Glossary
What Harlen reads, in plain language. Each entry links to the source paper or population norm where applicable.
The gap between training stress and recovery the body has been given.
Recovery debt shows up when HRV trends down, resting heart rate trends up, and sleep quality slips, but training load held steady. The body is being asked to absorb stress it isn't getting the time to absorb.
Overtraining is a clinical state that takes weeks to dig out of, while recovery debt reverses with a handful of easier sessions and two solid nights of sleep, so it is cheap to fix when it is caught early.
The variation in time between consecutive heartbeats.
Higher HRV usually means stronger parasympathetic recovery; lower HRV signals the body is under load from training, illness, stress, or poor sleep. Most consumer wearables measure it overnight.
Read it as a trend against the athlete's own rolling baseline. A 42 ms morning for an athlete who averages 68 ms means something different than 42 ms for an athlete who averages 45 ms.
Population norms: Nunan et al., 2010. "A quantitative systematic review of normal values for short-term heart rate variability in healthy adults."
The athlete's typical morning RHR after a normal night's sleep.
An elevation of 5–10 bpm above baseline that holds for two or three days correlates with under-recovery, illness onset, or accumulated life stress. A single high reading is usually noise, so Harlen waits for the shift to hold before it raises anything.
Source: Quer et al., 2020. "Inter- and intraindividual variability in daily resting heart rate."
Two rolling measures of how much training stress the athlete has absorbed.
Acute load is roughly the last 7 days of training stress. Chronic load is roughly the last 28 days. The ratio (acute : chronic) is a coarse zone indicator. Above ~1.5 is a spike worth watching, below ~0.8 is a detraining zone.
Useful for catching sudden volume jumps and long stretches of under-training. Treat it as one input alongside what you see in the athlete in front of you.
The sameness of training across a week.
Foster (1998) found that monotony, meaning the same volume and intensity on the same days every week, predicted staleness and illness better than total load did, which is why a program needs its easy days.
A rolled-up estimate of whether an athlete is ready to train hard today.
Typically combines HRV, resting heart rate, sleep, and self-reported inputs (soreness, mood, motivation), and works as a daily check when it is read alongside those inputs.
Most wearable apps publish a single readiness number, so two clients can both show 72 while one has crashing HRV and the other has steady HRV after a short night.
A statistical method for finding the points where a time series moves to a new level.
Looks at a continuous signal (HRV, resting heart rate, sleep efficiency, training load) and marks the points where its level moved and stayed there, leaving day-to-day noise alone.
Harlen uses PELT (Pruned Exact Linear Time), a published algorithm from Killick, Fearnhead & Eckley, 2012, to decide which shifts get raised and which are ordinary variance.
The maximum rate at which the body can use oxygen during exercise.
Measured in ml/kg/min, and strongly tied to endurance performance and long-term health.
Lab measurement (treadmill or bike test with gas exchange) is the gold standard. Consumer wearable estimates from Garmin, Apple, and Coros are decent for trend tracking and order-of-magnitude reads, less reliable for absolute values.
Reference: FRIEND registry (Kaminsky et al., American Heart Association).
Missing a term? Write to kai@harlen.ai.