As I recently began adding a Peak 8 Interval routine (recumbent bike) to my twice weekly weight resistance gym workouts, I started researching Target Heart rate and Max Heart rate. 
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I found a plethora of scientific studies on the old formula being out-dated and a new formula's for computing.  There are several, all some what similar but slightly different.
Old formula's:  (M) 220 minus age, (F) 226 minus age
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So I put together a spread sheet of the various found scientifically created new formula's.
All one has to do is enter their age (I even used both years and months).  And the various formula's are used to calculate, and then averaged, to get an approximately good figure for the various Heart rate Zones:  %50% MaxHR for warm-up, Low Target Zone, High Target Zone, and 95% MaxHR for short interval high intensity.
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If anyone would like the excel spreadsheet for themselves, please feel free to e-mail me, separately.  (jaydpiii at yahoo dot com)
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I also found - which is probably common knowledge for most who have been regular exercisers: 
<!--[if gte mso 9]> Normal 0 unctuationKerning/> false false false oNotPromoteQF/> EN-US X-NONE X-NONE ontGrowAutofit/> ontVertAlignCellWithSp/> ontBreakConstrainedForcedTables/> ontVertAlignInTxbx/> Healthy Heart Zone (Warm up) --- 50 - 60% of maximum heart rate: The easiest zone and probably the best zone for people just starting a fitness program. It can also be used as a warm up for more serious walkers. This zone has been shown to help decrease body fat, blood pressure and cholesterol. It also decreases the risk of degenerative diseases and has a low risk of injury. 85% of calories burned in this zone are fats!

Fitness Zone (Fat Burning) --- 60 - 70% of maximum heart rate: This zone provides the same benefits as the healthy heart zone, but is more intense and burns more total calories. The percent of fat calories is still 85%.

Aerobic Zone (Endurance Training) --- 70 - 80% of maximum heart rate: The aerobic zone will improve your cardiovascular and respiratory system AND increase the size and strength of your heart. This is the preferred zone if you are training for an endurance event. More calories are burned with 50% from fat.

Anaerobic Zone (Performance Training) --- 80 - 90% of maximum heart rate: Benefits of this zone include an improved VO2 maximum (the highest amount of oxygen one can consume during exercise) and thus an improved cardiorespiratory system, and a higher lactate tolerance ability which means your endurance will improve and you'll be able to fight fatigue better. This is a high intensity zone burning more calories, 15 % from fat.

Red Line (Maximum Effort) --- 90 - 100% of maximum heart rate: Although this zone burns the highest number of calories, it is very intense. Most people can only stay in this zone for short periods. You should only train in this zone if you are in very good shape and have been cleared by a physician to do so.

very good read. please email me, i'll send you a note seperately.

I've recently been training a very solid 30-45 minute cardio routine. When I get to the gym, I work up to the Fat-Burning level, then during resistance training, tend to stay at that rate expect for exertion which rockets up the rate for very brief spurts.

Then when I get into Cardio, i'll spend 35% of my time in the Fitness range, 25% in the Aerobic Range, 15% in Anerobic and finally 5% in Red Line. Recently, I've been able to sustain normal breathing and other signs of stress while pushing upward of 10-12 beats per minute compared to my old max, when I would nearly faint. I'm at about 176 BPM today, which is about 95% on a 32 yr old male. I'll only hit that level for 1 minute max or so on the last interval of a 30-45 minute routine, but that's the minute that is the most satisfying and hopefully helps my metabolism the rest of the day. Whats most amazing is how fast my heart recovers. Since I started taking 100mg of Ubiquinol daily with breakfast, I'll decent from the mid 160's (lower redline) in a matter of 3 minutes back to the Warm Up Zone, which is astonishing. I've never had this recovery in my life, ever. It's a blessing at this point!

Super cool exercise. Quite a detailed list of different ways to do it, but most interestingly, the average of them all if 175BMP for my 95% Max, which is terrific as this is where I'll crest on a "great" cardio routine just as I close it out (explained above). I think it's a strong sign of health that I can even hit that 95% threshold. It means that my heart isn't outaging my body due to my stimuli and diet etc. When I first got back in the gym 5 months ago, I would regularly hit 160 within 3 minutes and then top out at about 165 to the point of real discomfort/ needing to lower intensity to make the whole session, my heart was weaker and aged! Now at 176 BPM after 5 months of Zone/FO etc, I'm focused and peaking my heart rate for what I hope is maximum effect. Thanks for sharing your great work!

Glad to do it, and glad it was useful for you!  I am just starting to look at and monitor my Heart Rate, so I learned something in doing the research.
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Curious:  Do you use a particular Heart Rate monitor or just the gym equipment machines monitors?  And if you use a Heart Rate monitor, a strap with wrist receiver or a strapless wrist only unit?  I've been looking at SportLine Heart Rate monitors - they seem to have the better reviews and appear not to be over-priced.

I purchased one of the chest band and wrist watch combinations from Polar from amazon but have never used it. when I get into more outdoors activity, I would likely use it more. I'm using the gym equipment, mostly by Procor, which has heart rate monitors on all the equipment on the hand grips. I realize they could be off slightly, but I always use different machines and the numbers tend to be consistent across different ones

Steven;
There was a slight flaw in my thinking in computing the Target Zones in the Excel spreadsheet.
I did not keep your e-mail address.
So send it to me, and I will resend the new Excel spreadsheet to you.

Hi Steven,

Polar montiors are nice.  I used to use one for running, to keep my HR in the range I wanted.