..can speed loos be permanent…well yes and no…..
1) pure speed definitely (espec as u get older and even more dramatic if you haven't been doing much in the way of speed, weights, etc…)
2) pure speed can be replaced by strength speed as in longer intervals, more volume, etc….as Bob Kennedy used to say (paraphrasing here) having great speed is nothing unless u can get can use it (and that at the end of a 5km it was more about strenght vs pure pure all out speed)
3)you can get it back, but not overnight
want proof……the other day I did 6 x 800m and it was the first time I had done this type of session in a few yrs (I am going back to 5-10km training) and off no real spped workouts (except long intervals and fartlek/hill sessions) I did 2:13/14 (and did so negative splitting and running very controlled). Now recognize when i was in my prime i would roll out 2:07s (for 6-8) but that was when I was fresher, had done more intense intervals, etc…..but early in the season i would only roll out say 2:11/12s my first time out (if even that). The biggest difference is that back in the day I would run 2:13 pace and then easily drop it down to say 64 and run 2:10/11…..right now (and i would say more lack of doing change of pace sessions and doing session like this as opposed to loss of speed) I cannot do that….whereas now I ran more even or slight negatives (egs 67-66), but even then I still dropped it down to 32s for the last 200…
..but then again it could also be getting old…..I'd like to belief it's not though 😉