Ok, as far as calorie estimation goes there are several schools of thought. I personally have always used the 100 cal/10 minutes of cardio or per 1 mile. It’s not exact but it was easy mathmatically. Since then I have expaned my knowledge on calorie burning. It seems that it all comes down to heart rate which directly translates into the amount of oxygen consumed and from that you can get a fairly accurate calorie count.
First, calculate your maximum heart rate. 220-age…..for me thats 220-30=190 bpm.
We are going to assume that you are working at the maximal oxygen uptake level of 3.5 liters/min.
Next we will say that I worked at an average HR of 160. Then to get the % of Max HR you say 160/190 = 0.84 or 84% of my max HR. Using the formula below you can calculate the amount of oxygen consumed/burned per minute of physical activity.
Calories = 3.5L/min. times .84(%MHR) = 2.947L/oxygen per minute of physical activity.
Multiply 2.947 by 5 = 14.7kcal/min. 14.7kcal/min is the approximate number of calories you burn per minute of exercise when working at a heart rate of 160bpm.
Bottom line: If you swim or bike or run for a half hour at 160bpm you would burn about 442 calories. Do whatever you want to do in the gym as long as you elevate your heart rate and it remains elevated for a significant period of time. This is the reason that I started doing 1 minute jump rope intervals between all of my supersets. This signficantly increases my average heart rate over the course of my workout compared to lifting weights alone, which translates into more calories burned!
This principle is why Tabata, HIIT, Crossfit, & P90X can work so well. They raise your average heart rate over the course of the workout which boosts calories burned. HIIT is very interesting and I may write on that subject after I review the Spartan Sprint and Hurricane Heat.
To get the most accurate reading you would have to do a VO2 max test in a sports science lab, but until then this formula will give you a close estimate of what you really burn.
You can use some VO2 max calculators to estimate your VO2 max, likehttp://www.shapesense.com/fitness-exercise/calculators/vo2max-calculator.aspx but I prefer to just use the population average of 3.5L/min used above.