Glossary/18 terms
Endurance training glossary
The numbers on your watch and in your training log, one page each: what they measure, how they are calculated, a worked example and where they stop being useful.
Load and form
How much a session costs, how fatigue builds up and fades, and how to read readiness.
- CTL, ATL and TSBCTL (fitness) and ATL (fatigue) are exponentially weighted averages of daily training load over about 42 and 7 days, and TSB (form) is the difference between them, CTL minus ATL.
- HRV (heart rate variability)Heart rate variability (HRV) is the beat-to-beat variation in the time between heartbeats, most often reported as rMSSD in milliseconds, and used by athletes as a marker of how their autonomic nervous system is coping with training.
- Session RPESession RPE is a training load measure that multiplies how hard the whole session felt, rated from 0 to 10, by its duration in minutes.
- TRIMPTRIMP (training impulse) is a training load score that multiplies the duration of a session by its heart rate intensity, weighted exponentially so that hard minutes count more than easy ones.
Intensity and capacities
The ceilings that set your training paces and zones, and how they are measured or estimated.
- Aerobic decouplingAerobic decoupling is the percentage by which your output per heartbeat (pace or power divided by heart rate) falls from the first half to the second half of a steady effort, used as a marker of aerobic endurance.
- Critical speedCritical speed is the slope of the line linking distance and time across your best efforts of about 2 to 20 minutes, the highest speed at which your body can still reach a steady state.
- FTP (functional threshold power)FTP (functional threshold power) is the highest power, in watts, that you can hold in a roughly steady state for about an hour, usually estimated as 95% of a 20-minute all-out effort.
- Heart rate reserveHeart rate reserve is the difference between your maximum and resting heart rate, used by the Karvonen method to set training intensities as a share of that range rather than of maximum heart rate alone.
- Lactate thresholdThe lactate threshold is the exercise intensity at which blood lactate stops staying stable and starts to accumulate, used to separate easy, sustainable running from efforts you can only hold for a limited time.
- Polarized trainingPolarized training is a training intensity distribution in which most of the volume is done below the first threshold, a smaller share above the second threshold, and very little between the two.
- VDOTVDOT is a running fitness score devised by Jack Daniels and Jimmy Gilbert: the VO2max that would explain a race result if your running economy were average, used to predict times at other distances and to set training paces.
- VMA (maximal aerobic speed)VMA (vitesse maximale aérobie, maximal aerobic speed) is the lowest running speed at which you reach your VO2max, usually held for 4 to 8 minutes, and the reference used to set interval paces as a percentage.
- VO2maxVO2max is the maximum rate at which your body can take up and use oxygen during exercise, usually expressed in millilitres per kilogram of body weight per minute (ml/kg/min).
- Zone 2Zone 2 is the easy, steady intensity at or just below the first lactate threshold, usually set at 60 to 70% of heart rate reserve, where you can talk in full sentences and keep going for hours.
Racing and terrain
Arriving fresh on race day, and comparing efforts across hills, trails and distances.
- Grade-adjusted pace (GAP)Grade-adjusted pace (GAP) is the pace on flat ground that would cost the same energy as the pace you ran on a slope, computed from the energy cost of running at each gradient.
- Km-effortKm-effort is a trail running measure of course difficulty that adds one kilometre for every 100 metres of ascent: km-effort = distance in km + D+ in metres / 100.
- Negative splitA negative split is a race or run in which the second half is covered faster than the first.
- TaperA taper is the period of reduced training before a goal race, usually one to three weeks, in which volume drops while intensity is kept, so that accumulated fatigue clears faster than fitness is lost.
See these numbers on your own training
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