Cycling intensity: interpreting power, heart rate and training load

Kilometers tell us where the rider arrived, but they do not fully describe the effort needed to get there. Chapter 4 adds tools to monitor intensity, estimate load and evaluate conditioning changes.

Friel's argument is to combine information. Power shows production; heart rate, a response; perceived exertion, the overall experience. Interpretation improves when the athlete knows which question each measure can answer.

Three measures, three functions

The perception scale discussed in this edition is the Borg from 6 to 20. It should not be mixed with 0 to 10 scales. A rating of 14 does not mean the same thing in different systems.

The heart rate is useful in relatively stable efforts, but responds with delay and is influenced by the context. Trying to accelerate a sprint until reaching a certain frequency may lead to overcoming the intended stimulus before the response appears.

Power allows you to observe rapid changes in production. Its value does not eliminate the need to evaluate sensation, conditions and data quality. A usual production that requires abnormal effort deserves attention, even if the meter shows the planned number.

How the edition organizes power zones

Friel uses the reference CP60, the power associated with a 60-minute effort, to present the Allen and Coggan system. As selective examples of the table 4.3, the aerobic zone corresponds to 56–75% of the reference; that of threshold, 91–105%; and that of aerobic capacity, 106–120%.

Editorial example: with CP60 hypothetical 250 W, these intervals would be 140–187.5 W, 227.5–262.5 W and 265–300 W, respectively. The calculations explain the system of the work; they do not establish the reader's personal areas. A power rating should also not be imported to heart rate by the zone number.

Two load calculations presented in the chapter

In the perceived-exertion method, session duration in minutes is multiplied by the session’s average rating. The book’s example uses 60 minutes and an RPE of 14: 60 × 14 = 840 units.

In the simplified heart-rate-zone calculation, time in each zone is multiplied by the zone number, then the results are added. Twenty minutes in zone 1, twenty-five in zone 2 and fifteen in zone 3 give 20 × 1 + 25 × 2 + 15 × 3 = 115.

The results are not interchangeable. They use different scales and assumptions. The value is in following a consistent series within the same method, without treating the sum as a direct measurement of all fatigue.

The TSS appears as another way to relate power, individual reference and duration. The chapter does not offer an ideal weekly load for all people: history and response remain necessary.

Decoupling: does the power continue to cost the same heart effort?

Friel compares the power ratio/heart rate between two halves of a stable aerobic stretch. If production is maintained and frequency rises, this ratio decreases. The book uses 5% as a practical reference to discuss coupling.

Your example starts from 180 W/135 bpm in the first half and 178 W/139 bpm in the second. With the quotients rounded to 1.33 and 1.28, the text reaches approximately 3.8%. With the full values, the drop is close to 4.0%: the difference comes from rounding.

Friel relates stability of this ratio to the development of aerobic endurance and cites two hours coupled as a milestone within its method. It is not a universal physiological diagnosis. Heat, hydration, feeding, terrain and measurement quality also need to enter into interpretation.

Conditioning, fatigue and shape

A training block can develop capacity and increase fatigue at the same time. Before competition, the reduction of load seeks to reduce fatigue while preserving as much as possible what was built. Rest indefinitely also does not produce the same result because conditioning needs maintenance.

The conclusion of the chapter is to use the metrics to relate purpose, dose and response. The number helps when it clarifies a decision; it loses usefulness when it comes to command training without context.

Reference: FRIEL, Joe. The Cyclist’s Training Bible. 4th ed. VeloPress, 2009. Chapter 4, “Intensity”. Pages in the PDF file: 69–101. A selective synthesis written in our own words. Examples labeled as editorial are Enduran-se’s own examples; they are not additional cases reported by the author.

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