Protocol Glossary
Science-backed definitions for every term in your health data: plain English and the mechanism behind it.
Heart Rate Variability (HRV)
Your nervous system's daily readiness signal
→ Read definitionCortisol Awakening Response (CAR)
The first hormonal signal that sets your day
→ Read definitionSlow-Wave Sleep (Deep Sleep)
The deepest sleep stage, where your body actually rebuilds
→ Read definitionVO2 Max
The strongest single predictor of long-term health and longevity
→ Read definitionZone 2
Low-intensity cardio that builds the engine everything else runs on
→ Read definitionCortisol
Your body's primary stress hormone: essential in the short term, destructive in excess
→ Read definitionCircadian Rhythm
Your body's internal 24-hour clock: the master scheduler of nearly every biological function
→ Read definitionResting Heart Rate (RHR)
How hard your heart works when it doesn't have to
→ Read definitionSleep Architecture
The internal structure of your sleep, not just how long, but how deep
→ Read definitionREM Sleep
The sleep stage where your brain consolidates memory and regulates emotion
→ Read definitionAdenosine
The molecule that makes you sleepy: what caffeine is actually blocking
→ Read definitionBDNF (Brain-Derived Neurotrophic Factor)
The protein that grows your brain, most powerfully triggered by exercise
→ Read definitionAllostatic Load
Your total accumulated stress burden: the body cannot separate the sources
→ Read definitionProgressive Overload
The principle that drives all adaptation: consistently increase the demand to keep improving
→ Read definitionInsulin Resistance
When your cells stop listening to insulin: the metabolic dysfunction behind energy crashes and fat gain
→ Read definitionLeucine Threshold
The minimum leucine dose that triggers muscle protein synthesis, and why meal size matters
→ Read definitionMetabolic Flexibility
Your body's ability to switch fuel sources: the difference between steady energy and crashes
→ Read definitionMitochondrial Biogenesis
Growing new mitochondria: the cellular adaptation that drives aerobic fitness
→ Read definitionSleep Efficiency
The percentage of your time in bed actually spent asleep
→ Read definitionSleep Latency
How long it takes to fall asleep after getting into bed
→ Read definitionSleep Debt
The accumulated deficit between the sleep you need and the sleep you get
→ Read definitionSleep Fragmentation
Repeated brief awakenings that break sleep continuity without always waking you fully
→ Read definitionSleep Inertia
The grogginess and cognitive impairment that follows waking from deep sleep
→ Read definitionMelatonin
The darkness hormone that tells your body when to sleep
→ Read definitionChronotype
Your biological preference for when to sleep and be alert
→ Read definitionSocial Jetlag
The circadian disruption of sleeping on a different schedule every week
→ Read definitionSleep Pressure (Homeostatic Sleep Drive)
The biological urge to sleep that builds every hour you are awake
→ Read definitionWASO (Wake After Sleep Onset)
Total minutes spent awake after first falling asleep
→ Read definitionRMSSD (Root Mean Square of Successive Differences)
The beat-to-beat calculation that powers your HRV score
→ Read definitionSDNN (Standard Deviation of NN Intervals)
The HRV metric Apple Watch uses, and why it reads higher than Oura
→ Read definitionVagal Tone
The strength of your parasympathetic recovery signal
→ Read definitionSpO2 (Blood Oxygen Saturation)
The percentage of your red blood cells carrying oxygen
→ Read definitionRespiratory Rate
Breaths per minute: your body's quiet early warning signal
→ Read definitionTotal Daily Energy Expenditure (TDEE)
The total calories your body burns in 24 hours
→ Read definitionBasal Metabolic Rate (BMR)
Calories your body burns at rest just to stay alive
→ Read definitionExercise Energy Expenditure (EEE)
Calories burned during formal exercise, often overestimated
→ Read definitionLean Body Mass
Total weight minus fat, the mass that drives your metabolism
→ Read definitionBody Fat Percentage
Fat mass as a fraction of total body weight
→ Read definitionThermic Effect of Food (TEF)
The calories your body burns digesting what you eat
→ Read definitionNon-Exercise Activity Thermogenesis (NEAT)
The calories you burn moving without trying to exercise
→ Read definitionBlood Sugar Regulation
How tightly your body controls glucose all day
→ Read definitionGlycemic Index (GI)
How fast a food raises blood glucose
→ Read definitionEnergy Availability
Calories left for recovery after training cost
→ Read definitionEPOC (Excess Post-Exercise Oxygen Consumption)
The temporary afterburn cost of hard training
→ Read definitionBody Composition
The ratio of fat mass to lean mass
→ Read definitionMore terms added regularly. Check back for new entries across all categories.
