Exercise intensity and oxygen uptake kinetics in African-American and Caucasian women

The effect of exercise intensity on the on- and off-transient kinetics of oxygen uptake (VO2) was investigated in African American (AA) and Caucasian (C) women. African American (n = 7) and Caucasian (n = 6) women of similar age, body mass index and weight, performed an incremental test and bouts of square-wave exercise at moderate, heavy and very heavy intensities on a cycle ergometer. Gas exchange threshold (LTGE) was lower in AA (13.6 ± 2.3 mL kg−1 min−1) than C (18.6 ± 5.6 mL kg−1 min−1). The dynamic exercise and recovery VO2 responses were characterized by mathematical models. There were no significant differences in (1) peak oxygen uptake (VO2peak) between AA (28.5 ± 5 mL kg−1 min−1) and C (31.1 ± 6.6 mL kg−1 min−1) and (2) VO2 kinetics at any exercise intensity. At moderate exercise, the on- and off- VO2 kinetics was described by a monoexponential function with similar time constants τ1,on (39.4 ± 12.5; 38.8 ± 15 s) and τ1,off (52.7 ± 10.1; 40.7 ± 4.4 s) for AA and C, respectively. At heavy and very heavy exercise, the VO2 kinetics was described by a double-exponential function. The parameter values for heavy and very heavy exercise in the AA group were, respectively: τ1,on (47.0 ± 10.8; 44.3 ± 10 s), τ2,on (289 ± 63; 219 ± 90 s), τ1,off (45.9 ± 6.2; 50.7 ± 10 s), τ2,off (259 ± 120; 243 ± 93 s) while in the C group were, respectively: τ1,on (41 ± 12; 43.2 ± 15 s); τ2, on (277 ± 81; 215 ± 36 s), τ1,off (40.2 ± 3.4; 42.3 ± 7.2 s), τ2,off (215 ± 133; 228 ± 64 s). The on- and off-transients were symmetrical with respect to model order and dependent on exercise intensity regardless of race. Despite similar VO2 kinetics, LTGE and gain of the VO2 on-kinetics at moderate intensity were lower in AA than C. However, generalization to the African American and Caucasian populations is constrained by the small subject numbers.