Endurance Athlete Performance

Welcome to Activity.icu, your Nordic-inspired training ecosystem.

Track your CTL (Fitness), ATL (Fatigue), and TSB (Form) with precision. Connect your Intervals.icu account to get started.

Product Capabilities & Disciplines

Engineered for Modern Multi-Discipline Athletes

Deep scientific modeling across cycling, running, and swimming. Explore our specialized analytical engines with zero login required.

Nordic architecture modeling Chronic Training Load (CTL), Acute Fatigue (ATL), and Freshness (TSB) with multi-component decay.

Automated rolling 6-week Critical Power detection, Power Duration curves, durability kJ depletion profiling, and Coggan zones.

Minetti 5th-degree polynomial Grade Adjusted Pace (GAP), Critical Speed, Jack Daniels VDOT race predictions, and Stryd power.

Critical Swim Speed threshold pace, SWOLF stroke efficiency telemetry, 5-zone aquatic matrices, and open water GPS decimation.