Physical inactivity is an important modifiable risk factor for noncommunicable diseases and premature mortality. Regular physical activity is associated with substantial health benefits, including improved cardiovascular and metabolic health, physical fitness, musculoskeletal function, and psychological well-being [1,2]. Current World Health Organization recommendations advise adults to undertake at least 150–300 minutes of moderate-intensity aerobic physical activity or 75–150 minutes of vigorous-intensity aerobic activity per week, or an equivalent combination, together with muscle-strengthening activities [1]. The physiological adaptations associated with habitual exercise involve several organ systems. Regular aerobic activity increases skeletal muscle oxidative capacity, improves peripheral oxygen extraction, enhances cardiovascular efficiency, and increases functional exercise capacity [3]. Cardiorespiratory fitness represents the integrated ability of the respiratory and cardiovascular systems to deliver oxygen to working muscles and the capacity of those muscles to utilize oxygen during sustained physical activity. Higher cardiorespiratory fitness is associated with better long-term health outcomes [4]. The respiratory system has considerable reserve in healthy individuals, and the lungs are generally not considered the primary factor limiting maximal exercise in most healthy young adults. Nevertheless, regular physical training can influence ventilatory responses, respiratory muscle function, breathing pattern, and efficiency during exercise [5,6]. Consequently, the relationship between habitual physical activity and resting spirometric indices remains of physiological interest. Spirometry is a widely used, non-invasive method of evaluating pulmonary function. Forced vital capacity (FVC) represents the maximum volume of air that can be forcibly expired after maximal inspiration, whereas forced expiratory volume in the first second (FEV₁) represents the volume expired during the first second of the FVC manoeuvre. The FEV₁/FVC ratio is particularly useful in identifying airflow obstruction. Peak expiratory flow (PEF) reflects maximal expiratory flow and is influenced by airway calibre, lung volume, effort, and expiratory muscle function [7,8]. Studies comparing athletes or physically active individuals with less-active controls have reported differences in selected pulmonary function variables, although results vary according to the type and intensity of training, participant characteristics, body composition, and sport [9,10]. Exercise training may also improve respiratory muscle strength and endurance, although the magnitude and clinical relevance of such adaptations in healthy individuals vary [6]. Exercise capacity can be assessed using laboratory cardiopulmonary exercise testing or simpler field tests. The six-minute walk test (6MWT) measures the distance an individual can walk over six minutes and provides a practical assessment of functional exercise capacity [11]. Although extensively used in clinical populations, it can also provide useful comparative physiological information when standardized appropriately. Young adulthood provides an important period for studying the relationship between lifestyle and physiological function because overt cardiopulmonary disease is relatively uncommon, while physical-activity patterns may differ substantially. Examining healthy young adults may therefore help characterize associations between habitual activity, lung function, and exercise performance with less confounding from chronic disease. The present study was designed to compare spirometric pulmonary function and functional exercise capacity between regularly physically active and sedentary young adults and to investigate the relationship between pulmonary function parameters and exercise performance

A cross-sectional comparative study was designed in the Department of Physiology at a tertiary-care teaching institution. The study population comprised apparently healthy young adults aged 18–30 years. Sample Size For this model manuscript, 120 participants were considered, with 60 participants in each group. For an actual study, the required sample size should be calculated prospectively using the anticipated difference in a prespecified primary outcome, such as FVC or six-minute walk distance, together with the expected standard deviation, desired statistical power, and significance level. Study Groups Participants were classified into two groups: Group A – Regularly physically active: Participants meeting a predefined criterion consistent with recommended moderate-to-vigorous physical activity levels. Group B – Sedentary/insufficiently active: Participants not meeting the predefined physical-activity threshold and reporting predominantly sedentary behaviour. Physical activity should preferably be quantified using a validated questionnaire or objective activity-monitoring method rather than classification based solely on participant impression. Inclusion Criteria Apparently healthy men and women aged 18–30 years who provided informed consent were eligible. Participants were required to be free of known acute cardiopulmonary illness at the time of testing. Exclusion Criteria Participants with known asthma, chronic respiratory disease, significant cardiovascular disease, major musculoskeletal or neurological conditions limiting exercise, acute respiratory infection, or contraindications to exercise testing were excluded. Current smokers should preferably be excluded or analysed separately because smoking may independently influence pulmonary function. Anthropometric Assessment Age and sex were documented. Height was measured without footwear using a stadiometer and recorded in centimetres. Body weight was measured using a calibrated weighing scale. Body mass index was calculated as: BMI = weight (kg) / height² (m²). Pulmonary Function Testing Spirometry was performed using a calibrated computerized spirometer following accepted technical standards [7,8]. Participants were instructed regarding the procedure and allowed adequate familiarization. Testing was performed in a seated position with appropriate infection-control precautions. Participants performed maximal inspiration followed by rapid, forceful, and sustained expiration. Repeated manoeuvres were obtained until acceptable and repeatable measurements were achieved. The following variables were recorded: • FVC (L) • FEV₁ (L) • FEV₁/FVC (%) • PEF (L/s) Where appropriate, spirometry results should also be expressed as percentage predicted or z-scores using suitable reference equations. Six-Minute Walk Test Functional exercise capacity was evaluated using the 6MWT following standardized procedures [11]. Participants were instructed to walk as far as possible during six minutes along a marked walking course while standardized instructions and encouragement were provided. Six-minute walk distance (6MWD) was recorded in metres. Heart rate and peripheral oxygen saturation (SpO₂) were documented before and immediately after the test. Symptoms such as breathlessness and fatigue could additionally be assessed using a standardized Borg scale. Statistical Analysis Data were analysed using suitable statistical software. Continuous variables were expressed as mean ± standard deviation for approximately normally distributed data and median with interquartile range for skewed data. Categorical variables were expressed as frequency and percentage. An independent-samples Student's t-test or Mann–Whitney U test was used for between-group comparisons as appropriate. Categorical variables were compared using the chi-square test. Pearson's or Spearman's correlation was used to evaluate relationships between pulmonary function and exercise capacity. Because pulmonary function is strongly influenced by age, sex, height, and body size, multivariable regression should preferably be performed to evaluate whether physical-activity status remains associated with pulmonary function after adjustment for these variables. A two-tailed p-value <0.05 was considered statistically significant.

Table 1. Baseline characteristics of participants Parameter Physically active (n=60) Sedentary (n=60) p-value Age (years) 23.1 ± 2.8 23.4 ± 2.9 0.57 Male/Female 32/28 31/29 0.85 Height (cm) 168.7 ± 8.2 167.9 ± 8.5 0.60 Weight (kg) 64.2 ± 9.1 66.7 ± 9.8 0.15 BMI (kg/m²) 22.5 ± 2.4 23.6 ± 2.7 0.02 Resting HR (beats/min) 69.8 ± 6.9 76.1 ± 7.5 <0.001 Resting SpO₂ (%) 98.2 ± 0.8 98.0 ± 0.9 0.20 The two groups were comparable regarding age, sex distribution, and height. The physically active group had a lower mean BMI and resting heart rate. Table 2. Comparison of pulmonary function parameters Parameter Physically active (n=60) Sedentary (n=60) p-value FVC (L) 4.08 ± 0.64 3.72 ± 0.61 0.002 FEV₁ (L) 3.42 ± 0.55 3.10 ± 0.53 0.002 FEV₁/FVC (%) 83.9 ± 4.6 83.4 ± 4.9 0.57 PEF (L/s) 7.62 ± 1.31 6.91 ± 1.28 0.003 In this illustrative analysis, FVC, FEV₁, and PEF were significantly higher among physically active participants. The FEV₁/FVC ratio did not differ significantly between groups. This pattern suggests differences in lung volumes and expiratory performance without evidence from the ratio alone of a meaningful between-group difference in airflow obstruction. Table 3. Comparison of functional exercise parameters Parameter Physically active (n=60) Sedentary (n=60) p-value 6MWD (m) 624.5 ± 54.8 548.7 ± 61.2 <0.001 Pre-test HR (beats/min) 70.2 ± 7.1 76.4 ± 7.4 <0.001 Post-test HR (beats/min) 112.6 ± 12.4 124.8 ± 13.7 <0.001 HR after 1-min recovery 87.4 ± 9.8 101.6 ± 11.2 <0.001 Post-test SpO₂ (%) 97.8 ± 1.0 97.5 ± 1.1 0.12 Physically active participants walked approximately 76 m farther during the 6MWT. They also demonstrated lower post-exercise and one-minute recovery heart rates. Post-exercise oxygen saturation was similar between groups. Table 4. Correlation between pulmonary function and six-minute walk distance Parameter Correlation with 6MWD (r) p-value FVC 0.41 <0.001 FEV₁ 0.38 <0.001 FEV₁/FVC 0.08 0.39 PEF 0.29 0.001 BMI −0.22 0.016 Six-minute walk distance showed moderate positive correlations with FVC and FEV₁ and a weaker positive correlation with PEF. These unadjusted correlations should not be interpreted as evidence that pulmonary function independently determines exercise performance because body size, sex, and physical conditioning may influence both variables.

The present study was designed to compare pulmonary function and functional exercise capacity between regularly physically active and sedentary young adults. In the illustrative results, physically active participants demonstrated higher FVC, FEV₁, PEF, and six-minute walk distance together with lower resting and post-exercise heart rates. These findings are compatible with the broader physiological benefits associated with habitual physical activity. Regular physical activity produces important cardiovascular and peripheral adaptations. Exercise training increases stroke volume and improves oxygen transport and utilization, while peripheral adaptations include increased mitochondrial density, oxidative enzyme activity, capillarization, and skeletal-muscle efficiency [3]. These mechanisms can contribute to greater exercise capacity and reduced cardiovascular demand at a given submaximal workload. The lower resting heart rate observed among physically active participants is consistent with adaptations commonly associated with regular aerobic training. Exercise training alters intrinsic cardiac and autonomic regulation, although the magnitude of resting bradycardia and its underlying mechanisms vary according to training status and individual characteristics [12]. Pulmonary function results require more cautious interpretation. The respiratory system in healthy individuals possesses substantial functional reserve, and conventional endurance training does not necessarily produce large improvements in static lung function. Nevertheless, some studies comparing athletes and non-athletes have demonstrated higher lung volumes or flow parameters among trained populations [9,10]. Such differences may reflect respiratory muscle conditioning, body dimensions, selection effects, specific sports, or long-term adaptations rather than a simple causal effect of exercise. The significantly greater 6MWD among physically active individuals in the illustrative dataset provides a clearer indicator of functional conditioning. The 6MWT reflects integrated responses from the pulmonary, cardiovascular, neuromuscular, and metabolic systems [11]. Consequently, higher walking distance among physically active participants is physiologically plausible and consistent with improved functional exercise capacity. Positive correlations were observed between 6MWD and FVC, FEV₁, and PEF. However, these associations should be interpreted cautiously. Both lung volumes and walking performance are influenced by factors such as sex, height, body composition, motivation, habitual activity, and muscular fitness. Adjusted regression analysis would therefore provide stronger evidence than simple correlations. Physical activity also has substantial benefits beyond respiratory performance. Large bodies of evidence demonstrate associations between higher levels of physical activity and lower risks of cardiovascular disease, diabetes, several cancers, and premature mortality [1,2,13]. The findings of the present study therefore reinforce the importance of promoting regular activity during young adulthood, although the observed spirometric differences should not be interpreted as the principal mechanism underlying these broader health benefits.

Regularly physically active young adults may demonstrate greater functional exercise capacity and favorable differences in selected pulmonary function parameters compared with insufficiently active individuals. In the illustrative dataset, physically active participants had higher FVC, FEV₁, PEF, and six-minute walk distance, along with lower resting and post-exercise heart rates. The findings support an association between habitual physical activity and better cardiorespiratory functional performance. However, because the proposed study is cross-sectional, causal conclusions regarding physical activity and pulmonary function cannot be made. Prospective and exercise-intervention studies using objective activity measurements and comprehensive cardiopulmonary testing are warranted.

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