Peak expiratory flow rate (PEFR) is the maximum rate of airflow achieved during a forced expiration after maximal inspiration. PEFR of healthy medical students were accessed. Body mass index (BMI), which is an important parameter to assess whether subjects are obese were significantly and positively correlated with PEFR. Physical activity reduces weight and improves fat distribution in the body. Therefore, it can be predicted that physical activity improves PEFR. The more the height and weight there will be more oxygen demand for the tissues. The increased oxygen demand should be met by more ventilation thus, increasing respiratory function and hence PFER.