The rider who assumed he was just getting old
A 44-year-old male cyclist. Ten hours a week on the bike, structured training, power meter, a coach. FTP had been 265 watts for eighteen months — not declining, but not moving either, despite consistent interval work. He was sleeping badly — waking at 3am, unable to get back down. He caught three colds between October and January. His mood had gone flat. Sex drive had disappeared sometime around September, though he could not pinpoint exactly when.
He assumed he was overtraining, so he took a recovery week. It did not help. He assumed he was ageing, so he accepted it. He was 44, after all. This is what happens.
What nobody had told him — not his coach, not his GP, not the cycling forums he read at night — was that he was eating 2,200 kcal a day while burning 800 to 1,200 kcal in training. His body weight was stable at 78kg and 15% body fat. He looked fine. He was not losing weight. But his energy availability — the energy left over after exercise for his body to run everything else — was 22 kcal/kg of fat-free mass per day. That number should be above 45.
He was not overtraining. He was under-fuelling. And this is not rare. It is one of the most common and most overlooked problems in masters cycling. Many of the riders who come through the Not Done Yet community describe exactly this pattern — years of stagnation, accumulating symptoms, and the quiet assumption that their body is simply winding down.
It is usually not winding down. It is running on empty.
What energy availability actually means
Energy availability (EA) is a specific measurement. It is not the same as calorie balance, and it is not the same as being in a deficit for weight loss. It is the amount of energy your body has left over, per kilogram of fat-free mass, after accounting for exercise.
The formula:
EA = (Energy Intake - Exercise Energy Expenditure) / Fat-Free Mass
Each variable matters, so take them one at a time.
Energy intake is total daily food consumption in kcal. Everything you eat and drink. Not what you intended to eat. Not what MyFitnessPal says your target should be. What you actually consumed.
Exercise energy expenditure (EEE) is the energy cost of your training — not your total daily expenditure, just the exercise component. If you have a power meter, kilojoules recorded on the bike approximate kcal burned with reasonable accuracy (the conversion is close to 1:1 when accounting for metabolic efficiency). Without a power meter, MET-based estimates from the Calories Burned Calculator provide a working approximation.
Fat-free mass (FFM) is your body weight minus your fat mass. A 78kg rider at 15% body fat carries 11.7kg of fat, leaving 66.3kg of fat-free mass. DEXA gives the most accurate measurement. Bioimpedance scales are within 3-5% on a good day. The Body Composition Calculator provides a quick estimate using the Navy circumference method.
Now run the numbers for that 44-year-old rider. He eats 2,200 kcal. He burns 900 kcal in training. His FFM is 66.3kg.
EA = (2,200 - 900) / 66.3 = 19.6 kcal/kg FFM/day
That number is catastrophically low. His body is receiving less than half the energy it needs to maintain normal function. And because his weight is stable — he is not visibly wasting away — nobody, including him, has any reason to suspect a problem.
The Energy Availability Calculator does this maths instantly. Plug in your numbers, and it returns your EA with a colour-coded assessment. But the number is a starting point, not a diagnosis.
The 30 kcal threshold — what happens below it
The 30 kcal/kg FFM/day threshold is not arbitrary. It comes from a specific line of research that began with Anne Loucks at Ohio University in the 1990s and early 2000s.
Loucks and Thuma (2003) conducted a tightly controlled study in which they manipulated energy availability in young women and measured the hormonal response. Below 30 kcal/kg FFM/day, luteinising hormone (LH) pulsatility — the rhythmic hormonal signalling that drives reproductive function — became disrupted. The disruption was dose-dependent: the lower the EA, the more severe the suppression.
This was the first clear quantification of a threshold. Subsequent work extended the finding far beyond reproductive hormones.
The IOC consensus statement on RED-S (Mountjoy et al., 2014, updated in 2023) synthesised decades of research into a comprehensive model. Below 30 kcal/kg FFM/day, the body begins rationing energy away from systems it classifies as non-essential for immediate survival. The affected systems include:
Reproductive and hormonal function. In women, menstrual irregularity progressing to amenorrhea (complete cessation of periods). In men, suppressed testosterone — sometimes dramatically so. Nattiv et al. (2007) documented testosterone levels in male endurance athletes with chronic low EA that were comparable to hypogonadal ranges.
Bone metabolism. This is the one that should alarm cyclists most. Low EA reduces bone formation markers and increases bone resorption markers — the body is simultaneously building less bone and breaking down more of it. In a weight-bearing sport, that is bad. In cycling, which is non-weight-bearing and already provides minimal osteogenic stimulus, it is compounding one risk factor with another.
Immune function. Increased frequency and severity of upper respiratory tract infections. The athlete who catches every cold that moves through the peloton is often assumed to be unlucky. More frequently, their immune system is compromised by chronic energy deficit.
Metabolic rate. Adaptive thermogenesis — the body's downregulation of resting metabolic rate in response to energy scarcity. This is the body actively slowing itself down to conserve fuel. It is why some chronically under-fuelled athletes stop losing weight despite eating very little. Their metabolism has adjusted downward.
Cardiovascular health. Impaired endothelial function and unfavourable lipid profiles, even in otherwise lean and fit athletes. De Souza et al. (2014) documented increased cardiovascular risk markers in female athletes with low EA.
Psychological wellbeing. Increased rates of depression, anxiety, irritability, and impaired concentration. These are often the first symptoms noticed — and the last to be attributed to nutrition.
The 45 kcal/kg FFM/day figure represents the level at which full physiological function is supported in most athletes. Between 30 and 45 is a grey zone — some systems may begin to compromise, particularly with prolonged exposure. Below 30 is clinical territory that warrants professional assessment.
RED-S is not just a female athlete issue
This section matters. If you skip it, you will miss the point.
The condition now known as RED-S was originally described as the "Female Athlete Triad" — a constellation of disordered eating, amenorrhea, and osteoporosis identified primarily in female athletes in the 1990s. The name was accurate for its time. It was also limiting, because it implied the problem was confined to women.
It was renamed Relative Energy Deficiency in Sport (RED-S) by the IOC in 2014, and the 2023 update (Mountjoy et al.) is unambiguous: RED-S affects athletes of all sexes. The diagnostic framework applies identically to men and women, though the specific symptoms differ.
Male cyclists are particularly vulnerable for several reinforcing reasons.
First, cycling is non-weight-bearing. Bone mineral density in competitive cyclists is consistently lower than in age-matched non-athletes — a finding that seems paradoxical until you consider that cycling provides almost no mechanical loading to stimulate bone formation. Nichols et al. (2003) found that male competitive cyclists had significantly lower lumbar spine bone mineral density than runners or non-athletes. This baseline disadvantage means that any further insult to bone metabolism — such as chronic low EA — lands harder.
Second, endurance cycling burns substantial energy. A three-hour weekend ride at moderate intensity for a 75kg rider will burn 1,800-2,400 kcal depending on terrain and effort. That is an enormous amount of energy to replace, and many riders do not come close.
Third, cycling culture has historically celebrated leanness. Watts per kilo. Race weight. The implicit message that the lighter you are, the faster you climb. This is not entirely wrong — power-to-weight ratio does matter — but it has created a culture in which chronic energy restriction is normalised and even admired.
Fourth, the symptoms in men are easier to dismiss. Women have a clear biomarker — menstrual disruption or loss — that signals low EA early and obviously. Men have no equivalent. Reduced testosterone, declining libido, and persistent fatigue are attributed to ageing, stress, poor sleep, or overtraining. The correct diagnosis — under-fuelling — may not be considered for months or years.
The research is catching up. Torstveit et al. (2019) reported that 36% of male endurance athletes in their sample met criteria for low EA. Heikura et al. (2018) found that male race walkers and distance runners with low EA had impaired bone turnover markers. The evidence is now substantial: this is not a sex-specific condition.
The symptoms — what to watch for
The difficulty with RED-S symptoms is that each one, in isolation, has a dozen plausible explanations. It is the pattern that matters.
Persistent fatigue that does not respond to rest. Not the normal tiredness after a hard training block. A bone-deep, background-level flatness that persists through recovery weeks and easy periods. The rider who wakes up tired, trains tired, and goes to bed tired — and has done so for months.
Declining performance despite consistent training. FTP that stalls or drops. Interval sessions that used to feel hard but achievable now feel impossible. Race results that slide. The training is being done. The adaptation is not happening. This is the signature of a body that does not have enough energy to repair and rebuild.
Increased frequency of illness. One or two colds per winter is normal. Four or five is a pattern. Persistent minor infections — a lingering sore throat, a cough that will not clear, a cold that resolves and returns within a fortnight. The immune system is an energy-expensive operation, and when energy is scarce, it is one of the first systems to be deprioritised.
Sleep disturbance. Difficulty falling asleep, early waking, or restless and unrestorative sleep. Cortisol dysregulation from chronic energy deficit disrupts the normal circadian rhythm. The rider who trains hard and then cannot sleep is often assumed to be over-stimulated. They may be under-fed.
Mood changes. Irritability. Anxiety. A loss of motivation for training and racing — and often for other activities too. Flat affect. These changes are often gradual, and the rider may not recognise them until someone else points them out.
In women: menstrual irregularity or amenorrhea. Any change in cycle regularity, flow, or timing is significant and should not be dismissed as normal variation. Complete loss of menstruation is a medical event, not a training adaptation. If your period has stopped or become irregular, see a doctor.
In men: reduced libido and sexual dysfunction. Testosterone suppression from low EA is real and measurable. It is also one of the symptoms men are least likely to discuss, particularly with a coach or training partner.
Bone stress injuries. Stress fractures or stress reactions — particularly in the feet, tibiae, or pelvis. In a cyclist, any bone stress injury should prompt an immediate assessment of energy availability. The combination of low bone mineral density from non-weight-bearing exercise and chronic under-fuelling creates a compounding risk.
GI disturbances. Bloating, constipation, or discomfort that is not explained by dietary intolerance or in-ride nutrition issues.
None of these symptoms alone confirms RED-S. Several of them together, persisting over weeks and months, should prompt investigation. The Masters Recovery Score can help track some of these markers over time, but a calculator cannot diagnose a medical condition. If you recognise this pattern in yourself, the next step is a professional assessment.
How to calculate your own energy availability
This is a practical guide. It is also imperfect — every input has measurement error, and a three-day food log is not a blood panel. But a working estimate of your EA is still more useful than no estimate at all. Think of it as a screening tool.
Step 1: Track food intake for 3-5 days.
Use Cronometer (more accurate for micronutrients), MyFitnessPal, or any food logging app. Log everything — meals, snacks, drinks, the extra handful of cashews at 10pm. Accept that this will be approximately 10% inaccurate. Most people under-report food intake, so if anything, your real intake is likely slightly higher than what you log. Include at least one rest day and one big training day in the 3-5 day window. If you are also trying to dial in your on-bike nutrition, the Fuelling Calculator handles in-ride carbohydrate and fluid targets separately — useful context, but a different question from total daily EA.
Step 2: Calculate exercise energy expenditure.
If you ride with a power meter, the maths is simple. Total kilojoules recorded during a ride approximate total kcal burned during that ride (the mechanical efficiency conversion and metabolic conversion roughly cancel out). A ride that records 900 kJ on the head unit cost approximately 900 kcal.
Without a power meter, use MET-based estimates. The Calories Burned Calculator provides these based on ride duration, intensity, and body weight. They are less accurate than power-based measurements but adequate for a screening estimate.
Include only deliberate exercise, not general daily activity (walking, commuting, standing). EA is specifically about the relationship between food, exercise, and what is left over.
Step 3: Estimate fat-free mass.
Gold standard: DEXA scan. Costs between $50 and $150 depending on location, and gives accurate body fat percentage, lean mass, and bone mineral density. Worth doing once as a calibration point, particularly if bone health is a concern.
Working estimate: bioimpedance scales under consistent conditions (same time of day, fasted, after urinating). They are 3-5% less accurate than DEXA but track trends well. The Body Composition Calculator gives a quick estimate using waist and neck circumference measurements.
Calculate FFM: body weight in kg minus (body weight x body fat percentage). A 75kg rider at 18% body fat has 13.5kg of fat mass and 61.5kg of FFM.
Step 4: Run the formula.
EA = (average daily energy intake - average daily exercise energy expenditure) / FFM
Or use the Energy Availability Calculator. It does the same maths and provides an immediate colour-coded assessment.
Interpret the result:
- Above 45 kcal/kg FFM/day. Adequate. Full physiological function is supported.
- 30-45 kcal/kg FFM/day. Grey zone. Some functions may begin to compromise, particularly with prolonged exposure. Monitor symptoms, consider whether intake needs to increase on heavy training days.
- Below 30 kcal/kg FFM/day. Clinical concern. See a sports dietitian. This level of energy deficit, if sustained, will impair health and performance.
Why "just eat more" is not the answer
This needs to be said carefully, because for some riders, increasing food intake is exactly the right intervention and the sufficient one. The rider who is unintentionally under-eating because they have not recalculated their nutrition for a heavier training load — that rider can often solve the problem by adding 400-600 kcal of carbohydrate around training. Problem identified, problem fixed.
But for many others, chronic under-eating is not a simple miscalculation. It is entangled with patterns that run deeper.
Years of "race weight" culture leave marks. The cyclist who has spent a decade weighing food, tracking macros, and equating leanness with performance does not flip a switch and start eating more. The anxiety around food is real. The fear of gaining weight — particularly in a sport that quantifies power-to-weight to two decimal places — is real. These are not weaknesses. They are learned responses to a culture that has, for decades, rewarded thinness.
For some riders, chronic restriction has crossed into disordered eating territory — patterns of restriction, guilt, compensation, and avoidance that meet clinical criteria. This is more common in cycling than the sport acknowledges, and it is not confined to any one demographic.
This is why a sports dietitian — not a calculator, not a podcast, not a well-meaning training partner — is the appropriate professional for this. A sports dietitian understands the interaction between athletic performance demands and the psychological relationship with food. They can build an intake plan that addresses the physiological deficit while respecting the reality that changing eating behaviour is not simply a matter of information.
Seeking professional help for this is not weakness. It is the same kind of smart decision as seeing a bike fitter for knee pain instead of watching YouTube videos and guessing. You can try to fix it yourself. You will probably get it wrong. The professional route is faster, safer, and more likely to hold.
Performance impact — the numbers
There is a version of this conversation that focuses entirely on health, and that version is important. But many riders will act on performance data before they act on health data. That is human nature, not a character flaw. So here are the performance numbers.
Melin et al. (2019) studied female endurance athletes and found that those with low EA had significantly lower VO2max and impaired endurance capacity compared to athletes with adequate EA. The relationship was dose-dependent — the lower the EA, the greater the performance impairment.
Loucks (2004) demonstrated that low EA reduces protein synthesis rates. For a cyclist, this means impaired muscle repair after training and reduced capacity to build new mitochondria and capillaries — the structural adaptations that endurance training is supposed to produce. You are doing the work. Your body does not have the raw materials to convert that work into adaptation.
Oxygen transport is affected. Substrate utilisation shifts unfavourably — the body becomes more reliant on protein catabolism, breaking down muscle for fuel rather than preserving it for function.
For the masters cyclist who is training 8-12 hours a week and not getting faster, low EA may be the single biggest limiter. Not interval selection. Not FTP test protocol. Not equipment. The body cannot build fitness if it does not have the energy to fund the construction.
A rider at adequate EA who completes four interval sessions per week will, over a twelve-week block, produce measurably more adaptation than the same rider at low EA completing the same sessions. The training stimulus is identical. The adaptive response is not. Energy availability is the variable that determines whether training stimulus converts to training adaptation.
The race weight trap
Power-to-weight matters in cycling. This is not controversial. On a 10% gradient at threshold, every kilogram costs roughly 3-4 watts. A rider who drops from 76kg to 73kg without losing power gains a meaningful climbing advantage.
The problem is not the goal. The problem is the method.
The most common pathway to race weight in amateur cycling is sustained energy restriction — eating less, sometimes dramatically less, while maintaining or increasing training load. This is also the most common pathway to RED-S.
The Race Weight Calculator provides a target based on performance body fat ranges — the zone where further fat loss produces diminishing returns and increasing risk. That target is useful. But the critical question is not "what should I weigh?" It is "can I reach that weight while maintaining energy availability above 30 kcal/kg FFM/day?"
If the answer is no — if achieving your target race weight requires sustained EA below 30 — then the target weight is wrong. It may be physiologically possible to reach that weight. It is not physiologically possible to perform at that weight, because the hormonal, metabolic, and recovery impairments from low EA will offset the power-to-weight gains from the lost kilograms.
A rider at 74kg with full energy availability — normal testosterone, functional immune system, proper sleep, positive mood, intact bone metabolism — will outperform the same rider at 71kg who is hormonally suppressed, sleeping badly, catching every cold, and unable to absorb training load.
The framework that works: periodise body composition into specific low-load phases, use a modest deficit (200-400 kcal/day), protect training days with full fuelling, and monitor EA throughout. If EA drops below 30 at any point, increase intake immediately. The target weight is not worth the damage.
When to get professional help
Some indicators are clear enough that they should prompt action regardless of what a calculator says.
See a sports dietitian if:
- Your calculated EA is below 30 kcal/kg FFM/day for more than two weeks
- Your menstrual cycle has become irregular or has stopped (this is not a normal training adaptation — it is a medical symptom)
- You have sustained a bone stress injury (stress fracture or stress reaction)
- Your performance is declining without a clear training explanation
- You recognise multiple RED-S symptoms and they have persisted for more than a month
- The idea of eating more feels distressing rather than simply inconvenient — this distinction is important and worth being honest with yourself about
How to find the right professional:
Look for a registered sports dietitian with experience in endurance athletes. In the UK and Ireland, the Sport and Exercise Nutrition Register (SENr) lists accredited practitioners. In Australia, the Accredited Sports Dietitians Board (ABSD). In the US, the Certified Specialist in Sports Dietetics (CSSD) credential through the Academy of Nutrition and Dietetics.
A qualified sports dietitian typically charges $80-$200 for an initial consultation. That is comparable to a set of carbon bottle cages or a power meter head unit mount. It is a fraction of the cost of a new wheelset. And for a rider with chronically low EA, it will produce more measurable performance improvement than any equipment purchase.
This is the most important page on this site
That is not marketing language. It is an assessment of harm.
Under-fuelling is widespread in amateur cycling. It is largely invisible because the symptoms are nonspecific and accumulate gradually. It masquerades as overtraining, ageing, bad luck with illness, or simply "not being talented enough." Most under-fuelled cyclists do not know they are under-fuelled. They believe they are eating adequately because their weight is stable, their meals seem normal, and nobody has suggested otherwise.
The Energy Availability Calculator is a starting point. Five minutes with the calculator will tell you whether your numbers land in a concerning range. But the calculator is a screening tool — it identifies a signal. The next step is a conversation with a qualified professional who can interpret that signal in the context of your full clinical picture.
In the NDY community, energy availability comes up regularly. Riders share their numbers, their symptoms, and their experiences with professional support. The fact that experienced cyclists are willing to talk about this openly — including the parts that involve admitting they were wrong about their nutrition for years — makes it easier for newer members to recognise the pattern in themselves.
If you have read this far and some of it resonated, run your numbers. And if the numbers come back low, treat that result not as a verdict but as the beginning of a conversation that could change the next decade of your riding.