what is FTP or functional threshld power?

If you've spent any time around triathletes or cyclists talking about training, you've heard three letters that seem to dominate many conversations (and humble brags): FTP. It gets tossed around at group rides, scribbled on whiteboards at coaching sessions, and plastered across training platform dashboards. But what is it, really? And more importantly, why should you, as a triathlete trying to get faster, actually care?

The short answer: FTP is the foundation upon which nearly every other meaningful performance metric is built. Get it right, and your training becomes targeted, your race pacing becomes precise, and your post-race analysis becomes genuinely useful. Get it wrong, and you're essentially flying blind.

What Is FTP? A Complete Guide for Cyclists and Triathletes

FTP stands for Functional Threshold Power, and it represents the highest average power output you can sustain for approximately one hour. It's measured in watts and was developed by Dr. Andrew Coggan, an exercise physiologist who wanted a practical way for athletes to measure their aerobic fitness without the need for a laboratory.

Think of FTP as a line in the sand. Below it, your body can manage most of the metabolic byproducts of exercise — primarily lactate — and keep going. Above it, those byproducts accumulate faster than your body can clear them, and you're on a countdown timer to exhaustion. The higher your FTP, the faster you can ride before crossing that threshold.

For a triathlete, this matters enormously. The bike leg is the longest portion of most triathlon distances, and it's the leg where disciplined pacing has the biggest impact on your run. FTP gives you a concrete, measurable anchor to build your entire race strategy around.

How to Determine Your FTP

The 20-Minute FTP Test

The most common field test is the 20-minute protocol. After a thorough warmup that includes a few hard efforts to open up your legs, you ride as hard as you can sustain for 20 minutes. Your average power for that effort, multiplied by 0.95, gives you an estimate of your FTP.

For example, if you average 250 watts for the 20-minute test, your estimated FTP is 250 × 0.95 = 237 watts.

The 0.95 multiplier accounts for the fact that most athletes can sustain a slightly higher intensity for 20 minutes than they can for a full hour. It's not perfect — some athletes need a 0.92 multiplier, others could use 0.97 — but it's a solid starting point.

A few tips for getting an accurate result:

  • Start conservatively. The single biggest mistake athletes make is going out too hard for the first five minutes and then fading badly over the remaining fifteen. A well-executed test feels controlled for the first half and genuinely difficult for the second.
  • Be rested — treat this like a race. A test done on tired legs after a hard training week will underestimate your true FTP, making all your training zones too easy.

Ramp Tests

Ramp tests, offered by platforms like Zwift and TrainerRoad, provide an alternative approach. These start easy and increase power in small steps every minute until you can't continue. They're less mentally demanding than a 20-minute effort, but they tend to favor athletes with strong anaerobic capacity and can sometimes overestimate FTP for endurance-focused athletes — including most triathletes.

The Metrics Your FTP Unlocks

FTP isn't just a standalone number. It's the denominator in a family of derived metrics that, together, give you a remarkably complete picture of every ride you do and every race you plan.

Normalized Power (NP)

When you ride outdoors, your power output is never constant. You surge up hills, coast down descents, accelerate out of corners, and ease up in drafts. Your average power for a ride captures the arithmetic mean of all those moments, but it doesn't reflect the actual physiological cost. A ride where you alternate between 300 watts and 100 watts is far more taxing than a ride at a steady 200 watts, even though both have the same average.

Normalized Power solves this. It applies a mathematical algorithm — a rolling 30-second average, raised to the fourth power, then averaged, then root-extracted — that weights high-power moments more heavily. The result is a single number that represents what your effort "felt like" in terms of metabolic cost. Think of it as "the constant power you could have ridden at for the same physiological price."

For triathletes, NP is the metric to watch on race day, not average power. If your NP is close to your target, you're executing well — regardless of the natural power fluctuations caused by terrain and wind.

Intensity Factor (IF)

Intensity Factor is beautifully simple: it's your Normalized Power divided by your FTP.

This ratio tells you how hard a ride was relative to your personal threshold. An IF of 1.0 means you rode at your FTP — the absolute maximum sustainable effort for an hour. An IF of 0.75 means you rode at 75% of your threshold, which is a moderate endurance effort.

IF Range What It Means Typical Context
< 0.65 Recovery effort Easy spin, warmup/cooldown
0.65–0.75 Endurance pace Long training rides
0.75–0.85 Tempo / steady-state Hard group rides, 70.3 racing
0.85–0.95 Threshold territory Short TTs, aggressive racing
0.95–1.05 At or near FTP Hour-long efforts, sprint tri
> 1.05 Unsustainable Short, maximal efforts

Target IF by Triathlon Race Distance

For triathlon racing specifically, IF targets are one of the most important pacing guidelines. These ranges exist because you need to get off the bike and run — an IF that's sustainable for the bike distance alone might leave you unable to run at your target pace, or at all.

Race Distance Target TSS Range Why It Matters
Sprint Triathlon 0.95–1.05
Olympic Distance 0.85–0.95
70.3 / Half Ironman 0.75–0.85
Full Ironman 0.68–0.78

Training Stress Score (TSS)

If IF tells you how hard a ride was, TSS tells you the total load — combining both intensity and duration into a single number. The formula is:

The reference point is simple: riding at your FTP for exactly one hour produces a TSS of 100. A two-hour endurance ride at IF 0.70 produces a TSS of about 98. A 30-minute interval session at IF 0.95 produces a TSS of about 45. A full Ironman bike leg might accumulate 250–320 TSS.

Race Distance Target TSS Range Why It Matters
Sprint 30–45 Short enough that going over isn't catastrophic
Olympic 60–90 Starting to matter — overshoot and the run suffers
70.3 150–180 Discipline is critical — go over 190 and the run gets ugly
Full Ironman 250–300 Exceed 310+ and you're likely walking the marathon

TSS is one of the three inputs BestBikeSplit uses to build race plans. You can create a plan based on a target TSS, and the model will determine the optimal power for every segment of the course to hit that number while minimizing overall time.

Variability Index (VI)

Variability Index is the ratio of your Normalized Power to your average power:

A perfectly steady ride would produce a VI of 1.00. In practice, a VI of 1.02–1.05 represents excellent pacing discipline. Once VI creeps above 1.05, it indicates significant surging and fading — which has real metabolic consequences.

Because of the nonlinear relationship between power and physiological cost, variable-power cycling produces up to 64% higher blood lactate concentrations than constant-power cycling at the same average wattage. For triathlon, a high VI on the bike is one of the strongest predictors of a poor run. A well-paced Ironman bike leg should have a VI below 1.05. If yours consistently comes in above 1.08, you have a significant pacing problem that's costing you 5–15 minutes over the full race.

Power Training Zones

FTP also defines your training zones — the intensity ranges that target specific physiological adaptations. The most widely used system, developed by Dr. Coggan, defines seven zones:

Zone Name % of FTP Purpose
1 Active Recovery < 55% Easy spinning, recovery
2 Endurance 56–75% Aerobic base building
3 Tempo 76–90% "Sweetspot" range, sustained effort
4 Lactate Threshold 91–105% Improving FTP itself
5 VO2max 106–120% Short, hard intervals
6 Anaerobic Capacity 121–150% Very short, maximal efforts
7 Neuromuscular Power > 150% Sprints, explosive power

For triathletes, the bulk of training and racing happens in Zones 2 through 4. Ironman racing is predominantly Zone 2 with touches of Zone 3. Half-distance racing pushes into upper Zone 3. Understanding where you are in relation to these zones — all anchored to your FTP — transforms training from "riding hard and hoping" into targeted physiological development.

Managing Training Over Time: CTL, ATL, and TSB

TSS feeds into three longer-term metrics that help you manage your training load over weeks and months.

  • Chronic Training Load (CTL) is a rolling 42-day average of your daily TSS, representing your accumulated fitness. Think of it as your training "bank account" — built up gradually over weeks of consistent work.
  • Acute Training Load (ATL) is a rolling 7-day average of daily TSS, representing your current fatigue. After a hard training block, ATL spikes. During a recovery week, it drops.
  • Training Stress Balance (TSB) is CTL minus ATL, representing your "form" — how fresh you are relative to your fitness. A positive TSB means you're rested and ready to perform. A negative TSB means fatigue is outweighing fitness.

For triathlon race preparation, the goal is to arrive at the start line with a TSB between approximately +5 and +15. Too positive (above +30) and you may have lost some fitness. Too negative, and you're still carrying too much accumulated fatigue. All of this traces back to one number: your FTP.

Why FTP Matters More for Triathletes Than for Cyclists

Pure cyclists can afford to have a less precise FTP because their races involve tactics — drafting, surging, attacking, and responding. Power data is useful, but not the primary determinant of success. Triathlon is different. The bike leg is, for most athletes at most distances, a time trial. You're alone against the course, the clock, and your own physiology. Pacing precision directly determines your result.

More importantly, triathletes face a constraint that cyclists don't: the run that comes after. The bike isn't the finish line — it's the setup for the finish line. Every watt over your target on the bike has a compounding cost on the run. Having an accurate FTP, understanding the metrics it drives, and using them to build a disciplined race plan is the difference between a race you're proud of and one you'd rather forget.

Putting It All Together with BestBikeSplit

All of these metrics — FTP, NP, IF, TSS, VI, and power zones — are inputs and outputs in the BestBikeSplit race-planning model. When you create a race plan in BBS, you enter your FTP as part of your athlete profile. The model then uses the course's elevation data, wind forecasts, and your equipment profile to calculate the optimal power for every segment of the course, targeting your chosen IF or TSS ceiling.

After the race, BBS's Analytics tools compare your plan to your actual data, showing you where you deviated, what your VI was, and — critically — what the time cost of those deviations was. It closes the loop between planning and execution, turning every race into a learning opportunity for the next one.

Want a quick preview? Best Bike Split uses your FTP to estimate race power targets and shows how pacing strategy affects your bike split — no account required.

If you're a triathlete who's been training by feel or heart rate alone, getting a power meter and establishing your FTP is the single highest-ROI investment you can make. And once you have that number, BestBikeSplit turns it into a precise, course-specific race plan — not a rough guess, but a segment-by-segment strategy built on physics.

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