Most recreational athletes combined aerobics and strength training so that they can develop well-rounded fitness and not spend too much time in the gym. A Brazilian study showed that the order of training was important for optimizing strength performance. Performing either treadmill or stationary bike exercise prior to strength training decreased the quality of the strength training workout, with the stationary bike causing a greater decrease than the treadmill. Train for strength first and then practice aerobics. In other studies, Japanese researchers found that practicing aerobics after strength exercises was healthier for blood vessels.
Source: Journal Strength Conditioning Research, 29: 1077-1082, 2015