Questions, answered.

CTL (Chronic Training Load) is your Fitness — a ~42-day exponentially weighted average of your daily Training Stress Score (TSS). ATL (Acute Training Load) is your Fatigue — a ~7-day exponentially weighted average of your TSS.TSB (Training Stress Balance) is your Form, computed as CTL − ATL: negative means tired, positive means fresh. The math is the Banister 1965 impulse-response model, the same one TrainingPeaks uses for its Performance Management Chart.

Training Stress Score (TSS)is one number that combines a workout's duration and intensity. By definition, one hour at your threshold (FTP) equals 100 TSS. CTL, ATL and TSB are rolling averages of your daily TSS, so a steady diet of 100 TSS per day holds your CTL at 100.

Power gives the most accurate TSS, but TrainCurve also accepts HR-only workouts (running without a power meter) and manual entries with a single TSS number. If you have a power meter you get Normalized Power (NP) and Intensity Factor (IF) for free.

TrainCurve pulls daily HRV / resting HR / sleep from Apple Health (when you connect it in the iOS app) and shows a recovery band on the dashboard. Recovery doesn't change your TSS — it's context the coach uses when you ask “should I rest today?”

Bring Your Own Key. Paste your Claude Pro or ChatGPT Plus API key once, and TrainCurve uses your existing subscription for unlimited coaching. We don't add a per-token markup. TrainCurve stores your key encrypted at rest with AES-256-GCM and never logs it.

Anthropic (Claude), OpenAI (ChatGPT), and Google (Gemini). OAuth sign-in is available for OpenAI and Google, so you don't even have to paste a key. Anthropic requires a paste-your-key flow because they don't expose delegated OAuth.

Yes. Open Settings → Data and you can export your full database as JSON or CSV at any time. The coach sees only what you have uploaded: workouts, recovery, and the profile fields you filled in (FTP, max HR, threshold pace, goals). It doesn't have access to your calendar, email, or anything outside TrainCurve.

Anything that exports .fit, .tcx, or .gpx files. That covers Garmin, Wahoo, Coros, Polar, Suunto, Hammerhead, Zwift, TrainerRoad, and most other head units. Strava sync is built in for two-click import of the last 90 days.

Strava is fully supported today (OAuth + webhook + historical sync). Garmin is on the roadmap — TrainCurve is open source so you can self-host with a Garmin Connect developer key if you want it sooner.

Yes — always, in JSON or CSV. Open Settings → Data → Export. There's no lock-in. TrainCurve is AGPLv3 open source, so even if we shut down the SaaS, you can self-host the same code.

Yes. TrainCurve is free forever for your first 100 workouts, with no credit card. Free includes the math (CTL/ATL/TSB), manual workout entry, and FIT/TCX/GPX uploads — just not Strava sync, the BYOK AI coach, or the iOS app.

€9/month for unlimited workouts, Strava sync, the BYOK AI coach, and the iOS app. €29/month per coach for the Team tier, which covers up to 25 athletes per seat and a coach dashboard.

Settings → Billing → Cancel. Your data stays accessible for 30 days in case you change your mind. After that the account is deleted (you can export first).

EU-hosted (Frankfurt for the production API, Cloudflare's EU edge for the web). GDPR-compliant by design. Your provider keys never leave the EU.

Yes. Settings → Account → Delete account. We delete your data within 30 days. Provider keys are deleted immediately.

No. TrainCurve never sends your data to anyone except the AI provider you connect (via BYOK), and only at the moment you ask the coach a question. We don't sell, share, or train on user data.