Engaging ATP-PC: The Primal Energy Pathway

Whenever Grok needed to lift something really, really heavy, he drew upon the adenosine triphosphate phospho-creatine (ATP-PC) energy system. If he saw an opportunity to cut off a fleeing buck and had mere seconds to act, Grok would engage his ATP-PC energy to summon the requisite sprinting speed. Today, we use the very same energy pathways. The very same potential for feats of immense, instantaneous strength and power resides in our muscles (some of us more than others, sure, but that can be altered through training). Of course, the ATP-PC energy system is just one of three primary pathways in our bodies. All three utilize adenosine triphosphate (ATP) as the primary energy source, but the speed, intensity, and duration of our muscle contractions determine exactly how that ATP energy is tapped, released and recycled.

Like I said, the ATP-PC system is the path to instant, raw power, but it doesn’t last for long. It’s our first choice for immediate high energy, and we can tap into it for around 10-15 seconds of maximum output, almost like touching flame to gasoline. ATP already present in the muscle is used and then reproduced (recycled) by breaking down creatine phosphate (the same stuff that’s sold over the counter also stores naturally in our muscles). It flares up brilliantly and fleetingly and allows us to move big weights or run really fast, and then it goes out. Sprinters, heavy lifters, golfers (yes, golfers!), home run hitters – these guys all have to engage their ATP-PC system to perform at a high level.

After we’ve exhausted our ATP-PC, anaerobic glycolysis begins to kick in. Also called the glycolytic or lactic acid system, the anaerobic energy system breaks down some of our muscle glycogen to form more ATP. Our muscles are thusly fueled, but the byproducts are the production of lactate and a dramatic increase in hydrogen ion (acid) secretion. The burn you get when you sprint for longer than 20 seconds, do Tabata intervals, or reach higher reps on the weights? That’s the build-up of these hydrogen ions which literally prevent further muscle contractions at high levels. You can go longer in this zone than on ATP-PC, but you can’t go as hard or as heavy. One nice side effect of the lactate and hydrogen ion production is improved human growth hormone secretion, which is partly why moderately-higher reps are effective for increasing muscle mass (to a point).

The next level is aerobic energy production. This kicks in after about five minutes of output, supplementing the anaerobic pathway (but not fully replacing it until around half an hour of work). The aerobic energy system, unlike the anaerobic pathway, requires both oxygen (hence “aero”) and glycogen to produce enough ATP to fuel our muscle contractions. Yes, fat (fatty acids) contributes to this phase of energy production, but glycogen is still the limiting factor. Though there are certainly healthy doses of aerobic activity allowed and encouraged (slower is better), on the Primal fitness plan there is much less emphasis put on this aerobic energy path. I was a long-distance aerobic junky, as you probably already know, for years. It required massive amounts of carb-derived glycogen. For our purposes here – building muscle, increasing strength, reducing insulin load, overall better health – extended, high-end aerobic exercise (chronic cardio) can be counterproductive. Still, it’s nice to know that a level of long-range energy production is there if we need it.

What really interests me is the ATP-PC pathway. It’s the most purely Primal, visceral energy system and seems to be the key to developing raw strength (without necessarily getting “huge”). When I tried cycling the supplement creatine a few years back and got some appreciable strength gains for the duration, I was simply increasing my muscles’ short-term ATP reservoir. My creatine post a couple weeks back got me thinking. What if I were to engage my ATP-PC pathway exclusively – would I then increase my ATP stores along with my strength?

So for the past couple weeks, I’ve been trying something new on those occasional days I’m in the weight room (because otherwise I’m doing mostly bodyweight stuff as a rule now). Instead of lifting moderately heavy stuff for a few sets of 10-12 reps, I tried lifting a heavier weight for 5-6 reps until muscle fatigue, followed by a 5-10 second long break where I maintained the weight in the “starting” position while recovering. I then attempted another single rep, rested 5-10 seconds again and so on until I was at true “failure” and couldn’t do another. Most literature I’ve come across suggests that the ATP-PC pathway replenishes fairly quickly, especially if you’re already a trained athlete, so I was hoping I could take advantage of that. I didn’t want to venture into anaerobic glycolysis; I wanted to strictly stay in the ATP-PC zone. For the most part, I was able to pound out reasonably heavy weights repeatedly, as long as I rested a few seconds in between each rep. Because I was only spending around 1-2 seconds per rep, I wasn’t using all my ATP, so the recovery time was more manageable (as opposed to the recovery time after all-out 10 second sprints, for example). After a few sets of squats, deadlifts, weighted pull-ups and presses, I was totally beat.

I wasn’t breathing especially hard, though, and I wasn’t sore. I felt (for lack of a better word) Primal and totally energized. And over the past two weeks, the weights have gotten heavier and I’ve felt stronger. Now, it could be that the strength gains came simply because I was really focusing on pushing heavier weights and not because of any energy pathway tinkering, but I don’t know. I definitely felt a difference. If nothing else, it’s a refreshing way to lift weights, get stronger, and maybe even burn some fat (the ATP replenishment process draws on stored body fat, so depleting your body’s supply is great for leaning out). When I do find myself in the gym and just hitting the weights, I think I’ll try lifting this way a bit more often for a change of pace.

If anyone wants to try this out, I’d be interested to hear how it goes. Let us know in the comments!

About the Author

Mark Sisson is the founder of Mark’s Daily Apple, godfather to the Primal food and lifestyle movement, and the New York Times bestselling author of The Keto Reset Diet. His latest book is Keto for Life, where he discusses how he combines the keto diet with a Primal lifestyle for optimal health and longevity. Mark is the author of numerous other books as well, including The Primal Blueprint, which was credited with turbocharging the growth of the primal/paleo movement back in 2009. After spending three decades researching and educating folks on why food is the key component to achieving and maintaining optimal wellness, Mark launched Primal Kitchen, a real-food company that creates Primal/paleo, keto, and Whole30-friendly kitchen staples.

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41 thoughts on “Engaging ATP-PC: The Primal Energy Pathway”

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  1. Have you been reading Body by Science, by any chance? 🙂 I know @paynowlivelater has been experimenting with it, and probably a few others in the #primal community. Definitely seems interesting.

  2. Mark, seems like you are Alactic training as described by Art Devany. He uses that cycles that with his hierarchal sets. I do the same but with Doug McGuffs BBS.

  3. Hey Mark! What about the lactate shuttle system – the so-called “fourth energy pathway”? It’s only really been “discovered” by the exercise physiologists in the last few years, but it seems to explain why high intensity training like CrossFit or what you do seems to work. Smart coaches and athletes always knew this stuff worked, but now the science guys have given it a biological explanation. As far as my understanding goes, the lactate shuttle system turns lactic acid back into energy directly in the muslces rather than cycling it out as a by-product into the blood stream and over to the liver for processing. Please correct me if I’m wrong!

    People used to think lactic acid was what caused muscular fatigue, based on that old french study using dead frog legs. Turns out lactic acid was actually a highly efficient fuel source generated in the muscles as they approached fatigue where glycogen and ATP sources were depleted. Once again it was one of those cases where researchers confused two things that occur together (lactic acid and muscular fatigue) with one thing CAUSING another.

    The body sure is an endlessly fascinating machine!

  4. Hi Mark,

    Is your goal to avoid glycolysis purely based on improving strength, or is there another reason that’s based more on avoiding unnecessary burden?

    If not for the same reason, why do you prefer body weight exercises over lifting weights?


    1. I don’t know about Mark, but I prefer body weight exercises because they’re cheaper. Gym membership costs money. Weight set costs money. Body weight, I’ve got lots of that, and it’s all free!

      1. I hear you, Furious Mittens. More and more these days I’m doing bodyweight exercises as my main routine focus.

  5. Would people who don’t want to bulk up want to do this? I’m not one to use those dinky pink 3 pound weights, but I’m still careful about wanting to “tone” rather than “bulk up” being a woman. Maybe its me still fighting CW that makes me not want to use super high weights for only a couple reps…

      1. Maybe I am just unusual, but I do carry around a lot of lean mass even when I am not weight training. When I work out, I really have to be careful with my legs, or they look “husky” YMMV, but i don’t think it is true for all women that there will be no bulkiness anywhere. Blame my good Slavic genes I guess.

        1. Maybe you are unusual, but I wish you weren’t.

          Bird legs are for the birds, and I don’t mean the British kind.

    1. Sure. Its all going to come down to your diet. Plus, women dont possess the harmones to get huge unless you’re a freak. You’ll gain some muscle mass but you’ll still be lean, especially that you’ll be burning fat as well with heavy lifting. Correct me if I’m wrong 🙂

  6. This is the same as described by Fredrick Hahn in “The Slow Burn Fitness Revolution”.

    Just finished reading the book and will be giving it a try.

    Thanks for the more scientific explanation.

    1. Eastburce, That’s exactly what I was thinking. Good book. The focus is on small (slow) intense reps to failure of each muscle group so the body goes into a muscle building / repair mode.

      Its a REALLY quick way to build noticeable muscle mass – esp when combined with a quality primal or low-carb high-protein diet.

      Its nice to hear Mark heading down that path too – I like it when all my “teachers” begin to agree on specific things. 🙂

  7. I’ve heard of similar strength training strategies being used before – so there must be something to it.

    But I don’t think we have enough research to know about the ATP-PC adaptations as a result of specific training and its impact on performance. So, my guess would be that it’s simply a new physiological adaptation based on a new training program – you’ve likely found the sweet spot between progression and variation.

  8. Nice!! I’ve been doing a heavy, 4×5 (4 sets x 5 reps) program, but it’s about to come to a close. I’m going to research the stopping and re-starting as my next cycle.

    Note that when I do this program, I can eat like a madman and the weight goes on as muscle with just a touch of fat.

    Since cutting down for my triathlon, I’ve put on 10 pounds, and I’d say 8lbs was muscle. Definitely a primal-friendly routine, and I am by far the craziest and loudest dude in the gym.

  9. Jocelyn R,
    Lactic acid doesn’t actually exist in the human body. What does exist is lactate and hydrogen ions as a by-product of the glycolytic system. The lactate is reused by the muscles for fuel, while the acidosis from the hydrogen ions results in reduced ability of the muscle to contract (i.e., decreasing power). You can train your body to better use lactate and buffer hydrogen ions.

    Scott Kustes
    Fitness Spotlight

      1. Thanks Jocelyn!

        Of course, training to increase one’s lactate threshold is a painful, humbling endeavor. I did a workout the other day of 2 x (4 x 225m) @ 29-31 seconds per run. 4:00 between runs, 15:00 between sets. The purpose is that each run results in an increase in lactate and acidosis and 4:00 is an incomplete rest. By the 4th run of the set, it’s like a duel to the death…it’s like you stuck your legs in an acid bath.

        It’s brutal, but it works. I wasn’t even able to finish the 2nd set…over-programmed that workout having never done one like it before.

        Scott Kustes
        Fitness Spotlight

  10. Really nice overview of the topic Mark! And your experimental attitude in the weight room is awesome. Christian Thibaudeau has written some good stuff about the basic approach you’re using. It’s essentially a variation on what he calls Cluster Training.

    But I’m with ya… When the sun is shining I’m outdoors with bodyweight exercise!!


  11. Nice article Mark. The only anaerobic workouts I do now are using burpees, weighted chins/push ups/squats (tabata and over interval methods) and of course hill sprints (my worst nightmares!. I packed the weights in last year. I look forward to seeing where this type of training takes you. Cheers, Andy.

  12. Scott, appreciate the breakdown(of the breakdown). True on all fronts. Lactate is a fuel substrate in and of itself (cardiac muscle likes it). It’s acidosis we feel when the work load overwhelms (my training buddy used to call it “plastic asses”). Thanks, too, Jocelyn for pointing that out.

    Ryan, to be clear, I an not doing slow stuff here, but stay as dynamic (almost explosive) as form will allow. I almost never do slow, steady stuff on weights.

    Jane, no intention of bulking up here…I am shooting for maximum power-to-weight ratio. Pure strength. As Jim says, unless you are shooting up the ‘roids, you won’t “bulk up.”

    The reason I generally prefer bodyweight exercise is the fuller range of motion and the greater involvement of complementary muscle groups. It’s more about balance and symmetry. The increase in strength I get from these sets described above can be applied to the bodyweight stuff later.

    1. Mark,

      your training here is similar to what I’ve been doing, a variant of rest-pause training.

      There are many brands of this, but what I do is pick a weight that’s around 85-90% of my 1RM in the weighted pullup, weighted dip, press, or deadlift, and I do 1 rep every 20 or 30 seconds, on a timer, for about 10-15 total reps. This allows me to focus more on these high-power energy pathways, and I feel the same pump you describe after workouts. I also only work a given muscle group like this once every 7-10 days because the fatigue is so deep.


    2. Gotcha. Thanks for clarifying, Mark.

      I actually tried it today. Very VERY nice. I was doing 5-8 heavy reps to failure before (sometimes slow and sometimes quick).

      In comparison, If my old way was my version of “to failure”, then doing what you talk about above (with the same weight) DEF qualifies as “UTTER failure”. : )

      Very nice. Cheers!

  13. Bill Starr 5×5 type routine. Classic style that many, many strength coaches have used to help their athletes gain strength. Sounds like you are tapping into that area.

    I personally like to change my routines often and use various forms of full body routines, 5×5, split rountines, body-weight, etc.
    I like the change and think my body does also.

  14. When I was doing bodybuilder-style “upper body, lower body” days with the accepted set and rep schemes- 8-10 reps, three sets- three to four times a week, I made some progress.

    When I started doing Crossfit in which weights-only days are maybe once a week, usually only one move, very heavy weights, I made much, much more progress. Training for a year on the old scheme my maximum back squat never exceeded about 80 pounds on a good day; training for a few months like I am now and it shot up to 120. I’m sure I could get it much higher if I were focusing on strength exclusively.

    So regardless of biochemical basis, I do believe there’s something to that training pattern…

    1. CrossFit works no doubt, the problem is going 3 on 1 off for years without enough rest will eventually lead to burnout as well as overtraining. Planned rest cycles are just as important in CrossFit as they are in any routine, and people who go cultish with CrossFit are much more prone to injury than those who take a periodic complete week off or do scaled down weeks.

      1. AHAHAHAHAHHAHA dude if you knew me outside a comment box on the interweb you’d know I am waaaaaay far away from being one of the cultish folks. I do take rest cycles both planned and whenever I judge I’m feeling a little too cumulatively tore up.

        And yes, I do believe this is why I’ve never been injured beyond a mild muscle “tweak” that takes a few days of not doing feindish amounts of work with that muscle group to heal up.

        Observing that it works much better for me than traditional bodybuilding ain’t the same as an indicator I’m swimming in the Kool-Aid. 🙂

  15. Sounds like clusters, where you set the weight down and rest about 10 seconds between reps, for somewhere around 5 reps. I use this for deadlifting because I have to reset my feet, regrip, and realign between every rep to make sure I don’t hurt myself. It amounts to about 8 or 10 seconds.

  16. Hi mark,
    and firstly thanks for a lifechanging website. I started on the primal or actually ef way of life (as i first got the spark from art devanys site) 2 years ago. It was an easy shift for me as i had already left out grains from my “diet” before that and had also been lifting weights and also hiking for years. Untill just recently (untill about 3 months ago) i had been a firm believer in weights, bodyweightcirquits and HIIT with very occasional SS cardio (dogwalking mostly and hiking). I avoided long-duration highimpact cardio like the plague- mostly because i was afraid to ruin my hardearned muscular physique and also because i wanted to avoid fatigue as my diet is just too low on carbs to sustain long aerobic workouts. But about 3 months ago my life changed (moved out of town and got a new job. Now i live 50 km from work, with no public transport near and 1 car in the family. That forced me to come up with a solution- now i bike to work 2-3 times a week. My bike is a proffessional one and the terrain is hilly so its quite a workout- 2 h allout effort (one way). Sometimes i do both ways in one day, but i rearly have the need for that. And what has changed?- NOTHING!! I have still all the energy, i still lift weights n do bodyweight cirquits 2-3 x a week, i have a huge garden n lots of work there- ( for example taking down a couple of trees every weekend to get wood for winter). N i havent changed my eating- its still at about 40% protein, 40% fat n 20% fibrous carbs from veggies, berries n fruits…
    N i havent lost any musclemass either…
    Plus i enjoy the biking early in the morning in fresh awakening neture pushing my muscles up the next hill n speeding down afterwards with wind in my face n great music in my ears… I have been thinking that is it maybe more individual… do i simply “endure” cardio better?? Maybe i have a good glucose-sensitivity history? Whats up w that? Would just like to know the scientific explanation…..

    Thanx for reading n greetings from the middle of nowhere in the Finnish forests :))


    1. Eva,

      Some are born with a genetic and physiologic advantage, like myself, for endurance exercise.

      I don´t agree with the bashing endurance sport is receiving. If performed and trained properly, it is perfectly safe.

      Marathons and endurance exercise should not be undertaken without a proper cardiovascular checkup to rule out any potential cardiac problems.


      1. The biggest problem with endurance exercise is that few people incorporate any kind of strength training to manage the imbalances that too much running causes. Also, few are actually running at a good clip. Most people just plod along at 10-12 minute miles for years on end, never actually improving.

        Though marathons are an excessive amount of wear and tear on the body if undertaken too often.

        Scott Kustes
        Fitness Spotlight.

        1. Running is not the only form of Endurance exercise. Rowing, biking and swimming are all much better than running. An yes, strength exercise must be incorporated.

          I compete in several bike marathons every year, including stage races. I never have any problems.

          In the off season, I lift 3x a week. During the biking season, only 1x per week, usually just powerclean/pushpresses (20 sets of 3 reps) some pullups and rings.


  17. I’ve been performing 6 to 8 exercises twice per week (and for the last two months, only once per week) since February. Before then, it had been years since I regularly went to the gym. My routine has been to perform 10 second reps (5 seconds positive, 5 seconds negative) in a single set of 8 to 12 reps. These rep amounts have not been hard and fast rules, but rather just the approximate amount of time it takes to reach muscular failure. If I’m able to do more reps, then the next time I increase the weight.

    In the 5 months since I started using this method, my maximum chest press has gone from 66 lbs to 111 lbs; my pull down from 88 to 122; and my leg press maximum has increased to 288, up from 181. I have gained 15 pounds of muscle, and my body fat has decreased from 19% to 13%.

    All in about 30 minutes per week! (Okay, an hour per week if you count the time you spend lying on the floor, utterly drained and unable to move, when it’s all over).

  18. Mark,
    Great stuff, as always.
    I love hearing about expirimentation with Fitness. It’s often hard for athletes (or non-ahtletes) to take the leap of faith from where they are so comfortable (ala your departure from chronic cardio).

    At the lowest level of approach, if you lift heavy often, and fuel appropriately, you will get stronger. The minutia is in the specific approach. Yep, Devany has written on similar approaches. Rippetoe (“starting strength”) allows more time for CNS recovery following near maximal loading efforts. In the end, it comes down to the desired outcome. I posted on your blog last week about CrossFit and the efficacy of any protocol that helps us do what we were genetically designed to do. My athletes range from elite Special Forces soldiers to 67 year old grandmas. They all reap the benefits of moving large weights (relative to their abilities…and this includes their body weight!) over varying distances quickly. Sometimes, we get lost in the approach. What I really like is that you quantified HOW YOU FELT after doing it. Sometimes, the numbers aren’t our best indicators of progress (ala your “scale” post). I’ll borrow a phrase from one of my Nutrition Mentors, Robb Wolf: “Ask yourself: how do you feel, how do you look, how do you perform?” So often I hear of people feeling like crap, looking like crap and performing like crap…but they stick with what they’re doing because a magazine, or their friend said it was the thing to do and they’ve been doing it for 15 years. Come to think of it, i just had a heated discussion with a Registered Dietician with the same dogmatic and stagnant approach–i feel for her clients. Leaping from our security into the unknown potential of “other ways” is difficult, but it often leads the most rewarding gains we’ll ever experience.
    Keep up the remarkable work!!


  19. It’s called rest / pause training. The technique has been around in the bodybuilding world for decades.

  20. Lately I like to use the 30-40 second set rule….and then increase weights progressively each workout (using an A/B workout day type of split). Could be 10 reps one week…increase the lbs next workout and then it could be 6 with pauses…continue 10% increases for a few weeks, then step back down the weights and go again. I’ve found more continual strength and muscle growth in that strategy alone (plus it’s fun and I enjoy it).

  21. Smurf, what are “negatives” ?..

    Mark, you should write up a post sometime on the specifics of your body weight routines. My routines are (unintentionally) only bodyweight, so I’d love if you gave some ideas that posed some new challenges. 🙂

    1. The negative portion of an exercise (also called eccentric) is the part where you lower the weight back to your starting position. For example on bench press it is the portion where you lower the weight to your chest, as opposed the the positive/concentric part where you push the weight away from your chest.

      BTW – You are MUCH stronger on the eccentric portion and many people have routines where they train only the eccentric portion and make great strength gains. An example: on a pullup using a step stool to jump to the top position and then very slowly lower yourself back down and repeat again.

  22. This sounds similar to what is often recommended for Chronic Fatigue Syndrome. People with this condition easily go into anaerobic respiration, even during aerobic activity. So doing strengthening is better, with few reps and lots of rest breaks. People with CFS have to pace their daily activities as well. The ATP system is believed to be impaired in individuals with CFS and fibromyalgia. Some of the pain is from lactic acid (besides a dysfunctional central nervous system).