Short answer: Why runners get injured so often: it is often one run that is too long. In 5,205 runners, a run 10 to 30% longer than their longest of the last 30 days was linked to 64% more injuries. Know your number and grow it by no more than 10%.
The short version
- A run 10-30% longer than your longest of the last 30 days was linked to 64% more injuries.
- More than double your longest run: 2.3 times the injury rate.
- The week-to-week change did not show the same link; the single long run did.
- About 1 in 3 runners (1,820 of 5,205) got hurt in 18 months.
- Longest run 10 km? Plan the next long run up to about 11 km.
The one long run that raises the risk
The same Garmin study compared every run with the runner’s longest run of the last 30 days. Runs up to 10% longer than that were the normal rate. A run 10 to 30% longer was linked to 64% more overuse injuries. A run 30% longer up to double: 52% more. A run more than double: 2.3 times the rate.
Any jump over 10% raised the risk. The middle group was a little lower than the 10 to 30% group, so this is not a straight line. But the message is the same: one run far past your usual longest run is the danger.
How common is running injury?
In a study that followed 5,205 runners for 18 months, each runner wore a Garmin watch, so every run was counted. During those 18 months, 1,820 of them reported a running injury. That is about 1 in 3. Most were overuse injuries, the kind that build up from load rather than a fall.
New runners get hurt more often. When 13 studies were pooled, new runners had about 18 injuries for every 1,000 hours of running. Regular runners had about 8. So the first months of running are the time to be most careful.
Why runners get injured by one long run
Muscles, tendons and bones get stronger when you load them, but they need time to catch up. The Garmin study names the problem plainly: running too much before your body’s tissues can take the load. One sudden long run asks for more than they are ready to give.
Not the weekly total
Many runners follow the 10% weekly rule. In the Garmin study, the change from one week to the next did not show the same link with injury. It was the single long run that did.
A trial in 532 new runners tested a slow 13-week plan built on adding 10% a week against a normal 8-week plan. About 1 in 5 got hurt on both plans: 20.8% and 20.3%. In an earlier study of new runners, a weekly jump of more than 30% over 2 weeks was linked to more injuries of the type that comes from distance, though that result was not certain.
How to plan your next long run
Know your number: your longest run of the last 30 days. Keep your next run within 10% of it. If your longest run was 10 km, your next long run should be up to about 11 km. Do not copy a friend’s long run. Their number is not yours.
Building endurance means small steps, not one big jump. Easy runs make most of the week. The heart side of this story is on the Cardiac Rehab blog: one long run and injury.
Your questions, answered
Why do runners get injured?
Often from one run that is too long for the body’s tissues. In a study of 5,205 runners, a run 10 to 30% longer than their longest of the last 30 days was linked to 64% more overuse injuries (Frandsen 2025).
Should I follow the 10% weekly rule?
Watch your single long run more than your weekly total. The week-to-week change did not show the same link with injury in the Garmin study (Frandsen 2025), and a slow 10% weekly plan did not cut injuries in new runners (Buist 2008).
How do I plan my next long run?
Take your longest run of the last 30 days and add no more than 10%. Up to 10% longer was the normal injury rate in the study (Frandsen 2025). Longest run 10 km? Next long run up to about 11 km.
Can I run what my friend runs?
Not safely, unless your own longest run is close to theirs. The risk in the study came from going far past your own longest run of the last 30 days, not from the distance itself (Frandsen 2025). Your number is yours, so grow it slowly.
Build Your Endurance Now
Grow your long run a little at a time and keep most runs easy. Read the heart side on Cardiac Rehab: one long run and injury.
References
- Frandsen JSB, 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. pubmed.ncbi.nlm.nih.gov/40623829
- Buist I, Bredeweg SW, van Mechelen W, et al. No effect of a graded training program on the number of running-related injuries in novice runners: a randomized controlled trial. Am J Sports Med. 2008. pubmed.ncbi.nlm.nih.gov/17940147
- Videbaek S, Bueno AM, Nielsen RO, Rasmussen S. Incidence of running-related injuries per 1000 h of running in different types of runners: a systematic review and meta-analysis. Sports Med. 2015. pubmed.ncbi.nlm.nih.gov/25951917
- Nielsen RO, Parner ET, Nohr EA, et al. Excessive progression in weekly running distance and risk of running-related injuries: an association which varies according to type of injury. J Orthop Sports Phys Ther. 2014. pubmed.ncbi.nlm.nih.gov/25155475