This is something I've been wondering: what would be the effect of mixing in low-intensity endurance training once/twice a week on explosiveness and reactivity? For example, if you had a pair of identical twins with the same RVJ, with identical training programs for vertical (involving plyos, lowerbody weights etc) but one twin ran 2 miles twice a week in addition to this and the other did not, how would their vertical differ after 3 months?
I'm asking because I've never really had to train for endurance and so don't really know anything about its effects. I know that the general opinion is that you can't adapt your body for high level endurance and high level power at the same time (e.g. skinny marathon runners who probably can't jump over a phonebook), but can you train for vertical and still keep up a decent level of aerobic fitness as well? Or is any level of endurance training (running, swimming, cycling) counteractive to power development?