Power Meters

What is a Power Meter?

A power meter is a measuring device that captures a cyclist's mechanical power in real-time and outputs it in watts. This objective measurement has revolutionized cycling training and enables precise control of training load as well as optimal race preparation.

Unlike heart rate monitoring, which reacts with delay to changes in load and is influenced by many factors such as sleep, stress, or caffeine, a power meter provides immediate and direct feedback on current power output. This makes it the most valuable training tool in modern cycling.

How Power Meters Work

Basic Principle of Power Measurement

Power meters use strain gauges that are applied to mechanical components such as cranks, pedals, or hubs. These highly sensitive sensors measure minimal deformations of the material under load.

The measurement occurs in three steps:

1. The strain gauges capture the deformation of the component through pedaling force
2. This mechanical deformation is converted into an electrical signal
3. A microprocessor calculates the current power in watts from the signal and cadence

Important Metrics

Modern power meters provide far more than just the current wattage:

Types of Power Meters

Crank-Based Power Meters

Advantages:

• High accuracy through measurement at the power source
• Capture of total pedaling force of both legs
• Transferable between different bikes (when changing the complete crank)
• Many models offer left/right balance
• Protected position, less susceptible to damage

Disadvantages:

• Compatibility with bottom bracket and frame must be checked
• Medium to high acquisition costs (800-1,500 €)
• Complex installation required

Known Systems: Quarq DZero, Stages Cycling, 4iiii Precision, Power2Max

Pedal-Based Power Meters

Advantages:

• Simplest installation - just swap pedals
• Perfectly transferable between different bikes
• Left/right balance standard with dual systems
• Pedaling Dynamics possible
• No compatibility issues with frame or cranks

Disadvantages:

• Higher costs with dual systems (1,000-1,400 €)
• Exposed - more susceptible to damage in crashes
• Pedal system-bound (Look, Shimano SPD-SL, Speedplay)

Known Systems: Garmin Vector 3, Favero Assioma, Wahoo Speedplay, Look Exakt

Hub-Based Power Meters

Advantages:

• Very reliable and durable
• Protected position in rear hub
• Low maintenance
• Proven technology with years of experience

Disadvantages:

• Bound to a specific wheel
• No left/right balance possible
• Wheel change only possible with power meter
• Transfer between bikes very complex

Known Systems: PowerTap G3, PowerTap C1

Spider-Based Power Meters

Advantages:

• Compact design
• Chainring change without dismounting power meter
• Good accuracy
• Protected central position

Disadvantages:

• Compatibility with crank and bottom bracket must be checked
• Usually no left/right balance
• Medium costs (700-1,200 €)

Known Systems: Power2Max NGeco, Quarq DZero

Crank Arm-Based Power Meters

Advantages:

• Most affordable entry option (from 300 €)
• Simple retrofitting
• Chainrings can be changed
• Easy installation

Disadvantages:

• Only one leg is measured (extrapolation to total power)
• No precise left/right balance
• Can provide inaccurate values with asymmetries

Known Systems: Stages Cycling, 4iiii Precision

Bottom Bracket-Based Power Meters

Advantages:

• Central position
• Good transferability
• Protected from external influences

Disadvantages:

• Bottom bracket standard must match
• Installation requires special tools
• Limited model selection

Known Systems: Rotor 2INpower, SRAM Rival AXS Power Meter

FTP and Power Zones

Functional Threshold Power (FTP)

FTP is the power in watts that an athlete can maximally maintain over one hour. It forms the basis for calculating individual training zones and is the most important reference value in power-based training.

Training Zones Based on FTP

Performing FTP Test

Classic 20-Minute Test:

1. Warm-up: 20 minutes progressively increasing intensity
2. High-intensity block: 5 minutes at maximum intensity (all-out)
3. Recovery: 10 minutes easy riding
4. Main test: 20 minutes maximum sustained power
5. Evaluation: Average power × 0.95 = FTP

Alternative: Ramp Test (shorter variant):

Gradual increase in power until exhaustion. Highest achieved minute power × 0.75 = FTP. This test is less stressful but equally informative.

Training with Power Meter

Structured Interval Training

Example Training Session: Sweet Spot Training

• Warm-up: 15 minutes Zone 2
• Main part: 3 × 10 minutes at 88-94% FTP
• Rest: 5 minutes Zone 1 between intervals
• Cool-down: 10 minutes Zone 1-2

Total duration: 75 minutes
TSS: ~85
Goal: Improvement of threshold power at moderate load

Pacing in Time Trials

The most important application of the power meter in competition is optimal pacing. Studies show that an even power profile (even pacing) leads to the best results.

Use in Hill Races

On climbs, the power meter shows its true value: While speed drops dramatically, power remains objectively measurable. Professionals use watts/kg as a comparison value for climbs.

Typical power values on climbs:

• Category 1 climbs (ProTour): 5.8-6.5 W/kg
• Category 2-3 climbs: 5.2-5.8 W/kg
• Hobby athlete long climb: 3.5-4.5 W/kg

Post-Training Analysis

Modern platforms like TrainingPeaks, Today's Plan, or Strava offer extensive analysis options:

1. Power Curve: Shows maximum power over various time spans (5 seconds to 90 minutes)
2. TSS Accumulation: Monitors training load and recovery needs
3. Performance Management Chart (PMC): Visualizes fitness, fatigue, and form
4. Quadrant Analysis: Compares force and cadence at different intensities
5. Mean Maximal Power: Historical comparison of best performances

Power Meter Buying Guide

Selection Criteria

Price-Performance Recommendations

Accuracy and Calibration

High-quality power meters have an accuracy of ±1-2%. Regular zero-point calibration before each ride is important:

1. Place bike on level surface
2. Bring cranks to horizontal position
3. Activate zero-offset function in bike computer or app
4. Wait 5 seconds - done

Common Problems and Solutions

Integration into Training Planning

Periodization with Power Meter Data

Systematic evaluation of power data enables precise training planning over weeks and months:

Macrocycle (12-week example):

Weeks 1-4: Base Block
- Volume: High (10-15h/week)
- Intensity: Low (70-80% in Zone 2)
- Goal: Develop aerobic base
- TSS/week: 400-600

Weeks 5-8: Build Phase
- Volume: Moderate (8-12h/week)
- Intensity: Medium-High (Sweet Spot, Threshold)
- Goal: Increase FTP
- TSS/week: 500-700

Weeks 9-11: Specific Preparation
- Volume: Moderate (7-10h/week)
- Intensity: High (Intervals, race simulation)
- Goal: Race-specific form
- TSS/week: 450-650

Week 12: Taper
- Volume: Low (4-6h/week)
- Intensity: Moderate with short peaks
- Goal: Recovery before main race
- TSS/week: 250-350

Performance Management Chart (PMC)

The PMC is the most important tool for monitoring training and recovery:

• CTL (Fitness): Average TSS of last 42 days - should gradually increase
• ATL (Fatigue): Average TSS of last 7 days - shows current load
• TSB (Form): Difference between CTL and ATL - optimal between -10 and +10 on race day

Power Meters for Different Disciplines

Road Racing

Ideal for pacing during long breakaways and to avoid overexertion. Professional teams use real-time data for tactical decision-making.

Time Trials

The absolute king's domain of the power meter. Allows perfect pacing and avoids the most common mistake: starting too fast.

Track Cycling

Specially calibrated systems for fixed gear. Important for optimizing start acceleration and lap times.

Mountain Bike

Especially valuable in XC races. Helps preserve energy reserves for technical sections and optimally dose climbs.

Gran Fondo and Ultra Distance

Indispensable for events over 100+ km. Prevents too intense pace at the start and secures energy for late climbs.

Scientific Background

Why Watts Instead of Heart Rate?

Heart rate reacts with 20-60 seconds delay to changes in load. Power meters show power in real-time, enabling precise intervals.

Factors that affect HR but not power:

• Caffeine (+5-10 beats)
• Heat (+10-20 beats at same power)
• Dehydration (+5-15 beats)
• Stress and sleep deprivation
• Illness or overtraining
• Medications

Normalized Power (NP) vs. Average Power

With variable loads (intervals, hilly terrain), average power is misleading. NP weights higher powers more and better represents physiological load.

Example:
Training A: 60 minutes constant 200 watts → Average 200W, NP 200W
Training B: 30× (1min @ 250W, 1min @ 150W) → Average 200W, NP 215W

Training B is significantly more stressful, even though average power is identical!

Variability Index (VI)

VI = NP ÷ Average Power

• VI = 1.00-1.05: Very even load (time trial, indoor training)
• VI = 1.05-1.10: Moderately variable (group ride, flat race)
• VI = 1.10-1.20: Highly variable (criterium, hilly terrain)
• VI > 1.20: Very variable (hill race, attack-rich race)

Future of Power Measurement

Dual-Leg Power Metering

More and more systems measure both legs separately. This enables:

• Detection of asymmetries
• Targeted strength work on weaker leg
• Injury prevention
• Optimization of pedaling technique

Pedaling Dynamics

Analysis of force distribution over the entire pedal stroke:

• Power Phase: Where is force applied?
• Dead Spots: Where is energy lost?
• Pedal Smoothness: How round is the stroke?

Integration with Other Sensors

Modern ecosystems connect power meters with:

• Heart rate monitoring → Determination of aerobic decoupling
• Muscle oxygen sensors (SmO2) → Metabolic state in real-time
• Core body temperature → Overheating warning
• Aerodynamics sensors → CdA measurement during ride