My 5k times have been getting slower recently. I am aiming to get to 21:30 or better. In June I clocked 21:44 then 21:55, a week ago 22:05, and yesterday 22:35. I am wondering whether I am ging out too fast at 4:00/Km as I find that I seem to slow at Km 3,4&5. Yesterday every Km was slower than the previous. Should I concentrate on endurance or speed?