ellerose said:
I know this sounds daft, but I'm very new to running........... Did 2 miles yesterday and barely ache today - is this wrong? I usually ache the day after the gym!
Pain or aching generally occurs as a result of
over exertion, which of course is all relative to how accustomed to a particular exercise regime you are. At any given time, we all have a physical limit to our capabilities; and when we exert ourselves too much beyond those boundaries, we damage muscle fibres.

No, this isn't as serious as it sounds... The damage takes the form of micro-trauma, where the tiny fibres which comprise the muscles, are torn. (This is on a microscopic level, remember). As the body begins repairing itself, scar tissue is formed on the muscle fibres. Scar tissue is inflexible, which means that when the damaged muscles are used, the scar tissue isn't able to work as smoothly as the undamaged parts of the muscle: in fact, sort of pulling
against them... causing the pain of "tired" muscles.
Quite often, it takes over 24 hours for the scar tissue to form completely (compare it to when you graze your knee, or something... you don't get a scab forming until the next day...?); which means that the muscle pain is often worse
two days after the damage is done... How are you feeling
today, Ellerose?