Zone 2 training is simple in theory: keep your effort aerobic. In practice, it's easy to drift over the line — especially on trails where terrain constantly changes your power output. Standard Garmin alerts watch one metric at a time, so they miss the compound effect of power and heart rate both creeping up together. Z2 Training Monitor fixes that.
What It Does
Z2 Training Monitor is a Connect IQ data field for the Garmin Edge 840. It replaces a standard data screen with a four-row layout showing:
- Instant power and 30-second normalized power
- Heart rate and cadence
- Distance
All rendered in high-visibility typography designed for quick glances while riding.
Smart Two-Stage Alerts
The real value is the alerting system. It works in two stages:
- Warning — when a metric approaches its threshold, the tile background inverts (dark on light). This is your first cue to ease off.
- Alert — when a metric exceeds its threshold, the tile flashes at ~0.5 Hz. Unmissable even in peripheral vision.
Dual-Threshold Detection
Here's what makes it different from standard alerts: if both power and heart rate are in the warning zone simultaneously, both tiles flash — even though neither has individually crossed the alert threshold. This catches the "quietly overcooked" scenario where each metric is just below the line but together you're well past sustainable effort.
Bonk Detection
A dedicated bonk alert triggers when power drops below your Z2 floor for 60+ consecutive seconds while heart rate is also declining. That combination — fading power with dropping HR — is the telltale sign of fatigue onset. The alert fires before you're fully bonked, giving you time to fuel up or back off.
Fully Configurable
All eight thresholds are adjustable through Garmin Connect IQ settings:
- Power warning and alert thresholds
- Heart rate warning and alert thresholds
- Normalized power limits
- Bonk threshold and alert delay
No recompiling. Change your thresholds, sync your watch, and ride.
Get It
Clone the repo and sideload to your Edge 840:
git clone https://github.com/midyear66/840-Data-Screen-JD
Check out the full Z2 Training Monitor project page for features and setup details, or browse the source on GitHub.
The SSETCO Team