To be honest, at present all the sessions I am doing seem to be killing me but an old favourite (?) used to be 20 minute warm up followed by 20 min at 80% effort then up the pace and straight into 6 x 3 minutes - no recovery between the 20 minutes and first 3 minutes, but 2 minutes jog between the subsequent efforts.
I have just been reading through details of other such sessions at www.wearerunners.uk Where it lists Julian Goater's 'killer session' as 6 x (2x300m) repetitions on a slight gradient, where you run
The same website also gives details of a track session Mo Farah completed in his build up to the 2015 World Championships:
All with 2 laps jog recovery and reps carried out at near maximal effort - 1 x mile; 1x1200m; 1x1000m; 1x800m; 1x600m; 1x400m; 1x 200m.
Sounds tough but the website also reports on the times he was doing for the reps:
1 x mile - 3.55; 1200m - 2.57; 1000m - 2.27; 800m - 1.57; 600m - 1.20; 400m - 50 seconds and 200m 25seconds. Plus the fact that this session was carried out at altitude!
For us mere mortals the stuff of dreams.