So that you can have a balanced training plan for the marathon you should then build up your total weekly mileage gradually. Personally I use the 10% rule in that I never improve my total weekly mileage by more than 10% in any given 7 days that I train. I discover that if I adhere with the 10% rule then I’m less likely to produce niggling injuries in the build-up phase of my marathon training plan. Nevertheless if I increase my complete weekly mileage by more than 10% in any given 7 days then I become prone to developing such injuries. I really feel the main reason for this is that growing my weekly mileage by more than 10% in any given week does not give my system the possibility to recover properly.