What are double bricks?

Double Bricks are bike, run, bike, run sets. They can be key sessions for Ironman training. An example of a double brick for an Ironman prep is a 2 hour bike 2x20 min Ironman pace followed by a 1 hour run, 30 min at ½ marathon pace. Then another 2 hour bike 2x20 min at ½ Ironman pace and a 1 hour run, 20 min at 10k-½ marathon pace. This breaks up the long workout into quality intervals. Each work/rest ratio is one to one. So there is a twenty minute recovery to be performed at endurance pace between the intensity intervals. The purpose of double bricks enables athletes to fine tune their nutrition, hydration and sodium strategies for race day. It also prepares the athletes psychologically for the longer training days, as well as providing physiological adaptations of increasing mitochondria size and density, increasing stroke volume, improving lactate tolerance, increasing capillary development, improving respiratory endurance, and improving thermodynamic regulation.