Recovery

The autonomic nervous system (ANS) runs all the things you do not consciously control: heart rate, blood pressure, digestion, breathing. It has two main branches. The sympathetic…

Baroreflex sensitivity (BRS) measures how strongly your heart rate responds to quick changes in blood pressure. It is given as milliseconds of change in the gap between beats,…

Delayed-onset muscle soreness (DOMS) is the diffuse ache, stiffness, and tenderness that shows up 24 to 72 hours after unfamiliar or eccentric-heavy exercise. It peaks around 48…

Heart rate variability (HRV) is the tiny beat-to-beat change in the time between your heartbeats, measured in milliseconds. Within a healthy sinus rhythm, higher values usually…

Frequency-domain HRV analysis breaks your heartbeat-interval signal into frequency bands. The high-frequency band (HF, 0.15 to 0.4 Hz) mostly reflects your vagus nerve's…

Overtraining syndrome (OTS) sits on a continuum with functional overreaching (FOR) and non-functional overreaching (NFOR), per the ECSS/ACSM consensus. It is a maladaptive state…

Parasympathetic activation means engaging your 'rest-and-digest' nervous system. It is the calm-down branch of your autonomic nervous system. It works mainly through the vagus…

pNN50 is a time-domain measure of heart rate variability (HRV). It is the percentage of consecutive normal heartbeat intervals (NN, or R-R pairs) that differ by more than 50 ms.…

A readiness score is a daily index defined by each vendor. Devices like Oura and Garmin made it popular (Garmin's version is branded Training Readiness or Body Battery). Whoop's…

A recovery score is a generic category of vendor-defined composite metrics. Each one tries to estimate how well your body has recovered from earlier strain. The branding differs…

RMSSD (Root Mean Square of Successive Differences) is a time-domain measure of heart rate variability (HRV). It is the square root of the mean of the squared differences between…

Rate of perceived exertion (RPE) is a subjective scale for how hard exercise feels to you. The two most common versions are the 6-to-20 Borg scale and the 0-to-10 modified scale.…

SDNN (Standard Deviation of NN intervals) is a time-domain measure of heart rate variability (HRV). It captures the overall spread of your normal heartbeat intervals. Per HRV…

Sympathetic dominance is when your nervous system gets stuck in 'go' mode. The fight-or-flight (sympathetic) side chronically outweighs the rest-and-digest (parasympathetic)…

Vagal tone is the baseline activity of your vagus nerve. The vagus is the main parasympathetic pathway, connecting your brainstem to organs like your heart, lungs, and gut.…