Running on soft forgiving surfaces is best for training where possible. It will help prevent injury and help you achieve consistent training without interruptions.
When you train on roads and footpaths it puts massive force on your body and joints. If you weigh 10 stone for example, that is 35 stone of force per foot strike. Over and over again. Day in day out. Mixing your surfaces on runs is best way to avoid injury.
PatrickDavorenCoaching. 