Free Breathing Tools
Test, pace and program your breathing with free interactive tools from the team behind the O2Trainer and Bas Rutten. No signup, no downloads — open a tool and start training.
BOLT Score Test
Measure your CO₂ tolerance in under a minute with a guided breath-hold timer and instant score interpretation.
Open tool →VO₂ Max Calculator
Estimate your aerobic ceiling from resting heart rate — no lab required — with age and sex adjusted ratings.
Open tool →Breathing Protocol Builder
A progressive 4-week respiratory training plan built for your sport: MMA, running, swimming, cycling, voice or tactical.
Open tool →Breathing Pacer
Guided box breathing, 4-7-8, coherent breathing and warm-up rhythms with an animated visual pacer.
Open tool →Why train your breathing?
Your diaphragm and intercostal muscles power every breath you take, and like any muscle they can be measured, trained and strengthened. These tools give you the two things every training program needs: a baseline to measure and a structure to follow. Test your BOLT score and estimated VO₂ max, build a protocol for your sport, and use the pacer for daily practice and recovery.
When you're ready to add progressive resistance — the same principle that builds every other muscle — the O2Trainer gives you 16 levels to grow through.
Stronger breathing in 30 breaths a day
Join 54,000+ athletes, singers and everyday trainers building respiratory strength with the O2Trainer.
Shop the O2Trainer
