Sports Sensor Terms
This glossary defines non-branded sensor technology and physiological metrics used across every sport this site covers: what a sensor measures, how it works, and the terms used to describe accuracy and interference. Several entries here are algorithmic estimates derived from multiple inputs rather than a direct sensor measurement, and the definitions say so explicitly. Sport-specific applications of these metrics, such as cadence in running or power in cycling, are defined on their respective glossary pages and cross-reference the fuller technical definitions here.
Quick answers
What is an accelerometer in a sports watch?
An accelerometer is a motion sensor that measures acceleration along one or more axes, used in sports watches to detect steps, cadence, and movement patterns.
What is aerobic threshold?
Aerobic threshold is the effort level at which the body’s energy production begins shifting from predominantly aerobic to a mixed aerobic-anaerobic contribution, sitting below lactate threshold on the intensity scale.
What is anaerobic threshold?
Anaerobic threshold is a term some coaches and devices use interchangeably with lactate threshold, though its precise definition varies by methodology; where a distinction is drawn, anaerobic threshold typically marks a slightly higher effort than aerobic threshold.
What is a barometric altimeter?
A barometric altimeter measures air pressure to estimate elevation, typically more responsive to short-term changes than GPS-derived altitude alone.
What is barometric calibration?
Barometric calibration, or autocalibration, is the process of correcting a barometric altimeter’s drift, caused by changing weather pressure, using a GNSS elevation reading or a manually entered reference point.
What is a body battery-type recovery score?
A body battery-type recovery score is a composite daily energy or readiness figure derived from heart rate variability, sleep, and activity data, a platform-level estimate rather than a direct measurement, intended to reflect how much physical reserve a person has available.
What is a cadence sensor?
A cadence sensor is the hardware, whether built into a watch or a dedicated accessory, that detects the cadence metric defined under Running.
What is a chest strap heart rate sensor?
A chest strap sensor is a heart rate monitor worn around the chest, typically detecting the heart’s electrical activity rather than optical blood-volume changes, generally considered more accurate than wrist-based optical sensing, particularly at high intensity.
What is contact quality in a sensor?
Contact quality describes how firmly and consistently a sensor sits against the skin, with a loose strap, movement, or sweat weakening the signal a sensor can read, distinct from motion artifact, which corrupts the signal itself rather than its strength.
What is dead reckoning in a sports watch?
Dead reckoning is a technique for estimating position from a known starting point using motion sensor data alone, relied on by a device’s inertial sensors when GNSS signal is unavailable, such as in tunnels or under dense canopy.
What is dual-frequency GNSS (multi-band positioning)?
Dual-frequency GNSS, also called multi-band positioning, is satellite positioning that receives signals across two frequency bands per satellite rather than one, improving accuracy in urban canyons, under tree cover, and other signal-reflective environments.
What is ECG (electrocardiography) in a sports watch?
ECG, or electrocardiography, is the measurement of the heart’s electrical activity through skin-contact electrodes, the sensing method used by chest straps and by the electrical heart rate feature on some watches, distinct from the optical method used by PPG.
What is EPOC?
EPOC, or excess post-exercise oxygen consumption, is the elevated rate of oxygen consumption that continues after exercise ends, used by some platforms as an input to training load and recovery time estimates.
What is fitness age?
Fitness age is an estimated age figure derived from VO2 max, resting heart rate, and other fitness markers, a platform-level presentation intended to compare cardiovascular fitness against population norms rather than chronological age.
What is GLONASS?
GLONASS is Russia’s global satellite navigation system, one of several GNSS constellations a device may use alongside GPS for positioning.
What is GNSS?
GNSS, or global navigation satellite system, is the umbrella term for all satellite positioning systems, including GPS, GLONASS, Galileo, and BeiDou.
What is a GNSS fix?
A GNSS fix, sometimes still called a satellite fix, is the point at which a device has received enough satellite signal data to calculate its position.
What is GPS?
GPS, or Global Positioning System, is the United States’ satellite navigation constellation, and the specific GNSS system most commonly referenced by name in everyday use.
What is a gyroscope in a sports watch?
A gyroscope is a motion sensor that measures rotational movement, used alongside an accelerometer to track orientation and refine motion-based metrics.
What is heart rate?
Heart rate is the number of times the heart beats per minute, the base physiological measurement that maximum heart rate, resting heart rate, and heart rate variability are all derived from.
What is heart rate recovery (HRR)?
Heart rate recovery is how quickly heart rate drops in the period immediately following exercise, with a faster drop generally associated with better cardiovascular fitness.
What is heart rate variability (HRV)?
Heart rate variability is the variation in time between successive heartbeats, used as an indicator of autonomic nervous system balance and recovery status.
What are heart rate zones?
Heart rate zones are defined ranges of heart rate, usually expressed as a percentage of maximum heart rate, used to guide training intensity across sports.
What is an inertial measurement unit (IMU)?
An inertial measurement unit combines an accelerometer, gyroscope, and often a magnetometer into a single sensor package used to track motion and orientation.
What is lactate threshold?
Lactate threshold is the effort level at which lactate begins to accumulate in the blood faster than the body can clear it, commonly estimated by wearable devices from heart rate and pace data rather than measured directly from blood samples. See the full breakdown of how Garmin estimates lactate threshold.
What is the LED in an optical heart rate sensor?
The LED in an optical heart rate sensor is the light source shone into the skin, with reflected light changes used to detect blood volume pulses.
What is a magnetometer in a sports watch?
A magnetometer is a sensor that detects the Earth’s magnetic field, used to provide compass heading independent of movement.
What is maximum heart rate?
Maximum heart rate is the highest heart rate a person can achieve during maximal exertion, used as the reference point for calculating heart rate training zones.
What is motion artifact in a heart rate sensor?
Motion artifact is noise introduced into an optical heart rate signal by movement of the sensor against the skin during activity, the dominant cause of wrist-based heart rate errors, distinct from contact quality, which concerns how well the sensor sits against the skin in the first place.
What is an optical heart rate sensor?
An optical heart rate sensor uses light shone into the skin to detect blood volume changes and estimate heart rate, most commonly from the wrist.
What is oxygen saturation (SpO2)?
Oxygen saturation, or SpO2, is the percentage of oxygen-saturated haemoglobin in the blood, estimated by wearables using light absorption at the wrist.
What is performance condition?
Performance condition is a real-time estimate of how a person’s current effort compares to their established fitness level, typically shown as a plus or minus adjustment during an activity.
What is a power meter?
A power meter is a device, typically mounted on a bike’s pedals, crank, or hub, that measures the force and cadence applied to estimate power output in watts.
What is PPG (photoplethysmography)?
PPG, or photoplethysmography, is the optical sensing method used to detect blood volume changes at the skin, the underlying technology behind wrist-based heart rate measurement.
What is recovery time on a sports watch?
Recovery time is an estimate of how long a person should wait before their next hard training session, based on the intensity and duration of a completed activity.
What is resting heart rate?
Resting heart rate is a person’s heart rate measured at complete rest, typically upon waking, and used as a baseline indicator of cardiovascular fitness and recovery.
What is respiration rate?
Respiration rate is the number of breaths taken per minute, estimated by wearables from chest movement or from fluctuations in the optical heart rate signal.
What is a running dynamics pod?
A running dynamics pod, also called a footpod or stride sensor, is a small accessory clipped to a runner’s waistband or shoe, or a sensor built into the watch itself, that captures form metrics such as cadence, ground contact time, and vertical oscillation, and can supply pace and distance independently of GPS where satellite signal is poor.
What is sampling rate in a sensor?
Sampling rate is the frequency at which a sensor takes readings, typically expressed in hertz, with a higher rate capturing finer detail at the cost of greater power use.
What is sensor drift?
Sensor drift is a gradual loss of measurement accuracy over time or across a session, caused by factors such as sensor movement, temperature change, or battery depletion.
What is sensor fusion?
Sensor fusion is the combination of data from multiple sensors, typically an accelerometer, gyroscope, magnetometer, and GNSS receiver, into a single, more accurate estimate of motion or position than any one sensor could provide alone.
What is sensor placement?
Sensor placement refers to where a device sits on the body, a variable that significantly affects the accuracy of optical heart rate and other skin-contact sensors.
What is signal obstruction (GNSS)?
Signal obstruction is the blocking or weakening of satellite signal by physical barriers such as buildings, cliffs, or dense tree cover, a primary cause of reduced GNSS accuracy.
What is skin temperature (wearable sensor)?
Skin temperature is the surface temperature measured at the point of wrist or body contact with a device, used by some platforms as an input to recovery and readiness scores.
What is training load?
Training load is a cumulative figure representing the physiological stress of recent training, typically calculated from heart rate or power data over a rolling multi-day or multi-week window; it is a derived training metric rather than a direct sensor measurement.
What is training readiness?
Training readiness is a composite, platform-level score estimating how prepared a person is for a hard training session, drawing on recovery time, sleep, HRV, and recent training load, rather than a quantity any single sensor measures directly.
What is training status?
Training status is a categorical assessment, such as productive, maintaining, or overreaching, describing the trend in a person’s fitness relative to their recent training load, a platform interpretation rather than a direct measurement.
What is VO2 max?
VO2 max is the maximum rate at which the body can consume oxygen during exercise, commonly estimated by wearable devices from pace, heart rate, and other activity data rather than measured directly in a laboratory. See the full breakdown of how Garmin estimates VO2 max.
What is the wavelength used in optical heart rate sensors?
Wavelength, in the context of optical sensors, refers to the colour of light used by a device’s LEDs, with green light commonly used for heart rate during activity because it is well absorbed by blood, and red or infrared light typically used for SpO2 measurement.
