If you’re a stickler for the 10 per cent mileage rule–never adding more than 10 per cent to your weekly mileage–you might still be doing it wrong. A new study published in the British Journal of Sports Medicine suggests it’s not increasing weekly mileage too quickly that puts runners at risk, but how much farther they go in a single session.
Researchers found that completing a run that exceeds 110 per cent of their longest run during the month prior can increase a runner’s risk of overuse injury by more than 64 per cent.
Researchers followed 5,205 adults from 87 countries for 18 months as part of the Garmin-RUNSAFE Running Health Study. Participants (average age of 46, 22 per cent women, 78 per cent men), all of whom had between four and 20 years of running experience, uploaded every run via Garmin watches and completed weekly injury questionnaires. Participants could declare themselves injury-free, uninjured yet with problems or injured (painful/irritating and leading to a reduction in running activity). Injured runners also described how the injury occurred, overuse or traumatic; participants with an existing injury were excluded from the study.
In total, the study analyzed more than 588,000 running sessions and recorded 1,800 injuries, 72 per cent of which were from overuse.
Each run was compared to the longest distance the athlete had completed in the previous 30 days and categorized as:
Baseline: up to a 10 per cent increase
Small spike: 10-30 per cent increase
Moderate spike: 30-100 per cent increase
Large spike: more than 100 per cent increase
The results were striking: compared to a steady progression (up to 10 per cent), the risk of overuse injury rose 64 per cent with a small spike, 52 per cent with a moderate spike and more than doubled after a large spike.
Surprisingly, weekly training load measures, like week-to-week mileage changes and acute:chronic workload ratio (weekly mileage compared to the past four weeks), didn’t predict injuries well. The biggest danger evidently came from a single-session spike, not gradual mileage increases. But even baseline increases of up to 10 per cent can still add up if repeated week after week without allowing for an adjustment period.
So how should you increase your mileage?
Avoid piling all your extra distance into a single long run. Instead, spread the mileage across your week–add a few minutes to easy runs, or go just a bit farther in warmups and cooldowns. These smaller, lower-stress additions are easier for your body to handle than one big jump.
If you’re building toward a long-run goal, break it up into baseline increments every other week. And when you’re pushing the distance on these long runs, balance it by keeping that week’s overall training intensity lower, giving your body room to adapt. Don’t progress mileage and intensity simultaneously, and never try to “make up” an increase if you fell off track for a week or two.
How to increase your weekly mileage (with minimal effort)
