Glossary

The variation in time between consecutive heartbeats. Higher HRV generally indicates better cardiovascular fitness and recovery capacity. Used as a biomarker for stress, recovery, and readiness to train.

The maximum rate at which your body can consume oxygen during intense exercise. Measured in mL/kg/min, it's considered the gold standard for aerobic fitness. Elite endurance athletes typically have VO2max values above 70.

A low-intensity aerobic training zone where you can maintain a conversation. Typically 60-70% of max heart rate. Builds mitochondrial density and fat oxidation capacity without accumulating significant fatigue.

The "powerhouses" of cells that produce ATP (energy). Mitochondrial density and function are key determinants of endurance performance and metabolic health. Can be increased through endurance training and various interventions.

The body's internal 24-hour clock that regulates sleep-wake cycles, hormone release, and metabolism. Disruption leads to poor sleep, metabolic issues, and reduced performance. Anchored primarily by light exposure.

The cellular "cleanup" process where damaged proteins and organelles are recycled. Activated by fasting, exercise, and certain stressors. Important for longevity and cellular health.

A biological phenomenon where low doses of stressors (cold, heat, exercise) that would be harmful at high doses actually trigger beneficial adaptive responses. The principle behind many biohacking interventions.

Proteins produced in response to heat stress that protect cells from damage and aid in protein folding. Increased by sauna use and exercise. Associated with longevity and cellular resilience.

The process of generating heat in response to cold exposure. Activates brown adipose tissue (BAT) and increases metabolic rate. Can improve cold tolerance and metabolic flexibility over time.

A protein that supports neuron growth, survival, and plasticity. Often called "Miracle-Gro for the brain." Increased by exercise, cold exposure, and certain interventions. Important for learning and mood.

The primary energy currency of cells. Produced mainly by mitochondria. All cellular work—muscle contraction, nerve signaling, protein synthesis—requires ATP.

A coenzyme essential for cellular energy production and DNA repair. Levels decline with age. Can be boosted through precursors like NMN and NR, as well as exercise and fasting.

A metabolic state where the body primarily burns fat and ketones for fuel instead of glucose. Achieved through carbohydrate restriction or fasting. Associated with mental clarity and fat loss.

The exercise intensity at which lactate begins to accumulate in the blood faster than it can be cleared. Training at or near this threshold improves the body's ability to buffer and use lactate.

A subjective scale (typically 1-10) for measuring exercise intensity based on how hard the effort feels. Useful for autoregulating training when heart rate monitors aren't available or accurate.

Muscle pain and stiffness that peaks 24-72 hours after unaccustomed exercise. Caused by microscopic muscle damage. Not necessarily an indicator of workout quality or muscle growth.

The increase in muscle size through growth of individual muscle fibers. Achieved through progressive resistance training with adequate volume, intensity, and recovery.

The gradual increase of stress placed on the body during training. The fundamental principle for continued adaptation. Can be achieved by increasing weight, reps, sets, or decreasing rest.

The systematic planning of training into distinct phases (base, build, peak, recovery) to optimize adaptation and prevent overtraining. Used by athletes to peak for competitions.

The "rest and digest" branch of the autonomic nervous system. Promotes recovery, digestion, and relaxation. Activated by slow breathing, meditation, and sleep. Measured indirectly through HRV.

The "fight or flight" branch of the autonomic nervous system. Increases heart rate, blood pressure, and alertness. Chronically elevated sympathetic tone impairs recovery and health.

The narrowing of blood vessels, which increases blood pressure and reduces blood flow to the skin. Occurs during cold exposure. Followed by vasodilation during rewarming.

The widening of blood vessels, which decreases blood pressure and increases blood flow. Occurs during heat exposure and after exercise. Important for nutrient delivery and recovery.

A neurotransmitter and hormone that increases alertness, focus, and mood. Released during cold exposure, exercise, and stress. Responsible for many benefits of cold therapy.

A neurotransmitter associated with motivation, reward, and pleasure. Released during and after accomplishing goals, exercise, and certain interventions. Important for drive and mood.

The "sleep hormone" produced by the pineal gland in response to darkness. Regulates sleep-wake cycles. Suppressed by blue light exposure at night. Can be supplemented for sleep support.

The primary stress hormone. Follows a circadian pattern—high in morning, low at night. Chronically elevated cortisol impairs recovery, sleep, and immune function. Acute spikes are normal and beneficial.

How effectively cells respond to insulin to uptake glucose from the blood. High sensitivity is healthy; low sensitivity (insulin resistance) precedes type 2 diabetes. Improved by exercise, fasting, and muscle mass.

The stored form of glucose in muscles and liver. Primary fuel for high-intensity exercise. Depleted during long or intense workouts and replenished through carbohydrate intake.

A type of fat that burns calories to generate heat. More metabolically active than white fat. Can be activated and potentially increased through cold exposure.

The use of red and near-infrared light to stimulate cellular function. Light absorbed by mitochondria enhances ATP production. Used for recovery, skin health, and various therapeutic purposes.

The body's ability to tolerate elevated carbon dioxide levels without triggering the urge to breathe. Can be trained through breath holds and slow breathing. Associated with calmness and breath control.

A network of tissues and organs that help rid the body of toxins, waste, and other unwanted materials. Unlike blood, lymph doesn't have a pump—it relies on movement and muscle contractions.

The longest cranial nerve, connecting the brain to the gut and other organs. Key regulator of parasympathetic function. Can be stimulated through breathing exercises, cold exposure, and specific techniques.

Direct physical contact with the Earth's surface, theorized to transfer electrons and reduce inflammation. Proponents claim benefits for sleep, pain, and stress. Evidence is preliminary.