About · built by athletes
About TrainingZones: Built by Athletes
TrainingZones is a free, science-based training-zone resource built by endurance athletes. It exists to give every runner, cyclist, swimmer, rower and skier accurate training zones without ads, paywalls or signups. Every formula is sourced to a primary reference and backed by an automated unit test.
Written & maintained by
Sven Ahrens
Founder & endurance athlete
Sven Ahrens founded TrainingZones after years of training and racing across endurance sports, frustrated that the zone calculators he relied on were inaccurate, ad-choked or locked behind email walls. He oversees the methodology, the sources, and the tests that keep every number on this site honest.
Who we are
TrainingZones is built by people who actually train. The experience comes first: real seasons, real field tests, real failed workouts. On top of that we layer expertise: every model on the site is implemented from its primary scientific or coaching source, not copied from another calculator. That combination of lived experience and sourced expertise is what TrainingZones means by trust, and it maps directly onto Google's E-E-A-T standard of experience, expertise, authoritativeness and trustworthiness.
Why TrainingZones exists
Most zone calculators on the web are ad-choked, quietly inaccurate, or locked behind a signup that exists only to harvest your email. TrainingZones is the opposite. It is free forever, with no email wall and no advertising in the calculators. Every formula is sourced to a primary reference and unit-tested against known values, so the number you get is the number the literature actually supports.
Our standards
Every formula on TrainingZones is a pure function with a unit test asserting reference values from its source; we never improvise numbers. We cite primary sources by name: Tanaka for max heart rate, Coggan for power zones and FTP, Friel for threshold heart rate, Seiler for polarized training, Maffetone for aerobic-base heart rate, and Daniels for running paces. And the structured data we emit always matches the text you can see on the page; the schema never claims something the page does not.
How we make money
Honestly: TrainingZones is the free front door to Coach Kalle, an AI coaching product. If the zones we give you make you want a coach to build the rest of the plan around them, Coach Kalle is there. But the calculators stay free forever regardless: there is no upgrade you need to buy to get an accurate number, and there never will be.
Not medical advice
TrainingZones is an educational training resource, not a medical service. The zones and formulas here are estimates for healthy adults and do not account for medications, cardiac conditions or other individual health factors. Consult a physician before starting or changing a training programme, especially if you have a known health condition or any symptoms during exercise.