Competitor.com has some great running articles. One recent one was to do with how one maintains one's speed while training for the marathon.
Why Maintaining Your Speed Is Important
Experienced marathoners know the key components to race day success are a high aerobic threshold (the fastest pace you can run while still staying in the aerobic zone, which closely correlates to marathon pace) and the ability to burn fat as a fuel source. The most effective way to improve these two things is a steady diet of aerobic mileage and threshold work.
Unfortunately, these two types of training don’t directly improve your speed. That means if this is the only type of training you’re doing, you can go months neglecting an important energy system during marathon training.
Born Adelaide 1948. Moved to Canberra 1969. Married Jenny 1970. Three children - Nathan Moore, Loani Falconer, and Mon Hall; children-in-law Lisa Moore, Wes Falconer, and Scotty Hall. Thirteen grandchildren - Jackson, Tyler, Charlie and Samuel Moore; Kayleigh, Jarod, Alex, Olivia, Will, and Sophie Falconer; Josiah, Liana, and Amelie Hall.