many have problems getting the training intensity high enough to progress.
here are few suggestions:
1) get chased by a bear, like in above video. 3 x 2 mins bear chase with 3 min rest is a good workout.
2) run your 5 km tempo in south african township at sunset chasing runners who are 2 mins faster than you;
3) do a swim race in white shark infested waters and suddenly find yourself all alone in the lead.
i heard of a guy who shaved off 2 mins of 5 km pb (to 17 something) doing the workout 2.
be creative with your training :)