Today, I got a fascinating bit of experiential evidence of something lots of sports scientists have known for years: the impact of mental state on running, and particularly on perceived exertion. I took my weekly endurance run earlier with a major source of mood variation available:

• This morning, I got a rejection from a job I hoped to get, and was feeling rather morose as a result.
• As part of working through that in a healthy way, I picked a long-deferred part of a side project to work on, and started in on it.

What I found experientially on my run was: When I was thinking about the rejection, I felt tired and slow. When I was thinking about the side project, I felt energized and fast. I could actually see my pace shift on my watch to match as my mind went back and forth between the two. It was… odd, honestly. But it was kind of fun to see in practice, too.