Glossary of Exercise Physiology Terms

Definitions for 55 terms used across the HAM.RUN performance models — VO₂max, lactate thresholds, cardiac drift, running economy, periodization, ACWR, the Banister model, the Riegel model, and more.

ACWR (Acute:Chronic Workload Ratio)

Ratio of the last 7 days of training stress to the 28-day average. Sweet spot 0.8–1.3; values >1.5 carry stepped injury hazard. (see Training Adaptation)

Adaptation Budget

A saturation curve relating session frequency (0–4×/wk) to total weekly reward and risk. Captures diminishing returns as the same workout type is repeated. (see Training Adaptation)

Aerobic Decoupling

The percentage drift between heart rate and pace over the course of a run. Values >5% suggest insufficient aerobic fitness for the target pace. (see HR Pacing)

ATL (Acute Training Load)

A 7-day exponentially weighted average of training stress. Represents recent fatigue accumulation. (see Periodization)

Banister Model

A fitness-fatigue impulse-response model that tracks CTL and ATL to predict performance readiness (TSB = CTL − ATL). (see Periodization)

Caffeine

A CNS stimulant (methylxanthine) that reduces perceived exertion and improves endurance performance by 2–4% at doses of 3–6 mg/kg body weight. Peak plasma concentration occurs ~45 minutes after ingestion; half-life ~5 hours. (see Stimulants)

Caffeine Habituation

Chronic daily caffeine intake above ~300 mg attenuates the acute ergogenic response by ~30%. Tracked via the habitualCafMgPerDay field on the athlete profile. (see Stimulants)

Cardiac Drift

The gradual rise in heart rate at a constant pace during prolonged exercise, caused by dehydration, thermal stress, and reduced stroke volume. (see HR Pacing)

CHO Oxidation

The rate at which carbohydrates are burned for energy, measured in g/min. Increases with exercise intensity. (see Substrate & Tlim)

CNS (Central Nervous System)

The brain and spinal cord. Stimulants like caffeine and nicotine act on the CNS to increase alertness, reduce perceived exertion, and modulate pain signaling during exercise. (see Stimulants)

Compound Stress

A severity-weighted aggregation of flags across modules (info=1, warn=3, danger=6) into LOW / MODERATE / HIGH / DANGER tiers. Surfaced as the Combined Stress badge on the Race Predictor. (see Race Predictor)

Cr (Cost of Running)

Oxygen cost per unit distance, measured in mL O₂/kg/m. The headline metric of the Running Economy module. Lower values mean less energy per stride. (see Running Economy)

CTL (Chronic Training Load)

A 42-day exponentially weighted average of training stress. Represents accumulated fitness. (see Periodization)

Dose-Response

The relationship between the amount of a substance consumed and the magnitude of its effect. For caffeine, performance benefits plateau around 6 mg/kg; higher doses increase side effects without additional benefit. (see Stimulants)

Dual Transport (Glc+Frc)

Using both glucose and fructose to increase exogenous carbohydrate absorption beyond the ~60 g/hr SGLT1 limit, up to ~90–120 g/hr. (see Substrate & Tlim)

Ergogenic Aid

Any substance, technique, or device that enhances exercise performance. Includes legal stimulants (caffeine), nutritional strategies (carbohydrate loading), and mechanical aids (carbon-plate shoes). (see Stimulants)

Fat Oxidation

The rate at which fat is burned for energy, measured in g/min. Dominant at lower intensities; decreases as intensity rises. (see Substrate & Tlim)

FIT File

A binary activity file format created by Garmin and used by most GPS watches. HAM.RUN parses .fit files in-browser to extract pace, heart rate, cadence, power, and other sensor data.

GAP (Grade-Adjusted Pace)

Pace normalized for elevation gradient using the Minetti polynomial: hilly stretches get more time, downhill less. Used for course split tables. (see Courses)

GI Distress

Gastrointestinal discomfort during exercise, including nausea, cramping, and diarrhea. High caffeine doses (>400mg) and concentrated carbohydrate intake increase GI risk during racing. (see Stimulants)

Glycogen

Stored carbohydrate in muscle (~400–600g) and liver (~90–120g). Primary fuel source during moderate-to-high intensity running. (see Substrate & Tlim)

Heat Acclimation

Repeated heat exposure (sauna or hot-weather training) that triggers plasma volume expansion, earlier sweat onset, and lower core temperature at a given effort. The Sauna module models a 1–4 week protocol. (see Sauna)

HRR (Heart Rate Reserve)

The difference between maximum and resting heart rate. Used to express intensity as a percentage: target HR = resting + (HRR × %). (see HR Pacing)

Hyponatremia

Dangerously low blood sodium (<135 mmol/L), typically caused by overdrinking hypotonic fluids during prolonged exercise. (see HR Pacing)

Joyner Model

An endurance-performance composite weighting ~45% VO₂max, 30% LT fraction, 25% running economy. Used to convert physiological gains into a race-time prediction. (see Race Predictor)

Kinematic Plausibility

A sanity check that stride length × cadence does not imply a pace faster than ~6 m/s; flags biomechanically impossible inputs. (see Running Economy)

LT1 (Lactate Threshold 1)

The intensity at which blood lactate first rises above baseline (~65–75% HRR). Marks the upper boundary of Zone 1 easy running. (see Periodization)

LT2 (Lactate Threshold 2)

The intensity at which lactate accumulation accelerates rapidly (~80–88% HRR). Approximate marker for sustainable race pace ceiling. (see Periodization)

MCP (Model Context Protocol)

An open protocol that lets AI assistants call external tools. The HAM.RUN MCP server exposes pacing, fueling, economy, and race-prediction calculators so conversational agents can use the same models as the web UI. (see MCP)

Minetti Gradient Cost

A polynomial cost-of-running model (Minetti et al. 2002) covering −45% to +45% gradient. The basis for GAP and the course split-table weights. (see Running Economy)

Monotony (Foster)

Mean weekly TSS divided by its standard deviation. Values >2.0 associate with overtraining due to insufficient hard/easy variation. (see Periodization)

Neuromuscular Load

A 0–1 coefficient capturing the eccentric, impact, and sprint character of a workout type. Multiplies injury hazard on top of ACWR. (see Training Adaptation)

Nicotine

A CNS stimulant found in tobacco. Delivered via gum (peak ~35 min) or transdermal patch (steady-state). Evidence for endurance performance benefit is weak — 12 of 16 studies found null effects. WADA monitoring program since 2012. Highly addictive. (see Stimulants)

Pareto Frontier

The upper-left envelope of the workout-type scatter (reward vs risk): the set of non-dominated choices. The visual headline of the Training Adaptation module. (see Training Adaptation)

Periodization

The systematic planning of training phases (base, pre-competitive, competitive) to peak fitness for a target race. (see Periodization)

Pharmacokinetics (PK)

The study of how a substance is absorbed, distributed, metabolized, and eliminated over time. Plasma concentration curves model the time-course of drug availability in the bloodstream. (see Stimulants)

Plasma Na+

Blood sodium concentration, normally 135–145 mmol/L. Affected by sweat sodium losses and fluid intake during exercise. (see HR Pacing)

Plasma Volume Expansion

An increase in blood plasma volume triggered by heat acclimation or endurance training. Improves stroke volume and thermoregulation, reducing cardiac drift at race pace. (see Sauna)

Polarized Training

A TID model with ~75–80% easy (Z1) and ~15–20% hard (Z3), minimizing time in the moderate (Z2) zone. (see Periodization)

Pyramidal Training

A TID model emphasizing high Z1 volume with progressively less Z2 and Z3. The dominant approach among elite marathon runners. (see Periodization)

Ramp Rate

Week-over-week percentage increase in volume. The "10% rule" caps safe ramps near 10%/wk; larger jumps drive ACWR spikes. (see Training Adaptation)

RER (Respiratory Exchange Ratio)

The ratio of CO₂ produced to O₂ consumed. Ranges from ~0.70 (pure fat) to 1.00 (pure carbohydrate). Indicates fuel mix at a given intensity. (see Substrate & Tlim)

Riegel Model

A race time prediction formula: T₂ = T₁ × (D₂/D₁)^1.06. Estimates performance at one distance from a known result at another. (see Race Predictor)

RPE (Rating of Perceived Exertion)

Borg 6–20 scale measuring subjective effort. 13 = somewhat hard, 15 = hard, 17 = very hard, 19+ = maximal.

Running Economy (RE)

The oxygen cost of running at a given speed, measured in mL O₂/kg/km. Lower values indicate better economy. (see Running Economy)

Scenario Stack

The Race Predictor feature that composes percentage gains from periodization, heat acclimation, stimulants, running economy, and training adaptation into a single predicted finish time. (see Race Predictor)

Session Spike

A single session whose distance exceeds the 30-day longest run by >10%. Carries stepped hazard ratios (Frandsen 2025). (see Training Adaptation)

SGLT1

Sodium-glucose cotransporter in the intestine. Rate-limits glucose absorption to ~60 g/hr during exercise. (see Substrate & Tlim)

TEE (Total Energy Expenditure)

Total energy burned per unit time during exercise, measured in kJ/min. Calculated from VO₂ and RER. (see Running Economy)

Threshold Training

A TID model with heavy Z2 (tempo) volume (~40–50%). Elevates LT2 fastest but accumulates fatigue aggressively. (see Periodization)

TID (Training Intensity Distribution)

How total training volume is distributed across intensity zones (Z1 easy, Z2 tempo, Z3 hard). (see Periodization)

Tlim (Time to Exhaustion)

The predicted duration until glycogen depletion at a given intensity and carbohydrate intake rate. (see Substrate & Tlim)

TSB (Training Stress Balance)

CTL minus ATL. Positive values indicate freshness; negative values indicate accumulated fatigue. Optimal race readiness is typically slightly positive. (see Periodization)

TSS (Training Stress Score)

A composite measure of training load that weights volume by intensity zone. Higher zones contribute disproportionately more stress. (see Periodization)

VO₂max

Maximum rate of oxygen consumption during exercise, measured in mL/kg/min. The primary determinant of aerobic performance ceiling. (see Race Predictor)