Postmenopausal African American and Caucasian women performed aerobic exercise 3 or 4 times per week for 6 months. While both groups had similar positive results, the African American women experienced a greater reduction in resting metabolic rate.
The sample size was particularly small. Only 47 women participated and with control groups that puts each group at 11 or 12 each….small enough that one or two individuals might have skewed the results.