Recently, I've been reading a lot about how cardio reduces muscle mass and strength.
The following is an excerpt from crossfit.com that seems to sum up what I've been reading:
Aerobic training beneﬁts cardiovascular function and decreases body fat – all good. Aerobic conditioning allows us to engage in low power extended efforts efﬁciently (cardio/respiratory endurance and stamina). This is critical to many sports. Athletes engaged in sports or training where a preponderance of the training load is spent in aerobic efforts witness decreases in muscle mass, strength, speed, and power. It is not uncommon to ﬁnd marathoners with a vertical leap of only several inches! Furthermore, aerobic activity has a pronounced tendency to decrease anaerobic capacity. This does not bode well for most athletes or those interested in elite ﬁtness.
I've also seen some dramatic pictures(if unflattering to endurance runners) that emphasize this:.
So here is my question. Why is there a decrease in muscle mass etc. with aerobic, but not with anaerobic activities? Is cross training enough to offset this? Or should everyone give up on long distance running and other endurance sports if they want muscles, more power, etc.? Is there any benefit to endurance sports other than better cardiovascular function when compared to strength training (if this in fact the case)?