I think the great sprint coach, Boo Schexnayder, put it quite nicely in his exposition on training distance runners (
http://www.sacspeed.com/pdf/distance.pdf
) in which he explains the why of two things:
1. doing heavy static lifts (which he actually recommends doing on the day of a pure speed workout e.g. not a taxing running workout aerobically but just a neuromuscular effort)
2. doing more body building lifts on the day of a "hard" workout (200s, 400s, anything at a really high level of exertion involving anaerobic and aerobic fatigue)
I think they both together answer your question with number 2. specifically answering your question.
1. Heavy lifting
"Static lifts, provided full ranges of motion are employed (such as deep
squatting) strengthen the body in the correct proportions… they develop the correct ratios of core
strength to peripheral strength. This fixes many running mechanic problems. They also involve huge
amounts of muscle tissue, so the positive blood chemistry changes that result from them are huge.
Finally, more than anything else you do, they stimulate calcium metabolism, strengthening bones and
battling bone degeneration. "
2.Body building circuits post workout
"Why for Distance Athletes? These circuits, when done following the protocol described, create
endocrine profiles that permit increases in strength, speed, and endurance. They also accelerate recovery
from the tough work you are doing elsewhere in the program. They stimulate the replenishment of
glycogen more effectively than anything else you can do on or off the track (provided nutritional support
is present). For these reasons they are a great follow-up to the tougher threshold, interval, or repetition
workouts you do, assisting recovery and improving work on the subsequent day. "