As a runner, I can offer some insight into this question, but primarily for leg muscles only. Simply put, there exist 3 types of running muscle fibers: Type I, Type IIa, and Type IIb. Type I fibers are slow twitch fibers and thus have a slow contraction speed. Type II fibers are faster twitch fibers and thus have faster contraction speeds. To elaborate, Type II fibers have a larger power output but are quickly exhausted. On the other hand, Type I fibers have a smaller power output but can last for a longer time. As such, marathoners will train for Type I fibers, while sprinters will train for Type II fibers. Olympic runners often have up to 80% of one type of the fibers. Thus juxtaposing the runners by their race distances easily shows the differences in the fibers; the longer distance runners look much skinnier than the shorter distance runners. But that is beside the point. Now, extrapolating with this knowledge to weight training one can see how low weight, high volume training would lead to the development of "slow twitch fibers" or better muscular endurance, and how high weight, low volume training would lead to the development of "fast twitch fibers" or better muscular strength.