Based on my own experience, I say yes. Back in my 20s, I could get out of bed and go for a run at a sub-7:00 minute pace right away and I'd alright. Now that I'm in my 30s, it seems not so easy to crank out a sub-7:00 right out the door. My latest experience was on an 8-mile run. I started slow as usual (8:30-9:00 pace), gradually increased the pace, and then tried to run the second mile at a 7:00 minute pace. To my surprise and utter disappointment, I was panting at the end of that mile. It was very slightly uphill but not so much that I should be panting like a locomotive engine. Anyway, I continued thereafter at about an 8 minute pace or so. Just over half an hour into the run, I had recovered enough to run mile 5 in 6:28 and mile 6 in 6:22 and at the end of that, I could still have run another sub-6:30 mile. What a difference some additional minutes make. A complete turnaround. I'm thinking that by half an hour or so, my system (legs, muscles, etc.) had warmed up sufficiently to facilitate a better performance. Anyone else have a similar experience?