Forget the 10% Rule — Watch Your Long Run Instead

For years, the go-to injury-prevention rule was "don't increase weekly mileage by more than 10%." A new study of over 5,000 runners says that rule is mostly noise. Researchers tracked training loads and injuries and found that week-to-week mileage jumps had almost no relationship to overuse injuries. What actually mattered was whether a single run got too big, too fast.

Specifically, runs that exceeded 110% of the longest run someone had done in the previous 30 days were linked to a 64% higher risk of overuse injury. So if your longest recent run was 10 miles, pushing to 11 miles is fine — but jumping straight to 13 or 14 is where things start to break down. It's not about your total weekly volume; it's about asking a single run to do too much work your body hasn't been prepared for.

This makes physiological sense. Tendons, connective tissue, and bone adapt more slowly than your cardiovascular system does. You can feel "fine" aerobically during a big long run while your Achilles or IT band is quietly accumulating damage that shows up days later. Weekly totals smooth over this risk because they don't capture the size of any one session — and one session is often the actual stressor.

The takeaway for your training: stop obsessing over whether your week went from 30 to 34 miles. Instead, watch your long run specifically. Keep any single long run within about 10% of your longest run from the past month. If you want to add distance, spread it across easy days and warmups instead of stacking it all into one big Saturday effort. Progress the long run gradually — think inches, not leaps — and let your weekly volume rise as a byproduct of that discipline, not the other way around.