Protocol Glossary
Science-backed definitions for every term in your health data: plain English and the mechanism behind it.
Actigraphy
Movement-based sleep measurement across days and weeks
→ Read definitionActive Recovery
Low-intensity movement that accelerates physiological recovery faster than rest alone
→ Read definitionAcute:Chronic Workload Ratio (ACWR)
The ratio that separates productive overload from injury risk
→ Read definitionAdenosine
The molecule that makes you sleepy: what caffeine is actually blocking
→ Read definitionAdiponectin
The fat cell hormone that fights insulin resistance
→ Read definitionAdrenaline (Epinephrine)
The acute alarm hormone that prepares the body for immediate action
→ Read definitionAerobic Threshold (AeT)
The Zone 2 ceiling: where fat starts ceding to carbohydrates
→ Read definitionAldosterone
The hormone that controls your salt and blood pressure balance
→ Read definitionAllostasis vs. Homeostasis
How the body maintains balance not by staying fixed, but by anticipating and adapting
→ Read definitionAllostatic Load
Your total accumulated stress burden: the body cannot separate the sources
→ Read definitionALT & AST (Liver Enzymes)
Your liver's distress signal in a blood draw
→ Read definitionAnabolic vs. Catabolic States
Build mode versus breakdown mode
→ Read definitionAnaerobic Threshold (AT)
The intensity ceiling where fat fuel gives out
→ Read definitionAnti-inflammatory Foods
Foods that lower the immune system background noise
→ Read definitionApoB (Apolipoprotein B)
The best single number for cardiovascular risk
→ Read definitionAutonomic Nervous System (ANS)
The body’s automatic regulatory control system
→ Read definitionBaroreflex Sensitivity (BRS)
How quickly your body corrects blood pressure swings
→ Read definitionBasal Metabolic Rate (BMR)
Calories your body burns at rest just to stay alive
→ Read definitionBDNF (Brain-Derived Neurotrophic Factor)
The protein that grows your brain, most powerfully triggered by exercise
→ Read definitionBlood Sugar Regulation
How tightly your body controls glucose all day
→ Read definitionBlue Light Exposure
The evening light signal that delays your biological clock
→ Read definitionBody Composition
The ratio of fat mass to lean mass
→ Read definitionBody Fat Percentage
Fat mass as a fraction of total body weight
→ Read definitionBurnout (Physiological Definition)
Systemic physiological failure from chronic unrecovered stress load
→ Read definitionCaffeine Metabolism
How your body processes caffeine and why the timing matters
→ Read definitionCaloric Deficit
The engine behind every fat loss outcome
→ Read definitionCaloric Surplus
The fuel requirement for building muscle
→ Read definitionCarb Periodization
Matching carbohydrate intake to training demand day by day
→ Read definitionCBT-I (Cognitive Behavioral Therapy for Insomnia)
The evidence-based cure for chronic insomnia
→ Read definitionChronotype
Your biological preference for when to sleep and be alert
→ Read definitionCircadian Phase
Where you are in your 24-hour biological clock right now
→ Read definitionCircadian Rhythm
Your body's internal 24-hour clock: the master scheduler of nearly every biological function
→ Read definitionCognitive Load
The total mental demand placed on working memory at once
→ Read definitionCold Exposure
A deliberate thermal stressor that activates recovery and adaptation
→ Read definitionCompression Therapy
Mechanical pressure that accelerates fluid clearance after training
→ Read definitionConcurrent Training
The interference effect between strength and endurance training
→ Read definitionContinuous Glucose Monitoring (CGM)
Real-time blood sugar dynamics on demand
→ Read definitionCortisol
Your body's primary stress hormone and morning alarm signal.
→ Read definitionCortisol Awakening Response (CAR)
The first hormonal signal that sets your day
→ Read definitionCortisol-to-DHEA Ratio
The biochemical score for how well you are aging under stress
→ Read definitionCreatine
The most evidence-backed supplement for strength and power output
→ Read definitionCRP (C-Reactive Protein)
Your body's systemic inflammation signal
→ Read definitionDecision Fatigue
Declining decision quality as cognitive resources deplete through the day
→ Read definitionDefault Mode Network (DMN)
The brain circuit that runs when you stop focusing
→ Read definitionDeload Week
The planned reduction in training stress where adaptation actually lands
→ Read definitionDetraining
How fast your fitness actually disappears when you stop
→ Read definitionDHEA (Dehydroepiandrosterone)
The adrenal precursor hormone that declines steadily with age
→ Read definitionDOMS (Delayed Onset Muscle Soreness)
The 24 to 72 hour soreness signal after novel or hard training
→ Read definitionDopamine
The motivation and anticipation signal, not the pleasure hormone
→ Read definitionEnergy Availability
Calories left for recovery after training cost
→ Read definitionEnergy Balance
The master equation of body composition
→ Read definitionEPOC (Excess Post-Exercise Oxygen Consumption)
The temporary afterburn cost of hard training
→ Read definitionEssential Amino Acids (EAAs)
The 9 amino acids your body cannot make and must obtain from food
→ Read definitionEstradiol (E2)
The primary estrogen that governs more than reproduction
→ Read definitionEstrogen
The hormone that shapes bone, brain, and recovery in both sexes
→ Read definitionExecutive Function
The brain's control system for thinking and behavior
→ Read definitionExercise Energy Expenditure (EEE)
Calories burned during formal exercise, often overestimated
→ Read definitionFasting Glucose
Your baseline blood sugar after an overnight fast
→ Read definitionFat Adaptation
Training your body to burn fat as its primary fuel
→ Read definitionFerritin
Your iron storage tank, and an inflammation marker
→ Read definitionFight-or-Flight Response
Your body's hardwired emergency activation system
→ Read definitionFlow State
Peak performance where effort disappears
→ Read definitionFree T3 and Free T4
The active and storage forms of thyroid hormone your labs should show
→ Read definitionFree Testosterone
The biologically active fraction that actually reaches cells
→ Read definitionFSH (Follicle Stimulating Hormone)
The pituitary hormone that drives egg and sperm development
→ Read definitionFunctional Overreaching
The productive edge where fatigue becomes adaptation
→ Read definitionGGT (Gamma-Glutamyl Transferase)
The liver enzyme most sensitive to alcohol and metabolic stress
→ Read definitionGhrelin
The stomach hormone that drives hunger before meals and after poor sleep
→ Read definitionGlucagon
Insulin's counterpart: the hormone that raises blood sugar when it drops too low
→ Read definitionGlucocorticoids
The stress and metabolism hormone class cortisol leads
→ Read definitionGlucose Variability
How much your blood sugar swings across the day
→ Read definitionGlycemic Index (GI)
How fast a food raises blood glucose
→ Read definitionGrowth Hormone (GH)
The pituitary hormone that repairs tissue during deep sleep
→ Read definitionGut Microbiome
The ecosystem in your gut that shapes your health
→ Read definitionGut-Brain Axis
The two-way communication highway between gut and brain
→ Read definitionHDL Cholesterol (HDL-C)
The "good cholesterol" that is more nuanced than its label suggests
→ Read definitionHeart Rate Reserve (HRR)
The usable range between rest and maximum effort
→ Read definitionHeart Rate Variability (HRV)
Your nervous system's daily readiness signal
→ Read definitionHeat Acclimation / Sauna
A controlled heat stress that builds cardiovascular resilience and growth hormone response
→ Read definitionHemoglobin A1c (HbA1c)
A 3-month average of your blood sugar control
→ Read definitionHIIT (High-Intensity Interval Training)
Short bursts of hard effort for cardiovascular adaptation
→ Read definitionHippocampus
The brain's memory consolidation and learning center
→ Read definitionHOMA-IR (Homeostatic Model Assessment of Insulin Resistance)
The earliest measurable signal of insulin dysfunction
→ Read definitionHomocysteine
An amino acid byproduct that signals B-vitamin status and vascular risk
→ Read definitionHPA Axis (Hypothalamic-Pituitary-Adrenal Axis)
The three-gland stress response system that runs your cortisol
→ Read definitionHPG Axis (Hypothalamic-Pituitary-Gonadal Axis)
The command chain that controls sex hormones
→ Read definitionHypertrophy
The structural enlargement of muscle fibers in response to training stress
→ Read definitionHypnagogic State
The threshold between waking and sleep onset
→ Read definitionIGF-1 (Insulin-like Growth Factor 1)
The anabolic signal that turns growth hormone into muscle repair
→ Read definitionIGF-1 Signaling
The growth signal that converts effort into muscle
→ Read definitionInsulin
The master nutrient storage and signaling hormone
→ Read definitionInsulin Resistance
→ Read definitionIntermittent Fasting (IF)
Cycling between eating windows and fasting periods
→ Read definitionIron Panel & Ferritin
Your iron storage and delivery system, measured in full
→ Read definitionK-Complexes
The brain's noise-canceling response during light sleep
→ Read definitionKetosis
When the liver runs on fat and makes fuel for the brain
→ Read definitionLactate Threshold
The intensity above which your pace becomes unsustainable
→ Read definitionLDL Cholesterol (LDL-C)
The most tracked lipid marker, and the most misread
→ Read definitionLDL Particle Size (LDL-P vs. LDL-C)
Why two people with the same LDL number can have very different risk
→ Read definitionLean Body Mass
Total weight minus fat, the mass that drives your metabolism
→ Read definitionLeptin
The fat-cell hormone that tells your brain how much energy you have stored
→ Read definitionLeucine Threshold
The minimum leucine dose that triggers muscle protein synthesis, and why meal size matters
→ Read definitionLF/HF Ratio
A window into your autonomic nervous system balance
→ Read definitionLH (Luteinizing Hormone)
The pituitary signal that triggers sex hormone production
→ Read definitionLipoprotein(a) [Lp(a)]
The inherited cardiovascular risk factor most panels skip
→ Read definitionMagnesium
The mineral that keeps your nervous system calm
→ Read definitionMax Heart Rate (MHR)
The ceiling of your cardiovascular output
→ Read definitionMelatonin
The darkness hormone that tells your body when to sleep
→ Read definitionMetabolic Flexibility
Your body's ability to switch fuel sources: the difference between steady energy and crashes
→ Read definitionMineralocorticoids
The adrenal hormones that regulate fluid and electrolyte balance
→ Read definitionMitochondrial Biogenesis
Growing new mitochondria: the cellular adaptation that drives aerobic fitness
→ Read definitionMotor Unit Recruitment
How your nervous system scales force output
→ Read definitionMuscle Memory (Myonuclei)
Why returning to training after a break is faster than starting fresh
→ Read definitionMuscle Protein Synthesis (MPS)
The cellular process that builds and repairs muscle
→ Read definitionN1 and N2 Sleep
The lighter NREM stages where most of sleep actually happens
→ Read definitionNapping
Planned short sleep that restores alertness without full recovery
→ Read definitionNervous System Fatigue
The fatigue that hides beneath the muscle soreness
→ Read definitionNeuromuscular Fatigue
When your nervous system, not your muscles, is the limiter
→ Read definitionNeuroplasticity
The brain's capacity to rewire in response to experience
→ Read definitionNon-Exercise Activity Thermogenesis (NEAT)
The calories you burn moving without trying to exercise
→ Read definitionNon-Functional Overreaching
When too much training stops paying off
→ Read definitionNon-HDL Cholesterol
A better total atherogenic burden marker than LDL-C alone
→ Read definitionNorepinephrine
The alertness and arousal signal for brain and body
→ Read definitionOmega-3 Fatty Acids
Anti-inflammatory fats that support recovery, brain health, and cardiovascular function
→ Read definitionOmega-3 Index (EPA + DHA)
Your cell membrane fatty acid quality score
→ Read definitionOne-Rep Max (1RM)
The ceiling that calibrates everything else
→ Read definitionOrthostatic Heart Rate Test
A 60-second morning recovery readiness check
→ Read definitionOvertraining Syndrome
When accumulated stress outpaces recovery for long enough to break the system
→ Read definitionOxytocin
The social bonding and trust signal
→ Read definitionParasympathetic Rebound
The nervous system shift that signals genuine recovery
→ Read definitionPassive Recovery
Complete rest as a deliberate training input
→ Read definitionPeriodization
The structured organization of training stress and recovery across time
→ Read definitionPhosphatidylserine
A brain-dense phospholipid that blunts cortisol and supports cognitive recovery
→ Read definitionPolyphasic Sleep
Splitting sleep into multiple periods instead of one nightly block
→ Read definitionPolysomnography (PSG)
The gold-standard clinical measurement of sleep
→ Read definitionPolyvagal Theory
A framework for understanding how the nervous system governs safety, threat, and social connection
→ Read definitionPrefrontal Cortex (PFC)
The brain's executive control and decision-making center
→ Read definitionProgesterone
The calming counterpart to estrogen, with deep ties to sleep and recovery
→ Read definitionProgressive Overload
The principle that drives all adaptation: consistently increase the demand to keep improving
→ Read definitionProlactin
The pituitary hormone that suppresses sex hormones when elevated
→ Read definitionProtein Timing
When you eat protein matters less than most think, but more than some claim
→ Read definitionRate of Weight Loss
How fast you lose determines what you lose
→ Read definitionReadiness Score
Oura's daily verdict on your capacity for stress
→ Read definitionRecovery Score
Your body's readiness verdict after last night
→ Read definitionRecovery Window
The post-training period when adaptation either happens or stalls
→ Read definitionREM Sleep
The sleep stage where your brain consolidates memory and regulates emotion
→ Read definitionRespiratory Rate
Breaths per minute: your body's quiet early warning signal
→ Read definitionRest-and-Digest
The parasympathetic state where recovery actually happens
→ Read definitionResting Heart Rate (RHR)
How hard your heart works when it doesn't have to
→ Read definitionRMSSD (Root Mean Square of Successive Differences)
The beat-to-beat calculation that powers your HRV score
→ Read definitionRPE (Rate of Perceived Exertion)
Your body's internal intensity gauge
→ Read definitionSDNN (Standard Deviation of NN Intervals)
The HRV metric Apple Watch uses, and why it reads higher than Oura
→ Read definitionSerotonin
The mood and stability signal that lives mostly in your gut
→ Read definitionSHBG (Sex Hormone Binding Globulin)
The protein that determines how much testosterone your body can actually use
→ Read definitionSkin Temperature Deviation
Your body's overnight thermostat as a recovery signal
→ Read definitionSleep Architecture
The internal structure of your sleep, not just how long, but how deep
→ Read definitionSleep Debt
The accumulated deficit between the sleep you need and the sleep you get
→ Read definitionSleep Efficiency
The percentage of your time in bed actually spent asleep
→ 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 definitionSleep Latency
How long it takes to fall asleep after getting into bed
→ Read definitionSleep Pressure (Homeostatic Sleep Drive)
The biological urge to sleep that builds every hour you are awake
→ Read definitionSleep Regularity Index (SRI)
How consistent your sleep timing is: the dimension duration misses
→ Read definitionSleep Restriction Therapy
The counterintuitive insomnia treatment that works by reducing time in bed
→ Read definitionSleep Spindles
The brain's memory consolidation signal during N2 sleep.
→ Read definitionSleep Staging
How scientists classify the layers of a night
→ Read definitionSleep Window
The hours when your biology is aligned for sleep
→ Read definitionSlow-Wave Sleep (Deep Sleep)
The deepest sleep stage, where your body actually rebuilds
→ Read definitionSocial Jetlag
The circadian disruption of sleeping on a different schedule every week
→ Read definitionSoft Tissue Work / Massage
Manual therapy that addresses the texture and mobility of muscle and fascia
→ Read definitionSpO2 (Blood Oxygen Saturation)
The percentage of your red blood cells carrying oxygen
→ Read definitionStrain Score
Your daily cardiovascular load, accumulated
→ Read definitionStress Response (General Adaptation Syndrome)
Your body's blueprint for handling any stressor
→ Read definitionSupercompensation
The overshoot above baseline that makes training produce fitness
→ Read definitionSuprachiasmatic Nucleus (SCN)
The master clock that synchronizes every biological rhythm
→ Read definitionSympathetic vs. Parasympathetic
The two-branch system behind every readiness metric
→ Read definitionTestosterone
The primary anabolic hormone governing muscle, energy, and drive
→ Read definitionThermic Effect of Food (TEF)
The calories your body burns digesting what you eat
→ Read definitionThyroid Hormones (T3/T4)
The metabolic rate regulators every cell depends on
→ Read definitionTime-Restricted Eating (TRE)
Compressing daily eating into a consistent window aligned to your clock
→ Read definitionTotal Daily Energy Expenditure (TDEE)
The total calories your body burns in 24 hours
→ Read definitionTraining Load
The cumulative stress of your recent training
→ Read definitionTriglyceride-to-HDL Ratio
A proxy for insulin resistance hiding inside a standard lipid panel
→ Read definitionTRIMP (Training Impulse)
A single number for quantifying training stress
→ Read definitionTSH (Thyroid Stimulating Hormone)
The pituitary signal that runs your metabolic engine
→ Read definitionUric Acid
A metabolic waste product that predicts more than gout
→ Read definitionVagal Tone
The strength of your parasympathetic recovery signal
→ Read definitionVisceral Fat
The metabolically active fat that surrounds your organs
→ Read definitionVitamin D
The hormone your body makes from sunlight
→ Read definitionVO2 Max
The strongest single predictor of long-term health and longevity
→ Read definitionWASO (Wake After Sleep Onset)
Total minutes spent awake after first falling asleep
→ Read definitionWeekly Energy Balance
What actually moves the scale over time
→ Read definitionWorking Memory
The brain's mental scratchpad for active thinking
→ Read definitionZone 2
Low-intensity cardio that builds the engine everything else runs on
→ Read definitionZone 5 Training
Maximum-effort intervals that raise your aerobic ceiling
→ Read definitionMore terms added regularly. Check back for new entries across all categories.
