Editor28 pieces · Since May 2025

Stephen M. Walker II

Product leader, fitness operator, and AI founder. Former Head of Product at Freeletics, now building Titan Health.


Profile
Stephen WalkerFounder, Titan Health

Led product at Freeletics, now building performance analytics at Titan

Stephen is the founder of Titan Health and writes most of the Titan blog. He builds performance analytics from Apple Watch data for the same audience he has shipped products to for a decade: people who take training seriously and want software that respects it. He also founded Fuel, an AI nutrition coaching app that sends the meals you log to Titan through Apple Health.

From 2017 to 2020 he led product, design, research, content, and subscription monetization as Head of Product & Design at Freeletics, where his teams helped the digital fitness app surpass 50 million users worldwide across 100+ countries, with 70% week-one training activation. That stint — owning every surface that touches habit formation in a fitness app — is the operator lens behind every article here.

After Freeletics he grew Productboard 5x to $50M+ ARR as Senior Director of Product Management (2020–2022), reshaping the product from SMB/PLG-darling to enterprise roadmap software adopted by 6,000+ companies. Since 2022 he has been co-founder and CEO of Klu.ai, an LLM infrastructure platform used by thousands of AI teams, which is why the AI features in Titan feel less hand-wavy than most.

Earlier he ran global UX programs at Amazon (2016–2017) for cross-border eCommerce, led mobile investing design at Capital One (2014–2016), and spent a decade (2003–2014) running Smoov, a boutique design studio shipping work across consoles, desktop, mobile, and web. He speaks regularly at EU CPO Conference, SXSW, La Product Conf, and Product Led Alliance. Verifiable on SMW.ai, LinkedIn, and Speaker Deck.

Fitness product operatorHead of Product at Freeletics
AI infrastructure founderCo-founder & CEO, Klu.ai
Enterprise product scaleSenior Director PM at Productboard
Public speakerEU CPO Conference · SxSW
Career
Founder · Fuel Nutrition2025 – PresentAI nutrition coaching built around Apple Watch energy
Co-founder & CEO · Klu.ai2022 – PresentLLM evaluation and optimization for thousands of AI teams
Senior Director, Product Management · Productboard2020 – 2022Scaled to $50M+ ARR and 6,000+ customers — 5x growth
Head of Product & Design · Freeletics2017 – 202050M+ users worldwide across 100+ countries and 70% week-one training activation
Global UX Manager · Amazon2016 – 2017Mobile cross-border eCommerce expansion programs
Principal Designer / Design Manager · Capital One2014 – 2016Mobile investing design; lifted digital adoption
Founder · Smoov2003 – 2014Boutique studio across console games, desktop, mobile, and web
Areas of Expertise
Performance nutritionMacro trackingAI food loggingDigital fitness productsSports nutritionGLP-1 coachingApple Watch energy modelingSubscription monetizationProduct managementUX researchLarge language models
Selected Writing
Training
Recovery
Sleep
Longevity
Data
Elsewhere
All Articles

Everything by Stephen Walker

28 articles on the Titan blog, newest first.

What alcohol does to your HRV, resting heart rate and sleepSep 27, 2026RecoveryApple Watch training load and effort ratings compared with TitanSep 27, 2026TrainingHow to Calculate Heart Rate ZonesSep 27, 2026TrainingWHOOP vs Apple Watch for recovery, sleep, strain and trainingSep 27, 2026DataHow Apple Watch Measures HRV and Why the Number ChangesSep 25, 2026DataHow accurate is Apple Watch sleep trackingSep 25, 2026SleepNormal HRV by Age and SexSep 25, 2026RecoveryOura Ring versus Apple Watch for recovery, sleep and HRVSep 25, 2026DataRecovery scores explained, and why your devices disagreeSep 25, 2026RecoveryResting heart rate by age, fitness and what moves itSep 25, 2026RecoverySleep debt, what it is and whether you can pay it backSep 25, 2026SleepWhat hard training requires from your sleepSep 25, 2026SleepWhat your stress score is measuringSep 25, 2026RecoveryBiological age, fitness age, and what Titan Age can tell youSep 25, 2026LongevityHow WHOOP strain compares to Titan training loadSep 25, 2026DataAdjusting training to recoveryApr 16, 2026RecoveryAthlete Adherence and Behavior ChangeApr 16, 2026TrainingHRV and Recovery ReadinessApr 16, 2026RecoveryPerformance PhysiologyApr 16, 2026TrainingWearable data quality and how to interpret itApr 16, 2026DataHow Titan measures training loadFeb 10, 2026TrainingEndurance training and the 80/20 intensity splitMay 24, 2025TrainingSix Longevity Markers and the Week That Moves ThemMay 24, 2025LongevityMindfulness, Breathwork and Overnight HRVMay 24, 2025RecoveryMuscle Building Guide for High Quality HypertrophyMay 24, 2025TrainingProgressive overload, four progression schemes and when to use eachMay 24, 2025TrainingHow to recover between hard training sessionsMay 24, 2025RecoveryVO2 Max and Aerobic Capacity ExplainedMay 24, 2025Longevity