Protocol Glossary
Science-backed definitions for every term in your health data: plain English and the mechanism behind it.
Active 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 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 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 definitionAnti-inflammatory Foods
Foods that lower the immune system background noise
→ Read definitionApoB (Apolipoprotein B)
The best single number for cardiovascular risk
→ 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 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 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 definitionCold Exposure
A deliberate thermal stressor that activates recovery and adaptation
→ 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 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 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 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 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 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 definitionGhrelin
The stomach hormone that drives hunger before meals and after poor sleep
→ 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 definitionHDL Cholesterol (HDL-C)
The "good cholesterol" that is more nuanced than its label suggests
→ 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 definitionHypertrophy
The structural enlargement of muscle fibers in response to training stress
→ Read definitionIGF-1 (Insulin-like Growth Factor 1)
The anabolic signal that turns growth hormone into muscle repair
→ Read definitionInsulin Resistance
→ 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 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 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 definitionMitochondrial Biogenesis
Growing new mitochondria: the cellular adaptation that drives aerobic fitness
→ 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 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-HDL Cholesterol
A better total atherogenic burden marker than LDL-C alone
→ Read definitionOmega-3 Fatty Acids
Anti-inflammatory fats that support recovery, brain health, and cardiovascular function
→ Read definitionOne-Rep Max (1RM)
The ceiling that calibrates everything else
→ Read definitionOvertraining Syndrome
When accumulated stress outpaces recovery for long enough to break the system
→ 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 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 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 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 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 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 Spindles
The brain's memory consolidation signal during N2 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 definitionSpO2 (Blood Oxygen Saturation)
The percentage of your red blood cells carrying oxygen
→ Read definitionSupercompensation
The overshoot above baseline that makes training produce fitness
→ Read definitionSuprachiasmatic Nucleus (SCN)
The master clock that synchronizes every biological rhythm
→ 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 definitionTotal Daily Energy Expenditure (TDEE)
The total calories your body burns in 24 hours
→ 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 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 definitionZone 2
Low-intensity cardio that builds the engine everything else runs on
→ Read definitionMore terms added regularly. Check back for new entries across all categories.
