Apologies those are Renato Canova sessions so ill blame him. He means 10% slower or pace * 1.1
Canovas athletes gradually train more specifically by making the long runs faster and the reps lomger and of greater volume once aerobic power and resistance are developed. Another session he uses In every phase is called alternations. This involves running 20 X 1k alternating paces from around AnThreshold to a little slower than AErobic threshold.4 months out, the session works on improving the AnT k's while keeping the AT splits constant. Next month the AnTs reps are the constant base while the AT splits are improved. 1 session of each kind in the second last month. Last month, fast reps are slowed and slower reps are speeded in an effort to pull the thresholds even closer. Average speed for the session is now marathon race pave or thereabouts.
He mentions two gains from this session. AT is brought as close as posible to AnT. This is one of the fundamental goals of elite marathon training. The session is a 6 pointer though: these elites are burning relstively high amounts of glycogen to finish in just over two hours. This produces some lactic in the muscles, which can potentially be re-used. The body is taught to use the lactic during the slower alternation....i.e the body learns to re-use lactic at around marathon race pace. So this session produces surprisingly better results than youd expect because there is more goimg on under the bonnet. This elite session doesnt translate to us slower runners, because we dont run hard enough at MP to produce enough lactic to have those benefits. A bloody good one for the half though!
And a good on to do up and down a shallow gradient on a good grass surface where the body can learn to flush out lactic before hitting the heavy hill sessions.