Critical Power (CP) & W'

"You and your teammate both have an FTP of 280 W.
You can launch a winning sprint on a short climb; they can sustain a higher pace for 10 minutes. On paper, your FTPs match, but your real capabilities are different."

That’s the problem with relying solely on Functional Threshold Power (FTP). While useful, FTP is a single-point estimate that doesn’t capture the full range of an athlete’s performance abilities.

Performance is multi-dimensional. Two athletes with the same FTP can have vastly different sprint power, anaerobic reserves, and fatigue resistance.

FTP tells you about one thing: approximately how much power you can sustain for an hour. While useful, it’s a single-point estimate that can’t fully describe your performance across different durations.

Critical Power offers a more complete and robust alternative:

• Mathematical rigor: Derived from a power–duration relationship using multiple maximal efforts, rather than one test.

• Aerobic + anaerobic insight: CP represents aerobic capacity, while W′ captures your anaerobic reserve.

• Short bursts matter: Racing often requires repeated efforts above threshold, which CP modeling accounts for.

This modeling provides a science-based framework for understanding your performance across different time scales. It focuses on three key metrics:

1. Critical Power (CP)
   The maximum power you can sustain without rapid fatigue. The tipping point between steady, aerobic effort and unsustainable, anaerobic effort.

2. Available Work Capacity (W′)
   Your finite reserve of work above CP, measured in joules. Once W′ is depleted, holding power above CP is no longer possible without recovery.

3. Peak Power
   Your peak 1-second power, an indicator of short-term, high-intensity capacity.

Think of CP as your “sustainable speed limit”, W′ as your “fuel tank” above that limit, and Pmax as your “engine’s peak horsepower”.

Definition: The highest power output you can maintain in a “steady state” without accumulating fatigue that forces you to slow down.

Core Principles:

• Represents aerobic capacity

• Time to Exhaustion (TTE): often corresponds to an effort duration in the range of ~30–40 minutes, but varies by athlete and context.

Example: A rider with CP = 300 W can ride just under this for long stretches, but once power goes above CP, the “timer” starts on their anaerobic reserve.

Definition: The finite amount of work (in joules) you can perform above CP before exhaustion.

Core Principles:

• Once W′ is depleted, you must drop below CP to recover it

• Larger W′ benefits riders in races with repeated surges

• Recovery rate varies per athlete

Example:
Two riders both have CP = 280 W:

• Rider A has W′ = 20 kJ -> great at holding a high pace but fades quickly in repeated attacks

• Rider B has W′ = 30 kJ -> can make more hard surges before cracking

Definition: The theoretical maximum 1-second power you can produce.

Core Principles:

• Reflects neuromuscular and anaerobic capacity

• Important for sprints, starts, and short climbs

• Influenced by muscle fiber type, strength, and technique

Example:
Pmax = 1,200 W → Elite sprinter territory
Pmax = 800 W → Strong endurance rider, but sprint is not their strength

• Multiple durations: We use efforts from sprints to long climbs to shape your power–duration curve

• Continuous updates: Your CP, W′, and Pmax adapt as new best efforts are recorded

• Real-world accuracy: Data from training and racing reflects actual performance conditions

While Vekta estimates CP and W′ from your ride history, a structured CP test can provide a strong baseline:

1. 15-second max sprint: Measures peak anaerobic output (Pmax).

2. 3-minute all-out effort: Captures short-term power for W′ estimation.

3. 12-minute all-out effort: Anchors the CP calculation for sustained power.

These points feed the model, which can then predict your performance for any duration from a few seconds to over an hour.

Script that you can use to build the workout in Vekta:

- 15min warm up
- 3×1 min threshold @ 100–110 rpm - 1 min easy
- 3 min @ tempo
- 5 min recovery
- 15sec max neuromuscular sprint
- 30min aerobic
- 3min anaerobic max effort
- 40min aerobic
- 12min threshold max effort
- 15min cool down 

Performance is not one-dimensional, and your metrics shouldn’t be either.

Vekta’s Critical Power modeling gives you a three-dimensional view of your abilities, combining sustainable power, anaerobic reserve, and peak sprint capacity. This allows for smarter training design, more precise recovery planning, and better race strategy.

• Puchowicz, M. J., Baker, J., & Clarke, D. C. (2020). Development and field validation of an omni-domain power-duration model. Journal of sports sciences, 38(7), 801–813. https://doi.org/10.1080/02640414.2020.1735609

• Leo, P., Spragg, J., Podlogar, T., Lawley, J. S., & Mujika, I. (2022). Power profiling and the power-duration relationship in cycling: a narrative review. European journal of applied physiology, 122(2), 301–316. https://doi.org/10.1007/s00421-021-04833-y

• McGrath, E., Mahony, N., Fleming, N., Raleigh, C., & Donne, B. (2021). Do Critical and Functional Threshold Powers Equate in Highly-Trained Athletes?. International journal of exercise science, 14(4), 45–59. https://doi.org/10.70252/ISYH9512

• Chorley, A., & Lamb, K. L. (2020). The Application of Critical Power, the Work Capacity above Critical Power (W'), and its Reconstitution: A Narrative Review of Current Evidence and Implications for Cycling Training Prescription. Sports (Basel, Switzerland), 8(9), 123. https://doi.org/10.3390/sports8090123

• Morton R. H. (1996). A 3-parameter critical power model. Ergonomics, 39(4), 611–619. https://doi.org/10.1080/00140139608964484

Functional Threshold Power® (FTP®) is a registered trademark owned by TrainingPeaks, LLC.