Quote Originally Posted by dominion View Post
^^This!^^ I don't see the value of short sprints - eg, much below 400m reps to increase speed over 5K and above. Back when I used to train properly the key elements were short intervals, eg 12 x 400, 6 x 800, 3 x mile (eg, 3 miles worth of efforts + warm up / warm down), a tempo run of between 2 and 4 miles, again warm up for 2-3 miles then tempo then 2-3 miles cool off, and a long steady run on Sunday, typically 15ish miles at a steady pace. To put this into context, I was running 70ish miles a week with a couple of days running twice which I realise may not be achievable for some people due to time constraints. That said, I think the fundamental, short intervals, tempo, steady runs still holds true. If you can't have a chat to your training partners on a steady run - it ain't steady enough!
Any length would be of benefit as long its very hard to complete 6 reps. 400 m or 2 minutes, with the same recovery or less, would be a good sort of distance for fartlek for most. All miles count, but some more than others. The fast miles are the ones that will make you faster in a shorter time IMO. Tempo runs over longer distances are also important in order to learn to hold onto hard efforts, and allow you to understand how hard to push durring races. It's helped me, but I prefer Strava segments rather than fartlek as I struggle to motivate myself with no immediate goal.