Summer is about to end and I am proud to say that I've made the best of it: during the period starting from May till August I ran almost every day (I had only 15 days of rest out of 120) and I improved my PB on the 5K distance, thanks to interval training. Then I decided to have a long break (2 weeks) during which I stopped doing any physical activity, besides walking (and getting a new job, a performance that can be more exhausting than any running session).
When I started running again, I was convinced that I had lost all the benefits I had strenuously achieved all over the last months. Like Sisyphus, I feared, I was doomed to start all over again. But I was wrong. The hard summer training proved to be more long-lasting than I thought, as confirmed by my new PB on the 10K: 47:10 (4:43min/km). During the first 5 km I felt light and vigorous, filled with renewed energy. Conclusions: after a long period of training, it's always beneficial to stop for a week or two, in order to recharge the batteries and start again faster than before.