On top of the countless decisions we have to make in every match, here is some insight into how much fitness is involved.

Cover between 5.6 and 8.1 miles per game
High intensity running comprises about 18% of time on field
(High intensity running for refs has doubled since 2003)
Achieve 85% – 90% of max heart rate (same as a player)
45 sprints per match (same as a player)
Change in movement type or speed every 4 – 6 seconds