High Intensity Energy (HIE) – Knowledgebase

High-Intensity Energy (HIE) is a key component of your Fitness Signature, representing the amount of work you can perform above Threshold Power (TP) before fatigue. Measured in kilojoules, HIE determines your capacity for sustained and repeat high-intensity efforts, and is visualized in Xert apps.

Definition

High-Intensity Energy (HIE) is a core component of your Fitness Signature. It represents the amount of work you can perform above Threshold Power (TP) before reaching failure.

In simple terms:

HIE determines how much high-intensity work you can “absorb” before you run out of energy.

Unlike Threshold Power (TP) or Peak Power (PP), which are measured in Watts (a rate of energy production), HIE represents a capacity to perform work and is therefore measured in kilojoules (kJ).

What It Represents

When you ride above TP:

You begin drawing from your HIE
Fatigue accumulates
MPA declines

Building up a larger HIE means:

You can sustain hard efforts longer
You can repeat high-intensity efforts more effectively
Your power-duration curve is “wider” in the 2–10 minute range

HIE does not directly represent fatigue resistance. Instead, it represents how much high-intensity work you can perform before fatigue forces you to stop.

You could also think of HIE as your ability to burn carbohydrates quickly — higher HIE generally means greater high-intensity capability.

How It Looks in Xert

HIE is visually represented as the outer magenta-coloured arc of the Xert rainbow gauge in the Xert EBC app, Magic Buckets, Xert Dashboard (Garmin ConnectIQ data field), & the Remote Player.

Xert Rainbow Gauge.png — **The Xert "Rainbow Gauge".** The outer magenta ring shows your HIE (High-Intensity Energy). It starts full at the beginning of a ride and drains as you push above Threshold Power. Riding below Threshold allows it to refill as your MPA recovers.

At the start of a ride, the arc is full.

As you ride hard above TP → the arc empties (counter-clockwise)
As you ride easy below TP → HIE replenishes and MPA recovers

Note: it's not required to empty your HIE to achieve a Breakthrough. A breakthrough is achieved when your real-time power exceeds your current Fitness Signature's predicted MPA.

How Xert Determines HIE

HIE is derived from real-world maximal efforts via Signature Extraction — not from a fixed test. It is closely linked to Peak Power, and athletes with higher max power typically have greater HIE.

**Peak Power and HIE are closely related.** As Peak Power increases, High-Intensity Energy (HIE) typically increases as well, reflecting a greater capacity to produce and sustain high-intensity efforts.

Larger HIE values widen the power-duration curve at shorter durations, while smaller values narrow it.

HIE and Endurance Balance

While a larger HIE improves short- and mid-duration power, it also implies greater carbohydrate utilization. For ultra-distance or long steady events, a higher Threshold Power (TP) relative to HIE may be more beneficial.

This trade-off is captured in concepts like Lower Threshold Power (LTP) and durability modeling.

Where You’ll See It

In your Profile Header as part of your Fitness Signature
In the Activities Dashboard & Details Pages
In the Xert Rainbow Gauge
In Breakthrough Reports

Common Misunderstandings

HIE is not “anaerobic capacity” in isolation. It reflects work above TP in the context of your full Fitness Signature.
HIE is not the area under your power curve. It influences the curve’s shape.
More HIE is not always necessarily better. The ideal balance depends on your event type and goals.

Related Terms