METHODS

Participants

Thirty apparently healthy, male, sedentary students from the same socioeconomic background, having mean age of 22.6 years, body height of 166.4 cm, and body mass of 53.80 kg, were recruited for the study on the basis of random sampling from the postgraduate section of the University of Calcutta, West Bengal, India. The experimental protocol was fully explained to participants. They had a 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 did not follow any physical conditioning programme, apart from some recreational sports.

Experimental design

Maximum oxygen consumption of each subject was determined by both indirect and direct methods, respectively, at an interval of 4 days. Subjects were asked to take complete rest for at least half an hour before the exercise, so that pulmonary ventilation and pulse rate could come down to a steady state.⁹

Prediction of maximum oxygen uptake capacity (PVO₂max) by QCT

The step test was performed on a stool of 16.25 inches (41.3 cm) height for a total duration of 3 minutes at the rate of 24 cycles per minute, which was set by a metronome. After completion of the exercise, the subject was asked to remain standing and the carotid pulse rate was measured from 5–20 seconds of the recovery period. This 15 second pulse rate was converted into beats per minute and the following equation was used to predict the maximum oxygen uptake capacity:⁸

Direct measurement of maximum oxygen uptake capacity (VO₂max)

Muller’s magnetic brake bicycle ergometer (model of Max Plank Institute of Work Physiology) was used for the study. All the subjects first performed a submaximal exercise at 73.55 watt (450 kg/min) intensity for duration of 5 minutes. Immediately after performing the submaximal exercise the intensity was increased to the first incremental intensity of 155.28 watt (950 kg/min), and thereafter the intensity was increased by 24.52 watt (150 kg/min) every 3 minutes until the subject stopped due to exhaustion. In the present study VO₂max was considered to be maximum peak heart rate of greater than 180 beats/min and levelling off—that is, 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 in response to the next higher intensity for repeated tests followed at an interval of 4 days.⁹ Subjects did not endure more than 8 minutes of continuously increasing intensity of exercise.

Low resistance high velocity Collin’s triple “J type” plastic valve was used for the collection of gas by open circuit method.⁹ The valve was connected with the Douglas Bag (150 l) by a standard corrugated rubber tube and the expired gas was collected in the last minute of final intensity of exercise. Gas was collected in the second minute of the final workload if the subject showed signs of severe exhaustion. No gas collection was made in the first minute of the workload. The expired gas was measured in a wet gasometer (Toshniwal, Cat No CG 05.10) and the aliquots of gas samples were analysed in a Scholander microgas analysis apparatus following the standard procedure.¹⁰

The peak heart rate was recorded manually from the time taken for 10 carotid pulsations immediately after cessation of exhaustive exercise.⁹

The whole experiment was performed at a room temperature varying from 27–29°C and at a relative humidity ranging between 75% and 83%.

Statistical analysis

Paired t test, Pearson’s product moment correlation, linear regression statistics, and Bland and Altman approach for limit of agreement were used for statistical treatment of the data.

RESULTS

Means and standard errors of physical characteristics, predicted VO₂max (PVO₂max), directly measured VO₂max, and peak heart rate parameters of the participants are presented in table 1.

The mean value of VO₂max is in agreement with previous studies²¹²reported from the same laboratory involving an identical population.

The mean difference between VO₂max and PVO₂max is 0.46 ml/min/kg body mass with 95% confidence interval −0.092 to 1.012 ml/min/kg body mass, indicating that QCT predicts the maximum oxygen uptake capacity by between −0.092 to 1.012 ml/min/kg body mass. Despite this, the limits of agreement (−2.50 and 3.42) are a small enough parameter for QCT to be used confidently in place of the complicated and exhaustive direct procedure for prediction of VO₂max.

DISCUSSION

Because the VO₂max and PVO₂max values (ml/min/kg body mass) obtained by direct and indirect procedures, respectively, show no significant variation between the means, and also using Bland and Altman’s method of limit of agreement approach (fig 1), we have shown that QCT can be applied to predict the maximum oxygen uptake in a young population from West Bengal. This method is especially useful in field work where the survey and screening of large numbers of participants are essential.

Highly significant correlation (r = −0.96, p<0.001) existed between the recovery heart rate in QCT and VO₂max. The following equation, derived on the basis of the present data will better predict the cardiorespiratory fitness in terms of VO₂max in this particular population.

Therefore, from the present observations, the Queen’s College step test is recommended as a valid method to evaluate cardiorespiratory fitness in terms of VO₂max for large numbers within the young population of West Bengal, India.