Reference guide
Triathlon Metrics Glossary
Clear definitions of every triathlon training metric with practical context for how each number should inform your training and racing.
CSS
Critical Swim Speed
Definition
The fastest swim pace you can sustain without accumulating unsustainable fatigue. Derived from two maximal swim efforts at different distances.
Why it matters
CSS anchors your threshold swim training. Sets paced at or near CSS build aerobic swim capacity without the breakdown of all-out work.
FTP
Functional Threshold Power
Definition
The highest average power output (in watts) you can sustain for approximately one hour. Estimated through shorter field tests like 20-minute or 8-minute protocols.
Why it matters
FTP defines your bike training zones, race-day pacing ceiling, and helps you protect the run by not overcooking the bike.
VDOT
VDOT (Daniels' Running Score)
Definition
A running fitness score derived from a recent race result. Maps to training paces for easy, threshold, interval, and repetition work.
Why it matters
VDOT turns a single race performance into a full set of practical training paces. For triathletes, it provides fresh-leg guidance that must be adjusted for bike fatigue.
TSS
Training Stress Score
Definition
A single number representing the training load of a bike session. Calculated from duration, Normalized Power, and FTP.
Why it matters
TSS helps you plan weekly load, compare sessions, and avoid overreaching. One number captures both duration and intensity.
SWOLF
Swim Golf Score
Definition
The sum of your stroke count and time (in seconds) for one pool length. Lower is generally better within the same stroke and pool length.
Why it matters
SWOLF tracks swim efficiency over time. It is most useful as a repeatable trend metric when stroke, pool length, and counting method stay consistent.
VO2max
Maximal Oxygen Uptake
Definition
The maximum rate at which your body can consume oxygen during exercise. Can be estimated from field tests across swim, bike, and run.
Why it matters
VO2max provides a broad aerobic fitness benchmark. For triathletes, it is most useful as context rather than a direct training anchor.
IF
Intensity Factor
Definition
The ratio of Normalized Power to FTP for a given ride. An IF of 1.0 means you rode at your threshold.
Why it matters
IF tells you how hard a ride was relative to your capacity. Race-day IF targets help pace the bike to protect the run.
NP
Normalized Power
Definition
A weighted average power that accounts for the physiological cost of variable-intensity riding. More representative than simple average power.
Why it matters
NP is the foundation of TSS and IF. It captures the metabolic cost of surges, climbs, and accelerations that raw average power misses.
W/kg
Watts per Kilogram
Definition
Power output divided by body weight. The primary metric for climbing performance and cross-athlete comparison.
Why it matters
W/kg matters most on hilly courses and for comparing riders of different sizes. Flat courses reward raw watts more than W/kg.
T1 / T2
Transition 1 / Transition 2
Definition
T1 is the swim-to-bike transition. T2 is the bike-to-run transition. Includes equipment changes and the physical transition between disciplines.
Why it matters
Transitions are often where age-group athletes lose more time than expected. Practiced transitions can save 2 to 5 minutes.
Brick Workout
Brick Workout (Back-to-Back Disciplines)
Definition
A training session combining two disciplines in immediate succession, most commonly bike followed by run.
Why it matters
Brick workouts teach your body to handle the bike-to-run transition and help you understand how bike effort affects run pace.
Race Pace
Target Race Pace
Definition
The pace or speed you plan to hold during each discipline of the race. Should account for fatigue, conditions, and nutrition.
Why it matters
Race pace is the bridge between training fitness and race execution. Overestimating it is the most common pacing mistake in triathlon.
Use the right metric for the right decision
Each metric serves a different purpose. Matching the metric to the decision is more important than chasing the number itself.