Cardiovascular factors explain genetic background differences in VO 2 max

The purpose of this study was to further explore factors that may be related to ethnic differences in the maximum rate at which an individual can consume oxygen (VO 2 max) between 20 African American (AA) and 30 European American (EA) sedentary women who were matched for body weight (kg) and fat‐free mass (FFM). VO 2 max (l/min) was determined during a graded treadmill exercise test. Submaximal steady‐state heart rate and submaximal VO 2 were determined at a treadmill speed of 1.3 m/sec and a 2.5% grade. Hemoglobin (Hb) was determined by the cyanide method, muscle oxidative capacity by 31 P magnetic resonance spectroscopy (ADP time constant), and FFM (kg) by dual‐energy x‐ray absorptiometry. Genetic classification was self‐reported, and in a subset of the sample (N = 32), the determinants of ethnicity were measured by African genetic admixture. AA women had significantly reduced VO 2 max, Hb levels, and muscle oxidative capacity (longer ADP time constants, P ≤ 0.05) than EA women. Submaximal oxygen pulse (O 2 Psubmax), ADP time constant, Hb, and ethnic background were all significantly related to VO 2 max (ml/kg/min and ml/kg FFM/min, all P ≤ 0.01). By multiple regression modeling, Hb, O 2 Psubmax, muscle oxidative capacity, and ethnicity were found to explain 61% and 57% of the variance of VO 2 max in ml/kg/min and ml/kg FFM/min, respectively. Muscle oxidative capacity and O 2 Psubmax were both significantly and independently related to VO 2 max in all three models ( P ≤ 0.05), whereas Hb and ethnicity were not. These results suggest that mitochondrial muscle oxidative capacity and oxygen delivery capabilities, as determined by O 2 Psubmax, account for most if not all of the ethnic differences in VO 2 max. Am. J. Hum. Biol. 18:454–460, 2006. © 2006 Wiley‐Liss, Inc.