Training glossary
Training terms are useful when the method behind them is clear. This glossary defines threshold, CSS, FTP, GAP, training load and other endurance references in plain language. Each answer links back to the tools and guides where the definition matters. A familiar label does not mean every app uses the same formula or reference.
Threshold
A threshold is an intensity reference associated with a particular physiological or performance model. State the test and method: lactate threshold, ventilatory threshold and race-derived training pace are related concepts with different measurements.
CSS
Critical swim speed estimates sustained swimming pace from two maximal distance tests. A common calculation uses 400m and 200m times: their difference divided by two gives seconds per 100m.
FTP
Functional threshold power is a cycling performance reference used to organize training zones. A 20-minute test multiplied by 0.95 is an estimate, not a direct measurement that fits every athlete.
GAP
Grade-adjusted pace estimates an equivalent flat-ground running pace for a given slope. It depends on the energy-cost model and does not automatically account for surface, wind or downhill muscle damage.
TSS
Training Stress Score is a TrainingPeaks metric that combines duration and relative intensity. The power-based reference is hours multiplied by intensity factor squared, multiplied by 100.
CTL
Chronic training load is a smoothed history of training load, often modeled with a 42-day time constant. It describes the model’s recent load history; it is not a direct measure of fitness or an injury-risk score.
Dew point
Dew point is the temperature at which air would reach saturation with its current moisture content. It describes humidity, but is not a complete measure of exercise heat stress.
BQ
A Boston qualifier is a marathon performance that meets the B.A.A. standard and course requirements for a specified edition. Eligibility to apply does not guarantee a place.
Taper
A taper reduces training load before competition while retaining enough familiar stimulus. Its length and volume reduction depend on the event, training history and current fatigue.
Intensity factor
Intensity factor expresses training intensity relative to an athlete’s selected threshold. In cycling, it is commonly normalized power divided by FTP. The result depends on the threshold being appropriate.