Pre-testing: My arms only weigh 10 pounds?!
Since Andrew works in obesity prevention research, he knows people with really cool machines that can measure exactly how much fat, muscle, and bone is in our bodies (dual x-ray absorptiometry or DXA) and precisely measure how many calories we burn at rest (MOXUS). They drew some blood just for fun and we also worked with a personal trainer who used skin calipers to measure our subcutaneous fat. Although this is not practical for everyone, there are other ways to determine some of the same information.
Thanks to the great staff at Arkansas Children’s Hospital (ACH) Research Institute! We look forward to following up after our thru-hike.
|Weight||182.6 lbs.||114.2 lbs.||n/a… based on height, see BMI|
|Height||6’ 3.75”||5’ 3.5”||n/a|
|Subcutaneous Body Fat (measured by skin calipers on 3 points— not as accurate)||6.2%||12.8%||Andrew: 12-21%
Percentages are based on age and gender. Numbers vary by source and are still debated.
|Overall Body Fat (measured by DXA— very accurate)||14.2%||24.3%|
|VO2max||57 ml/kg/min||65 ml/kg/min||>46 ml/kg/min|
|BMR||2,344 calories||1,521 calories||n/a|
Determining your caloric needs
First of all, determine if your goal is to gain weight, lose weight, or stay the same (for the trail or just in life!). It is not a perfect tool and you may be saying, “… but I have big bones,” or “I’ve always been this size,” or “I have so much muscle mass and muscle weighs more than fat.” (Point 3 is true for professional athletes.) As a dietitian, I hear these phrases almost daily. However, BMI is the best evidence based tool that we have for determining risk for cardiovascular disease and diabetes. Good news- losing even 5-10% of your current body weight (if overweight or obese) can help reduce your risks! Note: if you are over the age of 65, your healthy BMI range changes to 23-28, rather than 18.5-25.
BMI tools, including calculator and chart.
Your basal metabolic rate (BMR) is an important number for you to know! Your BMR is the number of calories you would burn just staying alive for 24 hours, without additional movement or activity. Certainly, listening to cues from your body will tell you if you are losing or gaining weight while on the trail (or at home for that matter). However, when packing boxes and estimating how much food to bring, knowing your BMR will allow you to be as accurate as possible.
To determine my BMR, I spent 30 minutes at rest under a little contraption called a MOXUS metabolic modular. I was fasting and I was not allowed to move, talk, or sleep during the study. The MOXUS measured my metabolism based on the amount of oxygen I converted into CO2 during the test. In my case, I consumed 6.3 liters of oxygen and produced 5.8 liters of CO2 . Andrew went through the same process. His needs are much higher, consuming 9.9 liters of oxygen and produced 8.7 liters of CO2 . Based on these amounts, my BMR is 1,521 calories, and Andrew’s is 2,344.
Another interesting function was determining what percentage we use of various sources of energy. Energy in the form of calories comes from 3 main macronutrients: fat, carbs, and protein (alcohol is the 4th). Andrew is burning 43% of his energy from fat, whereas I am only burning 27%. The rest is from carbohydrates and a negligible amount from protein. In order to preserve lean muscle mass, the human body avoids burning protein for energy. It is helpful to burn energy from fat because our fat stores are much, much greater than our stores of glycogen (from carbohydrate). Therefore, if you can burn fat, you can last longer. This may explain why I require small, frequent meals (refueling with carbs) and why Andrew’s body fat percentage is so low (burning fat for energy). We will compare all of these numbers after our hike to see what changes have occurred.
BMR + Activity
Once you know your BMR, you can use either an activity factor (based on lifestyle), or metabolic equivalent (MET) factor, which is a multiple of your BMR. The MET Factor for hiking is 7, meaning that the average person needs 7 times more energy when they are hiking than when they are at rest. See tables below for comparisons!
Using a tool online, you can enter personal information such as age, gender, height, and weight with an activity factor (if thru-hiking, choose the highest level). This will estimate your BMR, as well as your actual needs which includes exercise. BMR Calculator
Note: the website uses estimates based on the Harris Benedict formula to predict resting energy expenditure. We found that ours were underestimated by the Harris Benedict formula. Andrew’s predicted calories in 24 hours is 1,974. However, the MOXUS indicates that his metabolism is significantly higher and so he is actually burning 2,344 calories per day at rest. Mine was also higher than the estimate, 1,522 calories compared to the predicted 1,292.
Table 1: One option: BMR + MET
|BMR||BMR/24||Activity||MET||Extra cals/hr||6 hrs hiking||6 hrs hiking +BMR||Total calories per day|
Table 2: Another option: BMR + Activity Factor
|BMR||Activity Factor 2.0||Activity Factor 2.4|
|Total calories per day||7730||9276|
Table 3: Comparison of estimated caloric needs based on different calculations
|Online Tool||MET||Activity Factors|
We’ll follow up at the end of our hike to let you know which one we believe to be most accurate!
DXA scans are pretty neat. If you’ve ever wanted to know what percentage of your left arm is muscle or fat or bone… this is the machine for you! With DXA, I laid down on a table and the RN positioned my arms and feet in a specific way. The machine scanned my body for 6 minutes and then produced a detailed report. It is simple and painless and provides a wealth of information. From this, I learned some trivial information, as well as some useful measures. For instance, my arms combined only weigh 10 pounds, and my legs weigh 40! Andrew’s arms weigh 21 pounds, and his legs are 63 pounds. We could only guess that we will gain muscle mass in our legs and lose mass in our arms while hiking. We are planning to use trekking poles, so we may use our arms enough to maintain muscle mass.
In addition, we met with a personal trainer and she measured our fat with skin calipers on 3 body points: arms, legs, and abdomen. This is a measure of subcutaneous fat. See comparisons in “initial results” chart above.
VO2max is a standard measure for athletes to test their aerobic fitness. The results of a VO2max test tell you the maximum amount of oxygen your body can process. The personal trainer at ACH measured our VO2max using a sub-maximal graded exercise test. She had us wear a heart rate monitor, and put us on a stationary bike. During the test she increased the resistance every few minutes, until we reached a certain heart rate threshold. Based on our amount of effort at our heart rate threshold, she calculated our VO2max. See results in “initial results” chart above.
Bottom line is that you need enough calories from food to provide your body with energy for the best performance. Know your needs. Do you need to lose weight? Do you need to gain weight? Are you at a healthy weight? Determine your baseline calories and adjust.
Our next post will give you tangible ways to pack food based on your calorie needs for backpacking. We have packaged our food based on a total of 9,000 calories per day between us. Will that be enough?! We’ll find out!
When we complete the AT, we will participate in a post-test for the researchers and if there are any interesting findings, we will become a case study!
Body composition and metabolism hypotheses:
- Gain muscle mass in lower body
- Lose muscle mass in upper body
- Decrease overall fat mass, both visceral and subcutaneous
- Metabolism will increase due to higher muscle mass
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