01 — THE EXPERIENCE OF ENERGY
The Misunderstanding of Energy
“Why am I always tired?” Most poeple assume energy is something you either have or you don’t. You wake up feeling good, feeling drained, or in between. You feel like you are in the zone and have a productive stretch, or you hit a wall and feel like you are in a swamp. The common assumption is that energy is something fixed, inherent to the individual or the circumstances and hence, outside of our control.
But this assumption is wrong, and it is the source of much of the confusion around energy levels and and the methods to improve them.
Energy is better understood as an output of multiple systems working together. It reflects how well the body is producing, allocating, and protecting usable capacity across the day. This is why the experience of energy can be so variable. You can be active, disciplined, and doing many of the right things, yet still feel flat. Or even worse: you could be feeling sharp and driven, but in reality you are quietly moving deeper into a hole.
Understanding why this happens requires a different way of thinking about how energy levels work.
Exercise is a good example. There is no doubt that regular training improves metabolic health, cardiovascular function, stress regulation, and long-term resilience. The data is in. It is also generally well accepted that exercise can increase energy levels. But here is the caveat: more work does not necessarily translate into feeling better. The body does not acutely respond to rising energy demands with unlimited energy production. Instead, it adapts, compensates, and reallocates. At a practical level, this means someone can be training harder while feeling drained – not because exercise is bad, but because energy is being deployed across a constrained system rather than being generated on demand and without limits.
Fatigue is not a simple readout of muscle failure or depleted willpower either. The brain and body are constantly regulating perceived effort to protect the system from running past what it can realistically sustain. This is why someone can feel exhausted halfway through a saparring session – well before being truly incapable, or feel alert while quietly accumulating strain they haven’t accounted for yet (borrowed energy).
This is the core misunderstanding and central topic of this article: some people treat energy like a feeling when in really it is a systems problem. Until that distinction is clear, it is easy to confuse stimulation with capacity, perception with reality, effort with adaptation, and short-term output with actual sustained performance.
The body does not acutely respond to rising energy demands with unlimited energy production. Instead, it adapts, compensates, and reallocates.
What Energy Actually Is (And Why You Keep Running Out of It)
Energy is not something the body stores and hands out on demand. It is something the body continuously produces, distributes, regulates, and spends based on current conditions.
At a practical level, energy depends on three systems working together:
THE THREE SYSTEMS
Production
How effectively the body generates usable energy from available fuel
Allocation
Where that energy is directed at any given moment
Constraint
The limits placed on total output to protect the system
Most people focus only on production. They assume that if they eat well, train hard, or use the right supplements, energy should simply increase. But a healthy body does not operate like a system that expands output indefinitely when demand goes up. Instead, it operates under constraint.
When demand increases acutely in one area, energy is often reallocated from other areas. More training, for example, does not just “add” energy expenditure on top of everything else. It shifts resources away from recovery, immune function, or long-term repair in order to support immediate output.
This is why the relationship between effort and energy is not linear. Increasing demand does not guarantee increased perceived energy capacity — meaning how energized you actually feel day to day — it simply changes how the body distributes what it already has.
Exercise makes this visible: Early on, training often leads to increased energy and improved performance. But as demands rise beyont that poit, that effect can plateau. Push further without adequate planning for adaptation, and the system is forced to compensate. Output may still be possible, but it comes at a cost—often felt as chronic fatigue, reduced recovery, or declining immune function.
This is a reflection of how the system evolved. The body prioritizes stability and survival over unlimited output. It will adjust, reduce, or redirect energy use before it allows itself to be pushed beyond what it can sustain.
Understanding this mechanism changes how energy should be interpreted. It is not just about how much energy you can produce in a moment, but how well that output can be generated and maintained without forcing tradeoffs elsewhere in the system (Sustained Energy vs. Borrowed Energy).
Once you see energy this way, a different pattern becomes clear: the question is not how much output you can sustain or what your perceived energy level is, but whether that output is properly supported by your system, or coming at a cost.
Energy is not something the body stores and hands out on demand. It is something the body continuously produces, distributes, regulates, and spends based on current conditions.
The question is not how much output you can sustain — it’s whether that output is properly supported by your system, or coming at a cost.
Sustained Energy vs. Borrowed Energy
Once energy is understood as something that is produced, allocated, and constrained, a clearer distinction begins to emerge. Not all increases in output reflect an improvement in the system. Some reflect a change in how the system is being forced to distribute energy. This is where the difference between sustained energy and borrowed energy becomes useful:
Sustained energy is built through adaptation. It reflects improvements in the underlying systems that support output: metabolic efficiency, oxygen delivery, substrate utilization, and recovery capacity. These changes take time and require planning, but they result in energy that is stable, repeatable, and resilient to variation in workload.
Borrowed energy, in contrast, is an acute increase in output that is not supported by a corresponding increase in capacity. It is typically driven by changes in the nervous system and hormonal signaling: external demands, higher arousal, increased adrenaline, or reduced perception of fatigue. Output goes up, but the system itself has not improved. And because of that, borrowed energy is always supported by tradeoffs.
When you borrow energy, resources are shifted away from other functions to maintain short-term output. Recovery may be deferred, substrate stores may be drawn down, and regulatory systems may be pushed outside their usual range. This allows performance to increase temporarily, but it does not come without cost.
This is why energy often feels unstable. Periods of sharp focus or alertness are followed by noticeable drops or deficits in other areas, sometimes within hours. Many people experience this as an afternoon crash, a drop after caffeine, a sudden loss of energy during the day, or getting sick after finals.
These fluctuations are not random. They reflect a system that has increased output without increasing its ability to sustain that output. Once the temporary support is removed or depleted, output falls back, oftentimes below baseline.
Importantly, this distinction is not about avoiding effort or stimulation. Both can be useful when applied deliberately. The problem arises when borrowed energy becomes the default strategy, when short-term output is repeatedly prioritized without allowing the system to adapt and rebuild.
Over time, this habit creates a pattern where performance becomes harder to maintain, recovery becomes less effective, energy feels increasingly inconsistent, and other systems pay the price. In the workplace, this may contribute to burnout, in the training room, to injuries and overtraining.
The issue, then, is not how to increase energy output in a given moment. The issuse is how to increase capacity. And the relevant question is whether that energy is supported by the system—or coming at the expense of it.
Sustained Energy
Built Through Adaptation
Improvements in metabolic efficiency, oxygen delivery, and recovery capacity. Takes time, requires planning — but the result is energy that is stable, repeatable, and resilient.
Borrowed Energy
Drawn From Future Reserves
Resources shift away from recovery to maintain short-term output. Performance increases temporarily — but it always comes at a cost paid later.
Drifting Into Borrowed Energy
Most people do not deliberately choose to rely on borrowed energy. They drift into it — gradually, and often without recognizing the early signs of overtraining or overworking until the pattern is already established. It usually starts with a reasonable goal — train more, get that promotion, stay consistent. Early on, this often works. Output increases, performance improves, and energy can even feel better for a period of time.
The shift happens when demand continues to rise, but the system does not adapt at the same pace. At that point, the body has two options: build more capacity, or maintain output by reallocating resources. When recovery, fueling, and time are not sufficient to support adaptation, the system defaults to the second option.
Increasing Output Without Matching Recovery
A common pattern is increasing training volume or intensity without increasing recovery capacity. More sessions, more volume, more frequency — but sleep stays the same, nutrition is inconsistent, and time between sessions is compressed.
In the short term, output can still be maintained. In some cases it even improves. But this is not because the system has adapted. It is because more of it is being directed toward immediate performance.
Over time, this shows up as persistent soreness, slower recovery between sessions, increased injury rates, and declining performance despite continued effort. But the effects are not limited to training. Mental sharpness, focus at work, and emotional resilience often deteriorate alongside physical performance — because the same system supports all of it. This is often interpreted as a need to push harder or do more. In reality, it reflects a system that is no longer keeping up.
Using Stimulation to Compensate for Fatigue
As fatigue builds, many people introduce or increase stimulation — caffeine, pre-workouts, or simply pushing through with higher effort. This can restore a sense of energy in the moment. Focus improves. Output feels possible again.
But nothing about the underlying system has changed.
Stimulation increases what the system is willing to do, not what it is capable of sustaining. As a result, it often accelerates the same pattern — maintaining output by drawing further on limited resources.
Early Signs Your System Is Running on Borrowed Energy
The early signs of this shift are usually subtle. Energy becomes less consistent. Recovery takes slightly longer. Motivation fluctuates. Small drops in performance appear without obvious cause.
Because these changes are gradual, they are easy to dismiss. Most people continue increasing effort, assuming the issue is discipline or consistency. But these signals reflect something more specific — the system is already operating under constraint, and output is being maintained at a cost that has not yet become fully visible.
When the Pattern Becomes Hard to Ignore
As the gap between demand and capacity widens, the signs become clearer. Training feels harder without producing clear progress. Soreness lingers longer than expected. Energy becomes more variable across the day. The consistent effort that used to produce results starts to feel like it is just holding the line.
This is often described as overtraining, but in many cases it is not a discrete condition. It is the result of repeatedly relying on borrowed energy without allowing the system to rebuild and adapt.
The Progression
This pattern is not random. Output increases. Recovery is not adjusted. The system reallocates to maintain performance. Fatigue accumulates. More effort or stimulation is applied. The gap widens.
At each step, the system is still functioning — but it is doing so under increasing strain. Most people encounter this pattern at some point, especially those who are consistent and willing to push.
The issue is not effort. It is that the system being asked to support that effort has not been given the conditions required to adapt. And without that adaptation, output is maintained the only way it can be — by borrowing from the rest of the system.
Most people do not deliberately choose to rely on borrowed energy. They drift into it — gradually, and often without recognizing the early signs until the pattern is already established.
Why More Effort Often Makes Energy Worse
At first glance it seems obvious: if something is good for you, doing more should make you feel better. But with energy, that relationship breaks down quickly.
More effort increases demand. It does not automatically increase capacity.
5.1
Demand Can Outpace Capacity
Every training session and sustained focus block draws on available resources. When effort rises without corresponding adaptation, output begins to outpace what the system can provide.
5.2
Fuel Availability Becomes a Limiting Factor
Glycogen stores are finite. When training volume exceeds replenishment capacity, the body begins operating in a fuel-depleted state — and energy output reflects that constraint directly (Coyle et al., 1986)
5.3
Nervous System Fatigue
The nervous system controls motor output, focus, and recovery(Noakes, 2012). When chronically taxed, signal quality drops — resulting in reduced power, slower reaction times, and difficulty concentrating.
5.4
Chronic Stress Signaling & Energy Regulation
Sustained high cortisol suppresses recovery processes, disrupts sleep quality, and alters how energy is allocated. This is why stress and poor energy are so frequently paired.
5.5
Incomplete Recovery Cycles
Adaptation happens during recovery — not during training. When recovery is consistently cut short, the system never fully rebuilds. Output eventually declines to match the reduced capacity.
More effort is not the solution to low energy — progressive adaptation and proper recovery are.
Why Stimulation Feels Like It Works
THE MECHANISM
Adenosine Blockade
Caffeine blocks adenosine receptors in the brain. Adenosine accumulates during wakefulness and signals fatigue. When this signal is blocked, perceived effort decreases and alertness increases.
Catecholamine Activation
Stimulants increase dopamine and norepinephrine activity, raising arousal and improving the ability to initiate and sustain effort. These are changes in signalling — not in the system’s underlying capacity.
Stimulants are effective in the short term because they change how effort is perceived.
Caffeine acts primarily by blocking adenosine receptors in the brain. Adenosine accumulates during wakefulness and sustained activity, signaling fatigue and promoting reduced neural activity. When this signal is blocked, perceived effort decreases and alertness increases (Fredholm et al., 1999).
At the same time, stimulants increase catecholamine activity, including dopamine and norepinephrine. These changes increase arousal, improve focus, and enhance the ability to initiate and sustain effort (Meeusen et al., 2013).
These effects are real. They can improve performance in the short term. What they do not do is increase the system’s underlying capacity in the long run.
Substrate availability does not change. Mitochondrial function does not increase acutely. Recovery state is not restored. The system is operating under the same constraints, but with altered signaling.
This is why output can increase even when the system has not improved.
Perceived Energy vs Capacity
The distinction between perceived energy and actual capacity becomes important here.
Stimulants reduce the sensation of fatigue; They do not resolve the conditions that produced it. More importantly, stimulants force your system to borrow energy from other areas that need it.
This creates a situation where:
- Effort feels easier
- Output increases
- Underlying strain remains
Over time, this mismatch accumulates.
The system is asked to sustain higher output without a corresponding increase in recovery, fuel availability, or adaptation. This accelerates the same pattern described earlier, where performance is maintained through increasing cost.
Why Stimulants Stop Working the Same Way
With repeated use, the response to stimulation changes.
One mechanism is receptor adaptation. Regular caffeine intake leads to upregulation of adenosine receptors, which reduces the effect of a given dose. More stimulation is required to produce the same perceived effect (Fredholm et al., 1999).
At the same time, baseline fatigue often increases.
If recovery remains incomplete and demand stays high, the system enters each day with a higher level of accumulated strain. Stimulants can still reduce perceived fatigue, but they are acting on a system that is already further from baseline.
This is why people often report:
- Needing more caffeine to feel the same effect
- Pre-workouts feeling less effective
- Persistent fatigue despite continued use
The issue is not only tolerance. It is that a) the underlying system has not recovered, and b) neighboring systems are being forced to give up their own energy. Chronically.
The Functional Effect
Stimulation increases what the system is willing to do. It does not increase what the system can sustain.
In the short term, this can be useful. It allows output when needed.
When it becomes the default strategy, it shifts the system further away from adaptation.
Output is maintained, but capacity does not improve. Over time, this makes performance less stable and recovery less effective.
The issue with stimulants is not only tolerance. It is that a) the underlying system has not recovered, and b) neighboring systems are being forced to give up energy they need for their own functions. Chronically.
What Sustained Energy Actually Requires
Sustained energy is built by improving the system’s ability to support that output repeatedly.
That requires specific conditions. Without them, the system will default to short-term compensation instead of long-term adaptation.
Recovery Capacity
Recovery is the process through which capacity is restored and expanded. This includes glycogen replenishment, tissue repair, nervous system downregulation, and hormonal normalization. Sleep plays a central role because many of these processes are coordinated during deep and REM sleep cycles (Van Dongen et al., 2003).
If recovery is incomplete, the system does not return to baseline before the next demand. Instead, it carries residual fatigue forward, which reduces the ability to adapt to subsequent stress.
Over time, this limits how much energy the system can reliably produce.
Substrate Availability
Sustained output depends on the availability of usable fuel. This includes muscle glycogen, circulating glucose, and, over longer durations, the ability to oxidize fat efficiently. When substrate availability is insufficient, the system compensates by increasing perceived effort and reducing output.
Adequate fueling allows existing capacity to be expressed consistently. Without adequate substrate availability, performance becomes more variable and less repeatable across sessions and throughout the day.
Matching Demand to Adaptation Capacity
Training and workload must be aligned with the system’s ability to adapt. If demand exceeds what recovery and physiology can support, the system cannot build capacity. It maintains output through reallocation instead.
If demand is too low, the system is not challenged enough to adapt. Sustained energy emerges when demand is high enough to stimulate adaptation, but not so high that recovery is consistently incomplete.
This balance changes with training status, sleep, nutrition, and overall life load.
Time
Adaptation occurs over repeated cycles. Mitochondrial density, capillary development, and improvements in substrate utilization develop gradually (Granata et al., 2018). These changes require consistent exposure to appropriate stress followed by sufficient recovery.
There is no way to accelerate this process without compromising its outcome. Attempts to increase output faster than the system can adapt tend to shift the system toward borrowed energy rather than sustained capacity.
The Constraint
Sustained energy is the result of aligning demand, recovery, and resources over time. When those constraints are respected, energy becomes more stable across the day and more repeatable across weeks.
When they are not, the system relies on compensation, and energy becomes inconsistent.
Sustained energy emerges when demand is high enough to stimulate adaptation, but not so high that recovery is consistently incomplete.
Practical Signals
Energy is easier to evaluate through patterns than through single moments. A single good or bad day does not say much. What matters is whether output and recovery remain stable across repeated cycles.
The following signals reflect how well the system is supporting sustained output.
01
Day-to-Day Energy Consistency
Consistent energy across days signals recovery and fuel availability are keeping pace with demand. Large swings — sharp one day, flat the next — often indicate borrowed energy patterns.
02
Performance Stability Across Sessions
Output should remain relatively stable under similar conditions. Progressive drops over multiple sessions without obvious cause suggest accumulating fatigue beyond the system’s recovery rate.
03
Sleep Quality and Depth
Sleep quality often deteriorates before subjective fatigue becomes obvious. Difficulty falling asleep, frequent waking, or unrefreshing sleep are early signs the system is under sustained load.
04
Irritability and Motivation Drift
Reduced motivation, increased irritability, and lower tolerance for discomfort reflect nervous system and hormonal changes associated with accumulated fatigue — not just mental attitude.
Reframing Performance
Most people are taught to think about performance in terms of peak output.
How hard can you push today. How much can you get out of the system right now. How much intensity can you tolerate before you slow down. That framing is incomplete.
A single high-output effort does not tell you much by itself. Systems can produce impressive output for short periods while quietly accumulating cost in the background. The more useful question is whether that output can be repeated without progressively degrading recovery, stability, or function. This is the distinction that matters.
Performance is not best understood as the ability to generate the highest possible output in one moment. It is better understood as the ability to maintain meaningful output under repeated load. That includes training, work, cognitive demand, disrupted sleep, and all the other constraints that define real adult life. This changes how effort should be judged.
If high output today creates a deeper deficit tomorrow, the performance was real, but it was not durable. If a strategy depends on repeated stimulation, unstable recovery, or rising physiological cost, it may improve short-term output while weakening long-term capacity. At Mydos Performance we explicitly rejects that model of performance-borrowing, and instead, we prioritize approaches that hold up under repeated use.
Can the system produce again tomorrow? Can it keep producing next week? Can it do so while carrying real responsibility, limited recovery, and competing demands? That is a more serious definition of performance, and it is the one this article has been building toward.
Viewed this way, the goal is not to extract the maximum possible output from the body at every opportunity. The goal is to build a system that remains capable, stable, and responsive over time. That is a slower standard, but it is also the only one that compounds.
Performance is not best understood as the ability to generate the highest possible output in one moment. It is better understood as the ability to maintain meaningful output under repeated load.
“The goal is not to extract the maximum possible output from the body at every opportunity. The goal is to build a system that remains capable, stable, and responsive over time.”
Energy Is a System That Needs Time to Adapt.
Treat It Like One.
Understanding the difference between sustained and borrowed energy is the first step toward building capacity that actually lasts.
MyDos Performance
— Sustained Vs. Borrowd Energy Series —
Why Am I Always Tired?
The Real Problem With Energy
· By Ricardo Londono, MD/PhD ·