Where is your energy actually made?
Energy is not an abstraction. Nearly every cell you own contains mitochondria, microscopic power stations that turn food and oxygen into the currency every heartbeat, thought and step is paid in. And here is the fact that changes everything: their number and capacity are not fixed. In one of the founding experiments of modern exercise physiology, Washington University’s John Holloszy showed that when muscle is asked to work regularly, it responds by building more mitochondrial machinery, substantially more. Your energy supply is not a fuel gauge you are stuck with. It is infrastructure, and infrastructure responds to demand.
Why does spending energy make more of it?
That is why the strangest finding in energy research keeps replicating. At the University of Georgia, researchers took sedentary adults with persistent, unexplained fatigue and prescribed, of all things, exercise. Six weeks of regular, gentle movement significantly lifted feelings of energy and cut fatigue, and the low-intensity group did as well or better than the harder-working one. Energy does not behave like money in a vault, where spending leaves less. It behaves like a muscle: used wisely, the capacity grows. Saved too carefully, it quietly shrinks.
Who keeps your energy budget?
Supply is only half the story, someone has to run the budget. Neuroscience increasingly describes the brain’s core job as exactly that: a body budget, continuously predicting what the day will demand and allocating resources ahead of need, the framework laid out in Nature Reviews Neuroscience. The treasurer is your nervous system, and its allocation policy depends on the state it believes you are in. A system that reads the world as safe invests in repair, digestion, learning: the things that feel like energy. A system stuck on high alert runs the most expensive program in the body: vigilance, everywhere, all the time.
This is not metaphor. Columbia’s Martin Picard, with Rockefeller’s Bruce McEwen, reviewed the evidence that chronic stress reaches all the way down to the mitochondria themselves: altering their function and, over time, their health. Sustained vigilance doesn’t just spend your energy. It degrades the equipment that makes it.
Why is the budget balanced at night?
And the budget is balanced at night. University of Pennsylvania researchers restricted healthy adults to six hours of sleep, an amount many people call normal, and watched performance fall night after night, accumulating like a debt. The unsettling part: by the end, the sleep-restricted group rated themselves as only mildly tired while performing like people who had missed a whole night. Chronic energy shortage hides from the person carrying it. If your baseline has drifted down slowly, you may not feel what is missing: which is exactly why it is worth measuring rather than guessing.
How much capacity can actually be built?
A surprising amount, and faster than most people assume. Holloszy’s discovery has since been traced to its controlling switch: a molecule called PGC-1 alpha, characterised by Bruce Spiegelman’s group at Harvard, which acts as the chief regulator of mitochondrial biogenesis. Demand raises it; raised, it instructs the cell to build more power stations. Weeks of regular endurance work can substantially increase the mitochondrial content of trained muscle. This is infrastructure being laid, not a battery being topped up.
And the dose required is smaller than the gym implies. Martin Gibala’s group at McMaster University has shown repeatedly that brief, low-volume interval work, a handful of hard efforts inside a short session, produces mitochondrial and metabolic adaptations comparable to far longer moderate training. That matters for exactly the people who feel they have no energy to spare: the entry price to building capacity is minutes, not hours. Which is fortunate, because the people who most need the adaptation are the least able to afford the traditional prescription.
Why does the afternoon dip happen?
Almost everyone blames lunch. Lunch is largely innocent. The Swiss sleep researcher Alexander Borbély described human alertness as the sum of two independent processes: a sleep pressure that builds steadily from the moment you wake, and a circadian rhythm that rises and falls on its own schedule regardless of what you have eaten. Those two curves cross in the early-to-mid afternoon, producing a genuine dip that shows up even in people who skip the meal entirely.
This is worth knowing because of what people do about it. A dip that is circadian in origin is not evidence of a failing, and it does not require correcting with a third coffee: which, taken after about two in the afternoon, buys alertness now at the cost of the sleep that would have paid for tomorrow. The dip is a scheduling problem, not an energy problem. The most reliable response is to put the least demanding work of the day in it.
Why does light set the supply?
Because the budget runs on a clock, and the clock is set by light. The human circadian pacemaker, as Charles Czeisler’s work at Harvard established, runs to a period very slightly longer than twenty-four hours and must be reset daily, and the principal signal that resets it is bright light reaching the eye in the morning. Get it, and the whole cascade lines up: alertness rises on schedule, the evening melatonin rise arrives on time, and sleep pressure lands when you want it to. Miss it, and the clock drifts later, which is felt not as a timing problem but as tiredness.
The asymmetry is the useful part. Indoor lighting is far dimmer than most people realise, typically a small fraction of what an overcast morning outdoors delivers. Ten or fifteen minutes outside early, without sunglasses, is a larger intervention than almost anything sold as an energy product, and it costs nothing. We have written about this at greater length in our article on morning light.
When is tiredness a question for your GP?
This article is about capacity, which is the right frame for most ordinary tiredness. It is not the right frame for all of it, and we would be doing you a disservice to pretend otherwise. Persistent, unexplained fatigue is one of the most common reasons people see a GP, and a number of the causes are straightforward to identify with a conversation and a blood test.
Worth a medical conversation rather than a lifestyle one: fatigue that came on suddenly or has a clear starting date; tiredness with breathlessness, unusual pallor, or heavier-than-usual periods; unexplained weight change; loud snoring with unrefreshing sleep and daytime sleepiness; excessive thirst or urination; persistent low mood or loss of interest; fatigue alongside any new symptom you cannot account for; or simply tiredness that has not shifted over months despite sleeping, eating and moving reasonably well.
Iron deficiency, thyroid function, blood sugar, sleep apnoea, coeliac disease, medication effects and depression are all common, all worth ruling in or out, and none of them is something a wellness practice should be guessing at. Please see your GP. The capacity-building described in this article works better, not worse, when whatever else is going on has been properly looked at.
How does Diskin Life support the energy budget?
We named our approach around this. Vitality, energy you can actually spend, is what Premium Vitality means, and everything we do serves the two sides of the ledger this article describes. On the supply side, the levers are yours, and the 13 Vitality By Design presentations teach them: Respond Better, Move Better, Eat Better, Think Better. On the budget side, our care works with the treasurer itself: gentle, Whole-Person support for a nervous system stuck in its most expensive mode, so the spend on defence can come back down and the investment in repair can come back up. The Life Assessment shows where your budget is actually going, measured against your own baseline, not a guess. We’ve written elsewhere about the drains (The Energy Equation); this is the other half of the story. Energy is made, not found, and the body that makes it responds to how it is asked, rested, fed and regulated.
General information only, not a diagnosis or personal health advice. Persistent fatigue can have many causes, for questions about your energy and health, please also speak with your GP.