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Training Load

The Training Load feature provides advanced training metrics computed from your Garmin activity data. These metrics help you understand your fitness level, monitor fatigue, and optimize your training to avoid injury.

Overview

Training Load metrics are displayed in two places:

  • Dashboard — A widget showing 9 key metrics with color-coded values
  • Charts — A Performance Management Chart (PMC) showing trends over 90 days

All metrics are computed from your cached Garmin data (heart rate, duration, distance). No external service is needed.

Data Requirements

Metrics improve with more data. At least 14 days of activity history is recommended. With less data, a warning banner will appear.

Metrics Explained

TRIMP Today

Training Impulse — measures the total training stress of today's workouts.

  • Formula: Duration (min) x Heart Rate Intensity x Exponential Factor
  • Uses the Banister TRIMP formula with gender-specific coefficients
  • Green: < 150 (moderate session)
  • Orange: 150–300 (hard session)
  • Red: > 300 (very hard session)

Fitness (CTL)

Chronic Training Load — your 42-day exponentially weighted average training load.

  • Represents your overall aerobic fitness level
  • Built up gradually over weeks of consistent training
  • Green: >= 60 (well-trained)
  • Orange: 30–59 (moderate fitness)
  • Red: < 30 (low fitness base)

Fatigue (ATL)

Acute Training Load — your 7-day exponentially weighted average training load.

  • Represents how much stress you've accumulated recently
  • Rises quickly with hard training, falls quickly with rest
  • Green: < 60 (manageable fatigue)
  • Orange: 60–100 (moderate fatigue)
  • Red: > 100 (high fatigue — consider recovery)

Form (TSB)

Training Stress Balance — the difference between Fitness (CTL) and Fatigue (ATL).

  • Formula: TSB = CTL - ATL
  • Positive values mean you're fresh and rested
  • Negative values mean you're carrying fatigue
  • Green: -10 to +15 (optimal training zone)
  • Orange: +15 to +25 (losing fitness) or -10 to -25 (accumulating fatigue)
  • Red: < -25 (risk of overtraining)

A:C Ratio

Acute-to-Chronic Workload Ratio — compares recent load to long-term load.

  • Formula: ATL / CTL
  • The most important injury prevention metric
  • Green: 0.8–1.3 (sweet spot — optimal adaptation)
  • Orange: < 0.8 (undertraining) or 1.3–1.5 (elevated risk)
  • Red: > 1.5 (danger zone — high injury risk)

Monotony

Training Monotony — measures how varied your training is over the last 7 days.

  • Formula: Mean daily load / Standard deviation of daily load
  • Low monotony means good variation between hard and easy days
  • Green: < 1.5 (good variety)
  • Orange: 1.5–2.0 (moderate — consider more variation)
  • Red: > 2.0 (too monotonous — increases injury and illness risk)

Strain

Training Strain — the combined effect of training volume and monotony.

  • Formula: Weekly total load x Monotony
  • High strain with high monotony is a warning sign
  • Green: < 2000 (manageable)
  • Orange: 2000–4000 (moderate strain)
  • Red: > 4000 (high strain — monitor closely)

VO2max

Maximum oxygen uptake — extracted directly from your Garmin device.

  • The gold standard measure of cardiovascular fitness
  • Higher values indicate better aerobic capacity
  • Green: >= 50 (excellent)
  • Orange: 40–49 (good)
  • Red: < 40 (below average for active athletes)

VO2max Source

This value comes from your Garmin device's built-in VO2max estimation, not a separate calculation.

Marathon Shape

Marathon readiness percentage — how prepared you are for a marathon.

  • 70% weight: Average weekly running mileage over the last 26 weeks (target: 60 km/week)
  • 30% weight: Weeks with a long run (>= 13 km) in the last 10 weeks
  • Green: >= 70% (well prepared)
  • Orange: 40–69% (building up)
  • Red: < 40% (early preparation phase)

Performance Management Chart (PMC)

The PMC is available in the Charts view by clicking the PMC button. It shows three lines over 90 days:

  • CTL (Fitness) — Green line showing your chronic training load trend
  • ATL (Fatigue) — Orange line showing your acute training load trend
  • TSB (Form) — Purple filled area showing your stress balance

The PMC helps you visualize how your fitness, fatigue, and form evolve over time. Ideally:

  • CTL should trend upward gradually
  • ATL should spike during hard training blocks and drop during recovery
  • TSB should oscillate between slightly negative (training) and positive (recovery/taper)

Settings

You can configure physiological parameters in Settings > Training Load Settings:

Setting Description Default
Gender Affects the TRIMP coefficient (male: 1.92, female: 1.67) Male
Age Used for max HR fallback calculation (220 - age) Auto-detect
Max Heart Rate Your maximum heart rate in bpm Auto-detected from activities
Resting Heart Rate Your resting heart rate in bpm Auto-detected from daily data

Auto-Detection

Leave fields blank to use auto-detection. Max HR is detected from the highest recorded HR across all activities. Resting HR is the median of your daily resting HR values.

Color Coding

All metric values are color-coded based on their training significance:

  • Green — Good / healthy range
  • Orange — Caution / moderate concern
  • Red — Warning / action needed

Hover over the (i) icon next to each metric label for a quick explanation.

Scientific Background

The training load calculations are based on established sports science models:

  • Banister TRIMP — Banister et al. (1991), Training Impulse model
  • EWMA for ATL/CTL — Exponentially Weighted Moving Average, used by TrainingPeaks
  • PMC Model — Performance Management Chart, popularized by TrainingPeaks
  • A:C Ratio — Gabbett (2016), Acute:Chronic Workload Ratio for injury prevention
  • Marathon Shape — Inspired by the Runalyze marathon shape heuristic