Build up gradually. I always follow the S.M.A.R.T principle when designing a training plan. Specific, measureable, achievable, realistic and time. This gives clear direction around which you can build a schedule. The guideline to increasing mileage is to add no more than 10% each week. This is to allow your body to adapt to the high mileage and not overload the body and risk injury. Hasten slowly increase intensity gradually. For a typical training week I would include a 1.long slow run(for endurance, 2. tempo run (for lactate threshold) and then the 3. session would be either speed (for enhancing muscle strength and power)or interval(for maximum aerobic capacity vo2 max) or fartlek (speed play) or hills(for endurance and strength)session. I would also follow a hard day by an easy day or indeed a rest day.
By Maria O’ Keeffe McCarthy