Concurrent training combines aerobic and anaerobic fitness, when combined properly, maximizes overall health.
Resistance training increases high producing muscle fibers, while endurance causes a decrease in size. Too much aerobic training can also increase the release of catabolic hormones, reduce recovery capacity, and impact muscular adaptations patterns that can hurt anaerobic goals (i.e. too much endurance training). Ultimately, it is important to note that if you have anaerobic goals to increase lean muscle mass and strength, then aerobic exercises should be of high intensity and limited.