How much recovery do you take on your 1k reps? Will try and replicate them tomorrow :-)
Also 4 seems reasonably few, do you ever go up to 6?
PS: Good training at the moment!
Hi... the ones I normally do here in Edinburgh (set up for orienteers in the 1980s) start every 6 mins on the clock, for 5 reps, so about 3'45 on (well, at the moment, it was less...), 2'15 recovery (it was more...). I'd think 2'30 to be starting to get long and so when fitter I do 1.25ks off 6 minutes which gives about 1'30-1'45 recovery. Back at the 'bridge I remember it was 3 mins on, 2 mins off which was pretty good too.
The theory I normally work to is: the point is to max out aerobic systems so duration has to be at least 2.5-3 mins as it take a good 2 minutes to do that and get to threshold HR (well, "second half of a 5k" HR anyway), the recovery is however long you need to be able to keep getting to the aerobic limit each time. I might do 6 x 3 min reps but not really more as I would then have to back off a bit to be able to complete the session which would negate the point of the session which is to do some running maxxed out aerobically. The 4 is probably a bit lightweight, I'm nervous of getting injured which is why, but I've made progress on as little as 3 before today, again it's better to do fewer and run fast enough than more/longer and not actually get to threshold. Well, that's how I've understood the idea behind these sessions.
You've been doing some pretty good long sessions recently!