Aerobic Endurance
The capacity to sustain prolonged exercise on oxygen-based energy. Built by high volumes of easy and moderate training that strengthen the heart, grow capillaries and add mitochondria.
Glossary
The endurance training glossary
Every term an endurance athlete runs into, defined in plain English and grounded in the science, across running, cycling, swimming and triathlon. Where a term has a calculator, you can jump straight to it.
Training Concepts & Physiology
How endurance fitness is built, measured and improved.
Aerobic ThresholdAeT
The lower intensity at which blood lactate first rises above resting levels, around the top of easy Zone 2. Most long, easy training sits at or just below it.
Anaerobic ThresholdAnT
Another name for the higher of the two metabolic thresholds, where lactate production clearly outpaces clearance. Overlaps closely with lactate threshold and FTP.
Base Training
An extended block of mostly easy, high-volume work early in a training cycle. It builds the aerobic endurance that later high-intensity work depends on.
Bonking
The sudden, severe fatigue when glycogen runs low and blood glucose falls during long efforts. Adequate carbohydrate before and during exercise prevents it.
Carbohydrate Intake
The grams of carbohydrate consumed per hour during prolonged exercise to maintain blood glucose and spare glycogen. Endurance athletes target 30 to 90 grams per hour depending on event length and gut tolerance.
Fartlek
Swedish for speed play: a continuous session mixing faster surges with easier running by feel.
Fat Oxidation
Using fat as fuel during exercise. It dominates at low intensities and spares glycogen. Easy-intensity training raises the rate at which you burn fat.
Glycogen
Carbohydrate stored in muscle and liver, the dominant fuel for moderate to high intensity endurance exercise. Stores are limited, so depletion is the usual cause of bonking.
Hydration
Managing fluid and electrolyte balance before, during and after exercise. Needs vary with body size, intensity, heat and sweat rate.
Interval Training
Structured repeats of hard effort separated by recovery, so you accumulate time at intensities that cannot be held continuously. The main tool for raising VO₂max and threshold.
Lactate ThresholdLT
The intensity at which lactate accumulates in the blood faster than the body clears it. Training near it raises sustainable race pace.
Overtraining & Overreaching
Overreaching is a short-term performance dip from heavy training that resolves with a few days of rest. Overtraining is a deeper, longer decline from inadequate recovery. Signs: stalled performance, elevated resting heart rate, poor sleep, persistent fatigue.
Periodization
The planned organisation of training into phases that shift volume and intensity toward a goal event, so fitness peaks on time.
Polarized Training
Roughly 80 percent easy sessions and 20 percent hard, with little time in the moderate middle. Research in well-trained endurance athletes links it to strong gains with limited fatigue.
Rate of Perceived ExertionRPE
A subjective rating of how hard an effort feels, on a 1 to 10 or 6 to 20 scale. It works without devices and holds up when heart rate or power are unreliable, such as in heat or at altitude.
Repetition TrainingReps
Short, fast repeats well above threshold with full recovery. They target speed, power and neuromuscular economy, not the aerobic system.
Running Economy
The oxygen or energy you use to run at a given submaximal pace. Lower is better. Two runners with the same VO₂max can perform very differently on economy alone.
Supercompensation
The rebound after a training stress, when the body rebuilds to a slightly higher fitness level. Timing the next hard session on this upswing is the logic of progressive training.
Sweat Rate
Fluid lost through sweat per hour of exercise, in litres per hour, measured by weighing yourself before and after a session. It tells you how much to drink.
Taper
A planned cut in training volume in the days or weeks before a key event. Volume drops substantially, some intensity stays, fatigue clears while fitness holds.
Tempo
A controlled, comfortably hard effort between easy aerobic work and threshold. It improves fatigue resistance at a strong pace.
Threshold Training
Training at or near the lactate or functional threshold, the highest intensity sustainable for roughly 30 to 60 minutes. It raises the pace or power you can hold before fatigue accelerates.
VO₂maxVO₂max
The maximum rate at which your body can take in, transport and use oxygen during all-out exercise, in ml/kg/min. It caps aerobic power and predicts endurance potential in every sport.
Zone 2
A low-intensity band just below the aerobic threshold, where you can hold a conversation and fat is a major fuel. The bulk of an endurance athlete's weekly hours.
Heart Rate
Heart-rate metrics and the models that turn them into zones.
Heart Rate ReserveHRR
Maximum minus resting heart rate: the working range available for exercise. The Karvonen method sets zones as percentages of it.
Heart Rate VariabilityHRV
The variation in time between consecutive heartbeats, reflecting nervous-system balance and recovery. Higher means ready to train. A persistent drop flags fatigue or stress.
Heart Rate Zones
Bands of heart-rate intensity, commonly five or seven, that group training into easy, moderate and hard efforts.
Karvonen Method
A zone calculation that applies target percentages to heart rate reserve and adds resting heart rate back. It personalises zones better than percent-of-maximum, especially for very fit or unfit athletes.
Lactate Threshold Heart RateLTHR
The heart rate at your lactate threshold, usually taken from a hard sustained time trial. Coaches anchor zones to it because it is more individual and stable than maximum heart rate.
MAF MethodMAF
Phil Maffetone's Maximum Aerobic Function approach: cap most training at 180 minus your age, adjusted for health and experience. It keeps training aerobic and builds fat-burning endurance.
Maximum Heart RateHRmax
The highest beats per minute your heart reaches in all-out effort. Largely genetic, declining slowly with age. A hard field test beats an age formula.
Resting Heart RateRHR
Your heart rate at full rest, measured first thing in the morning. It falls as aerobic fitness improves. A sustained rise signals fatigue, illness or overtraining.
Power
Power metrics for cycling and running.
Critical PowerCP
The highest power sustainable in a metabolic steady state, derived from maximal efforts of different durations. Close to FTP, but built on a physiological model that also yields W′.
Functional Threshold PowerFTP
The highest power a cyclist can sustain in a quasi-steady state for roughly an hour, commonly estimated as 95 percent of a 20-minute test. The reference for cycling power zones.
Normalized PowerNP
An adjusted average power that weights surges and variability to reflect the true physiological cost of a ride.
Power Zones
Bands of power output as percentages of FTP or critical power. Power responds instantly and ignores fatigue and terrain, so power zones prescribe efforts precisely.
Power-to-Weight RatioW/kg
Sustainable power divided by body mass, in watts per kilogram. It determines climbing and acceleration and compares riders more fairly than raw watts.
Running Power
An estimate of the mechanical power a runner produces, measured by foot pods or watches in watts. A real-time, terrain-aware intensity metric like a cycling power meter.
Training Stress ScoreTSS
A single number for the total training stress of a session, combining intensity relative to threshold with duration. One hour at threshold equals 100.
W PrimeW′
The fixed amount of work, in kilojoules, you can do above critical power before exhaustion. A battery that drains during hard efforts and recharges below critical power.
Pace & Speed
Pace, speed and form metrics.
Cadence
Steps per minute in running or pedal revolutions per minute in cycling. It affects efficiency, impact forces and muscular versus cardiovascular load.
Maximal Aerobic SpeedMAS
The lowest running speed at which VO₂max is reached. Fractions of MAS give an individualised way to prescribe interval paces.
Negative Split
Running the second half of a race faster than the first. It limits early overexertion and is one of the most efficient ways to race distance events.
Pace Zones
Target pace ranges, derived from a recent race or threshold test, that define easy, marathon, threshold, interval and repetition efforts.
Positive Split
Finishing the second half of a race slower than the first, usually from starting too fast. Sometimes deliberate on hilly courses, otherwise a sign of poor pacing or fuelling.
VDOT
Jack Daniels' fitness number representing a runner's effective VO₂max, inferred from a recent race result. It prescribes training paces and predicts times at other distances.
Velocity at VO₂maxvVO₂max
The running velocity that elicits maximal oxygen uptake, combining VO₂max and running economy into one speed. Intervals around it develop aerobic power.
Swimming
Speed, efficiency and threshold in the water.
Bilateral Breathing
Breathing to alternate sides in freestyle, typically every third stroke. It balances the stroke and helps with sighting in open water.
Critical Swim SpeedCSS
The fastest pace a swimmer can sustain for a long distance, estimated from a short and a longer time trial such as 200 and 400 metres. The swimming equivalent of threshold.
Open Water Swimming
Swimming in lakes, rivers or the sea, with no walls, lane lines or black line to follow. It demands sighting, drafting and handling currents and waves.
Stroke LengthDPS
Distance travelled per stroke, also called distance per stroke. With stroke rate it sets swimming speed.
Stroke RateSR
Arm strokes per minute, the swimming counterpart to cadence. Balancing it against distance per stroke is central to efficient swimming.
Swim Pace per 100
The time to swim 100 metres or yards, the standard unit for swimming speed and training sets.
SWOLF
A swimming efficiency score: seconds per pool length plus strokes per length. Lower means more distance per stroke.
Racing & Events
Race formats, pacing tactics and event-day terms.
10K
A ten-kilometre race run just below to around lactate threshold, between the speed-oriented 5K and longer endurance distances.
5K
A five-kilometre race run largely at or above lactate threshold. It rewards aerobic power plus speed and is a common fitness benchmark.
Brick Workout
A triathlon session combining two disciplines back to back, most often a bike ride straight into a run. It trains the heavy-legged feeling of running off the bike.
Did Not FinishDNF
Recorded when an athlete starts a race but does not complete it, from injury, illness, mechanical failure or a missed cut-off.
Half Marathon
A 21.1-kilometre (13.1-mile) road race, run just below lactate threshold for most athletes. It demands disciplined pacing and fuelling.
Marathon
A 42.195-kilometre (26.2-mile) road race run at a sustainable aerobic intensity where durability and fuelling decide the result. Conservative early pacing and avoiding glycogen depletion are central.
Pacing
Distributing effort across a race so energy lasts to the finish. Good pacing matches intensity to fitness, distance, terrain and conditions.
Personal RecordPR / PB
An athlete's fastest time at a given distance or event: personal record in the United States, personal best elsewhere.
Race Time Prediction
Estimating a finish time at one distance from a known performance at another, using formulas that model how speed fades with distance.
Split
The time for a defined segment of a race, such as each kilometre, mile or lap. Splits reveal pacing patterns.
TransitionT1/T2
The timed changeover between disciplines in a triathlon: swim to bike (T1) and bike to run (T2). Practised transitions save real time.
Triathlon
A multisport race of swimming, cycling and running in immediate succession, from sprint to long-course Ironman distance.
UltramarathonUltra
Any running race longer than the marathon, often on trails over 50 kilometres, 100 kilometres or 100 miles. Aerobic endurance, fuelling, hiking efficiency and mental resilience matter more than speed.