Cardiorespiratory responses to moderate exercise and determination of aerobic power in first year medical students

INTRODUCTION

Physical exercise has gained prime importance in public life for its enormous health benefits. Cardio vascular and metabolic disease has become common in individuals leading a sedentary life. Practice of regular exercise not only prevents the occurrence of diseases in the community but also halts their progress and decreases their intensity, and sometimes also brings total cure from the disease.¹ Exercise stress tests are carried out as part of the investigations for determining the individual fitness level. Aerobic power or VO_2max or physical work capacity which involves a full functional support from cardio respiratory and metabolic pathways is an appropriate test to study cardio pulmonary fitness. The Bicycle ergometer and treadmill are the most commonly used dynamic exercise devices.¹ The advantage of the Bicycle ergometor are it is cheaper, takes up less space and makes less noise. Upper body motion is lessened that making blood pressure and E.C.G. recordings easier. By doing this study we can set a norm in assessing the physical fitness.

Aim

The aim of the study was to find out the normal cardiopulmonary responses to exercise and their aerobic power among untrained 1^st year medical students by Astrand 6 minute cycle test.

METHODS

The present study was designed to be an experimental study conducted in the department of physiology, Rajah Muthiah Medical College, Annamalai University, Annamalai Nagar, Chidambaram, Tamilnadu, India. Students volunteers from Rajah Muthiah Medical College belong to the age group of 17 to 18 years, who were not undergone any physical training were taken for the study. 11 males and 19 females’ students were selected after detailed history and physical examination. The students were asked to report at the department of physiology by 9.00 a.m. Subjects were explained the whole procedure in detail and were motivated prior to the start of exercise. They were told to report immediately if they felt any discomfort, fatigue or dizziness.

Inclusion criteria

Healthy students

Exclusion criteria

Alcoholics, smokers, students with any respiratory, cardiovascular disorders and lower limb surgery were excluded from the study.

Bicycle ergometer as instrument

Cardiorespiratory changes associated with exercise were studied using bicycle ergometer (Model-V_max 7380 magnetic recumbent bike) available in the physiology department of Rajah Muthiah Medical College, Annamalai University, Chidambaram, India. The instrument is equipped with a programmable computer to help to track the progress and motivate the subject to reach the fitness goal. The computer provides different programmes to match the subject’s fitness goals

Anthropometric measurements

Height was measured in centimeters while standing erect. Reading was taken nearest to 1cm by using inch tape. Weight was recorded in kilograms by using a locally made calibrated electronic weighing scale, accuracy±0.01kg and weighing machine was approximately calibrated from time to time. Subjects rested in supine position for 15 minutes before the start of exercise. The parameters namely pulse rate was examined by palpatory method, blood pressure, with a mercury sphygmomanometer and respiratory rate visually during rest. Cycle ergometer was arranged with correct handlebar and seat adjustments. The loading wattage 125 was selected for male and 100 for female. Subjects were asked to pedal at 60 rpm for 6 minutes. During cycling, pulse rate should be steady state between 130-160 beats per minute. If the subjects pulse rate is not in the target range after 2 minutes, then the loading wattage was adjusted accordingly by 25 watts for the remainder of the test. At the end of 6 minutes, pulse rate and loading wattage were noted down from monitor. After 6 minutes of exercise, the subjects were asked to lie down. Cardiorespiratory parameters like pulse rate, respiratory rate, blood pressure were immediately recorded. Subjects were allowed to take rest for 15 minutes. Cardio respiratory parameters were recorded 15 minutes after exercises. Aerobic power was determined from the heart rate noted at the end of 6 minutes cycling by using Astrand –Rhyming nomogram.

RESULTS

Statistical analysis was done by using ANOVA repeated measures and Boneferoni multiple comparison test. Table 1, shows the comparison of cardiorespiratory parameters. It showed a statistically significance with p value less than 0.001. Table 2 shows the mean aerobic power or VO_2max (L/min) of male & female students.

DISCUSSION

There was statistically significant increase in heart rate immediately after the exercise over the pre exercise value (p<0.001). Also there was persistent tachycardia 15 minutes after exercises. Tachycardia in exercise occurs due to following mechanisms: Increased sympathetic discharge, muscle heart reflex, increased release of catecholamines and thermogenic stimulation.^2-4 There was statistically significant increase in systolic blood pressure immediately after the exercise over the pre exercise value (p<0.001).

Chapman CB et al conducted a study regarding stroke volume and cardiac output have shown that the stroke volume continue to increase at higher levels of exercise.⁵ Other investigators found that the stroke volume after increasing promptly with low level of exertion reaches a plateau and does not increase progressively as exertion becomes more intense for untrained subjects.^6,7 Other researchers found that plateau in stroke volume may not occur for trained subjects.^8-10 The result discussed earlier regarding blood pressure states that the systolic blood pressure always increases in exercise proportionate to increase in cardiac output.¹¹ This occurs due to sympathetic induced cardio-accleration.

There was statistically significant decrease in diastolic blood pressure immediately after exercise over the pre exercise value (p<0.001). The diastolic blood pressure decreases with moderate exercise, which could be due to sympathetic cholinergic vasodilatation of skeletal blood vessels, metabolic vasodilatation and thermogenic vasodilatation leads to decreased peripheral resistance.¹¹

There was statistically significant increases in respiratory rate immediately after the exercise over the pre-exercise value (p<0.001). The respiratory rate increases with exercise, which could be due to neural mechanism, chemical mechanism and thermogenic mechanism.^12-16 VO_2max can be a limiting factor for individual capacity to do prolonged muscular work.¹⁷So the determination of aerobic power or VO₂ max gives an idea of the capacity and regulation of O₂ transporting system.

Jackson AS et al suggests that VO_2max or aerobic power increases during childhood and reaches a peak during early adulthood, after that a gradual and steady decline take place with the increasing age.^18,19

VO_2max varies greatly between individual, genetics play a major role.^20,21 Training in aerobic exercise may improve VO_2max. Resistance training alone does not increases VO_2max.^22,23

CONCLUSION

Aerobic power or VO_2max or physical work capacity which involves a full functional support from cardiorespiratory and metabolic pathways is an appropriate test to study cardiopulmonary fitness. Implication: Astrand 6 minutes cycle test can be used for screening measures before joining in a job or sports training where physical fitness is needed.

ACKNOWLEDGEMENTS

Authors would like to thank the Dean, Faculty of Medicine, RMMCH for allowing them to conduct the study, helping them in getting ethical committee approval. Authors would also like to thank their professors and faculty for their opinions and guiding them in the study. The study could not be completed without the wholehearted support from the students; hence authors are overwhelmed and thankful to them.

Funding: No funding sources

Conflict of interest: None declared

Ethical approval: The study was approved by the Institutional Ethics Committee

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