Training for cardiovascular endurance

http://running.competitor.com/2014/03/training/how-long-does-it-take-to-get-out-of-shape_70267

Many of your systems have to be built back up from the cellular level, synthesizing protein and increasing the number of mitochondria. The half-line of decline in mitochondrial enzyme is 12 days, which means 12 days of detraining requires 36 days of re-training to return to the same levels, according to Coyle.
Read more at http://running.competitor.com/2014/03/training/how-long-does-it-take-to-get-out-of-shape_70267#M6wQleb6j12yQYGc.99