Certainly the African athletes train mostly on uneven surfaces. Athletes need endurance in a great range of muscles across the entire fibre spectrum. Avoid frequent doses of long contact time running eg Sand,Hills it may cause the athlete to change their motor pattern in such a way as too decrease stride frequency at all running speeds. The change in running biomechanics will happen over a long period of time and decrease efficiency. Training focus needs to be stimulating improvements in relaxed speed.
Relaxation needs to be practised constantly .
An athlete that can relax at 51.0 in a fast male 800m may have more useable speed than an athlete that is faster over 400m but is not relaxed at 51.0 speed. Efficiency is very important in Middle Distance Races. Athletes that a nice movers last longer and more of them actually stay uninjured in the sport long enough to reach their potential. Athletes need to be able to change their style and change gears. This needs to be practised on a regular basis throughout the year.