Rethinking Running Injuries: Why One Big Run Might Be Riskier Than You Think

Running is one of the most popular and accessible forms of exercise worldwide. Whether you’re training for a marathon, jogging for health, or chasing a personal best, running offers countless benefits, but it also comes with a well-known downside: injuries.

Despite widespread use of smartwatches and training metrics to monitor performance, injury rates in runners remain stubbornly high, with overuse injuries being the primary culprit. In fact, injury is the leading reason runners abandon their training programs. But a recent study offers new insights into how and when these injuries happen, and it challenges the conventional wisdom we’ve relied on for years.

The Problem with “Too Much, Too Soon”

You’ve probably heard the advice: don’t increase your mileage by more than 10% per week. This guideline, known in the running world as the “10% rule,” has been the standard for injury prevention.

Traditionally, running injuries have been linked to spikes in weekly training loads, tracked using metrics like the Acute:Chronic Workload Ratio (ACWR), which compares your training over one week to the average of the previous three weeks. But does that tell the full story?

This new study, led by researchers from the Garmin-RUNSAFE Running Health study, proposes a different way of looking at injury risk: the danger might lie not in your weekly load, but in a single hard session.

The Single-Session Paradigm: A New Lens on Injury Risk

The study followed over 5,200 adult runners for up to 18 months, collecting GPS-based running data from Garmin devices alongside weekly self-reported injury questionnaires.

Key Question: Does a sudden spike in distance during a single run increase the risk of overuse injury more than gradual weekly increases?

The answer: yes, and significantly so.

Here’s what they found. Compared to runners who kept their session distances consistent, the risk of injury increased:

• 64% for small spikes (10% to 30% increase in distance)
• 52% for moderate spikes (30% to 100% increase)
• 128% for large spikes (more than doubling the distance of any run in the past 30 days)

These results were measured per session, not per week, and that’s crucial. It means that one overly ambitious long run after weeks of moderate training could be enough to trigger an injury, even if your weekly mileage seems balanced.

What This Means for Runners

The takeaway is simple: avoid running more than 10% farther in a single session than your longest run in the past month.

For example, if your longest run in the last 30 days was 10km, try not to exceed 11km in a single outing, even if you feel great or are catching up after time off.

But here’s an important caveat: even small increases (under 10%) carry some risk. The data showed a slight, though not statistically significant, increase in injury risk for spikes under 10%, so caution is still warranted, especially if you’re stacking multiple increases across sessions.

Practical Advice for Runners and Coaches

Based on this research, here are a few tips:

Track your longest run in the past month. Don’t increase your current session distance by more than 10% over that.

Don’t rely solely on weekly mileage or ACWR. While these metrics are useful, they may not capture single-session spikes that raise injury risk. A running assessment can help establish a clearer picture of your individual risk factors beyond what a watch alone can tell you.

Progress gradually. Even multiple small increases in short succession can lead to overload if recovery is insufficient.

Log more than just distance. Include terrain, pace, elevation, and how you felt. Injury risk isn’t just about numbers.

Listen to your body. The study found most injuries were reported within 2 days of a run, so don’t ignore post-run soreness or fatigue.

Final Thoughts

Running is a rewarding and accessible sport, but like any form of physical activity, it carries risks. This new research suggests that how much you run in one session, not just over the week, plays a major role in injury risk.

So the next time you’re tempted to double your distance on a whim, remember: more isn’t always better. Stick to gradual progress, give your body time to adapt, and let data like this guide you toward sustainable, injury-free running.

If you’re managing a running-related injury or want a running assessment to reduce your risk, our Sports Physiotherapy team can help.

Book an appointment at BeFit Training Physiotherapy — no referral needed.

Edgecliff: (02) 9327 7749 | Coogee: (02) 7205 2805

References

Nielsen RO, et al. How Much Running Is Too Much? Identifying High-Risk Running Sessions in a 5200-Person Cohort Study. Br J Sports Med. 2025.

Australian Physiotherapy Association. Clinical guidelines. physiotherapy.asn.au.