Energy Budget - Special Edition

Last month I shared that I had joined Calorify. I thought it would be fun and informative to walk through my own test results and share how I’m using the results to think about the topic I’ve been writing about all year, namely how to optimally structure my training.

To refresh, in May I discussed regulating overall training load and big training days with the CTL/ATL/TSB model (Chronic Training Load / Acute Training Load / Training Stress Balance). This article is a good reference on the topic.

There are many other methods to assess overall stress on the body, with HRV and resting heart rate being two popular methods. Each has its own place and value. While powerful, they don’t yield directly actionable guidelines for future training plans. Let’s examine how energy expenditure might support this planning.

Thurber et al documented an upper limit on total daily energy expenditure set by our BMR. At long term / steady state, all the data show that humans cannot exceed 2.5 x BMR for total daily energy expenditure. For shorter periods, ranging from one day up to a few months, we have data on how high humans have gone in extreme events like the Tour de France, Western States 100, Ironman triathlon, etc. Here’s the curve in log and linear scale:

Many of you will recognize this phenomenon, as it’s very analogous to a power-duration curve, which simply shows how we can produce larger power over shorter durations - pretty intuitive. The same applies to total daily expenditure - we can go above the 2.5 x limit, but our days are numbered, and the number is smaller as the energy expenditure goes higher.

This is a key observation and one reason I got so interested when I learned about Calorify and the science behind energy expenditure - it provides a fundamental limit on activity that covers a larger time scale than other metrics. To summarize some of the key variables:

• EE = Energy Expenditure

• EA = Energy Availability = Calories consumed minus calories burned on exercise, divided by weight in kg

• BMR = basal metabolic rate

• PAL = Physical Activity Level, equal to total EE / BMR

• NEAT = Non-exercise activity thermogenesis

• TEF = Thermic Effect of Food - the calories required to digest your food

On to my numbers…I measured from July 31 to August 7 to capture exactly 1 week. During this time, my TSS total was 442, a bit low because I was bouncing back from a tweaked SI joint, limiting my training. My daily energy expenditure was 3284 calories, which was in balance with my intake. This makes sense as I was neither eating to lose or gain weight, and I’m pretty in tune with maintaining weight over long periods of time. Based on my training and power meter data, my exercise energy expenditure was 559 kCal/day (almost exclusively from power meter data this week, so very accurate). This resulted in a PAL of 2.04 (3284 / 1610). Also not surprising, for a 51 yr old dude I train reasonably hard but at a level I feel like I can sustain long term (loyal and attentive readers will recall that long term sustainability was a key principle I built my training plan around).

These numbers are powerful because they let me calculate how much headroom I have to raise my steady state exercise level. To get to the PAL = 2.5, I could add 741 kCal/day of physical activity:

PAL limit of 2.5 = (3284 + X) / 1610 —> X = 741 kCal

To put that in more tangible terms, 741 kCal = 206 Watts for 60 minutes. You can go here to review the math on converting Watt-hours to calories. Considering my training was compromised that week I tested (442 TSS), my initial reaction was that the incremental 741 kCal seems doable. Taking a different view, at my current FTP of 223 W, 60 min / day at 206 W is right around 600 TSS per week. My gut reaction to that number feels very different. I don’t know that I’ve ever sustained 1000 TSS/week for any extended period and I am sure it would be quite hard to hold week after week.

I can also assess my EA, which is the key to maintaining basic health and recovery. EA is what tells you if you are in RED-S territory or not. My EA was:

45.6 kCal / kg = (3284 - 559 kCal)/(131.6 lbs LBM * 2.2 kg/lb).

The threshold for RED-S in men in generally regarded as about 40 kCal/kg although I find some differences in that cutoff depending on where I look. Either way, I’m in the safe zone on this number. Recall that for me, energy expenditure equaled calories consumed, as I was in balance.

Finally, DLW also provides an accurate body comp assessment via a method known as deuterium (isotope) dilution. Calorify said my BF% was 13.4% (which is how I got to 131.6 lbs LBM in the EA calculation above). This jives because my DEXA about 6 weeks prior was 14.4% and I know I leaned out a bit as my training ramped up.

I hope you found this informative and it gave you some ideas about how DLW testing might support your own athletic goals. In future installments I’ll share more of the research conducted with DLW and some of the findings. In the meantime, ask me anything.