Trail Notes | Female Athlete Health

when tired is more than training load

Running on Empty.

Iron, Ferritin and the Fatigue That Does Not Budge.

You can train consistently, sleep reasonably well, fuel with care, and still feel like you are dragging yourself through every session. If that pattern has been sitting with you for weeks or months, iron and ferritin deserve a closer look.

Fatigue is the most common complaint we hear from female trail runners. It is also the most commonly dismissed. Training stress, life load, poor sleep, under-fuelling, overtraining, hormonal fluctuations and low iron can all produce symptoms that look nearly identical. Without the right screening, it is easy to spend months adjusting training variables while the actual problem goes unaddressed.

This Trail Note is about iron and ferritin specifically: what they are, what low levels look like in a trail runner, what to ask your doctor to test for, and how to think about training and recovery when your numbers are below optimal.

Trail Note  ·  01

Fatigue in female trail runners is not simple

Tiredness in training is expected. But persistent fatigue that does not respond to rest, that sits at a level beyond what your training load justifies, or that creeps in despite doing everything right, is a signal worth investigating rather than pushing through.

Research on female endurance athletes consistently identifies iron deficiency as one of the most prevalent and underscreened nutritional issues in our population. Estimates suggest that between 15 and 35 percent of female endurance athletes have depleted iron stores, with rates potentially higher among trail and mountain runners who train on demanding terrain or at altitude.

Trail Note  ·  02

Iron and ferritin: they are not the same thing

Iron is the mineral. Ferritin is the protein that stores it. When you get a standard blood test, you may receive a haemoglobin result sitting within the normal range, while your ferritin is quietly depleted.

This matters because iron-deficiency anaemia is the end stage of the problem. Long before your haemoglobin drops low enough to trigger a clinical flag, your ferritin can be depleted to a point where it is compromising your oxygen transport, your recovery capacity, and your ability to adapt to training stress.

This is why a standard full blood count is not enough on its own. You need serum ferritin specifically. And you need to understand what an athlete-appropriate ferritin level looks like, which is not the same as what a standard laboratory reference range will tell you.

Trail Note  ·  03

Why female trail runners are at higher risk

Iron depletion in female endurance athletes has multiple drivers that compound each other. Menstrual blood loss is the most significant. We lose iron every month through bleeding, and for those of us with heavier cycles the cumulative loss can be substantial. At the same time, high training volumes increase iron demand as the body produces more red blood cells to support oxygen delivery.

Foot-strike haemolysis is a further contributor: the repetitive impact of running destroys red blood cells, returning iron to circulation in a form that is less efficiently reused. Add the effect of exercise-induced inflammation on iron absorption, and the picture of why we are vulnerable becomes clear.

Dietary patterns also play a role. Reducing overall food intake, following a plant-based diet without adequate absorption strategies, or consistently under-fuelling around training can all limit the iron available to replenish what is being lost.

Trail Note  ·  04

The symptoms that look like everything else

One of the most frustrating things about low ferritin is how indistinguishable it is from other training and life issues. The symptoms overlap significantly with overtraining, under-fuelling, burnout, thyroid dysfunction, low vitamin D, and general life fatigue. Without a blood test, there is no reliable way to know which is driving the feeling.

The presence of several of these symptoms together, particularly in the absence of a clear training explanation, is a strong case for getting blood work done before making further adjustments to your training or nutrition plan.

Trail Note  ·  05

What to ask your doctor to screen for

A standard full blood count will show haemoglobin and red blood cell indices but will not routinely include ferritin. You need to specifically request serum ferritin, ideally alongside a full blood count, transferrin saturation and, if fatigue is significant, thyroid function and vitamin D levels.

Timing matters. For the most accurate baseline, test after at least 48 hours of lighter activity and when you are well.

Trail Note  ·  06

Understanding what the numbers mean

Standard laboratory reference ranges for serum ferritin are generally set at 12 to 150 micrograms per litre for adult females. A result within this range will often be reported as normal. But for endurance athletes, a ferritin below 30 to 40 micrograms per litre is commonly associated with impaired performance, reduced recovery capacity and fatigue symptoms, even in the absence of frank anaemia.

Many sports medicine practitioners recommend a target ferritin above 50 to 80 micrograms per litre for female endurance athletes with high training loads or a history of fatigue. Athlete-optimal ranges sit higher than population reference ranges.

Trail Note  ·  07

Dietary iron: sources and absorption

There are two forms of dietary iron. Haem iron, found in animal products (red meat in particular), is absorbed at a rate of approximately 15 to 35 percent. Non-haem iron, found in plant foods including lentils, chickpeas, tofu, dark leafy greens and fortified cereals, is absorbed at a significantly lower rate of 2 to 20 percent.

Vitamin C substantially enhances non-haem iron absorption. Conversely, polyphenols in tea and coffee, and phytates in wholegrains, inhibit absorption when consumed at the same time. Separating coffee and tea from your iron-rich meals by at least one hour is a simple and effective strategy.

Trail Note  ·  08

Supplementation: what to know before you start

Iron supplementation can be highly effective when ferritin is depleted. Oral supplements are commonly prescribed and can take three to six months to meaningfully restore ferritin levels. Many athletes experience gastrointestinal discomfort with standard ferrous sulfate. Alternate-day dosing has emerging evidence suggesting it may improve absorption while reducing side effects.

Do not supplement without confirmed blood work showing depletion. Excess iron carries real risks and confers no performance benefit. Get the numbers first, then make a plan with medical support.

Trail Note  ·  09

Training with low ferritin

Training decisions while ferritin is low depend on how depleted your levels are and how pronounced your symptoms are. With mildly low ferritin and manageable symptoms, modified training is often appropriate while supplementation takes effect. With significantly depleted ferritin, a period of genuinely reduced load is usually necessary.

If you are training through a period of low ferritin, effort should guide your sessions rather than pace or heart rate targets, both of which will be unreliable when oxygen-carrying capacity is compromised.

Trail Note  ·  10

The coach's role: flagging, not diagnosing

As coaches at Her Trails, we do not diagnose iron deficiency. What we can do is notice when the pattern of your fatigue does not fit the training explanation, and gently direct you toward appropriate investigation.

Trail Note  ·  11

Iron is information, not weakness

Feeling flat is not a reflection of your commitment or your character as an athlete. It may be a physiological reality that a blood test can identify and a simple intervention can address. Getting your ferritin checked once a year, or whenever persistent unexplained fatigue arrives, is a form of athletic self-respect.

The female athlete who gets her numbers, understands what they mean, advocates for an athlete-appropriate interpretation of them, and uses that information to make smarter decisions about training and nutrition is being strategic. That is exactly the kind of self-knowledge we are building at Her Trails.

Trail Note  ·  12

The invitation

If you have been sitting with unexplained fatigue and have been blaming your training plan, your sleep, your stress, your life stage or simply your body being difficult, consider the possibility that there is a physiological answer worth looking for.

Ask your GP to test serum ferritin specifically. Understand your results in the context of athlete-appropriate ranges, not just population reference ranges. And if the numbers are low, work with your doctor and your coach to make a plan that includes both restoring your iron and protecting your training in the interim.

Running on empty is not a badge of honour. Running well-resourced, well-supported and with a clear picture of what your body needs is.

know your numbers, run your best

Keep going with us