Abstract
Background:
In India, obesity is rapidly growing health concern across all age groups. Obesity has significant effects on pulmonary function. The peak expiratory flow rate (PEFR) demonstrates the caliber of the airways and is widely recognized as an objective indicator of respiratory efficiency. This indicator is useful for the diagnosis and management of respiratory disorders.

Aim:
This study aimed to determine the relationship between BMI and immediate post-exercise changes in PEFR among medical undergraduate students.

Methods:
A cross-sectional study was conducted among 120 healthy undergraduate medical college students. Baseline anthropometric data, including height and weight, were collected for assessment of BMI. BMI was calculated using the Quetelet index. PEFR was measured using a Wright Peak Flow Meter. PEFR Measurements were taken before and after performing a 5-min moderate-intensity Harvard Step Test by participants.

Results:
The results showed that individuals with a normal BMI had the highest mean increase in PEFR (mean difference: 27.85 ± 7.97, p< 0.0001), followed by the overweight group (mean difference: 15.23 ± 12.04, p < 0.0001). The obese group exhibited the least improvement (mean difference: 5.49 ± 11.82, p < 0.0001). The P values in all three groups for PEFR before and after exercise were low (<0.0001) indicating a statistically significant difference in PEFR across BMI categories.

Conclusion:
This study assessed the impact of BMI on immediate post-exercise changes in PEFR among young medical students. A significant negative association was observed between BMI and PEFR. This relationship was present both before and after exercise. The study found that students with a normal BMI group demonstrated the most substantial improvement in PEFR after exercise, followed bythe overweight group. The obese group exhibited the least improvement in PEFR. These findings suggest that excess weight has a direct impact on PEFR. Further research is warranted to explore the underlying mechanisms.

Key words: Peak Expiratory Flow Rate ,Body Mass Index (BMI),Harvard step Exercise,obesity