Background: Cardiorespiratory fitness is a distinct health characteristic that relates to the ability to perform physical activity. Higher cardiorespiratory fitness was reported to have reverse relationship with overall mortality and morbidity rates due to various chronic disease. The assessment of cardiorespiratory fitness was measured by maximal oxygen uptake (VO2max; mL/kg/minute) on a submaximal treadmill test. This study was aimed to examine cardiorespiratory fitness among U.S. adults 20-49 years of age, to describe the distribution of cardiorespiratory fitness and cardiovascular risk factors depends on different ethnicity for without physical limitations or indications of cardiovascular disease.
Method: Data from the 1999-2004, National Health and Nutrition Examination Survey were used to describe the distribution of cardiorespiratory fitness for adults 20-49 years of age. 8324 out of 31126 subjects have valid values of cardiopulmonary fitness in the dataset with 5391 in low category of cardiorespiratory fitness (VO2max < 27), 2606 in medium category (37.1 > VO2max ≥27) and 327 in high category (37.1 ≥ VO2max). The risk factors for cardiopulmonary fitness was assessed by using logistic regression after adjusting all cardiovascular risk factors. All data were analyzed using SAS Ver. 9.4.
Result: Overall, there is no significant association of cardiorespiratory fitness with ethnicity (P=0.08). 65.9% of study population was male in all races. Among, non-Hispanic whites, those with 25 m2/kg > BMI had better cardiorespiratory fitness (more than 37.1 mL/kg/minute) than those with BMI ≥ 35 [Odds ratio (OR): 0.496, Confidence Interval (CI): 0.258-0.957]. A similar pattern was observed for Mexican Americans. Non-Hispanic black with 25 m2/kg > BMI had better cardiorespiratory fitness than ones with BMI ≥ 35 m2/kg [OR:0.137, CI:0.059-0.318], 35 m2/kg > BMI≥30 m2/kg [OR:0.269, CI:0.124-0.583], 30 m2/kg > BMI≥25 m2/kg [OR: 0.241,0.123-0.318]. Non-Hispanic white with higher diastolic blood pressure over 90 mmHg had tendency to have lower cardiorespiratory fitness. Among metabolic panel, only Mexican American with LDL<100 mg/dl has higher cardiorespiratory fitness [OR:0.559, CI:0.319-0.981].
Discussion: Our findings on cardiorespiratory fitness level among non-Hispanic blacks, non-Hispanic whites and Mexican Americans are similar to previously reported studies, however, non-Hispanic black had different risk factors related to cardiorespiratory fitness, especially significant benefit from lower BMI less than 25 m2/kg since other ethnicities with BMI less than 25 m2/kg had benefit only compared to BMI> 35 m2/kg. These results can be used to improve cardiorespiratory fitness level for future population based on ethnicities. The different risk factors in fitness status can also be used to develop health policies and targeted educational campaigns.