I run 2 hours most mornings and never felt that it's been a problem. But who knows if we're missing out on gains?
2 hours every morning? What is your mileage?
I went through a few months of 90-minute morning runs, daily. Approximately 14 miles a day in singles, with one longer run on the weekend. Very hard thing to do on a daily basis, but I was in tremendous shape. PRed by 8 minutes in the marathon after that time period.