Running Without Wrecking Yourself

Here is a number that should change how you start. In the Garmin-RUNSAFE study, researchers followed 5,205 recreational runners in 87 countries for 18 months, using data from their watches. 35% of them got an overuse injury in that time. Older reviews of the research report injury rates anywhere from about a fifth to four-fifths of runners, depending on how a study counted. Either way, getting hurt is the normal outcome for runners who don't plan for it. The good news is that the main causes are known.

Mistake 1: the one run that's too long

For decades the rule was "don't increase your weekly mileage by more than 10%." It sounds sensible, but when Dutch researchers tested it in 2008 on 532 beginners training for a 4-mile race, the group on a gentle 10%-style plan got injured at almost exactly the same rate as the group on a faster plan: 20.8% versus 20.3%.

The 2025 Garmin-RUNSAFE analysis suggests why the old rule missed. Looking at week-to-week changes in total distance, it found no link with injury. Looking at single sessions, it found a strong one. When one run was more than 10% longer than the longest run that person had done in the previous 30 days, the injury rate rose:

Your body doesn't keep a weekly spreadsheet. It notices the single run that's much longer than anything it has recently done.

The practical version: know your longest run of the past month, and keep any single run within about 10% of it. If your longest recent run is 5 km, your next long one is 5.5 km, not 8.

Mistake 2: every run is a hard run

New runners tend to run at the same moderately hard pace every time: fast enough to feel like work, too slow to be real speed training. Elite endurance athletes do something very different. Exercise physiologist Stephen Seiler's analyses of rowers, skiers, cyclists and runners found that they do roughly 80% of their training at low intensity, with a small share of genuinely hard sessions. (Most of that evidence comes from describing what elites already do, not from controlled trials, so treat 80/20 as a strong pattern, not a law.)

For everyone else the lesson is simpler: most of your runs should be easy, truly easy, so that you can run again tomorrow. But "easy" is exactly where people get confused, because the usual tool for measuring it, heart-rate zones, is built on a guess.

Why your "max heart rate" is a guess

220 minus your age is the formula on every gym poster. It was never the result of a proper study. When physiologists Robert Robergs and Roberto Landwehr traced its history in 2002, they found it had been eyeballed from about a dozen earlier data sets around 1971 rather than derived from original research, and that age-only formulas like it typically miss individuals by more than 10 beats a minute.

Better formulas exist. Hirofumi Tanaka and colleagues pooled 351 studies covering 18,712 people in 2001 and got 208 − 0.7 × age, which fits older adults better (220 − age underestimates them). Martha Gulati's 2010 study of 5,437 women found 206 − 0.88 × age fits women better than the traditional formula, which overestimates them. But all of these describe averages. Two healthy 40-year-olds can have maximums 20 beats apart. Some medications, especially beta-blockers, lower heart rate a lot, and heat, dehydration and caffeine all push it around on the day.

Try the checkbox above, too. Switching from a plain percentage of max to the resting-heart-rate method moves a 40-year-old's "easy zone" up by roughly 20 beats. Same person, same words, different numbers. That's a good reason to hold zones loosely.

The test that needs no gadget

Easy running has a simpler check: can you speak in full sentences? Exercise scientists at the University of Wisconsin–La Crosse, led by Carl Foster, have found that the point where talking first becomes difficult sits close to the ventilatory threshold, the boundary between comfortable aerobic work and harder effort. The studies are small, but the talk test is free, works with any heart, and never needs charging. If you can chat, you're easy. If you can only manage a few words, you're not.

Shoes: buy comfort, not a cure

Running shops used to sort customers by how much their feet roll inward ("pronation") and sell them motion-control shoes to correct it. A 2015 review led by biomechanist Benno Nigg found that the evidence for pronation and impact forces as the main causes of injury was not convincing. The authors proposed instead that runners pick the shoe that feels most comfortable, on the theory that comfort keeps you in your natural way of moving. That's a sensible rule of thumb, though no study has yet proven that comfortable shoes prevent injuries. What is clear: an expensive, "corrective" shoe is not protection against a training mistake.

A start that respects all of this

If you're new or returning, use a walk-run plan. The UK's NHS Couch to 5K takes nine weeks at three runs a week, starting with short running intervals between walks. It builds gradually and keeps you at a conversational effort, which is exactly the pattern the research favours. Leave a rest day between runs at first, and treat pain that changes how you run, or gets worse as you go, as a signal to stop rather than push through.

Sensitive-topic note: this is general information, not medical advice. If you have a heart condition, take heart or blood-pressure medication, have chest pain, dizziness or unusual breathlessness on exertion, or are returning after a long break with health concerns, check with a doctor first. Heart-rate formulas do not apply to people on beta-blockers. A pain that is sharp, localized to a bone, or doesn't settle with rest deserves a professional look.