In my mind these are long slow runs. Greg McMillan* defines it as between 30 seconds to 2 minutes slower per mile than your average marathon pace. So go figure what that really means (I have no idea). Key benefits are:

• Increases stroke volume (i.e., the amount of blood pumped by each heart beat) while in in the muscles there’s a increase in the number of capillaries that the deliver blood. The net result is more blood pumped and delivered to the muscles more efficiently.

• The body also becomes more more efficient at using fat as a fuel source so there’s less reliance on limited carbohydrate stores (muscle glycogen). Conversely it stimulates the muscles to store more glycogen, which can then fuel long or high intensity workouts.

• Changes to the nervous system include much more efficient use of slow-twitch muscle fibres (helps improve running economy) and some re-orienting of fast-twitch fibres which become more “endurance-like”.

*The information on the benefits of different types of running in this and forthcoming posts is cribbed from Greg McMillan’s Six-Step Training System, Step #2: The 4 Key Training Zones – Endurance, Stamina, Speed & Sprint.