800m/400m backwards/800m/400m backwards
Distances aren’t exact. Used mapmyrun.com for a route starting at my house. The best route worked out to be 880 meters for the forward and 380 for the backwards.
I think on a slightly cooler day, I could take a bit more time off this. Also the 120 meters of extra doesn’t help. Oh yeah, and if I ran faster . . .