Extended Critical Power (ECP) & Anaerobic Reserve (W'bal) (Free & Pro)

Available in Free & Pro: Extended Critical Power (ECP) analysis and real-time Anaerobic Reserve tracking are included in both the free SuperCycle Bike Computer and SuperCycle Pro. Scientific theory developed and tested by Dr. Charles Dauwe (www.typhooncycling.org).

SuperCycle incorporates Dr. Charles Dauwe's advanced Extended Critical Power (ECP) model to track your physiological energy systems dynamically during any ride paired with a Bluetooth or ANT+ power meter:

1. Anaerobic Reserve (W'bal)

Anaerobic Reserve represents a live 'battery gauge' of your high-intensity work capacity:

Dynamic Depletion: When riding above your Recovery Threshold (RT) or Critical Power, your anaerobic reserve depletes (measured in Joules and percentage from 100% down to 0%).
Dynamic Replenishment: When easing up below RT, the dynamic replenishment algorithm calculates your anaerobic recovery in real time based on how far below threshold you are pedaling and your current depletion level.
Gauge & Numerical Widgets: Add numeric or dial gauge widgets directly to your ride screen to pace hard climbs, breakaways, or sprints without blowing up.
Negative Values ("Super Legs"): At 100%, your full anaerobic energy tank is available. On an exceptional day with "super legs" or when setting a new all-time personal best, your remaining reserve may occasionally drop slightly below 0% into negative numbers. However, if negative values occur frequently, it is a clear indication that your reference power values need updating.

Anaerobic Reserve Dial Gauge in SuperCycle — Live ride screen featuring the Anaerobic Reserve dial gauge, remaining energy (kJ), and 7-zone ECP status.

2. 7-Zone ECP Power Model

Rather than standard 5-zone power models based solely on FTP, ECP uses 7 personalized metabolic zones reflecting true physiological thresholds. During your ride, these zones are represented by color-coded round icons (shades of green for aerobic, yellow for Slow Death, and shades of red for Fast Death):

Zone 1 — General Recovery (Aerobic): Easy spinning promoting circulation and active recovery (light green).
Zone 2 — FatMax (Aerobic): Optimal fat oxidation for long base endurance miles (green).
Zone 3 — CarbMax (Aerobic): High aerobic tempo relying primarily on glycogen, ending at the Recovery Threshold (dark green).
Zone 4 — Slow Death (SD): Supra-threshold intensity between RT and Supercritical Power (SCP) where anaerobic work begins accumulating gradually (yellow). Ideal for pacing long sustained climbs and time trials.
Zone 5 — VO_2max (Fast Death): Maximal aerobic uptake, rapid fatigue accumulation (light red).
Zone 6 — High Anaerobic (Fast Death): Severe anaerobic capacity depletion during punchy surges and attacks (red).
Zone 7 — Explosive (Fast Death): Neuromuscular sprinting and instantaneous peak wattage (dark red).

3. Specialized Physiological Load Metrics

SuperCycle provides 3 dedicated real-time load indices and oxygen tracking widgets to evaluate the physical cost of your ride:

Aerobic Load Index: A reference value of 1.0 corresponds to 1 hour of continuous cycling at your Recovery Threshold (RT). It measures purely aerobic training volume and the duration spent in the zone where anaerobic recovery occurs.
Slow Death Load: A reference value of 1.0 indicates that your entire Anaerobic Reserve (W') was depleted once within the Slow Death zone (between RT and SCP).
Fast Death Load: A reference value indicating the number of times your entire Anaerobic Reserve (W') was completely depleted at supra-SCP intensities (attacks, steep ramps, and final sprint finishes).
Real-Time % VO_2max Widget: Displays a real-time running average of required oxygen consumption as a percentage of your VO_2max. For efforts below Supercritical Power (SCP), it tracks aerobic demand; at SCP, oxygen uptake reaches 100% and caps there, as all additional power is delivered anaerobically.

4. Managing & Calibrating Reference Values

The ECP engine fits your personalized power-duration curve using five reference durations: 2, 5, 10, 20, and 40 minutes. Under Settings → Sensors → Power Meter → Anaerobic Reserve Reference Values, four management options are available:

From history: SuperCycle automatically scans your recorded rides for your best peak power milestones across the 5 reference durations.
Enter manually: Directly enter values from laboratory testing or field tests.
Save: Save your current reference values to create a fitness snapshot or seasonal baseline.
Load: Retrieve previously saved reference sets at any time.

ECP Settings and Power Duration Regression in SuperCycle — ECP settings screen in SuperCycle showing the 5 reference points, hyperbolic regression line, and calculated parameters.

The 3-Point Regression Check: In the reference plot above, the top right point corresponds to the 2-minute effort and the bottom left point corresponds to the 40-minute effort. For mathematically correct analysis, the three highest points (2-minute, 5-minute, and 10-minute) must align almost exactly on the same regression line. If a point falls noticeably below the line, that duration is an underestimate of your true performance—often indicating you have not performed an all-out test at that duration recently. In this case, schedule a targeted maximum-effort test for that interval.

Off-Season Calibration Note: Because SuperCycle's automatic scan looks for all-time peak values in your history, reference values may remain calibrated to peak summer fitness after an off-season or less intensive training period. If you find your Anaerobic Reserve depleting unrealistically fast, enter current fitness values manually or use Load to revert to an earlier baseline.

5. Post-Ride Anaerobic Reserve Analysis

After your ride, review exactly how your energy reserves fluctuated during the session. Open History, select the completed ride, and tap the Power tab:

Post-Ride Power and Anaerobic Reserve Chart — Post-ride History analysis: Delivered power in yellow vs. Anaerobic Reserve balance in purple.

The dual-axis graph plots your delivered power (yellow line) against the dynamic course of your Anaerobic Reserve balance (purple line). You can pinpoint where hard attacks or steep climbs drained your battery, see how low your reserve dipped, and evaluate how effectively you recharged on subsequent descents.

Detailed Mathematical & Physiological Breakdown: For a deep dive into how Dr. Charles Dauwe's ECP formulas, Recovery Threshold (RT), and dynamic exponential replenishment kinetics operate—and why a direct-force power meter is strictly required—read our comprehensive guide: How Anaerobic Reserve (W'bal) is Calculated: The Extended Critical Power (ECP) Model.

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