A Smaller Energy Reserve at Rest
Baseline capacity is reduced compared to healthy individuals.
- ~100%: Resting reserve capacity (Scaled to patient baseline)
- Lower ceiling: Healthy comparison (Reduced relative to norms)
- 55%: Crash threshold (Individualized draw-down limit)
- Non-linear: Recovery pattern (Unlike normal fatigue)
A finite, reduced starting reserve
Reserve capacity sits below typical healthy levels at rest.
Why baseline matters for PEM
Small reserve means routine tasks approach the threshold sooner.
Exertion Begins Drawing Down the Reserve
Physical or cognitive activity depletes the limited energy pool.
- Physical + cognitive: Exertion types (Both draw the same pool)
- Intensity-linked: Draw-down rate (Scales with activity level)
- ~32%: Mild activity draw (Below typical threshold)
- ~94%: Severe activity draw (Well past threshold)
Shared pool for mind and body
Mental and physical exertion draw from one shared reserve.
No warning during the activity itself
Symptoms rarely appear while the exertion is happening.
Exertion Exceeds the Individual Threshold
Crossing the crash line triggers a disproportionate response.
- 55%: Threshold line (Individualized crash point)
- Non-recoverable: Overdraw effect (Unlike normal tiredness)
- Often small: Trigger size needed (Even routine tasks qualify)
- Disproportionate: Response type (Not matched to effort)
The crash line is not a soft limit
Past threshold, the body responds far out of proportion.
Thresholds vary by person and by day
The line shifts with illness severity, sleep, and stress.
Symptoms Arrive 12–48 Hours Later
A second wave rises well after the triggering activity ends.
- 12–48 h: Typical delay window (Peak often near 24–30h)
- High: Misattribution risk (Trigger easily overlooked)
- Gradual rise: Wave shape (Not a sudden spike)
- Fatigue, pain, cognition: Symptom domains (Multi-system worsening)
A second, offset symptom wave
The delay separates cause from effect in patients' experience.
Why the delay complicates pacing
Feeling fine today does not predict how tomorrow feels.
A Prolonged Crash, Then Partial Recovery
Amplified symptoms persist for days to weeks before easing.
- Days–weeks: Crash duration (Highly variable by severity)
- Disproportionate: Symptom amplification (Exceeds triggering activity)
- Slow, partial: Recovery trajectory (Often below prior baseline)
- Repeat crashes: Cumulative risk (Can lower baseline further)
Recovery rarely returns to full baseline
Each crash can leave a lower functional floor behind.
Pacing as the primary mitigation strategy
Staying under threshold is the main protective approach.
Placeholder: pacing within the energy envelope reduces crash frequency.