Why Runners Get Slower Mid-Season: 4 Causes for Coaches

Every season I have the same Tuesday. It lands in the third or fourth week of September.

The workout is one they have run before. The splits should be routine. Instead the athletes who looked sharp in August come through the first repetition slow, and it gets worse from there. One of them steps off. Another misses her target for two consecutive reps.

For a long time my first thought was that they had stopped trying. School started. Homework, friends, a phone, a boyfriend. I was wrong.

Here are four things make a high school distance runner slower in week four. One of them is training. The other three follow the school calendar.

The symptom is not the diagnosis

Coaches want one cause. A slow workout feels like it should have a single reason, and the reason we reach for is the one we can act on that afternoon.

The research says the opposite. A 2024 critical review of the relative energy deficiency model made the point bluntly: the symptoms are generic, and the causes are almost always multiple. Poor sleep, sickness, injury, mental health and under-fueling all produce the same tired, flat, slowing athlete. It’s often hard to pinpoint any one cause.

That’s not a reason to shrug. It’s worth investigating further. Four causes, in order, with a different fix for each.

Cause one: the fatigue you actually planned

Some of what you are seeing is supposed to happen.

Sports science splits training fatigue into three stages. Functional overreaching is a short dip in performance caused by a deliberate rise in load. It lasts days to about two weeks, and after the rest comes an improvement above where the athlete started. Every good training plan uses it. Non-functional overreaching is the same picture without the payoff, and recovery runs weeks to months. Overtraining syndrome is rarer, more severe, and can take a full season to clear.

The only reliable way to tell them apart is time. That is inconvenient and it is also the truth. If you planned the load, a week-four dip is the plan working. Give a down week and watch it come back.

Signs it is still functional

• The athlete is tired but still wants to train.
• Easy days feel easy. The problem shows up only in hard sessions.
• Sleep is normal. Appetite is normal or up.
• The dip followed a real rise in load two or three weeks earlier.

Signs it is not

• Resting heart rate has climbed and stayed there.
• Easy days feel hard.
• Motivation has gone. The emotion is flat.
• Repetitive illness.
• Two weeks of reduced load changed nothing.

One more thing from the same body of work, and it is the reason the rest of this article exists. Training is not the only stressor. The overtraining literature is explicit that sleep loss, poor nutrition and psychological stress feed the same continuum. A moderate training load plus a wrecked school schedule produces the same athlete as an excessive training load. If you adjust only the training, you may be fixing the one problem you didn’t have.

Cause two: iron

Researchers followed a group of high school cross country runners through a fall season and tested them at both ends. At the start, around 40 percent of the girls were iron deficient. By the end of the season it was 45 percent. The boys went from about 3 percent to 17 percent.

Read the boys number again. It rose nearly 600% across one cross country season. Most of us file iron under girls’ issues and stop thinking about it.

That study is decades old. The prevalence figures may have moved. But, the mechanism has not. Distance running costs iron through sweat, through the gut, and through the repeated impact of foot strikes. Girls carry menstrual loss on top of it all.

Why the bloodwork comes back fine

This is the part that costs athletes their seasons.

A standard panel looks at hemoglobin. Hemoglobin falls last. The stage that wrecks a cross country season is the one before that, where iron stores are drained but hemoglobin still reads normal. Sports medicine calls it iron-deficient non-anemic, and performance and recovery start to suffer around 20 to 30 ng/mL of ferritin, well before anything shows up on a routine test.

Lab reference ranges make it worse. A Cleveland Clinic pediatric hematologist put the problem plainly in 2026: traditional ferritin ranges are broad enough that everything between 15 and 200 ng/mL flags as normal. She described the exact athlete this article is about, a teenager who is exhausted, cannot finish workouts and has lost focus in class, whose coach assumes she is overtrained, stressed or not pushing hard enough.

Because ferritin swings from one blood draw to the next, by around 15 percent in men and up to 27 percent in women, a runner testing at 30 is not reliably at 30. That day-to-day variance is why sports practitioners generally want distance runners somewhere north of 35 to 40 ng/mL rather than at the bottom edge of normal. Cutoffs for younger adolescents sit lower again, which is another reason this belongs with a physician and not with a coach and a spreadsheet.

What a coach actually does

You cannot diagnose this. Do not try. What you can do is recognize the pattern and say one specific sentence to a family.

Ask your doctor to check ferritin, not just a standard blood count.

That sentence is the whole contribution and it is worth more than anything you will change in the training plan. Updated American Academy of Pediatrics guidance recommends screening hemoglobin and ferritin together, so you are asking for something a physician already has reason to order. Bring the pattern with you: how long it has gone on, what the workouts show, whether she is sleeping.

Cause three: the September fueling math changed

Nothing about your training changed between August and week four. Everything about the students’ day did.

In August they took naps, slept in and followed their own schedule. In week four they are up at six, they have a first lunch at 11:00 because that is the slot the schedule gave them, practice starts at 3:15, and they arrive home at six with homework still to do. Nobody decided to eat and sleep less. The day just got busier.

The 2023 International Olympic Committee consensus on relative energy deficiency describes low energy availability as a spectrum running from adaptable to problematic. Two weeks of a slightly short day is nothing. Six weeks of it, on top of a training load that went up, is a wrecked season.

Fixes that fit inside a school day

• A snack, eaten between the last class and practice. Not optional, not a treat. Make it as routine as lacing shoes.
• Food at practice, provided by the program. Whatever your boosters can fund, kept in a bin at the track. The athletes who need it most are often the ones who will not bring it.
• Carbohydrate and protein within the ride home.
• Look at the lunch schedule. If your distance group eats at 11:00 and trains at 3:15, that is a four-hour hole to plug.

Keep every one of these conversations about adding food. Nothing in this section is about weight, body composition or restriction. If you suspect a runner is restricting, that is not a coaching problem you solve on the track. Involve your athletic trainer, guidance counselor and the parents, and do it the same week you notice.

The deeper version of this is in our guide to energy needs and RED-S in high school runners.

Cause four: sleep debt

August had no homework. Week four has exams.

Milewski and colleagues surveyed 112 middle and high school athletes about training and sleep, then matched the answers against 21 months of injury records from the school’s athletic department. Athletes averaging under eight hours a night were 1.7 times more likely to have been injured.

The gap is not small. Adolescent athletes average somewhere near six and a quarter hours against a recommendation of eight to ten, and adolescent biology pushes bedtime later just as school start times pull wake-up earlier. Your runners are not choosing this. They are caught in it.

What a coach can change

• Ask the question directly. Not “are you sleeping enough”, which gets you a yes. Ask what time she went to bed last night and what time the alarm went off.
• Finish practice on time.
• Rethink optional morning runs in September.
• Put it in front of parents in August, before anyone is tired.

Telling the four apart

Most weeks you will find two of these at once. That is normal, and it is why the order matters more than the diagnosis.

What you change on Monday

Work in this order.

1. Sleep and food, this week. Both are free, and both are prerequisites for reading anything else.
2. A down week, next. Roughly two thirds of normal volume, one light quality session instead of two, races kept if they matter. If it was planned fatigue, the athlete comes back better than she left. You will know inside ten days.
3. Bloodwork, if the first two do not move it. By now you have ruled out the easy answers, which is exactly the information a physician wants. Send the family with specifics, not with “she seems tired”.
4. Stop adjusting and refer, if you are still guessing. Four weeks of a slowing athlete is not a training problem any more. Bring in your athletic trainer.

One warning about the calendar. Week four is also when coaches start making lineup decisions, and a depleted athlete posts times that look like a permanent verdict on her season. They are not. If you are choosing a varsity seven right now, read how to pick your varsity seven before you lock anything, and hold at least one spot open into October.

If an athlete is coming back from a down week or an illness, our 30-day ceiling calculator caps a single session at 110 percent of her longest run in the previous thirty days, which keeps the return from becoming the next problem.

What to say to the runner, and to her parents

The athlete has already decided she has lost her fitness. She has been watching her own splits for two weeks and has drawn the worst possible conclusion, and if you say nothing she will keep it.

Tell her what you actually think is happening. Name the four causes. Tell her which one you are testing first and how long it will take to know. A teenager who understands the plan is more likely to follow it. A teenager left to guess trains scared to catch up and gets injured.

With parents, stay in your lane and be specific. You are not saying their daughter is anemic. You are saying you have seen a pattern for three weeks, that it has not responded to rest, and that you would like their doctor to check ferritin alongside the standard count. Give them the dates and the workouts. A parent walking into an appointment with specifics gets a different visit than a parent saying the coach thinks something is wrong.

Common questions