Mixed

Concurrent resistance and aerobic exercise (CE) stimulates both myofibrillar and mitochondrial protein synthesis rates in sedentary middle-aged men without causing molecular interference compared to isolated resistance or aerobic exercise.

If you are sedentary and middle-aged, you can combine resistance and aerobic exercise in the same workout session without worrying that the cardio will negate the muscle-building benefits of the weights. This study shows that doing both together stimulates muscle protein synthesis just as effectively as doing weights alone, and mitochondrial synthesis just as effectively as doing cardio alone. You do not need to split these activities into separate days to see acute benefits.