FITIV Pulse records power from Bluetooth cycling power meters paired to your Apple Watch, and from Apple Watch running power, for more precise training data. Heart rate tells you how hard your cardiovascular system is working; power tells you how much actual work your muscles are producing. Heart rate takes 30 seconds to a minute or more to catch up to a change in effort, drifts upward during long efforts in heat, and is affected by fatigue, hydration, and caffeine. Power is immediate and objective, measuring the force applied to the pedals or ground independent of cardiovascular state.
What is Power in Cycling and Running?
Power is the rate of work output, measured in watts. In cycling, it's the force you apply to the pedals multiplied by how quickly you're pedaling. In running, it reflects the rate of work required to move your body mass at a given speed and gradient.
Power measures exercise intensity more directly than pace or heart rate, for two reasons. First, it's immediate. With 5-minute intervals at 280 watts on the plan, within a few pedal strokes you can see whether you're on target, while heart rate takes 30 seconds to a minute or more to catch up. That makes power essential for pacing interval sessions and races accurately.
Second, it doesn't depend on conditions. A 250-watt effort on a hot day is the same absolute work as 250 watts on a cold day, even if your heart rate is 10 bpm higher in the heat.
The limitation is that power measures external output, not internal stress. Two athletes can produce identical power at wildly different physiological costs, depending on their fitness, so power is always interpreted relative to your own Functional Threshold Power.
Functional Threshold Power (FTP)
FTP is the maximum power you can sustain for approximately one hour. It's the most important benchmark in cycling physiology, because your power zones, TSS calculations, and training targets all derive from it. Knowing your FTP turns raw watts into meaningful intensity information.
FTP is sport-specific and usually given in absolute watts (W) and in watts per kilogram of body weight (W/kg), which normalizes for body size so you can compare cyclists of different sizes. Elite male road cyclists produce FTP values of 5.5-6.5+ W/kg and elite female road cyclists 4.5-5.5+ W/kg. Strong amateur cyclists typically fall in the 3.0-4.5 W/kg range.
How FITIV Tracks Cycling Power
FITIV reads cycling power through your Apple Watch. Pair any Bluetooth power meter to the watch (on the watch, open Settings → Bluetooth and select the sensor), then start a cycling workout in FITIV on your Apple Watch. Crank-, spider-, and pedal-based power meters that broadcast Bluetooth all work this way, as do Bluetooth cadence sensors. Power meters that only broadcast ANT+ can't connect to Apple Watch. For step-by-step pairing, see the help center's guide to connecting a cadence or power sensor to Apple Watch.
During the ride you see live watts and power zones, and the data streams to the FITIV app on your iPhone. Post-workout analytics include:
- Normalized Power (NP): An intensity-weighted average that accounts for the metabolic cost of variable power output. More meaningful than average power for rides with varied terrain or pacing.
- Average Power: Total work divided by time, useful for steady-state efforts.
- Power Zones: Time spent in each of your seven power zones. On outdoor rides, you can also color the route map by power zone.
- 25w Power Distribution: Time spent in each 25-watt band, so you can see exactly where your effort sat.
- Peak Power: Maximum power achieved (key for assessing sprint performance).
- Power Curve: Best average power for durations from 1 second to 3 hours, revealing strengths and limiters.
FTP Testing
Two FTP test protocols are widely used.
The 20-minute test is a 20-minute all-out time trial effort. Take 95% of the average power to estimate FTP; the 95% factor accounts for a 20-minute effort being slightly more anaerobic than a true one-hour effort. You'll need a proper warm-up (20-30 minutes with short openers) and flat or controlled terrain.
In the ramp test, power increases by a fixed step every minute (often 20 W) until failure, and FTP is estimated as 75% of peak 1-minute power. It can overestimate FTP for riders with a strong anaerobic kick, but it's shorter and much easier to pace.
You can build either test as a custom interval workout in FITIV's workout builder and ride it with your power meter paired to your Apple Watch. Then enter your new FTP under More → Power → Cycling → Functional Threshold Power (or use the FTP value from Apple Health), and your power zones update to match. Retest every 6-8 weeks during a training block, or after any major change in fitness (illness, training break, training phase transition).
Cycling Power Zones
Power zones are calculated as percentages of FTP. FITIV Pulse uses Coggan's seven zones, labeled Zone 1 to Zone 7 in the app (the names below are Coggan's):
| Zone | Name | % of FTP | Duration at Which Sustainable |
|---|---|---|---|
| 1 | Active Recovery | <55% | Indefinitely |
| 2 | Endurance | 55-74% | Hours |
| 3 | Tempo | 75-89% | 20 min to 2 hours |
| 4 | Threshold | 90-104% | 45 min to 1 hour |
| 5 | VO2 Max | 105-119% | 3-8 minutes |
| 6 | Anaerobic | 120-149% | 30 seconds to 3 minutes |
| 7 | Neuromuscular | 150%+ | Under 10 seconds |
Structured cycling training is built on these zones. A Zone 2 endurance ride at 55-74% of FTP builds aerobic base without piling up meaningful fatigue, while a Zone 5 VO2 max session at 105-119% FTP directly stresses maximal cardiovascular capacity. To see these zones in watts for your own FTP, use our FTP calculator.
Running Power
Running power is newer than cycling power. Foot pods and wrist-based sensors use accelerometry to estimate the rate of mechanical work involved in running, and devices including Stryd, the Garmin Running Dynamics Pod, and Apple Watch (via Running Power in watchOS) report it in watts.
It solves the hill problem that makes pace an imperfect running metric: 5:00/km on flat ground is a very different effort from 5:00/km on a 10% gradient. Running power accounts for elevation change, giving you a gradient-independent intensity measure, similar to Grade Adjusted Pace but in watts instead of equivalent flat pace.
FITIV records Apple Watch Running Power during runs you track with the FITIV Apple Watch app, including current, average, and maximum power.
Running FTP and Power Zones
Running power zones are usually set from your Critical Power (CP), the running counterpart to cycling FTP. CP is typically estimated from two or more maximal efforts of different lengths (for example, 3 and 9 minutes) or from your best recent efforts. Running power zone models use their own percentages, which differ from the cycling zones above.
In FITIV, running has its own FTP and its own seven zones, separate from cycling: set them under More → Power → Running. FITIV doesn't estimate running FTP for you, so enter a value from your own testing. The running zones start from the same percentages of FTP as cycling, and you can edit them to match the running model you follow.
Running power is most valuable for pacing on variable terrain (trail running, cross-country), where pace stops meaning much, and on the treadmill, where GPS is unavailable. On flat roads, pace and running power give you similar information.
How Power Data Improves Training Load Accuracy
For cycling, TSS calculated from power data is significantly more accurate than heart rate-based training load estimates. Power measures the work done directly, while heart rate estimates it through a physiological proxy that varies with hydration, temperature, fatigue, and caffeine.
If you track training load seriously (planning periodization, managing your fitness and fatigue balance, preparing for a goal event), power-based TSS is the right metric. Choose Training Stress Score as your method in the Training Summary, and FITIV uses power-based TSS when power data is available, falling back to heart rate-based TSS when it isn't.
Why Power Tracking Matters for Cyclists and Runners
Power turns training from feel-based into precise work. Athletes who train with power consistently execute interval sessions more accurately, avoid the common error of starting too hard and fading on longer efforts, and have objective evidence of fitness improvement that doesn't depend on external conditions.
The biggest payoff is repeatability. If you do the same 20-minute threshold test on the same route every 6-8 weeks, the change in power output is a direct measure of fitness improvement, because wind and hills change your speed but not your watts. Pace or heart rate alone can't give you that. Keep your rest, fueling, and effort consistent from test to test.
Frequently Asked Questions
Do I need a power meter to use FITIV for cycling?
No. FITIV tracks cycling with heart rate as the primary intensity metric when no power meter is available. Training load comes from heart rate (TRIMP) by default, and if you choose the Training Stress Score method, rides without power use heart rate-based TSS. A power meter improves accuracy but is not required.
Which Bluetooth power meters are compatible with FITIV?
Any cycling power meter that your Apple Watch can pair with over Bluetooth, which covers most current models from brands like Garmin, Favero, Quarq, SRAM, 4iiii, and Stages. Pair the power meter to your Apple Watch (watch Settings → Bluetooth), then record the ride with the FITIV Apple Watch app. FITIV doesn't connect to power meters from the iPhone alone, and ANT+-only power meters won't work.
Is running power accurate enough to be useful?
Running power accuracy varies significantly by device. Dedicated foot pods such as Stryd are generally more precise, though FITIV doesn't connect to them. FITIV uses Apple Watch Running Power, which is best treated as a trend and average measure rather than a precise second-by-second reading. The metric is most valuable for relative comparisons within your own training (this interval at 300W is harder than that one at 260W) rather than absolute comparison against other athletes.
How often should I retest FTP?
FTP should be retested every 6-8 weeks during an active training block, or any time your training changes significantly (returning from illness, completing a training camp, transitioning from base to build phase). Do not retest during a heavy fatigue week: FTP tests require adequate freshness to produce accurate results.
