Right now all I am doing is sprinting, since I am training for masters track. I'm sure you are asking about strides or a track workout whie training for distance running though. Distance running and sprinting are a poor mix. If you are training for distance running races (like 99% of adult runners) you should not sprint. 85% is far too fast and you risk pulling a hammy or a groin.
That said, strides and speedwork are essential for distance running. But you should max out at about 70% top speed on those. You can do the strides at the end of a run. For example after a 5 mile run, do 4 x 200m strides. Do the first 200m slightly faster than your distance running pace, with each 200 increasing in speed until the last one (which should not be an all out sprint).
Also recommended is a track workout once a week. 6 x 800m repeats is a good example of a quality distance running speed workout.