Crash Triggers & Pacing (Non-Drug)

8. Crash triggers & pacing (non-drug)

What is a crash (PEM)?

The core phenomenon behind every "crash" is post-exertional malaise (PEM) – a delayed, disproportionate worsening after exertion. PEM is the cardinal symptom of ME/CFS and is also frequently observed in Long COVID [1][7]. In POTS, PEM is not a defining feature, but it can occur, especially when ME/CFS or Long COVID are present as a comorbidity. According to the NICE guideline NG206, PEM is characterised by three features: the worsening of symptoms (1) often sets in delayed by hours to days, (2) is disproportionate to the triggering activity and (3) has a prolonged recovery time [1]. An NIH study describes a typical onset 24–48 hours after exertion, a duration of 24 hours up to several weeks, and core symptoms such as exhaustion, brain fog, neuromuscular complaints, head/throat pain, pain, nausea and sensitivity to light and noise [5][11].

Recognising triggers

Crashes do not arise only from exercise. Triggers are varied [7][11]:

• Physical: also everyday activities (showering, cooking, shopping)
• Cognitive: reading, conversations, screen work
• Emotional: stress – including positive emotions
• Orthostatic: prolonged sitting or standing [15]
• Sensory: light, noise
• Others: infections, heat, hormonal fluctuations/menstruation, travel, vaccine reactions

A symptom and activity diary over 1–2 weeks helps to determine individual triggers and one's personal exertion limit [4][8].

Important safety note: not every worsening is automatically a PEM crash. New, sudden or unusually severe symptoms – e.g. chest pain, shortness of breath, fainting/syncope, neurological deficits, persistent fever – should not be hastily dismissed as PEM but assessed by a doctor, so that other treatable causes are not overlooked.

Pacing: the central strategy

Pacing means staying within one's individual exertion limit ("energy envelope") – through conscious activity and energy management [6][10]. Important: pacing is expressly not an increase in activity but symptom-contingent – activity is adapted to current capacity, with the aim of avoiding a crash [1][6]. As a rule of thumb, it is widely recommended to do only about 50 % of what you feel capable of [6]. Established helper models are the spoon theory (dividing the limited daily energy into "spoons") and the 3-P rule (prioritise, plan, pace) [10]. Early warning signs such as increased brain fog, head/throat pain or a weak voice can signal an approaching crash and are a reason for an immediate break [11].

Heart-rate-based pacing

One possible objective anchor is heart rate. The Workwell Foundation uses, as a conservative estimate of the ventilatory/anaerobic threshold, resting heart rate + 15 bpm (example: resting rate 60 → threshold 75 bpm) [2]. Practical rules [2]:

Putting this number in context. It comes from educational material by the Workwell Foundation and carries no study reference there; a literature search for it returns nothing. The only peer-reviewed threshold in this field is a different one — 10 % below the heart rate determined by cardiopulmonary exercise testing (Davenport et al., Physical Therapy 2010). And to date there is no controlled study showing that any heart-rate limit prevents a crash. None of this argues against the rule: the laboratory-free age formulas were checked in 90 people and deviated from the measured threshold by −28 to +23 beats (van Campen, Rowe and Visser 2020), so they are demonstrably worse. It only means that “resting heart rate + 15” is a sensible starting value and not a finding — to be adjusted to your own symptoms and your own experience. In full on our technical page.

• Measure the resting heart rate over several (e.g. 7) days in the morning before getting up and average it; a morning deviation of about +10 bpm can indicate overexertion.
• Exceed the estimated threshold only briefly if at all (on the order of a few minutes).
• Use a heart-rate monitor with an alarm; on the alarm, stop and rest until the heart rate returns close to the resting rate.

The threshold formula is a rough, individual estimate and does not replace a spirometrically determined (CPET) threshold. According to the Workwell Foundation, more than 85 % of those affected show a blunted heart-rate response to exertion (chronotropic incompetence); age-based maximum heart-rate formulas (220 minus age) are therefore not suitable [2].

Why not GET?

Graded exercise increase (graded exercise therapy, GET) is explicitly no longer recommended by NICE NG206 – no programmes based on fixed, stepwise increases in physical activity [1]. Reasoning: GET increases the load in a fixed/time-based way regardless of symptoms and can in doing so exceed the (in ME/CFS low) anaerobic threshold, which can trigger PEM and cause harm [3]. Objectively, the two-day CPET supports a bioenergetic disturbance: unlike healthy people, many of those affected cannot reproduce their performance on the second day – the VO2 at the ventilatory threshold fell in studies by about −10.8 % (Snell 2013) or −15.8 % (Keller 2014), and the wattage at the threshold by about −11 % (Snell 2013) to −21 % (Keller 2014) [9][12]. These findings come from small samples; the effect sizes vary between studies. According to reports, continued exceeding of the exertion limit (contrary to pacing) increases the duration and severity of crashes [6].

Additional non-drug measures

• Radical/aggressive rest: consistent, proactive resting – also before and after exertion, in a dark, low-stimulus environment. According to an NIH survey, complete rest is the most frequently named recovery method and is used preventively, not only after exhaustion has set in [5].
• Orthostatic intolerance/POTS (often comorbid): compression garments, avoid long standing and heat, and if needed lying/sitting rather than upright activities [15]. Increased fluid and salt intake is often recommended in POTS, but is only sensible after consulting a doctor and is contraindicated in high blood pressure, heart or kidney disease. Important distinction: the warning against GET above applies specifically to ME/CFS, i.e. to exertion involving PEM. In POTS without PEM, a slowly and guidedly increased exercise programme started reclined/lying down – such as the Dallas or Levine protocol – is an established and explicitly recommended part of treatment [5]. This matches an official clarification by Fedorowski and colleagues (Nature Reviews Cardiology, 2024) of their own earlier review, which is often cited as support for generic training programmes: they explicitly meant a supervised, individualised aerobic reconditioning programme for POTS, not a blanket training scheme – and note that a more cautious approach is needed where PEM is present, since a standard programme could cause harm [16]. When ME/CFS or Long COVID with PEM is also present, PEM caution takes priority; individual exercise progression then belongs in medically/therapeutically guided hands.
• Breathing/ANS techniques: slow breathing (about 6 breaths/minute) and HRV biofeedback can favourably influence heart rate variability and vagal activity. The evidence so far comes from pilot/feasibility studies in Long COVID (e.g. HEARTLOC) and is not yet secured by large RCTs – so this is a plausible hypothesis, not an established benefit [13][14]. In ME/CFS it should also be noted that even seemingly light "exercises" can be a strain.
• Sleep: characteristically unrefreshing in ME/CFS; sleep hygiene is recommended but does not cure the disease [1].
• Nutrition: no specific diet is evidence-based curative; recommended are sufficient hydration, if needed more salt in POTS (see contraindications above) and a balanced diet against accompanying symptoms [15].

Note on medications/supplements: this section deliberately deals with non-drug strategies. For all substances (e.g. salt tablets in POTS): clarify mechanism of action, strength of evidence and off-label/OTC status individually with the treating doctor. No promise of a cure – the measures named aim at symptom and exertion management, not at cure. This does not replace individual medical advice.

Leading guidelines and institutions (NICE NG206, CDC as well as relevant AWMF guidelines – in the German context above all the guidelines on Long/Post-COVID or "fatigue"; a standalone AWMF ME/CFS guideline does not currently exist) agree at their core: actively recognise PEM, use pacing as the core strategy, log exertion and avoid the push-crash (boom-bust) cycle [1][4][8].