Xert Strain Score Rate (XSSR)

XSS Rate (XSSR or XSS/hr) measures how quickly you accumulate strain during exercise, reflecting workout intensity calculated as the rate of Xert Strain Score (XSS) generated per hour. It varies based on your current power output and fatigue level (MPA), and is used in many of Xert's innovative SMART workouts to create adaptive, curvilinear intervals.

Summary Generated by AI

Definition

XSS Rate (XSSR or XSS/hr) represents how quickly you are accumulating strain. It shows the intensity required to generate a certain amount of XSS in one hour.

XSSR is also used to calculate difficulty score for workouts & activities.

In simple terms, it reflects how demanding your current effort is.

---

What It Shows

A higher XSS Rate means you are training at a higher intensity and accumulating strain more quickly.

XSS rate accounts for:

• How much power you are currently producing, and
• How fatigued you are while producing it (measured via MPA)

This means that the same absolute power output can produce a different XSSR depending on your fatigue level.

For example, holding 350 W when your MPA is near your Peak Power will produce a lower XSSR than holding 350 W when your MPA has dropped to 400 W. As fatigue increases, strain accumulates faster.

XSSR in SMART Workouts

XSSR is commonly used in Xert's SMART workouts to target specific strain levels rather than fixed power numbers. 

Because Xert accounts for fatigue, XSSR-based intervals may have variable power targets:

• As MPA declines, the required power for a given XSSR may decrease.
• As MPA recovers, the required power may increase.

This creates Xert's iconic curvilinear intervals - intervals that curve slightly up or down, instead of remaining perfectly flat.

For example, workouts such as SMART - Closer series of VO2max workouts use this dynamic feature:

Important Note: You will only experience fully dynamic SMART intervals when using the Xert EBC apps. These adaptive power targets cannot be exported to third-party workout platforms.

---

Where You’ll See It

• In SMART workout interval definitions
• In Xert EBC (Android & iOS)
• In the Activity Details MPA chart, beneath the MPA value

---

Related Terms

• Xert Strain Score (XSS)
• MPA (Maximum Power Available)
• SMART Intervals
• Difficulty Score