What is Negative Split?
Negative Split is a Chrome extension that adds running analytics to the Strava pages you already look at. Open an activity and it gains rTSS, grade-adjusted pace, aerobic decoupling, time in zones, detected intervals and race predictions. Everything is computed on your machine. No account, no login, nothing uploaded.
It doesn't use the Strava API at all. It reads the page as a logged-in user and works from the same activity data Strava's website loads, so the 2026 API changes don't touch it. It's free, made by one person, Gere Lajos, under the Ownward name. The Chrome Web Store listing asks for one permission, strava.com, and states that no data is collected.
Key Features
Training load on every run
rTSS and intensity factor, grade-adjusted pace using the Minetti energy-cost model, aerobic decoupling (how much your heart rate drifted for the same pace), and time in zones with an 80/20 easy-to-hard read.
Intervals found for you
It detects reps from the velocity data and lists each one, so a workout logged as a single run gets broken into its pieces without you marking laps. It also suggests a title and description for the activity from what it found.
Fitness, fatigue and form
Fitness, fatigue and form tracked across your history, with an acute-to-chronic workload flag for injury risk, shown in your profile card on the Strava dashboard.
Personal bests, age-graded
A sortable PB list, age-graded against the WMA 2025 tables with class bands, a VDOT estimate on the Daniels scale, race predictions from 5K to marathon built from your own PBs, and a pace-duration curve with critical velocity.
Run cards and a year-in-sport recap
A downloadable run card with the route, splits and heart-rate zones, generated locally. And a year-in-sport recap whenever you want one: totals, sport split, season bests, a daily heatmap, monthly volume, and a downloadable year card.
Who It's For
- Runners on free Strava who want training load, GAP and race predictions without paying for a subscription or a second app
- Anyone doing structured workouts who is tired of marking laps by hand
- People who don't want their data leaving the browser, since nothing is uploaded and there's no account to create
- Runners whose data comes from any watch, because it reads what Strava shows rather than syncing from the device
Worth Knowing
It's runner-first. Rides get the basics but there's no power analysis, so cyclists with power meters will get more from Sauce for Strava or Elevate. It's Chrome-only, including Chromium browsers like Edge, Brave and Arc. Like every extension it lives inside Strava's pages, so a Strava redesign can knock a feature out until the next update; version 1.4.2 shipped in July 2026. Segments, routes and safety features still come from Strava.
