Knowledge Bank

Explanations of the physiology and measurement concepts behind endurance training data.

• VO₂ Max — What It Is, What It Measures, and Why It Matters

  VO₂ max is the greatest rate at which the body can take in and use oxygen during intense exercise. This article explains what the number represents, how it is measured in a laboratory, how it is estimated from ordinary training data, and why it does not by itself determine endurance performance.

• Heart Rate — Understanding Your Body’s Response to Exercise

  Heart rate describes how hard the cardiovascular system is working to support the exercise being performed. This article explains what the number reflects, why it lags behind workload, how zones and maximum heart rate are derived, and why it is most informative when paired with the work the athlete is producing.

• Aerobic Decoupling — How Power-to-Heart-Rate Efficiency Changes During Sustained Exercise

  Aerobic decoupling examines whether the relationship between external workload and heart rate holds steady through a sustained effort. This article explains what the ratio compares, the conditions a valid calculation requires, and why a precise percentage from unsuitable data is meaningless.

• Cycling Power — What It Is, How It Is Measured, and Why It Matters

  Cycling power is the rate at which a rider performs mechanical work, measured in watts. This article explains what the number measures, how a power meter produces it, how it differs from speed and heart rate, and why it means little without duration, body mass and context.

• Weighted Avg Power — What It Is, How It Works, and Why It Matters

  Weighted Avg Power re-weights a variable power stream so that hard efforts count for more than easy ones, giving a single figure closer to the physiological demand of the ride. This article explains what the weighting does, how it differs from average power, and where it stops being meaningful.

• FTP — What It Is, How It Is Measured, and Why It Matters

  FTP is a practical estimate of the highest power a cyclist can sustain for a prolonged period. This article explains what the number represents, the test protocols used to estimate it, how it relates to Sustained Power and lactate threshold, and why a single value should never be read without context.

• Intensity — Understanding Workout Effort Relative to FTP

  Intensity describes how hard a workout is relative to the athlete's own current ability, most commonly by comparing the power produced with the rider's FTP. This article explains why the same wattage is easy for one athlete and near-maximal for another, how intensity zones divide the range, why intensity cannot be interpreted apart from duration, and what an accurate reference value is worth.

• Load — Quantifying the Physiological Impact of Workouts on Your Body

  Load is a calculated estimate of the physiological stress a workout places on the body, combining how demanding the work was with how long it lasted. This article explains why distance or duration alone cannot describe a session, how heart rate, power, pace and perceived effort each provide a basis for the estimate, and why the same Load can mean very different things for different athletes.

• Cycling Cadence — What It Is, How It Is Measured, and Why It Matters

  Cadence is how quickly a cyclist turns the pedals, measured in revolutions per minute. This article explains how cadence and torque combine to produce power, why there is no single ideal value, and what cadence can and cannot tell you on its own.

• Running Pace — What It Is, How It Is Measured, and Why It Matters

  Running pace is the time taken to cover a unit of distance. This article explains how pace is measured, why the same pace can represent very different efforts on different days and terrain, and what has to be held constant before two paces can be compared.

• Running Cadence — Understanding Steps Per Minute

  Cadence is the number of steps a runner takes each minute. This article explains what the number describes, how it combines with step length to produce speed, why it changes with pace, terrain and fatigue, and why no single value is a universal target.

• Running Distance — The Fundamental Measure of Training Volume

  Distance is the length of ground a runner covers. This article explains what it measures, how GPS, treadmills and footpods estimate it, why the same distance can demand very different physiological work, and how it relates to duration, pace and accumulated volume.

• Running Duration — Understanding Total Exercise Time

  Duration is the amount of time spent running. This article explains why time is a common unit across sports and terrains, how it interacts with intensity, the difference between elapsed and moving time, and why consistent exposure is easier to adapt to than irregular swings.

• Running Heart Rate — Understanding Your Physiological Response to the Run

  Running heart rate describes how hard the cardiovascular system is working to sustain a given pace. This article explains what the number responds to, how maximum and threshold references are established, why the same pace can produce different responses, and why data quality governs everything derived from it.

• Swimming Pace — Understanding Pace per 100 Metres or 100 Yards

  Swimming pace expresses how long it takes to cover a standard distance, usually 100 metres or 100 yards. This article explains what the number describes, why swimming time and rest time must not be confused, how pace relates to stroke rate and stroke count, and why the same pace means different things over different distances and in different conditions.

• Swimming Distance — Understanding Total Swim Volume

  Swimming Distance is the most basic measure of how much swimming was done. This article explains what the total does and does not describe, how pool length and unit conversion affect it, why the composition of those metres matters more than the figure itself, and how volume relates to duration, pace and the training an athlete can absorb.

• Swimming Duration — Understanding Total Workout Time

  Swimming Duration is the time a session occupies, which is rarely the same as the time spent swimming. This article explains the distinction between total workout time and active swimming time, why rest structure changes what a duration means, how duration interacts with intensity, and why the clock alone cannot describe a session.

• Stroke Count — Understanding the Number of Strokes Required to Complete a Length

  Stroke Count is the number of strokes a swimmer needs to complete a pool length. This article explains why a lower count is not automatically better, how push-off and underwater distance change it, why counting conventions differ between devices, and why the figure only becomes meaningful when it is read alongside pace.

• Stroke Rate — Understanding Strokes per Minute in Swimming

  Stroke Rate describes how frequently a swimmer takes strokes, usually in strokes per minute. This article explains what the number measures, how it trades off against the distance covered by each stroke, why there is no universally correct turnover, and what a change in stroke rate can and cannot tell you about technique and fatigue.

• SWOLF — Combining Time and Stroke Count as a Rough Swimming Efficiency Indicator

  SWOLF combines the time taken for a pool length with the number of strokes used to swim it, producing a single rough indicator of swimming efficiency. This article explains what the score rewards, why a lower value does not always mean better swimming, what changes it besides technique, and the conditions under which it can honestly be compared.