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!