Bob,
As far as your question on cardio workouts is concerned, the guideline on max rate is just that and each individual will have a greater or lesser personal max which you can discover yourself by gradually pushing yourself or with a stress test. One thing you can measure is your recovery rate which is an excellent, easily available measurement of your aerobic fitness.
This is very true: Different people have different maximum heart rates. The number I suggested (220 minus your age in years) is part of the Karvonen formula for calculating safe heart rate training zones for individuals in generally good health. If I remember right the "220" starting number is derived from the average max heart rate for men in their mid-fourties, and is designed to be a "safe" number for use by most people who aren't trying to be superstar athletes.
If you want to find a true maximum heart rate for yourself, you might try
this method from Wikipedia. From there you can calculate your training zones using the percentages I suggested earlier, but without subtracting and re-adding your resting heart rate in and out of the equation. I've used this method to calculate my max heart rate, which turns out to be a few beats faster than my Karvonen number.
Just remember, by design this test is designed to take your body right to its limits, very close to the breaking point. That's not the kind of testing I'd advocate to a lot of people.
I'm assuming you have a heart monitor - much better than using the indication on the machines. Let's say you are thrashing along at 130 - 140 bpm on your stationary bike or something around your 80% level. Now just pedal easily and watch your heart rate and the seconds counter on your watch. Wait unit your rate drops by a beat per minute (sometimes it temporarily goes up when you stop). Now count off 60 seconds and note how much your rate has dropped. Anything over 20bpm is satisfactory, more is better. If your recovery rate is 30 - 40, tell everyone you know, 'cos that is really good.
You're describing the "recovery heart rate" a little differently from the way I'm used to hearing it. As I understand it the recovery heart rate is calculated by exercising at 80% of the "220 beats minus your age in years" level for a period of time, followed by a two-minute active warm down (75% of the walking or running speed required to obtain the 80% heart rate), ceasing exercise and waiting one minute, then taking the subject's pulse for 15 seconds and multiplying that number by four to find the "recovery heart rate."
People with a recovery heart rate 12 beats per minute or less than their 80% heart rate were found to have a mortality rate four times higher than those with a recovery rate more than 12 beats slower.
You shouldn't need to push yourself to the limit (95%+) ever, although it does feel good to do so once a week or once a month. At this level you can't get enough O2 to your muscles and you get lactic acid build etc, plus the older you get the more chance of a heart attack, so certainly don't push it too often if your recovery rate is below 20.
The literature I've seen states that there are
no health or training benefits working above the 95% level, the point at which your muscles make more lactic acid than they can efficiently clear out of the system, so why even go there?
About lactic acid:
Creating lactic acid isn't a bad thing, by the way. Your muscles (and other cells of your body) actually have two separate energy systems. The first is an anaerobic (meaning no oxygen required) process that converts glucose sugar into two usable energy units (a chemical called ATP) per glucose molecule and something called pyruvic acid. That pyruvic acid is then fed into the second, aerobic (requiring oxygen) system that turns the pyruvic acid waste product of the anaerobic process into another 34 ATP energy units.
The interesting thing about this is that, while the aerobic (oxygen requiring) process can create a whole lot of ATP energy units, it's a slow process, while the anaerobic (no oxygen required) process is very fast and easy to do, So, when our muscles are working very hard (in the cardiac fitness band), they throw the inefficient aerobic process into high gear and make lots of ATP energy units along with lots of pyruvic acid waste, way more pyruvic acid waste than the aerobic energy system can process.
When that happens the muscles convert the excess pyruvic acid into lactic acid, dump the lactic acid into the blood stream, where the liver can grab it and (using more energy) convert it back into glucose sugar again.
In other words, the anaerobic system is very inefficient. It sucks calories down like a madman. Which is, of course, a good thing if you're trying to burn calories. The downside is that, beyond a certain exercise level, your muscles and liver can't keep up with the lactic acid, and that can cause the buildup of lactic acid Alan was referring to.
Which is why you don't want to exercise in the athletic performance band (heart rate 85% and above of max heart rate) too often, and why there is no training advantage (meaning it's a bad idea) to going over the 95% level at any time.
