How Much Running Is Too Much? A Physical Therapist’s Guide for Hillsboro Runners

When runners come to me with knee pain, Achilles pain, shin pain, or another stubborn running injury, the story often sounds familiar:

“I felt fine, so I went a little farther.”

The problem is that “a little farther” can be a much bigger training change than it feels like in the moment.

A large 2025 cohort study followed 5,205 adult runners across 588,071 running sessions to examine a practical question: Is injury risk better predicted by a sudden increase in one run, or by changes in weekly mileage?

The answer was surprisingly clear. The rate of overuse running injuries increased when a single run exceeded the runner’s longest run from the previous 30 days by more than 10%.¹

For runners in Hillsboro, Aloha, and North Plains, this gives us a simple way to think about progression. Your most important number may not be your total weekly mileage, instead it might be the distance of today’s run compared with the longest run your body has recently handled.

The Study Looked at Real Runs, Not a Theoretical Training Plan

The researchers followed adult runners for up to 18 months. Running distance was collected through Garmin devices, while runners completed weekly questionnaires about pain and injuries.

The study compared three ways of measuring increases in running distance:

1. The distance of one running session compared with the longest run completed during the previous 30 days.

2. The acute:chronic workload ratio, which compared one week of running with the prior three weeks.

3. A week-to-week ratio comparing one week of running with the week before it.

The researchers grouped single-run increases into four categories: no increase or an increase up to 10%, an increase greater than 10% to 30%, an increase greater than 30% to 100%, and an increase greater than 100%. An increase greater than 100% meant the runner more than doubled the distance of their recent longest run.¹

This matters because most running advice focuses on weekly mileage. This study tested whether the dangerous moment might be more specific: one run that becomes much longer than anything the runner has completed recently.

What Happened When One Run Became Too Long?

During the study, 1,820 runners reported a running-related injury. Of those injuries, 1,311 were classified as overuse injuries.

Compared with runners who stayed at or below a 10% increase:

• Runners who increased one session by more than 10% to 30% had a 64% higher rate of overuse injury.

• Runners who increased by more than 30% to 100% had a 52% higher rate.

• Runners who more than doubled their recent longest distance had a 128% higher rate.¹

That last number deserves attention. Doubling a recent longest run was associated with more than twice the hazard of an overuse injury.

Hazard is not the same as certainty. It does not mean every runner who makes a large jump will get hurt. It means injuries occurred at a higher rate in those exposure categories during follow-up. The study adjusted its results for age, sex, body mass index, previous problems, and running experience.

The practical message is not that runners are fragile. The message is that recent preparation matters. Fitness in your heart and lungs does not automatically mean that every muscle, tendon, bone, and joint is prepared for a sudden jump in distance.

A Simple Example for a Hillsboro Runner

Imagine your longest run during the past 30 days was 5 miles.

A 10% increase would bring your next longest run to 5.5 miles. Running 6 miles would represent a 20% increase. Running 8 miles would represent a 60% increase. Running more than 10 miles would more than double your recent longest run.

The study suggests that once the session exceeds that 10% threshold, the rate of overuse injury rises. That does not make 5.5 miles perfectly safe, and it does not make 6 miles automatically dangerous. It gives us a useful warning line.

The authors also cautioned against stacking repeated 10% increases too quickly. They used an example in which a runner whose longest recent run was 10 kilometers completed 11 kilometers, then 12.1 kilometers, then 13.3 kilometers during the same week. Each run was only 10% longer than the previous one, but the total progression could still be excessive because recovery time may be insufficient.¹

So the rule should not be interpreted as permission to increase every run by 10%. Recovery and repeated exposure still matter.

Why Weekly Mileage Rules May Miss the Risk

One of the most important findings was what the study did not show.

Week-to-week changes in running distance were not significantly associated with overuse injury risk. The acute:chronic workload ratio also did not behave as expected. Higher ratios were not associated with higher injury rates, and some analyses showed an inverse relationship.¹

That does not prove weekly mileage is irrelevant. It means these weekly calculations did not identify increased injury rates in this cohort the way single-session distance did.

This is a major distinction. A runner can keep total weekly mileage stable while making one unusually long run. For example, someone could shorten two weekday runs and dramatically lengthen a weekend run. Weekly mileage might look controlled, but the long run could still exceed what the runner has tolerated during the previous month.

From my perspective as a physical therapist, that is a much more useful conversation than asking only, “How many miles did you run this week?” I also want to know, “What was your longest recent run, and how did today compare?”

The 10% Threshold Is a Guide, Not a Guarantee

The study was large and used objectively measured running distance, but it was still observational. It can identify associations, not prove that staying below a 10% increase prevents injuries.

There were other limitations. Injuries were self-reported. Running distance was the primary measurement of load, even though distance may not capture every demand of a session. The sample was predominantly male and came mainly from Europe and North America. The researchers also could not provide separate recommendations for specific subgroups of runners.¹

This means the threshold should be used as a decision-making tool, not as a universal law.

A runner returning after an injury, a highly experienced runner, and a newer runner may respond differently to the same percentage increase. The study also did not establish that every increase below 10% is safe. In fact, increases between 1% and 10% showed a nonsignificant 19% increase in injury rate compared with staying at or below a 1% increase.¹

The honest interpretation is this: risk appears to rise when a single run extends beyond recent preparation, especially when the increase becomes very large.

What Good Running Physical Therapy Should Examine

When someone searches for physical therapy Hillsboro runners can trust, or even the best physical therapy Hillsboro has available for running injuries, the evaluation should go beyond the painful body part.

A useful running history should include:

• The distance of the injury-related session

• The longest run completed during the previous 30 days

• Recent repeated increases in distance

• The timing of symptom onset

The study found that most injuries were reported on the day of the run or during the following one to two days, which supports looking closely at the sessions immediately preceding the problem.¹

For runners in Aloha and North Plains, the same principle applies. The goal is not simply to stop running. The goal is to understand whether the current running dose exceeded recent capacity, then build a progression that is challenging without being reckless.

The Bottom Line

The most useful takeaway from this research is simple: before extending your next long run, compare it with the longest run you completed during the previous 30 days.

An increase greater than 10% was associated with a higher rate of overuse injury. Increases greater than 100% carried the largest risk. Weekly mileage ratios did not show the same relationship.

Do not treat 10% as a magic shield. Treat it as a reason to pause, calculate, and make an informed choice.

For many runners, the injury does not begin because running itself is bad. It begins when one session asks for much more than the body has recently practiced.

Better training is not always about doing less. It is about progressing with enough structure that your body has a chance to keep up.

Article cited:

1. Schuster Brandt Frandsen J, Hulme A, Parner ET, et al. How much running is too much? Identifying high-risk running sessions in a 5200-person cohort study. Br J Sports Med. 2025;59:1203-1210. doi:10.1136/bjsports-2024-109380.