Cycling Power & Running Power Tracker
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 lags effort by 15-30 seconds, 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 integrates with cycling power meters and running power devices to give you the most accurate training load data possible.
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 15-30 seconds to respond. 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 connects to Bluetooth-enabled cycling power meters, including single-sided crank-based, dual-sided crank-based, spider-based, and hub-based power meters from major manufacturers including Garmin Rally, Shimano Dura-Ace, SRAM Force/Red AXS, Quarq, and PowerTap.
Once a power meter is paired, Fitiv records power at 1-second intervals throughout every ride. 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 5 seconds to 60+ minutes, revealing strengths and limiters.
FTP Testing in Fitiv
Fitiv supports two validated FTP test protocols:
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: Structured increasing power increments (typically 20 watts every minute) until failure. FTP is estimated as 75% of peak 1-minute power. Less accurate than the 20-minute test for some athletes, but lower perceived exertion and more repeatable in fatigue.
Fitiv guides you through both protocols with on-screen instructions and automatic FTP detection from the results. 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:
| Zone | Name | % of FTP | Duration at Which Sustainable | |------|------|----------|-------------------------------| | 1 | Active Recovery | <55% | Indefinitely | | 2 | Endurance | 56-75% | Hours | | 3 | Tempo | 76-90% | 20 min to 2 hours | | 4 | Threshold | 91-105% | 45 min to 1 hour | | 5 | VO2 Max | 106-120% | 3-8 minutes | | 6 | Anaerobic | 121-150% | 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 56-75% of FTP builds aerobic base without accumulating meaningful fatigue. A Zone 5 VO2 max session at 106-120% FTP directly stresses maximal cardiovascular capacity.
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, 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 integrates with Stryd via Bluetooth and with Apple Watch Running Power (watchOS 9+) to record running power during outdoor and treadmill runs.
Running FTP and Power Zones
Running power zones are calculated from your Critical Power (CP) — the running equivalent of cycling FTP, typically tested with a 3-minute all-out effort combined with a 20-minute test, or estimated from recent race data. Running power zones follow similar percentages to cycling power zones.
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
Q: Do I need a power meter to use Fitiv for cycling? A: 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.
Q: Which Bluetooth power meters are compatible with Fitiv? A: Fitiv supports any cycling power meter that broadcasts over Bluetooth Low Energy (BLE) FTMS or Bluetooth SIG standard power profiles. This includes major brands: Garmin Rally series, Quarq, SRAM AXS power meters, Favero Assioma, 4iiii, and others. ANT+ power meters require an ANT+ to BLE bridge (such as the CABLE device) to connect to iPhone/Apple Watch.
Q: Is running power accurate enough to be useful? A: Running power accuracy varies significantly by device. Stryd is considered the most accurate consumer running power meter and is validated in multiple independent studies. Apple Watch Running Power is less accurate for real-time power but provides useful average values for load calculation. 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.
Q: How often should I retest FTP? A: 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. Fitiv can suggest an appropriate time to retest based on your training load trend.