For today’s edition of Dear Mark , I’m answering three reader questions. First, do anaerobic workouts—sprints , lifting , etc.—interfere with your ability to become a fat-burning , aerobic beast, or can you integrate them? Next, in last week’s post  I talked a lot about glycogen depletion in the context of the “sleep-low” carb partitioning. How can we actually achieve this without doing the intense intervals the elite triathletes were doing in the study? And finally, does carb-fasting after strength training also work?
I’ve read Primal Fitness, 21 Day, and now am halfway thru Primal Endurance. You could say I believe in and am an example of the efficacy of your teaching. I’ve been using the 4 days of play, 2 days of LHT, and one day of HIIT as outlined in PF and 21. My confusion comes from the emphasis in Primal Endurance on staying aerobic and how even a short duration of anaerobic can negatively effect body’s ability to function aerobically. I find even when playing Frisbee on a play day I can get my heart rate above my aerobic max after a short sprint, and I definitely get above my max aerobic HR when I do the LHT sessions and HIIT sessions. Im not training for any endurance competitions, just like being really fit so Im thinking the primal endurance model is more focused on those training for super endurance activity but any clarification of the confusion I have re aerobic and anaerobic would be appreciated.
Getting the heart rate up briefly on occasion as you are doing is good and won’t jeopardize your fat-burning pursuits. In the book, we emphasize becoming as efficient as possible at burning fat at the “low end” before you start adding speed if you are seeking the most efficient way to get to racing faster by burning more fat. For that reason, we like picking some workouts where you stay at or below that aerobic zone for as long as possible. So if you are training for a marathon, triathlon or Spartan event, you might put a few more of those dedicated low HR sessions into your routine. But doing harder workouts that rely more on glycogen for energy won’t “ruin” your aerobic base, especially if you’re just a “regular” exerciser looking to get fit, strong, fast, and more attractive. They’ll actually improve your ability to burn fat.
The problems arise when you rely on glycogen all the time and never force your body a chance to rely on fat. So in your case, mixing it up is fine and fun and desirable. I always hammer on this point, and it bears true here: there are no “right” answers here, just choices. In Primal Endurance , we wanted to offer choices that got you to your maximum fat-burning efficiency fastest for those athletes who needed it. People who aren’t hardcore endurance athletes can still learn from and implement the concepts described in the book, but they don’t “have” to follow them to a tee.
“Whatever you do, be sure to really deplete glycogen and wait for 12-16 hours to refill it.”
How do you know when you’ve depleted your glycogen?
Great question. Let’s talk about glycogen depletion.
Glycogen depletion is localized . High rep bicep curls will deplete bicep glycogen . They will not affect glycogen stored in other muscles. Compound movements like squats  and deadlifts are better because they’ll deplete multiple sites.
The higher the intensity, the greater the glycogen depletion. Walking depletes very little glycogen. Sprinting depletes the most. Anytime you increase the intensity, you’re increasing the glycogen burn.
Some ideas for glycogen depletion workouts:
Kettlebell  complex: 10 swings, 10 clean and presses (5 each arm), 20 reverse lunges (10 each leg), 10 bent over rows (5 each arm). 5 rounds, no rest between movements, minute rest between rounds. You hit pretty much every muscle group. This basic concept can also be done with dumbbells, barbells, and even weight machines.
High rep burpees: Twenty burpees, performed as quickly and cleanly (don’t sacrifice form) as you can. Rest two minutes. Repeat at least 5 times. Burpees are great because they hit arms, chest, legs.
Hill sprints: Run longer sprints with longer rest periods. Throw in some pushups  and pullups  in between sprints to hit other body parts (because sprinting only depletes the lower body, especially the posterior chain—hamstrings and glutes) if location and available equipment permit. Maybe some bodyweight squats, too, which are pretty quad-dominant.
One way to tell if you’re depleting glycogen is the difficulty. If a workout is easy, you’re not depleting a ton. If a workout is grueling, you’re depleting it. Strike a balance between hard work, sustainability, and willingness to perform. Short ultra-intense sprints  might deplete the most glycogen per second, but how many seconds can you keep it up? 200-meter hill sprints with 5-minute rest periods will blast your lower body glycogen stores, but how willing are you to do that workout on a regular basis?
Another indication of glycogen depletion is if the workout increases glycogen uptake into muscles. If your muscles are taking in more glycogen after a workout, they probably depleted it during the workout. Both sprint and moderate intensity training increase muscle-specific glucose uptake . And strength training definitely increases muscle glucose uptake .
Does this still apply to the more traditional full-body strength workout? I would love to try if so. My carbs have been in the 200-250g range but I’m doing three strength workouts, a sprint workout, and the other days are pretty active playing sports or hiking with my 3 year old. Thanks!
Sure, why not? Full body resistance training and sprinting can certainly deplete glycogen. Maybe not as completely as if you were a triathlete doing long intense intervals every day, but it works. Remember that strength training definitely increases muscle glucose uptake , a strong indicator for prior depletion. And you’re also not eating 6 grams of carbs for every kg of bodyweight like the triathletes in the study were eating, meaning you don’t have as much to deplete. So give it a try. Keep your carb intake constant, just eat them before your workouts rather than after. Try to time it so that you end your carb-free time with a hike or other “low-moderate intensity” activity to really boost fat utilization.
Here’s how it might go:
- Eat your carbs.
- Sprint or strength train.
- Have some protein post-workout, maybe a little whey . No carbs.
- Avoid carbs for at least 12 hours. Eat low-carb vegetables, meat, fat. Nothing starchy, nothing sweet.
- End your “carb fast” with a hike, walk, or play session. Nothing too strenuous.
- Now eat some carbs.
Keep that 200-250 gram carb range going. The implications of the study from last week are that you can eat the same amount of carbs as long as you partition them differently. It’d be cool to see if this works in a standard strength trainee, too. Don’t see why it won’t.
That’s it for today. Any other glycogen-depleting workouts you guys can share?
Thanks for reading, everyone. If any of you have additional tips, input, or questions, leave them down below!