ascents/minute. The result revealed a high and significant correlation of r = 0.77 at 22 and r = 0.81 at 26 and 30 ascents/minute. They concluded that the single-stage height adjusted step test provides an effective predictor of VO2max in the sample studied.
The high and significant test-retest correlation we found corroborates the finding in a study by Buckley, Sim, Eston, Hession and Fox (2004) to evaluate the reliability of measures taken during the Chester step test which revealed a correlation of 0.84.. The authors concluded Chester step test retest is reliable and recommended for cardiorespiratory fitness evaluation.
CONCLUSION
Based on the results of this study, it was concluded that the step test developed was a valid predictor of maximal oxygen consumption in boys of secondary school age. The new test also 49
International Journal of Sports Sciences and Fitness, Volume 5(1) 2015
had high test-retest correlation (reliability). However, the results must be interpreted with caution as more reliable or accurate results are likely to be obtained when criterion measure for the parameter (VO2max) is correlated with the results of this new test. Future researchers should endeavour to replicate this study using larger samples to corroborate the results of present study.
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