As I understand it, your max heart rate is whatever you manage to achieve, and is generally a sign of cardio vascular fitness, although heart rate varies considerably between people so is not directly comparable.
Once over 40 or so it will decline as you get older. Over something like a 5 year period I would expect this to be noticeable.
Whether it is a good idea to push to your max heart rate is another question? I heard a podcast a few years ago about a marathon runner who had a heart attack. It said that as you age your blood vessels get deposits of plaque and high heart rates (and high blood pressure) can dislodge these, which can in turn cause bleeding and clots leading to possible heart attacks and strokes. This is why very fit people can sometimes have one or the other during or after exercising. But not exercising is likely to lead to higher blood pressure all the time, so I guess you have to find a balance.
Speaking of cardio vascular fitness, do people pay much attention to their VO2 Max figures? My Garmin gives me a figure, it says using my heart rate, power meter and GPS. If I ride a bit more, especially on up and down terrain where I can interleave short efforts and rests, it can improve considerably.
It says I'm currently top 20% for my age and gender, which makes me wonder why I am so slow on climbs (I'm around 73 Kg), but I suppose riding at a heart rate limit is bound to slow you down without reducing your fitness. I'd be curious what kind of VO2 Max figures you fast boys are getting?
Geoff
That gets me 2 minutes closer to him (but 30 seconds further away from you 
)You must be pretty close to getting into B cat now
Can't get anywhere near you at the moment
Thanks @AAAC 76C for the company - it was a pleasure riding with you again
@Del C is way out in front, and I think hard to catch now, unless @BurningLegs does something amazing on the 2 stages he needs to catch up on.
