One of the things I remember from USMC boot camp was "grass week." One of the mottos of the Corps is, "every Marine is a rifleman," and all Marines are indoctrinated into this motto with a week's worth of "snapping in" drills and classroom sessions on rifleman basics. During this week, recruits learn how to BZO, or "battle zero" their rifles, which involves adjusting the windage and elevations settings on the M-16 so that the round will hit dead-center of the target.
This concept of zeroing is not something we do often, but it's not unique to marksmanship either. One of the more recent things I found myself zeroing is my food scale. It's convenient to place a bowl or a plate on a scale and then zero the scale so that the display only show the weight of the food that's added. Recently I've been pursuing the zeroing of something else--my metabolic rate.
When I started P90X in April, I did what most people do--I consulted the Nutrition Guide to determine how much I should be eating to get the most from the program. According to the number crunching, I was a "Level 2" eater, which put me at 2400 calories/day. As I continued on in the program, I discovered myfitnesspal.com (MFP), which assessed me at some other caloric deficit. I think it had me at 1800 cal/day, which became reasonable because I could eat more the harder I worked out. I kept up this sort of dieting for months, so long that I lost sight of exactly what my RMR (resting metabolic rate) is. I also realized that eating at a deficit for a significant period of time, while good for weight loss, is actually not optimal for long-term health. So with this last round of P90X, I decided that I needed to determine exactly what my RMR is and learn to eat at that level.
I've been progressively increasing my daily caloric intake for weeks. Starting at around 2000 cal/day, I've been increasing my caloric intake by about 250 cal/day every two weeks, and I feel that I've found my metabolic zero, that is the caloric intake that matches my daily burn, at around 2750 cal/day on exercise days. Since I exercise six days per week, I haven't gone so far as to try to figure out my metabolic zero on non-workout days, but I figure it's somewhere around 2250-2500. But when you're working out six days a week, it doesn't really matter if you lower your caloric intake on the non-workout day. As long as you don't increase your caloric intake on your rest day, you'll likely be fine. Still, it's an imperfect estimation, and I was hoping for something a little more concrete.
Cue the BodyMedia FIT Core (pictured above). The BMF Core is this really cool device that measures skin temperature, heat flux, galvanic skin resistance (perspiration), and motion via 3-axis accelerometer. The result is that you get info on how many calories you actually burn in a given day, how many steps you take per day, sleep information, and more. You can use the BodyMedia website to track your caloric intake if you want, but I'm not using that feature. I know roughly how many calories I consume per day; what I don't know is how many I burn. The Calories Burned portion is pretty cool because it shows you a bar graphic of the day, with cal/min on the y-axis and time of day on the x-axis. You can adjust a slider to whatever window size you want for that day to see how many calories you burned during a specific time frame, which is great for seeing how many calories you burned, say, during a workout. Now, I'm not sure how accurate the data is, since it told me that I burned 431 calories during my Insanity Asylum Game Day & Overtime workout yesterday, which seems low to me, but I was workout out extremely early and I had to shorten my workout, so it could be pretty close.
Now, the stated accuracy is 10%. This seems like a significant amount, since 10% of 2750 cal/day is 275--that's a 550 calorie window of accuracy! However, one thing I've learned about statistics like this is that the error percentage should be between devices, so my device could be within 10% of what a different device would read given the same measurements. Furthermore, a 10% error is better than the errors associated with various metabolic equations with the added benefit that baseline estimation is derived from sensor data than from height, weight, age, etc.
I think that the BMF Core will do for metabolic estimation what heart rate monitors do for exercise--it will give the user value data based on real-world inputs. All things considered, I expect that the BMF Core will go a long way in helping me to determine my unique metabolic rate, and armed with that data, 2012 should be a very successful year!
