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The Triathlete Blueprint Newsletter #115-The One Running Mistake That Increases Injury Risk by 64%, According to a New Study
- Yan Busset
- 3 minutes ago
- 5 min read
Read time: 5min.
By Coach Yan Busset
A New Study Reveals the Real Reason Runners Get Injured
You’re running more. You’re feeling good. Maybe your training plan said 12 km, but the weather’s nice, legs feel strong, and you’ve got time. So you go for 16. What could go wrong?
Well… quite a lot, actually.
A massive new study published in July 2025 just revealed something that flips a lot of common running wisdom. After tracking over 5,000 runners across 87 countries, researchers found that the most common trigger for running injuries isn’t high weekly mileage. It’s suddenly making a single run much longer than anything you’ve done recently.
In fact, if your longest run jumps by just 10 to 30 percent compared to the previous month, your injury risk increases by 64 percent. And if you double your longest run, that risk more than doubles.
This is a game-changer, especially in triathlon where running is already responsible for around 90 percent of all injuries. It’s not just about doing too much. It’s about doing too much, too fast.
Let’s break down what this study means for your training and how to use it to stay healthy, consistent, and race-ready.
Running Is Different
From experience, I can say that around 90 percent of the injuries I see in triathletes come from running. Why? Because unlike swimming or cycling, which support your body and are low impact, running sends shockwaves through your joints, tendons, and muscles with every single step. Over time, those impacts accumulate.
This is why I always advise athletes to keep the run volume focused on quality, not quantity. You don’t need to rack up endless kilometers on foot to build endurance. That’s what the bike is for. Long rides are far more forgiving and give you a safer way to build your aerobic engine. Swimming adds even more volume without taxing your recovery.
One of the great strengths of triathlon is mixing three disciplines. Use that to your advantage. Save your running for structured, smart sessions that your body can absorb and recover from, and let the other sports carry the load.
I wrote a full article on this topic previously. You can read it here:The TBN #46 – “90 % of triathlon injuries comes from running, here’s how to avoid them”https://www.tri-coaching-finland.com/post/the-tbn-46-90-of-triathlon-injuries-comes-from-running-here-s-how-to-avoid-them
The Study’s Key Insight
For a long time, most coaches and athletes suspected that running was the main source of injuries in triathlon. The impact, the load, the repetitive nature of the movement, it all pointed in that direction. Now, a very recent study confirms that idea but takes it one step further.
It shows that the real danger might not be in how much you run overall, but how suddenly you increase the length of a single run.
Published in July 2025 in the British Journal of Sports Medicine, the study followed over 5,000 runners from 87 countries for 18 months. Researchers compared each runner’s sessions to the longest run they had done in the previous 30 days.
Here’s what they found:
If your run is 10 to 30 percent longer than your longest recent run, your injury risk goes up by 64 percent
A 30 to 100 percent increase raises the risk by 52 percent
If you more than double your previous longest run, your injury risk more than doubles
Interestingly, changes in weekly mileage were not clearly linked to injury. What really matters is when your longest session suddenly gets much longer than your body is used to.
This confirms something many of us have seen over and over. Most injuries don’t come from big training weeks. They come from one or two sessions that go too far, too soon.
Let this be your guide. Look at your longest run from the past month. If you’re adding more than 10 percent, you may be pushing the line. Better to build gradually and keep the momentum going than to chase a breakthrough and end up on the sidelines.
Not Everyone Can Absorb the Same Volume
We all recover differently. A lean, experienced runner can handle more volume than a beginner or someone with higher body weight. That’s not judgment. It’s biomechanics.
The heavier you are, the more load each stride brings. If your running form is off or your muscles are weak, the risk increases again. Experience also matters. Your tissues need time to adapt. Just because your lungs and motivation can handle a session doesn’t mean your joints and tendons can.
That’s why copying someone else’s running plan rarely works. So stop comparing yourself to others. We are all different. We were not born equal, and that's okay. We have to work with our own strengths and weaknesses. Some of us can handle more training volume than others, especially when it comes to running. That needs to be taken into account when building a smart and sustainable training plan.
How to Train Smarter
Start with a simple habit. Look at your longest run in the past 30 days. Add no more than 10 percent to it. If you’re unsure or coming back from fatigue or injury, keep it closer to 7 percent. That’s your ceiling. Stick to it, and you’ll keep building without overloading.
But training smarter isn’t just about volume control. One of the biggest levers you can pull is running technique. The way you run affects how much peak impact each stride produces, and that impact is what often leads to injuries.
For example, if you tend to overstride by landing with your foot too far ahead of your body, you’re sending more force through your joints. Correcting this and slightly increasing your cadence can reduce peak impact per step, even at the same pace. Over time, these small changes can be what keeps you just below the injury threshold instead of crossing it.
So the message is simple. Progress gradually, and run efficiently. Your future self will thank you.
Final Thoughts
Injury prevention isn’t about staying in your comfort zone. It’s about understanding how the body adapts and giving it just enough stress to grow without breaking. That’s the key.
This recent study finally puts real numbers on something many coaches have known for years. Injuries don’t come out of nowhere. They come when you overreach, especially in running.
Train consistently. Build gradually. And above all, use each discipline wisely. That’s the beauty of triathlon. You have three sports. Use the cross-training effect to your advantage. Build your endurance on the bike, especially with long rides. Don’t underestimate swim volume. It plays a bigger role in your run performance than you might think, especially in terms of general aerobic fitness and recovery.
Running performance is a balance between your natural ability, your background, your genetics, and your experience. The keyword is progression. Give your body time to absorb the load before adding more. Let it adapt. Don’t chase the hero session that feels impressive but may cost you weeks on the sideline.
Shorter, more frequent runs are often a smarter path forward. If you get injured, you’re not training. And if you’re not training, you’re not progressing.
So yes, train hard, but train smart first.
Reference:Nielsen, Rasmus Østergaard et al. “How much running is too much? Identifying high-risk running sessions in a 5,200-person cohort study.”British Journal of Sports Medicine, July 2025.DOI: 10.1136/bjsports-2024-109380Available at: https://bjsm.bmj.com/content/early/2025/07/07/bjsports-2024-109380
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