I consider conversations with people to be mind exercises, but I don't want to pull a muscle, so I stretch a lot. That's why I'm constantly either rolling my eyes or yawning.

This person is saying they like having conversations with people, and that it can be compared to a type of mental exercise. However, they also recognize that these conversations can be mentally exhausting, so they like to “stretch out” their mind in order to avoid overexerting themselves. As a result, they often find themselves exhibiting behaviors that show their mental exhaustion, like rolling their eyes or yawning.