Heart rate tells you how hard your cardiovascular system is working. Power tells you how much actual work your muscles are producing. The distinction matters: 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 — it measures force applied to the pedals or ground independent of cardiovascular state. 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.
What is Power in Cycling and Running?
Power is the rate of work output, measured in watts. In cycling, power is the force you apply to the pedals multiplied by how quickly you're pedaling. In running, power reflects the rate of work required to propel your body mass at a given speed and gradient.
Power is a more direct measure of exercise intensity than either pace or heart rate for two reasons:
First, it is immediate. When you accelerate out of a corner on a bike, your power output spikes instantly. Heart rate takes 30 seconds to a minute or more to catch up. This makes power essential for pacing interval sessions and races accurately.
Second, it is context-independent. 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. Heart rate deceives; power does not.
The limitation of power is that it measures external output, not internal stress. Two athletes can produce identical power at wildly different physiological costs, depending on their fitness. This is why 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 is the most important benchmark in cycling physiology — your power zones, TSS calculations, and training targets all derive from it. Knowing your FTP transforms raw watt numbers into meaningful intensity information.
FTP is sport-specific and typically measured in W (absolute watts) and W/kg (watts per kilogram of body weight). W/kg normalizes for body size and allows comparison between cyclists of different sizes. Elite male road cyclists produce FTP values of 5.5-6.5+ W/kg; elite female road cyclists produce 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.
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 Distribution: Time spent at each power zone throughout the ride.
- Peak Power: Maximum power achieved (critical for sprint performance assessment).
- 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:
20-Minute Test: A 20-minute all-out time trial effort. Take 95% of the average power to estimate FTP. The 95% factor accounts for the fact that a 20-minute effort is slightly more anaerobic than a true one-hour effort. Requires a proper warm-up (20-30 minutes with short openers) and flat or controlled terrain.
Ramp Test: Power increases by a fixed step every minute (often 20 W) until failure. 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 (or use the FTP value from Apple Health), and your power zones update to match. FTP should be retested 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 |
These zones form the basis of structured cycling training. A Zone 2 endurance ride at 55-74% of FTP builds aerobic base without accumulating meaningful fatigue. 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 a newer metric than cycling power, enabled by foot pods and wrist-based sensors that use accelerometry to estimate the rate of mechanical work involved in running. Devices including Stryd, the Garmin Running Dynamics Pod, and Apple Watch (via Running Power in watchOS) produce running power in watts.
Running power solves the hill problem that makes pace an imperfect running metric: a 5:00/km pace on flat ground is a categorically different effort than 5:00/km on a 10% gradient. Running power accounts for elevation change and produces a gradient-independent intensity measure — similar to Grade Adjusted Pace but in watts rather than 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.
Running power is most valuable for pacing on variable terrain (trail running, cross-country) where pace becomes meaningless, and for treadmill running where GPS is unavailable. For flat road running, pace and running power provide similar information.
How Power Data Improves Training Load Accuracy
TSS calculated from power data is significantly more accurate than heart rate-based training load estimates for cycling. The reason is straightforward: power directly measures the work done, while heart rate estimates it through a physiological proxy that varies with hydration, temperature, fatigue, and caffeine.
For cyclists who track training load seriously — planning periodization, managing fitness and fatigue balance, preparing for goal events — power-based TSS is the appropriate metric. FITIV uses power-based TSS automatically when power data is available, falling back to heart rate-based estimates when it is not.
Why Power Tracking Matters for Cyclists and Runners
Power transforms training from feel-based to precision work. Athletes who train with power consistently execute interval sessions more accurately, avoid the common error of starting too hard and dying on longer efforts, and have objective evidence of fitness improvement that is independent of external conditions.
The most valuable application is repeatability. If you do the same 20-minute threshold test on the same route four times per year, power output improvement is a direct measure of fitness improvement — unaffected by wind, temperature, or how motivated you felt that day. This objectivity is impossible to achieve with pace or heart rate alone.
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. Heart rate-based TSS estimates are used for training load calculation. 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.
