How Much Running Is Too Much?

I had a patient earlier this week who's an ultra runner. She did an ultra race in December last year and then took 3 weeks off running. Her first run back was a 20 km run and she started having left knee pain since.

I told her about an interesting article I read last week about the "single-session paradigm" for running injuries (Frandsen et al, 2025). 

The study tracked 5,205 runners over 18 months. Their average age was 46 years and 22 percent of the runners were females. The runners accumulated 588,071 run sessions via the Garmin GPS watches during the study period. The researchers were interested in self reported running related overuse injuries rather than traumatic injuries.

The runners were categorized into training load "spike" states. If mileage was <  10 percent increase, it was categorized as regression. A small spike would be greater than 10 but less than 30 percent increase. A moderate spike would be greater than 30 percent but less than 100 percent while a large spike would be greater than 100 percent increase.

Weekly changes in mileage using acute : chronic workload ratio (ACWR) - 1 week versus past 3 weeks. Week to week ratio, that is change from week to week were also analyzed.

For the ACWR (weekly changes) and week to week ratio, the study did not find any clear positive association with injury. In fact in some runners, a "negative dose response" was observed meaning a higher ACWR did not always mean more injury.

They found that when there was a spike in running mileage in a single session (rather than a gradual weekly increase relative to the longest run in the previous 30 days, many injuries occurred. This was named a shift to a "single-session paradigm" for running injuries.

This matches exactly with how my patient was injured. No running for 3 weeks, then in her first run back she had her longest run in the past month. The body needs time to adapt, big increases in mileage overloaded her muscles, bones, ligaments and connective tissues.

Please note that this study had runners who self reported their injuries, they were not diagnosed, so we need to be cautious and sensible when interpreting the results. Please do not think 'never increase mileage', it is more about progressing and moderating.

Those of you who are wearing smart watches, other tech devices and perhaps using Strava, note that this study suggests that algorithms that measure your weekly mileage load rations (or ACWR) may be under calculating risk. Your devices may need to include "single session spike" metrics or at least be able to compare with longest session in the last month.

Whether you train under a coach or are self coached, plan sessions so that large increases in distances are avoided. Or make sure you monitor carefully and plan extra recovery. Do not just tally weekly mileage, look at how the session distances compare to your maximum long run in the past month. Monitor your "David Goggins /monster sessions" that deviate from your regular training.

The average mean age of the runners was 46 and 76 percent were male. Younger athletes and elite athletes may be different. Other than distance, I will also include running pace, prior fatigue levels, surface of run and shoes to be monitored.

For healthcare professionals working with ultra runners, you can educate them about the single session spikes having higher risk than weekly totals, like I did with my patient. Ask them in detail about their training regime and pay close attention to the longest run in the recent 30 day window.

Reference

Schuster Brant Frandsen J, Hlme A, Parner ET et al (2025). How Much Running Is Too Much? Identifying High-Risk Running Sessions In A 5200-Person Cohort Study? BJSM. 59 (17): 1203-1210. DOI: 10.1136/bjsports-2024-109380