If you know all that, you're a smart alec, but do you also know how many calories you've really left at the gym during your last resistance training workout? I can guarantee, it's not what your fitness tracker is telling you.
Now, I would be lying if I told you that I knew the correct value, what I can and will tell you, however, is how you can get much closer to a realistic estimate by using the data from Rodrigo Ferro Magosso, et al.'s recent review "of the relationship between aerobic and anaerobic metabolism and the main factors that affect EE during RT exercises" (Magosso 2017). As the Brazilian researchers point out, it is common for to determine the exercise-induced energy expenditure (EE) of resistance exercise (RE) using oxygen uptake (VO2) measurements. In that, scientists will usually sum up the aerobic component, the amount of energy that's spent on excess post-exercise oxygen consumption (EPOC), and the anaerobic component to arrive at an estimate of the total energy requirements of the workout. An estimate that may hold up to three surprises.
Surprise #1: Most of the energy you spend during your resistance training sessions feeds into the aerobic (="cardio"), not the anaerobic (=sprint & lift) energy cycle
The first thing that may seem counter-intuitive is that the existing scientific evidence clearly indicates that, despite the predominance of anaerobic metabolism during the actual lifts, the largest part of the energy you spend during and after your gym sessions is spent aerobically.
Surprise #2: In response to strength training you burn hardly more energy than you would if you took your dog for the literally walk in the park.
As a SuppVersity reader this shouldn't be that surprising, but for a handful of bros who've always wondered why they're getting fat despite spending 2h in the gym on a daily basis, this may come as a revelation: the highest hitherto recorded energy expenditure during a resistance training workout is 8.3kcal/min that's significantly less than what you'd burn during a decently paced jog.
|Figure 2: Plot of the influence of rest intervals, sequential vs. super-set training and using a slow 4s vs. fast 2s rep tempo on the energy expenditure (kcal/min) of healthy subjects in selected studies (based on tabular overview in Magosso 2017).|
Surprise #3: A single rep burns hardly more extra calories than what your body requires to maintain its basal metabolic function
Likewise inaccurate is the assumption that you'd spend a lot of energy on the actual act of lifting a weight or, as it was the case for two out of three studies the results of which I've plotted for you in Figure 3, pushing it up on the bench.
|Figure 3: Effect of exercise intensity expressed in % of 1RM on energy expenditure per repetition (kcal/rep) in studies w/ trained individuals by Scott et al. (2006, 2009 & 2011 | based on tabular overview in Magosso 2017).|
As you can see, the energy expenditure per rep ranges from 0.42kcal/min to 1.99kcal/min and increases exponentially (you can see that in Scott 2009) with the amount of weight (relative to your one-rep max = 1RM) you lift.
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- Magosso, Rodrigo Ferro, José Campanholi Neto, and João Paulo. "A Review of Ergogenesis and Effect of Training Variables on Energy Expenditure in Resistance Training Exercises." (2017).
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- Scott, Christopher B. "Contribution of blood lactate to the energy expenditure of weight training." The Journal of Strength & Conditioning Research 20.2 (2006): 404-411.
- Scott, Christopher B., Alicia Croteau, and Tyler Ravlo. "Energy expenditure before, during, and after the bench press." The Journal of Strength & Conditioning Research 23.2 (2009): 611-618.
- Scott, Christopher B., Michael P. Leary, and Andrew J. TenBraak. "Energy expenditure characteristics of weight lifting: 2 sets to fatigue." Applied Physiology, Nutrition, and Metabolism 36.1 (2010): 115-120.
- Scott, Christopher B., et al. "Aerobic, anaerobic, and excess postexercise oxygen consumption energy expenditure of muscular endurance and strength: 1-set of bench press to muscular fatigue." The Journal of Strength & Conditioning Research 25.4 (2011): 903-908.