It amazes me to hear of pacers at events who run the course in a specified time. How do they do that?
Anyhow, I set off today to do an HM in around 2:20. It felt harder than I'd intended and I misread my watch so thought I'd finish in 2:30. After I'd finished, the time was 2:18. Starting to think that there might be more to "perceived effort" than I'm aware of.