INTRODUCTION: Physical fitness and athletic performance can be assessed through parameters like volume oxygen maximum (VO2max), blood lactate levels, respiratory exchange ratio (RER), maximum heart rate (HR) and body fat %. Sedentary or physically active lifestyles can modify these parameters. The study determines and compares these fitness indicators in active bodybuilders and inactive non-bodybuilders. METHODS: A cross-sectional comparative pilot study was carried at the sport and exercise Physiology Lab at Post-Graduate Medical Institute Lahore, Pakistan. After Ethical board approval, twelve (12) healthy male subjects between age range of 20-30 years were recruited through stratified random sampling. Subjects with history of smoking or drug abuse were excluded. Participants were divided into two (2) equal groups; Group I (n=6): regularly active bodybuilders and Group II (n=6): inactive non-bodybuilders, as defined by ACSM’s guidelines for exercise. Exercise pre-participation health screening was done via the Physical Activity Readiness Questionnaire (PAR-Q+). Anthropometric measurements were recorded including age, weight, height and body fat percentage. Bruce protocol was used in which the participant underwent a graded exercise test till exhaustion on a treadmill. HR was recorded continuously using Bluetooth Polar belt. Cortex Metalyzer 3B-R3 was used for breath to breath gas analysis of various cardiorespiratory fitness parameters like VO2, VCO2, RER. Post exercise blood lactate levels were recorded from fingertip using Nova Biomedical Lactate Plus meter. Results were printed as 12-panel plots and quantitative values. SPSSv20 used for analysis. RESULTS: All 12 participants were in healthy weight BMI range. Values are expressed as mean±SD in active bodybuilders vs inactive non-bodybuilders: age 23.6±1.3 vs 24.2±2.3 years; Body fat % 16.2±1.4% vs 20.0±1.6%; VO2peak 40.2 ±2.8 vs 26.8±3.3 ml/kg/min (p<0.05); HRmax 185±3 vs 198±7 beats/min(p<0.05); Lactatemax 10.6±0.6 vs 12.9±0.9 mmol/L (p<0.05); RER: 1.02±0.04 vs 1.14±0.05 (p<0.05). CONCLUSION: A higher VO2peak in active bodybuilders means that physical activity/training improves oxygen uptake. Lower blood lactate and RER values mean that they have more active lipid oxidation metabolism and oxidize a greater proportion of lipids respectively than inactive participants. Comparable results have been found in studies of Milanovic Z et al-1 & Ramos-J et al. Active bodybuilders showed significant higher VO2peak, lower RER values and lower blood lactate concentrations than inactive non-bodybuilders. The data demonstrate that these parameters can be used to quantitatively assess physical fitness of sport athletes in Pakistan on a larger scale.