There's several things going on here, firstly it's unlikely that you were overtrained. Overtraining requires a lengthy (e.g., >6-months) recovery period, and isn't cured with a weeks rest. Although, i don't know about your personal circumstances, it's generally highly unlikely to be overtrained if you're not a full time athlete. Prior to being overtrained, you'd probably just ease up with either an infection or a heavy dose of fatigue. Basically, overtraining requires many months of forcing yourself to do too much.
You may, however, have been "over reached", which is really what you need to do improve your fitness, the recovery period provides a 'super compensation' effect, where you become fitter.
There's also unexplained under performance syndrome.
During intense training loads, and as fitness (e.g., VO2 max, LT) increase, maximum HR decreases. this is mainly because of a concomitant increase in blood plasma volume. This tends to happen right when you first start a training programme. there's also other cardiovascular changes that occur as fitness continues to increase causing a decrease in HR max (e.g., increase stroke volume, a-VO2 diff, etc.).
Very minor fatigue that may occur from day to day heavy training and/or on consecutive days racing can cause a decrease in max HR and average HR too. Often, on a second or more day of racing, my avg HR may be 10 b/min less (i know others who approach 20 b/min) at a given power output -- whilst the power output is the same on both days. This is nothing too worry about, and is one reason why HR is poor indicator of what's happening.
Having a high max HR doesn't actually mean anything -- the important aspect is to see how your power output is.
With having a weeks rest, what will have happened is that your plasma volume will have returned to normal levels (first in adaptation, first out), thus to maintain a 'normal' cardiac output, HR has to increase. Within about a week, your HR max will decrease again.
Personally, my max HR drops about 8 b/min under heavy training loads.
Your highest HR max would likely come after having a week off your bike with a moderate illness such as a cold. Not that i'd recommend anyone trying to find their HRmax after being ill -- as it might cause heart damage.
Ric
