Endurance training glossary
Plain-English definitions of the terms runners, cyclists and triathletes meet in training plans, on their watches and in race reports.
A
- Acute training load (ATL)
- Acute training load (ATL) is an exponentially weighted average of your daily training stress over roughly the last seven days. It's often labelled 'fatigue', because it reflects how much recent training your body is still absorbing.
B
- Base training
- Base training is the opening phase of a training cycle, focused on building aerobic endurance with mostly easy, steady training and gradually increasing volume. It lays the foundation that harder, race-specific training later builds on.
- Brick workout
- A brick workout combines two triathlon disciplines back to back with little or no break, most often a bike ride followed immediately by a run. It trains your legs to run well on bike-fatigued muscles and lets you practise transitions.
C
- Cadence
- Cadence is the rate of a repeating movement: revolutions per minute (rpm) of the pedals in cycling, steps per minute (spm) in running and strokes per minute in swimming.
- Carb loading
- Carbohydrate loading is eating more carbohydrate than usual in the day or two before a long endurance event, while training less, to fill your muscles' glycogen stores. It helps in events lasting longer than about 90 minutes.
- Chronic training load (CTL)
- Chronic training load (CTL) is an exponentially weighted average of your daily training stress over roughly the last 42 days. It's often labelled 'fitness': a higher CTL means you have been handling more training for longer.
- Critical swim speed (CSS)
- Critical swim speed (CSS) is the fastest pace a swimmer can hold continuously without tiring rapidly — the swimming equivalent of threshold. It is usually expressed as a pace per 100 metres and estimated from two time trials of different distances.
E
- ERG mode
- ERG mode is a smart-trainer setting that holds a target power, in watts, no matter how fast you pedal or which gear you're in. The trainer adjusts the resistance so you produce exactly the power the workout asks for.
F
- Fartlek
- Fartlek, Swedish for 'speed play', is a run that mixes faster surges with easy running in a loose, unstructured way. It was popularised in Sweden in the 1930s as a playful alternative to formal track intervals.
- Functional threshold power (FTP)
- Functional threshold power (FTP) is the highest average power, in watts, that a cyclist can sustain for roughly an hour. It marks the boundary between efforts you can hold for a long time and efforts that tire you quickly, which makes it the anchor for power-based training zones.
H
- Heart rate variability (HRV)
- Heart rate variability (HRV) is the variation in the time between consecutive heartbeats. A higher HRV relative to your own normal usually means your nervous system is relaxed and recovered; a drop below your baseline can signal fatigue, illness, stress or poor sleep.
- Heart rate zones
- Heart rate zones divide exercise intensity into bands, usually five, based on a percentage of your maximum heart rate, heart rate reserve or threshold heart rate. Training by zone helps keep easy days easy and hard days at the intended effort.
I
- Interval training
- Interval training alternates periods of hard effort with periods of easy recovery. Splitting the hard work into repetitions lets you spend more total time at a high intensity than you could in one continuous effort.
L
- Lactate threshold
- Lactate threshold is the exercise intensity above which lactate accumulates in the blood faster than the body can clear it. Above it, fatigue builds quickly; below it, you can keep going for a long time. It is one of the strongest predictors of endurance performance.
- Long run
- The long run is the longest run of a runner's week, done at an easy, steady effort. It builds endurance, durability and confidence for half marathons, marathons and ultras.
M
- Maximum heart rate
- Maximum heart rate is the highest number of beats per minute your heart reaches during an all-out effort. It is largely determined by age and genetics, doesn't rise with training, and is one way to set heart rate training zones.
N
- Negative split
- A negative split is finishing the second half of a race or workout faster than the first half. It's the opposite of going out too fast and fading, and many records have been set with even or slightly negative splits.
- Normalized power (NP)
- Normalized power (NP) is an estimate of the steady power that would have the same physiological cost as a variable ride. Because hard surges cost disproportionately more than easy riding, NP is usually higher than average power on hilly or stop-start rides.
O
- Overtraining
- Overtraining syndrome is a prolonged decline in performance, lasting weeks to months, caused by an imbalance between training stress and recovery. It sits at the far end of a spectrum that starts with normal, short-term overreaching.
P
- Periodization
- Periodization is the organisation of training into phases, each with a different focus, that build towards a target race. A common sequence for endurance athletes is base, build, peak and taper, followed by a recovery or transition period.
- Power-to-weight ratio (W/kg)
- Power-to-weight ratio is the power a cyclist produces divided by their body weight, expressed in watts per kilogram (W/kg). It's the best single predictor of climbing speed, where gravity rather than air resistance is the main force to overcome.
R
- Ramp test
- A ramp test is a short cycling fitness test in which the target power rises in small steps, usually every minute, until you can no longer keep up. Your best one-minute power from the test is used to estimate your functional threshold power, typically at 75% of that value.
- Rate of perceived exertion (RPE)
- Rate of perceived exertion (RPE) is a way of rating how hard an effort feels, most often on a scale from 1 (very easy) to 10 (maximal). It is a simple, surprisingly reliable guide to intensity that needs no device.
- Recovery week
- A recovery week, or deload week, is a planned week of reduced training, usually every third or fourth week. It lets your body absorb the previous block's training, so you start the next block fresher and adapt more from it.
- Resting heart rate (RHR)
- Resting heart rate (RHR) is the number of times your heart beats per minute when you are completely at rest, best measured just after waking. As aerobic fitness improves, the heart pumps more blood per beat and resting heart rate tends to fall.
- Running dynamics
- Running dynamics are measurements of running form recorded by a watch, chest strap or foot pod — such as ground contact time, vertical oscillation, vertical ratio, stride length and cadence. They show how you run, not just how fast.
S
- Sweet spot training
- Sweet spot training is cycling at roughly 88–94% of FTP — just below threshold. It produces a large training effect for the time invested while being easier to recover from than full threshold work.
- SWOLF
- SWOLF — a blend of 'swim' and 'golf' — is a swim efficiency score: the number of strokes plus the number of seconds it takes to swim one length of the pool. Like golf, a lower score is better.
T
- Taper
- A taper is a planned reduction in training in the days or weeks before an important race, so that fatigue clears while fitness is kept. A good taper can noticeably improve performance compared with training normally up to race day.
- Tempo run
- A tempo run is a continuous run at a comfortably hard effort — around RPE 6 of 10, where you can speak only in short sentences. It typically lasts 20–40 minutes after a warm-up and trains you to hold a strong pace for longer.
- Threshold pace
- Threshold pace is the fastest running pace you can sustain for roughly an hour without a steady build-up of fatigue. For many runners it falls between their 10K and half-marathon race pace, and it is the reference point for pace-based running zones.
- Training stress balance (TSB)
- Training stress balance (TSB) is chronic training load minus acute training load — fitness minus fatigue. Often labelled 'form', it shows whether you are currently building fatigue (negative) or fresh (positive).
- Training Stress Score (TSS)
- Training Stress Score (TSS) is a single number for how much stress a workout puts on your body, combining duration and intensity relative to your threshold. One hour at exactly your FTP or threshold pace scores 100. The name is a TrainingPeaks trademark; other tools use similar load scores.
- Training zones
- Training zones are bands of intensity — from easy recovery to all-out sprinting — calculated from a personal threshold such as FTP, threshold pace, critical swim speed or threshold heart rate. They let a plan prescribe the same session to different athletes at the right effort for each.
- Triathlon transition (T1 and T2)
- In triathlon, transitions are the changeovers between disciplines: T1 from swim to bike and T2 from bike to run. They take place in the transition area, and the time spent there counts towards your overall race time.
V
- VO2 max
- VO2 max is the maximum rate at which your body can take in and use oxygen during intense exercise, measured in millilitres of oxygen per kilogram of body weight per minute (ml/kg/min). It sets the ceiling of your aerobic engine.
Z
- Zone 2 training
- Zone 2 training is steady, low-intensity aerobic exercise — easy enough to hold a conversation, usually just below your first lactate threshold. It builds the aerobic base that endurance performance is built on, with little fatigue.
Put it into practice.
Free training plans that turn these numbers into your own targets.