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MILES OF MEANING / REFERENCE

Running & endurance nomenclature

Plain-language definitions for running, physiology and research. Start with the short answer, then check the context.

Educational definitions, not individual training or medical advice. Context-dependent terms are labelled. This AI-assisted seed collection has not received independent expert review.

Browse categories

A

Training load · context dependent

Acute load

Also: acute training load

Training load accumulated over a relatively short, explicitly defined time window.

Definition and context

Seven days is common but not universal. The metric and window must be stated.

Related terms

Training load · generally accepted

Acute-to-chronic workload ratio

Also: ACWR, acute:chronic workload ratio

A ratio comparing recent training load with a longer-term load estimate.

Definition and context

Calculation choices and statistical coupling can mislead. A supposedly safe ratio is not a validated individual injury-prevention rule.

Related terms

Further reading

Training intensity · generally accepted

Aerobic

Energy production through pathways that use oxygen.

Definition and context

Aerobic metabolism contributes at every running intensity; easy running is not its only setting.

Related terms

Running performance · context dependent

Aerobic decoupling

A change in the relationship between heart rate and pace or power across a session.

Definition and context

The calculation depends on software and conditions. Hills, heat and pacing changes can affect it; there is no universal pass/fail percentage.

Related terms

Training intensity · generally accepted

Aerobic threshold

Also: AeT

A lower exercise-intensity transition, often estimated from the first rise in blood lactate or ventilation.

Definition and context

The method matters: lactate and ventilatory markers are related but not interchangeable measurements.

Related terms

Further reading

Training intensity · generally accepted

Anaerobic

Energy production through pathways that do not directly require oxygen.

Definition and context

These pathways operate alongside aerobic metabolism. Anaerobic does not mean the whole muscle has no oxygen.

Related terms

Training intensity · inconsistently defined

Anaerobic threshold

Also: AnT

An inconsistently used label for a higher exercise-intensity transition.

Definition and context

Authors may mean LT2, a ventilatory threshold or another marker. Check the test method rather than assuming one universal threshold.

Related terms

Further reading

B

Training load · generally accepted

Back-to-back long runs

Also: back to back long runs

Long runs scheduled on consecutive days.

Definition and context

They can provide practice with accumulated fatigue but also add stress. They are not mandatory or proven superior for every ultrarunner.

Related terms

C

Running mechanics · generally accepted

Cadence

Also: step rate

The number of steps taken per unit of time, usually steps per minute.

Definition and context

Check whether a device reports both feet or one foot. There is no universal ideal of 180 steps per minute.

Related terms

Fueling and hydration · context dependent

Carbohydrate availability

The carbohydrate accessible to support exercise, including stored and recently consumed fuel.

Definition and context

Availability depends on timing, stores and the session. It is not identical to total daily carbohydrate intake.

Related terms

Endurance physiology · generally accepted

Carbohydrate oxidation

Using carbohydrate-derived fuel to release energy through oxidative metabolism.

Definition and context

Total carbohydrate oxidation includes stored and ingested fuel. The amount ingested per hour is not necessarily the amount oxidised.

Related terms

Running performance · generally accepted

Cardiac drift

Also: cardiovascular drift

A progressive rise in heart rate during prolonged exercise at a similar external workload, often alongside a fall in stroke volume.

Definition and context

Heat, hydration and other factors influence drift. It is not a stand-alone diagnosis of poor fitness.

Related terms

Endurance physiology · generally accepted

Cardiac output

The volume of blood pumped by the heart per minute.

Definition and context

It equals heart rate multiplied by stroke volume, helping determine oxygen delivery during exercise.

Related terms

Research terminology · generally accepted

Causation

A relationship in which changing one factor produces a change in another under specified conditions.

Definition and context

Causal inference requires a defensible design and assumptions, not merely a correlation or temporal sequence.

Related terms

Training load · generally accepted

Chronic load

Also: chronic training load

Training load summarised over a longer, explicitly defined time window.

Definition and context

It is a record or model of prior training, not a direct measurement of fitness or tissue capacity.

Related terms

Research terminology · context dependent

Clinical significance

Also: practical significance

Whether a result is important enough to matter in a real decision or outcome.

Definition and context

For runners, practical relevance depends on the outcome, trade-offs and context; it differs from statistical significance.

Related terms

Further reading

Research terminology · generally accepted

Cohort study

Also: cohort studies

An observational study that examines a defined group over time or reconstructs its follow-up.

Definition and context

It can identify associations and temporal patterns, but confounding remains possible.

Related terms

Research terminology · generally accepted

Confidence interval

Also: confidence intervals, CI

An interval produced by a method designed to capture the target parameter at a stated long-run rate.

Definition and context

It describes estimation uncertainty under assumptions, not a probability that a fixed true value lies inside this particular interval.

Related terms

Further reading

Research terminology · generally accepted

Correlation

A measure of how variables vary together.

Definition and context

An association can reflect other causes, chance or measurement choices; it does not by itself show that one variable causes the other.

Related terms

Training intensity · generally accepted

Critical speed

A parameter estimated from the relationship between running speed and time to exhaustion.

Definition and context

It helps describe the heavy-to-severe intensity boundary. Estimates depend on trials and modelling and are not an indefinitely sustainable pace.

Related terms

Further reading

D

Training load · context dependent

Deload

A planned short-term reduction in training demand.

Definition and context

The term is used differently across sports. Specify which loads are reduced and why.

Related terms

Recovery · generally accepted

DOMS

Also: delayed onset muscle soreness, delayed-onset muscle soreness

Muscle soreness that develops after an unfamiliar or demanding exercise bout, especially eccentric loading.

Definition and context

Soreness is not a direct measure of training benefit or muscle damage. Persistent or unusual pain should not simply be labelled DOMS.

Related terms

Ultramarathon / endurance · generally accepted

Downhill conditioning

Progressive exposure to descending demands to prepare for repeated downhill loading.

Definition and context

Descending includes substantial eccentric muscle work. Abrupt increases can cause pronounced soreness and impaired function.

Related terms

Running performance · emerging concept

Durability

Also: physiological durability

The ability to limit deterioration in physiological or performance characteristics during prolonged exercise.

Definition and context

An evolving research concept: studies differ in which characteristic they measure and after how much work. A fresh-state fitness test cannot fully describe it.

Related terms

Further reading

E

Research terminology · generally accepted

Effect size

Also: effect sizes

A measure of the magnitude of a difference or association.

Definition and context

Report its scale and uncertainty. A standardised effect is not automatically a meaningful race-time improvement.

Related terms

Further reading

Running performance · context dependent

Efficiency

Useful mechanical work divided by metabolic energy expended, under a specified definition.

Definition and context

Running involves elastic energy storage and difficult work estimates. Casual use of efficient often means economical, but the scientific quantities differ.

Related terms

Further reading

Fueling and hydration · context dependent

Electrolytes

Minerals that carry electrical charge in body fluids, including sodium and potassium.

Definition and context

They have different physiological roles. An electrolyte product is not automatically necessary for every run.

Related terms

Ultramarathon / endurance · context dependent

Elevation gain

Also: vert, vertical gain

The accumulated uphill height over a route or session.

Definition and context

Different sampling and smoothing methods can change the total. Gain is not the same as net altitude change.

Related terms

Fueling and hydration · generally accepted

Energy availability

Also: EA

Dietary energy remaining for body functions after subtracting exercise energy expenditure, often expressed relative to fat-free mass.

Definition and context

Persistently problematic low availability can impair health and performance. It is not the same calculation as total energy balance, and no single cutoff diagnoses every athlete.

Related terms

Further reading

F

Endurance physiology · generally accepted

Fat oxidation

Using fatty acids in metabolic pathways to release energy.

Definition and context

The rate varies with intensity, training, feeding and duration. Burning more fat during one session does not necessarily mean better performance or greater body-fat loss.

Related terms

Running performance · context dependent

Fatigue resistance

The ability to maintain a specified function or performance as fatigue develops.

Definition and context

Define the function and task: muscle force, pace and running economy are different outcomes. The term overlaps with durability but is broader.

Related terms

Fueling and hydration · generally accepted

Fluid balance

The relationship between fluid entering and leaving the body over time.

Definition and context

Sweat, urine, food and drink contribute. Body-mass changes during a race also reflect fuel use and other processes.

Related terms

Training load · generally accepted

Frequency

Also: training frequency

How often training sessions occur over a stated period.

Definition and context

Session count alone says little about duration, intensity or recovery between sessions.

Related terms

G

Fueling and hydration · generally accepted

Glycogen

The body's stored carbohydrate, found mainly in muscle and liver.

Definition and context

Muscle glycogen supports local work; liver glycogen helps maintain blood glucose. Stores are finite and vary with diet and training.

Related terms

Endurance physiology · generally accepted

Glycolysis

A pathway that breaks down glucose to help regenerate ATP, the cell's energy currency.

Definition and context

Glycolysis participates in both oxygen-supported metabolism and rapid energy production. It does not switch on only above a threshold.

Related terms

Running mechanics · generally accepted

Ground-contact time

Also: ground contact time, GCT

The time a foot spends in contact with the ground during a step.

Definition and context

It varies with speed, terrain and technique. A shorter value is not automatically better.

Related terms

Fueling and hydration · context dependent

Gut training

Repeated practice of eating and drinking during exercise to improve tolerance and delivery.

Definition and context

Tolerance is individual and depends on the food, amount, intensity and conditions. Practice does not guarantee freedom from gastrointestinal symptoms.

Related terms

H

Training intensity · context dependent

Heart-rate zones

Also: heart rate zones, heart-rate zone

Intensity bands defined using heart rate and a chosen training-zone model.

Definition and context

Models based on maximum heart rate, reserve or thresholds can disagree. Zone numbers are not universal across devices and coaches.

Related terms

Recovery · generally accepted

HRV

Also: heart-rate variability, heart rate variability

Variation in the time intervals between successive heartbeats.

Definition and context

Interpret the chosen metric under consistent conditions. A single high or low reading is not a diagnosis or a complete readiness verdict.

Related terms

Fueling and hydration · generally accepted

Hydration

The state and management of the body's water content.

Definition and context

Both insufficient and excessive fluid intake can be harmful. A fixed drinking rate is not appropriate for all runners and conditions.

Related terms

I

Training load · generally accepted

Intensity

Also: training intensity

How demanding an exercise bout is, expressed relative to a chosen measure.

Definition and context

Pace and power describe external demand; heart rate and perceived effort describe aspects of internal response.

Related terms

L

Training intensity · generally accepted

Lactate threshold

Also: lactate thresholds

An exercise intensity identified from changes in blood lactate as workload rises.

Definition and context

The label can refer to the first or a higher threshold. Lactate is a usable fuel and signalling molecule, not simply waste that causes soreness.

Related terms

Further reading

Running mechanics · context dependent

Leg stiffness

A model-based estimate of how strongly the leg resists compression during ground contact.

Definition and context

It is not the same as muscle tightness or joint range of motion. More stiffness is not universally better on every terrain.

Related terms

Training intensity · context dependent

LT1

Also: first lactate threshold

The first sustained rise in blood lactate above baseline during an incremental exercise test.

Definition and context

The detected point depends on sampling, stage duration and the rule used to identify a rise.

Related terms

Further reading

Training intensity · context dependent

LT2

Also: second lactate threshold

A higher lactate breakpoint identified during an incremental exercise test.

Definition and context

Different calculation methods give different values. LT2 is not automatically identical to maximal lactate steady state or critical speed.

Related terms

Further reading

M

Training intensity · generally accepted

MAF

Also: maximum aerobic function

A coaching approach commonly associated with an age-based heart-rate ceiling for aerobic training.

Definition and context

The 180-minus-age formula is not a direct measurement of LT1, and should not be treated as an individually validated physiological threshold.

Related terms

Research terminology · generally accepted

Meta-analysis

Also: meta-analyses

A statistical combination of results from multiple studies.

Definition and context

Pooling cannot fix biased studies or make incompatible questions equivalent.

Related terms

Endurance physiology · context dependent

Mitochondrial density

The amount of mitochondria relative to a quantity of muscle tissue.

Definition and context

Researchers use different structural and biochemical measures. A change in one marker does not by itself prove improved race performance.

Related terms

Ultramarathon / endurance · generally accepted

Muscular endurance

The ability of muscles to sustain repeated contractions or maintain force over time.

Definition and context

The task and load define the capacity being measured. It is related to, but not identical with, aerobic capacity.

Related terms

P

Recovery · inconsistently defined

Parasympathetic recovery

A loosely used description of the return of parasympathetic influence after stress or exercise.

Definition and context

Heart-rate measures can provide indirect information about autonomic activity, but cannot alone establish whole-body recovery.

Related terms

Training load · generally accepted

Periodization

Also: periodisation

Organising training into phases with changing priorities and demands.

Definition and context

Multiple models exist; the term does not establish that one sequence is best for all runners.

Related terms

Ultramarathon / endurance · context dependent

Power hiking

Purposeful, brisk walking used to cover demanding terrain efficiently for the task.

Definition and context

It can be part of race execution rather than a sign of failure. The best run-walk transition depends on slope and the runner.

Related terms

Training load · generally accepted

Progressive overload

Gradually changing training demands to provide a continued stimulus for adaptation.

Definition and context

Progress need not mean more distance every week. Recovery and tolerance constrain useful increases.

Related terms

R

Research terminology · generally accepted

Randomized controlled trial

Also: RCT, randomised controlled trial, randomized controlled trials, RCTs

A study that assigns participants to comparison groups using a random process.

Definition and context

Randomisation helps reduce confounding; small samples, missing data and poor implementation can still bias findings.

Related terms

Training load · generally accepted

Recovery week

A week with reduced training demands intended to support recovery and adaptation.

Definition and context

It is a planning convention, not a guarantee that all fatigue resolves in seven days.

Related terms

Recovery · generally accepted

Resting heart rate

Also: RHR

Heart rate measured at rest under specified conditions.

Definition and context

Sleep, illness, stress and measurement timing can affect it. Compare trends cautiously rather than treating one reading as definitive.

Related terms

Training intensity · generally accepted

RPE

Also: rating of perceived exertion, ratings of perceived exertion

A person's rating of how hard an effort feels.

Definition and context

State the scale: common scales run from 6–20 or 0–10. RPE reflects perceived effort, not a direct measurement of lactate.

Related terms

Ultramarathon / endurance · generally accepted

Run-walk strategy

Also: run walk strategy

A planned or responsive alternation between running and walking.

Definition and context

It can help manage effort and terrain; no single interval pattern is best for every ultra.

Related terms

Running performance · generally accepted

Running economy

Also: RE

The energy or oxygen cost of running at a specified submaximal speed.

Definition and context

Compare like-for-like speeds, surfaces and methods. A lower cost indicates better economy under those conditions; economy is distinct from mechanical efficiency.

Why it matters

Two runners with similar aerobic capacity can use different amounts of energy at the same speed.

Endurance relevance

Economy can change during prolonged running, so a fresh laboratory measurement does not describe an entire ultra.

Common misconceptions

  • Lower oxygen cost and higher mechanical efficiency are not interchangeable quantities.

Related terms

Further reading

Running mechanics · generally accepted

Running power

A device- or model-based estimate of the rate of mechanical work during running.

Definition and context

Unlike a directly measured cycling crank output, consumer running estimates depend strongly on assumptions and algorithms.

Related terms

S

Fueling and hydration · generally accepted

Sodium

An electrolyte involved in fluid regulation and nerve and muscle function.

Definition and context

Sweat sodium losses vary. Taking sodium does not make excessive fluid intake safe and does not reliably prevent all cramps.

Related terms

Training load · generally accepted

Specificity

The principle that adaptations depend partly on the demands actually practised.

Definition and context

For ultras, terrain, duration and movement can matter as well as pace. Specific practice still needs manageable loading.

Related terms

Research terminology · generally accepted

Statistical significance

A label applied when a statistical test meets a chosen threshold under its assumptions.

Definition and context

It does not establish a large, useful or causal effect. Read the estimate, uncertainty and study design together.

Related terms

Further reading

Running mechanics · generally accepted

Stride length

The distance between successive contacts of the same foot in biomechanical usage.

Definition and context

Some consumer devices use stride length to mean distance per step. Check the definition before comparing values.

Related terms

Endurance physiology · generally accepted

Stroke volume

The volume of blood ejected by a ventricle with each heartbeat.

Definition and context

It changes with filling, contractility and physiological conditions. A watch heart-rate reading does not measure stroke volume.

Related terms

Recovery · context dependent

Supercompensation

A simplified model in which a capacity rebounds above baseline after a training stress and recovery.

Definition and context

Different tissues and performance measures recover on different timescales. It is not a universal clock for timing every session.

Related terms

Research terminology · context dependent

Systematic review

Also: systematic reviews

A review using explicit methods to find, assess and synthesise studies addressing a question.

Definition and context

Its credibility depends on the search, included evidence and analysis. The label alone does not guarantee strong evidence.

Related terms

T

Training load · generally accepted

Taper

Also: tapering

A planned reduction in training load before a target event to reduce fatigue while retaining fitness.

Definition and context

Volume is commonly reduced while some intensity is retained. The appropriate timing and reduction vary.

Related terms

Ultramarathon / endurance · generally accepted

Technical terrain

Terrain whose footing, obstacles or steepness increase movement and attention demands.

Definition and context

The label is subjective. Describe rocks, roots, slope and exposure rather than relying on it alone.

Related terms

Training intensity · generally accepted

Threshold pace

A running pace tied to a stated threshold test or coaching definition.

Definition and context

Specify which threshold and conditions. Terrain, heat and fatigue can change the pace associated with the same physiological strain.

Related terms

Training intensity · context dependent

Threshold power

A power value tied to a stated threshold test or device model.

Definition and context

Running power is estimated differently by devices; a threshold wattage is not interchangeable across systems.

Related terms

Training load · generally accepted

Time on feet

Time spent upright and moving during a training session or event.

Definition and context

Useful for describing long run-walk outings. It does not capture intensity, terrain or tissue stress on its own.

Related terms

Training load · generally accepted

Training load

Also: training loads

A description of the work performed or the body's response to training.

Definition and context

External load includes distance and elevation; internal load includes heart rate and session RPE. No single score captures every stressor.

Related terms

V

Running mechanics · context dependent

Vertical oscillation

The up-and-down displacement of the body or a measured point during running.

Definition and context

Wearables estimate it at different locations. Minimising bounce is not by itself a validated route to better performance.

Related terms

Running mechanics · generally accepted

Vertical ratio

Vertical oscillation divided by a device's horizontal stride or step-length measure.

Definition and context

Usually expressed as a percentage. The denominator and sensor algorithm matter when comparing devices.

Related terms

Training load · context dependent

Volume

Also: training volume

The amount of training completed, commonly described by time or distance.

Definition and context

Elevation and terrain can make equal distances very different demands. Always state the unit and period.

Related terms

Training intensity · generally accepted

VO₂max

Also: VO2max, maximal oxygen uptake

The highest rate at which the body can take up and use oxygen during intense exercise.

Definition and context

Often reported per kilogram of body mass. It describes aerobic capacity, not a complete prediction of ultra performance.

Related terms

Training intensity · context dependent

vVO₂max

Also: vVO2max

The running speed associated with reaching VO₂max in a specified test.

Definition and context

The result depends on the test protocol and definition. It is not a pace every runner can hold for the same duration.

Related terms