The “Watts up with Power?” ride is likely the slowest group ride you’ll find on Zwift, because it focuses on learning the basics of power based training while riding together on Zwift. Each ride is streamed to Zwift LIVE by ODZ on Facebook, and focuses on teaching specific principles of power-based training. For viewers that are unable to attend live, the teaching is made available for all to review afterwards.

Here is the summary for May 24th from ride leader Taylor Thomas.


One of the first things riders that are new to training with power recognize is how random their power readings are due to wind, terrain, effort, etc. This randomness impacts average power and causes it to not accurately reflect the physiological “cost” of a ride. In order to quantify and plan for the metabolic demands of a ride we have to look outside of average power. Tools such as Normalized Power (NP), Intensity Factor (IF), Training Stress Score (TSS), and Quadrant Analysis help us to understand ride dynamics and energy expenditure when average power is no longer useful.

1: Normalized Power (NP)

Normalized Power is a rather complex algorithm that takes into account the body’s physiological response to rapid changes in intensity, and recognizes that the response and intensity maintain a curvilinear relationship.

Simplified, NP is your average power had you pedaled smoothly for a given effort. It’s the effort your body “thought” it was doing.

Variability Index (VI) is normalized power divided by average power. VI helps to clarify and understand the metabolic demands of a race or training session.

2: Intensity Factor (IF)

IF is the ratio of NP:Functional Threshold Power (FTP).

IF helps shed light on an individual’s adaptation over time. As athletes repeat the same races, or types of workouts, their IF becomes lower for a given intensity. It takes less energy to produce the same effort, meaning fitness has been gained.

3: Training Stress Score (TSS)

TSS takes both frequency and duration into account, rather than just intensity. TSS helps to accurately reflect the impact of volume on an athlete’s training.

TSS is based on the premise that a 1 hour time trial at FTP is equal to 100 TSS points. Grasping this concept enables athletes and coaches to understand how hard and how stressful a race or a workout was, and how much recovery is needed afterwards.

Due to the fact that TSS incorporates FTP, and FTP is relative for all athletes, riders can work at a level that is right for them regarding duration and intensity.

4: Quadrant Analysis

Quadrant analysis helps to capture the role and importance of neuromuscular power. Neuromuscular function is simply how fast, how strong, and for how long a muscle contracts before it fatigues.

Using quadrants for power file review allows for the singling out of outliers in the power data. It also enables athletes to realize how those outliers may have impacted their overall performance.

By illustrating force in relation to FTP quadrant analysis provides some idea of the amount of slow and fast twitch muscle, and when the body begins to recruit type II fibers during high intensity rides.

Quadrant analysis highlights the distinct difference and relationship between strength and power. Strength is the maximal force generating capacity of a muscle, and power is defined as the rate at which work is being done. Strength rarely limits a riders power.