To explain how the Activity Calc improved, I'll need to explain how it used to work. And any general questions can be answered too.
Simple Setup tab Activity Calculator was totally based on method found in several studies that found much better accuracy over the 5 level TDEE table. Just as that table is based on BMR x activity factor, these studies also used BMR x activity factor x minutes.
You've perhaps seen the exrx.net site, or the site that used radio dials, or couple others, you deal with minutes per day, trying to figure out if you are picking a standard day to get a TDEE figure on. And those used 5 different levels of activity type, from sleep to heavy activity. Rather detailed, plus 1 day rarely equaled the other days in a week.
For the spreadsheet I picked a sedentary with no exercise foundation to build upon, with activity factor 1.25 x BMR. I then let you enter in hours per week for increased work activity, and minutes per week for exercise activity. The different levels had different activity factors x BMR. The week averaged back to daily.
But I did not stick with the study's activity factors for exercise, which were based on healthy weight folks, and therefore lower BMR. Which was not correct when you weighed more and underestimated more as weight went up. So I took 2 extreme examples of low (1000) and high (2400) BMR, looked at how much they burned actually doing the stated walking speeds for the levels I used, and of course had to take an average of everything to get a BMR activity factor. But it scaled much better using same method as study did. But the farther away from average BMR yours was, the worse the inaccuracy. Lower BMR, over-estimated calorie burn, higher BMR, under-estimated calorie burn. Only talking 80 calories/hr either direction at high cardio at highest and lowest BMR. But lots of activity could make it worse over a week.
The other problem with the old method, if you were able to retain LBM and mainly lose just fat mass, your Katch BMR would actually stay the same. But if you weigh less, you actually burn less moving the same pace. So the whole goal of the spreadsheet, maintaining muscle mass and LBM, starting giving over-estimated calorie burn the closer you got to goal weight while maintaining LBM, and under-estimated when over weight. Again not talking a great amount, unless you had a lot of activity weekly.
So how does the Activity Calculator work now?
So the same foundation of sedentary desk job is still built on top of with increased daily work activity, and exercise activity. Still a weeks worth of activity averaged back out to daily level.
Studies, and now FitBit and BodyMedia and others, show that sitting and standing time is best represented by your BMR, actually RMR if awake (some of them don't do it right). So the increased work activity with standing/moving slightly is RMR x 0.5. The very active work day is based on walking about 2mph, which is what the study BMR activity factor matched.
The exercise levels are now based on your current weight. So if you have a lower than expected Katch BMR because of low LBM from bad past diets, but actually a high weight, you do burn more and this new method will correctly show burning more. Also means if you lost weight but maintained or increased your LBM, you get less calorie burn then you used to. May not be much, could be a lot, just depends on how much exercise and what type.
Weight lifting is also weight based now, with what some studies showed for direct calorimetry measurements of strength training.
To emphasize getting the right activity level for exercise if you have a variety, suggest testing treadmill speeds at walking 4 mph with HRM if you have exercise that might be between medium and high cardio. If your normal workout's average HR is higher or lower than that, you know what exercise level it is.
Those cardio levels were picked because each is almost double the calorie burn of the lower level, so major hops.
The TDEG recommendation is still based on studies and what should help maintain muscle mass, along with protein recommendation. Strength training is of course recommended.
Any questions on above or at all, let me know below, or in the wall posting for this blog.
