But do not despair. When you're able to train again, do no more than you are capable of at first - slower-by-10-seconds 400s and only three (slow) mile reps instead of the five - and you'll soon be your former self again (literally!)
Another article reported on leg-strengthening exercises undertaken by 90 year olds - yes, ninety - who were subjected to an 8 week programme "to train quadriceps and hamstring muscles during a seated leg extension/flexion movement". After 8 weeks of training for each of these 9 not so young people - like most of us! - the weight lifted by the right leg increased from an average of 8kg to 20.6kg (and for the left leg from 7.6kg to 19.3kg), an increase in strength of these muscles of rather more than 21/2 times! The "volunteers" could all walk more quickly afterwards, 2 without their walking sticks. At the end of the trial - in two senses of the word? - they sat back in their armchairs, remotes in hand : a month later they were hauled back into the lab again and a 32% loss in strength was noted!
Earlier research, on active athletes, has shown that endurance capacity can be maintained for over a month if even only one weekly tempo or hill session is carried out. So if it's just a holiday you're going on, as distinct from being sidelined by injury, job or family responsibilities, try to negotiate an agreement that you are allowed an hour by yourself, with trainers on, each week. It may cost you, but it'll keep the dreaded atrophy at bay!