Effort

Physiological Background

Effort quantifies the metabolic cost of running at different intensities. The relationship between pace and physiological strain is non-linear: running slightly faster requires disproportionately more energy due to increased oxygen consumption, lactate accumulation, and neuromuscular fatigue.

At easy paces (Zone 1-2), the body primarily uses aerobic metabolism, efficiently burning fat and carbohydrates with minimal lactate buildup. As pace increases into threshold and VO2max territories (Zone 4-5), anaerobic contribution rises sharply, glycogen depletion accelerates, and recovery time extends significantly. [4]

The Effort value captures this non-linear relationship. The exact multipliers depend on your personal Lactate Threshold pace configured in Settings, which anchors the entire pace-effort curve to your fitness level.

Formula: Quality Days (Intervals/Tempo)

For workouts with quality distance (intervals, tempo runs), effort is calculated as a weighted average of the hard and easy portions:

Where:

E

Total Effort for the workout

E_h

Hard effort (from interval pace)

E_e

Easy effort (from easy pace, or default Z2 pace)

Q

Quality ratio (quality distance / total distance)

Formula: Easy Days (Pace-based)

For easy runs without quality distance, effort is derived directly from pace using linear interpolation on a personalized reference table:

LT = Lactate Threshold pace (configured in Settings)

Lactate Threshold & Table Generation

The pace-effort relationship is anchored to your Lactate Threshold (LT) pace. LT is the intensity at which lactate begins accumulating faster than it can be cleared - the boundary between sustainable aerobic effort and unsustainable anaerobic work.

At LT pace, effort is defined as 2.85. The table is then generated using exponential functions that model the physiological reality:

Above LT (Faster). Effort increases exponentially. Each second faster requires disproportionately more energy due to rising anaerobic contribution, lactate accumulation, and glycogen depletion.

Below LT (Slower). Effort decreases gradually. The body efficiently uses aerobic metabolism, burning fat with minimal lactate buildup. Recovery between efforts is quick.

Where Δt = difference in seconds from LT pace.

Reading the Effort scale

Effort has no unit: it multiplies distance. Its anchor is the threshold, where a kilometre counts 2.85. From there, every 10 seconds per kilometre slower lowers Effort by about 11%, and every 10 seconds faster raises it by about 19%. At the default paces (threshold 4:00, easy 5:10), a kilometre a minute faster than threshold counts as much as 6.3 easy kilometres.

The ends of the table

The pace-effort table runs from 60 seconds faster than your threshold (never faster than 2:30/km) to 90 seconds slower, in steps of 10 seconds. Between steps Effort is interpolated in a straight line, which sits a hair above the curve. Beyond the ends it keeps the end value: anything more than 90 seconds slower than threshold counts 1.01, anything more than 60 seconds faster counts 8.02. Very slow running and walking still count as load, just never less than that.

Per-Workout LT Storage

Each workout stores its own Lactate Threshold value at the time it was recorded. This ensures that effort calculations remain stable over time - even if you update your LT in settings later, historical workouts will continue using their original LT for calculations.

This is important because:

• Your LT improves with training - a 5:00/km run today represents different effort than the same pace 6 months ago
• Historical trends remain meaningful and comparable
• You can see how your fitness has progressed relative to your LT at each point in time

When viewing a workout's effort tooltip, you'll see which LT was used for the calculation (e.g., "LT: 3:42" or "LT: settings" if no specific LT was stored).

Updating LT for Workouts

In Settings, when you change your Lactate Threshold pace, you have control over which workouts receive the new value:

• Apply from date: Choose a specific date - the new LT will be applied to that date and all future workouts
• Apply to all workouts: Enable this toggle to update your entire training history with the new LT

If you don't specify a date, the new LT applies from today onwards by default.

Use cases:

• New user: Enable "Apply to all workouts" to set your LT across your entire history
• Fitness improvement: Set a new LT from today - past workouts keep their original LT, reflecting your fitness at that time
• Correcting a mistake: Use "Apply from date" to fix LT from when you made an error

Why Lactate Threshold Matters

Different runners have vastly different LT paces based on training history, genetics, and current fitness:

• Elite marathoner: LT around 3:00-3:15/km
• Competitive club runner: LT around 3:30-4:00/km
• Recreational runner: LT around 4:30-5:30/km
• Beginner: LT around 6:00-7:00/km or slower

By setting your personal LT pace in Settings, the effort calculations become meaningful for your fitness level. A 5:00/km pace might be easy recovery for an elite but threshold work for a beginner - the personalized table captures this difference.

Special cases

• A quality session without an interval pace counts its hard part at Effort 3, just faster than threshold.
• Without an easy pace, the easy part of a quality session runs at the default Z2 pace from Settings.
• A planned run without a pace counts at the default Z2 pace, so the weeks ahead already show in Fatigue.
• An Effort you enter yourself replaces the whole calculation, conditions included.
• Rest days have no Effort. Strength work adds to Fatigue through its secondary distance (the Training Fatigue article).

Why pace, not heart rate

Effort comes from pace because pace is known before a run (a planned session has one) and means the same thing every day. Heart rate at a given pace rises with heat, humidity, dehydration, caffeine, poor sleep, illness and simply time on your feet (cardiac drift), so the same session can read very differently. Instead of letting those swings blur the load, the conditions that make a pace harder are counted one by one (the Conditions article).

Heart rate is used where it carries a clear signal: speed per heartbeat on easy runs, and pace for the heart rate on tempo runs, as measures of fitness (the Fitness Scores article).