Physical Activity Level: The Most Important Training Metric You’ve Never Heard Of
All serious athletes track training volume. Whether it’s weekly mileage as a runner, yards as a swimmer, CTL in TrainingPeaks, or sets and reps in the gym, understanding the total amount of work you’re doing as an athlete is essential.
The problem is that each of these metrics are crude proxies for what you really need to know: the total amount of work you’re doing. How much is too much? How do you plan your training volume?
Just how big of an issue is this?
No one really knows, but many suspect it’s a fundamental issue with athletic performance. Dr. Aitor Viribay Morales, Lead Performance Nutritionist for Team Ineos Grenadiers, a top World Tour cycling team, says, “Energy budget is probably the most determinant factor in endurance performance, limiting the capacity to adapt and perform. There is not movement without speed. There is not speed without force. There is not power without calories.”
What we need is a quantitative measure of the total amount of work you do above your baseline. This includes your exercise calories, of course, but also your nonexercise calories like fidgeting, digestion, grocery shopping, and picking up the kids.
Enter PAL: Physical Activity Level, the most important training metric you’ve never heard of.
PAL, also known as metabolic scope, is defined as ratio between the total calories you burn and the calories you burn at rest. In jargon: Total Energy Expenditure / Basal Metabolic Rate. Essentially, this means your total activity above your personal baseline…how much energy you burn above rest relative to your body size.
Calorify is the world’s only test that can measure PAL because other real-world tests do not measure total energy expenditure (the total number of calories you burn each day). Nutritionists, trainers, and sports scientists are often forced to guess this number when using other techniques such as a resting metabolic rate test or DEXA scan.
Take the example of a top professional running group that we’re working with. We tested an elite group of runners who all had similar lean body mass and all ran approximately the same amount during test week. We found that the runners burned vastly different calories… with a spread of up to 1000 calories per day! We’ve found similar results on an NBA team, with players burning thousands of calories different than their teammates!
What can account for these huge discrepancies between athletes doing the same training? Variations in nonexercise calories can be enormous! Things like stress and anxiety burn calories. Your immune system burns calories, so an overactive immune system like an autoimmune disease can increase your metabolic rate. Differences in diet can change the energy required to digest food. Fidgeting can account for large differences between individuals. And then there are all of the other differences in lifestyle. Think of all the activity you do between waking and sleeping that isn’t purposeful exercise.
OK, there are differences between individuals and how much they burn. What does that mean for me?
At Calorify, we’re on the front lines of using and interpreting PAL as a training metric. Until now, no one has ever been able to receive doubly labeled water results quickly enough to modify their training based on the results. But here’s what we’ve learned so far:
When we rank athletes doing the same work according to PAL, they stack from most injury prone to least injury prone. Essentially, the athletes with a lower PAL at the same workload have a greater energy reserve with which to either train more or recover. In the NBA, we’ve noticed athletes with a high PAL have a hard time maintaining or gaining weight.
Further, at Calorify we can calculate a sustainability time for any PAL based on current world records for endurance and ultra endurance sports. We’ve found an oddly close relationship between sustainability time and the interval at which athletes get sick or injured. A PAL of over ~2.5 is linked to an unsustainable level of activity.
Ultimately, in order to sustain a high PAL, you need to bring on sufficient calories in order to recover and maintain weight. If you can’t meet the energy demands of your activity level, you’ll either get injured, sick, need to reduce activity or lose weight. There are fundamental limits to PAL…a topic for a separate post.
What PAL should I have?
PAL is the ultimate indicator of your activity. There are no accepted PAL values for overall wellbeing, but generally, we recommend a PAL of at least 1.6, which we define as moderately active. This means you’re burning 60% more calories than at rest, which translates to moderate exercise a few times per week. More athletic folks often fall in the 1.8 – 2.0 range, with top athletes often residing in the 2.0 – 2.5 range. We consider a PAL of 2.5 and above to be overreaching, though we acknowledge the 2.5 threshold to be poorly constrained in the literature and probably determined by individual variability. More on this topic in our upcoming post on the limits of PAL!
Are men and women different metabolically?
Yes and no, but with an emphasis on no. Men and women tend to differ in their amount of lean body mass, which drives differences in basal metabolic rate. So while men tend to burn more calories overall, they don’t seem to burn more compared to their personal baseline as measured by PAL. When we analyze the Calorify leaderboards for PAL- essentially the most active customers we’ve ever measured- the results are split between men and women. Here’s how our results stack:
Female 3.20 Professional runner
Male 3.18 NBA Player
Female 3.05 Professional runner
Male 3.03 Amateur bodybuilder
Male 3.03 Amateur bodybuilder
Female 2.91 Professional wrestler
Male 2.91 Recreational triathlete
Male 2.89 Strength coach
Female 2.73 Amateur multi-sport athlete
Male 2.70 Professional racquet sport athlete
How do I optimize my energy budget?
There are two sides to the energy budget equation: calories in and calories out. First, make sure you’re getting the calories you need to fuel your activity. If your activity level is higher than 2.5, this may be challenging, and, if you continue to perform this level of activity, may lead to weight loss. If you’re limited in calories due to your high activity level, we recommend focusing on easy-to-digest foods and gut health. Essentially, the goal is to maximize your caloric paycheck. For calories out, it’s all about how you spend your caloric paycheck. As an athlete, you’d likely prefer to spend your paycheck on training as opposed to anxiety, fidgeting or an autoimmune issue. This is where an emphasis on recovery, lifestyle and mental health can become a focus for your performance goals.
What can Calorify’s PAL measurement do for me?
PAL is a fundamental measure of who you are. So much of ourselves comes down to diet and exercise, and Calorify gets to the heart of these by quantifying your calories in – calories out budget, body composition and activity level. Reach out to us and we’ll work with you to meet your goals.