Seosamh said it while I was checking a stat.
The distance run stat is misleading. It’s only about 12km in an average 90 mins, a distance runner would do closer to 30. And it’s not the fact that it’s often at a sprint – the refs do a similar distance, often at a sprint, yet while they are 40-45 year olds you don’t see them cramping up with 15 mins to go. It’s the constant direction changes, turns, acceleration, jumping, twisting.
Get 3 mates and a tennis ball. Mark out a 10*10 square. The 3 have to pass the ball between them inside the square while you try and intercept it. If you last a minute at full intensity, well done. Now rest for a minute and do it again, and again, and again….