A few weeks ago I ran a half marathon and started off around 6:10 pace, thinking I would bring it down to 6:00 / 5:55 after first few miles and hold steady there. In the first 3-4 miles I was running with a pack of 5 guys and we were all holding the same ~6:10 pace. One of the guys in the pack was breathing VERY heavy. At the end of mile 4, I picked up the pace a bit and left the pack, thinking I probably wouldn't see them again, and definitely wouldn't see the heavy breathing guy. Then around mile 8-9, heavy breathing guy (still breathing extremely heavy) passes me as I was running around 5:50/5:55! He even let out an audible battle cry at one point … clearly hurting, but just powering through and hammering. He ended up beating me and running a very solid time. Curious if this guy was working harder than everyone else relative to his level of fitness, or if some people just breathe heavy / let out battle cries to help ease the pain. In any event, I was impressed.