https://inertial.run/blog/ Every metric, benchmark and adjustment a runner meets on a watch, explained with numbers, methods and sources. No ads, no affiliates, nothing gated. en https://inertial.run/blog/is-sub-4-marathon-realistic/ https://inertial.run/blog/is-sub-4-marathon-realistic/ Tue, 01 Sep 2026 03:30:00 GMT Sub-4 needs 5:41/km (9:09/mi). Five inputs decide whether that is yours: half time, weekly volume, longest run, course and heat. https://inertial.run/blog/what-strava-fitness-score-measures/ https://inertial.run/blog/what-strava-fitness-score-measures/ Tue, 01 Sep 2026 03:30:00 GMT It is a 42-day average of training load, not fitness. That is why it can fall by 10 points in the block where you got faster. https://inertial.run/blog/why-garmin-strava-predict-different-times/ https://inertial.run/blog/why-garmin-strava-predict-different-times/ Tue, 01 Sep 2026 03:30:00 GMT One reads your training, the other reads one race. From a 25:00 5K, 3 published models already disagree by 6 minutes at marathon distance.