PB stands for Personal Best, meaning the fastest time you’ve ever run for a specific distance. If you run a 5K in 24:30 and that’s faster than any 5K you’ve done before, that’s your new PB. The term is most common in the UK and Canada, while runners in the United States typically say PR (Personal Record). They mean exactly the same thing.
PB vs. PR: A Regional Difference
If you’re reading race recaps or scrolling running forums, you’ll see both PB and PR used constantly. The split is almost entirely geographic. Runners in the UK and Canada say PB, runners in the US say PR. World Athletics, the international governing body for the sport, uses PB in its official documents and athlete profiles. So if you’re looking at results from a major international competition, you’ll see “PB” next to an athlete’s lifetime fastest time and “SB” (Season Best) next to their fastest time for the current year.
Beyond those two, you might also encounter WR (World Record), CR (Course Record), and QB (Qualification Best, used for championship qualifying standards). But PB and PR are the ones recreational runners use daily.
What Counts as an Official PB
For most recreational runners, a PB is simply your fastest time at a given distance, period. You track it yourself or let an app do it for you. But if you care about your time being nationally ranked or recognized for record purposes, the rules get stricter.
USA Track & Field requires that any road running performance submitted for records or national rankings come from a certified course. The certification program exists to guarantee the distance is accurate. As USATF puts it, no one can truly establish a personal best if the course distance isn’t right. A flat, short, or mismeasured course would inflate your time. For a performance to be fully recognized, it needs both a certified course and a sanctioned event.
World Athletics applies a similar logic at the elite level. Their technical rules are enforced in full for elite and designated competitive sections of races, while mass participation runners in the same event operate under a simplified set of rules. This is why your local 10K finish time is yours to celebrate, but it won’t show up in any official database unless the event met specific standards.
Gun Time vs. Chip Time
Large races use two timing methods. Gun time starts when the starting gun fires. Chip time (also called net time) starts when you personally cross the starting mat, which could be minutes later if you’re standing in a back corral. The running community has a clear consensus on which one defines your PB: chip time. Since chip time reflects only the minutes you actually spent running the course, it’s the fair measure of your performance.
Gun time still matters for one thing: overall placement. The first person across the finish line wins, regardless of when they crossed the start mat. And at the very top of the sport, official world and national records use gun time. But for your personal best as a recreational or competitive amateur runner, chip time is the standard almost everyone uses.
How Apps Track Your PB
Platforms like Strava and Garmin automatically detect personal bests across common distances (1K, 1 mile, 5K, 10K, half marathon, marathon) every time you upload a run. But the two platforms don’t always agree, and the reason trips up a lot of runners.
Strava calculates PBs using elapsed time, not moving time. If you pause your watch at a traffic light for 30 seconds, Strava’s PB clock keeps ticking. Garmin, on the other hand, often uses moving time. This means Garmin might credit you with a faster 5K than Strava does for the exact same run. There’s no setting to change Strava’s approach, and the reasoning is sound: if you could pause freely, you could run fast intervals with long rest breaks and stitch together a “5K best” that doesn’t reflect your actual ability to cover 5K continuously.
What Has to Improve to Run a New PB
Setting a new personal best comes down to your body getting better at delivering and using oxygen. Two markers matter most. The first is your peak oxygen uptake, a measure of how much oxygen your heart and lungs can supply to working muscles. The second is the speed you can sustain before lactate builds up faster than your body can clear it, often called your lactate threshold pace. Both are trainable.
A study in the Journal of Sports Science & Medicine found that runners doing a mix of high-intensity and steady endurance training improved their lactate threshold speed by 13 to 21 percent over the course of the intervention. The underlying changes include more blood vessels feeding the muscles, higher density of energy-producing structures within muscle cells, and a stronger heart pumping more blood per beat. In practical terms, the pace that once felt hard starts to feel moderate, and you can hold a faster pace before your legs start burning.
High-intensity training (intervals, tempo runs, hill repeats) produced slightly larger gains in both oxygen uptake and threshold speed compared to steady easy running alone. But both approaches worked. If you’re chasing a PB, the evidence supports including some harder efforts in your weekly training rather than running every session at the same easy pace.
Why Course and Conditions Matter
Not all PBs are created equal, and experienced runners know that course profile, altitude, and weather can make a significant difference. Running at altitude is harder because the air contains less oxygen. Research suggests that for every 1,000 meters of elevation above sea level, you can expect to slow down by roughly 3 percent at the same effort level. At 2,000 meters elevation, that translates to about 15 extra seconds per kilometer at a 4:15 pace.
Course elevation matters too. A net downhill course can produce faster times, which is why some runners specifically target races like the Boston Marathon or the St. George Marathon for PB attempts. On the flip side, a hilly course with lots of climbing will slow you down even if the net elevation change is zero. Most runners keep a mental note of which courses are “fast” and which aren’t, and treat their PB as their best time on a reasonably fair course rather than obsessing over whether every race was perfectly comparable.
Temperature and wind play a role as well. Cool, calm conditions (around 7 to 12°C or 45 to 55°F for most people) tend to produce the fastest times. Heat forces your body to divert blood flow to cooling, leaving less for your muscles. If you’re planning a PB attempt, picking the right race on the right day matters almost as much as the training you put in.