Physiology

Mathematical and physiological reference for Critical Swim Speed (CSS), the swimming analogue of Critical Power, derived from the slope of distance-vs-time linearity across two or more maximal time-trials. Documents the standard 200/400 m two-trial protocol, the relationship between CSS and the Maximal Lactate Steady State, the boundary conditions where the math overestimates the true sustainable speed, the pool-to-open-water adjustment factor, and the periodization heuristics for CSS-anchored set prescription.

Mathematical and physiological reference for durability, the time-dependent retention of physiological function during prolonged endurance exercise, in practice measured as the maintenance of threshold power, efficiency, or substrate utilisation after a defined prior-work load.

Mathematical and physiological reference for Heart Rate Variability, the millisecond-level variation in beat-to-beat intervals, used as a daily autonomic-nervous-system signal of recovery state in endurance training. Documents the RMSSD time-domain metric, measurement protocols, baseline-deviation interpretation, and the multi-source monitoring framework in which HRV is one signal among several.

Mathematical and physiological reference for Lactate Threshold Heart Rate, the heart-rate value corresponding to the second lactate threshold (LT2 / maximum lactate steady state), used as the heart-rate anchor for HR-based zone prescription and as a cross-modality intensity reference when power data is unavailable.

Mathematical and biomechanical reference for the running-dynamics metric family. Ground Contact Time (GCT), Vertical Oscillation (VO), Vertical Ratio (VR), Stride Length, and Cadence, captured by Garmin-compatible watches and dedicated foot-pod sensors. Documents the standard measurement methods (accelerometer-derived from chest/torso or foot pod), the empirical norm distributions across recreational-to-elite populations, the associations with running economy and injury risk, the interventions that move each metric, and the boundary conditions where chasing dynamics targets becomes counter-productive.

Mathematical and physiological reference for running economy (RE), the steady-state oxygen cost of running at a submaximal velocity, conventionally expressed as mL O₂ per kg per km. Documents the standard measurement protocol, the determinants that govern individual variation (anthropometric, biomechanical, neuromuscular, metabolic, and footwear), the empirical training adaptations that move RE on multi-month timescales, and the relationship between RE and race performance at the elite level where VO₂max has plateaued.

Mathematical and physiological reference for the dual-axis Training Effect (TE) construct popularised by Firstbeat and adopted across the modern wearable ecosystem. Documents the EPOC-based aerobic and anaerobic scoring algorithms (0-5 scale), the heart-rate-derivative classification rules that distinguish dominant energy systems, the relationship between TE scores and the underlying training-impulse and load-balance frameworks, and the recovery-time projections derived from TE accumulation.

Mathematical and physiological reference for maximal oxygen uptake (VO₂max), the upper bound on whole-body aerobic ATP production, integrating central oxygen delivery (cardiac output) with peripheral oxygen extraction (a-vO₂ difference) via the Fick equation.