I think one way to add more life to the running animations is to add various arm movement movement for the situation.For example, moving their arms and upper body more, when trying to get an extra step on a defender in the open field.they should also implement various leg speeds. to give the effect of faster running.
heavier players should reflect more of a struggle when running by having more violent arm and upper body movements.
Notice how in an l.t. highlight how he(can't upload link
) moves his arms in various ways depending on certain situations.ie. making on the dime cuts, or while running in the backfield with a defender luring in front I think thise gives a sense of weight and realism to the overall game as it makes it seem like the player is actually trying to balance and control weight by using their upper body.