Cold water afterdrop, rewarming, and cardiac risk: recent peer-reviewed findings contrasted with elite coach protocols
What researchers mean by afterdrop and why it happens
Afterdrop is the continued fall in core temperature that occurs after removal from cold stress during the initial phase of rewarming. Classic laboratory work demonstrated that both conductive cooling of deeper tissues and convective return of cold peripheral blood contribute to the nadir that follows exit from cold water. Experiments by Webb in 1986 and Romet in 1988 showed that afterdrop size is not fixed and depends on prior cooling profile and the specifics of rewarming, including how rapidly skin blood flow is restored. Contemporary consensus reviews emphasize that afterdrop is clinically important mainly when hypothermia is moderate or severe and is typically smaller in mild, well managed cases. These points are consistent with emergency medicine and mountain rescue guidance that frame afterdrop as a risk to be mitigated rather than an inevitability that always becomes dangerous (Webb 1986; Romet 1988; Paal et al., Br J Anaesth 2016).
How large and how long afterdrop is after cold swims
Field work from open water events demonstrates measurable post exit cooling. In the Alcatraz swim study, rectal temperature in participants continued to fall for minutes after leaving 11.7 C water, supporting the practice of supervised observation after finishing a swim. Reviews of accidental hypothermia report that in mild cases managed with insulation and appropriate warming, core afterdrop is often modest rather than dramatic. The practical implication is that organized recovery areas should expect a short delay to the temperature nadir and staff accordingly (Nuckton et al., Am J Emerg Med 2000; Paal et al., 2016).
Laboratory and clinical studies quantify afterdrop over different time windows rather than one fixed duration. In athletes and volunteers cooled to roughly 35 C, the lowest core reading often occurs within the first 10 to 30 minutes post exit, although some protocols monitor up to 45 minutes to capture late nadirs. That monitoring window aligns with event medicine practice in cold venues and with the observation period used in research on open water swimming. Where resources allow, teams extend observation toward the longer end of that range during very cold conditions or following prolonged immersion (Nuckton et al., 2000).
Rewarming methods and rates in recent studies
Active external warming can accelerate recovery and does not uniformly worsen afterdrop when used correctly. A randomized emergency department trial in 1996 found forced air warming rewarms accidental hypothermia patients faster than passive blankets, and a 2005 volunteer trial reported more predictable rewarming with active methods than with passive insulation alone. Observational work in 2019 linked slower in hospital rewarming rate with higher mortality in accidental hypothermia, underscoring the need to avoid prolonged under warming in unstable patients while still matching method to severity. Collectively, these findings support trunk focused heat within an insulating system rather than leaving an athlete to shiver in wet clothing (Steele et al., Ann Emerg Med 1996; Williams et al., Emerg Med J 2005; Watanabe et al., Scand J Trauma Resusc Emerg Med 2019).
Newer studies refine targets and research models. A July 2025 multicenter analysis associated early rewarming rate with survival and neurological outcomes in accidental hypothermia, adding granularity to earlier rate outcome links. A 2025 experimental protocol paper validated a reproducible cold air cooling model with drug suppressed thermogenesis so future trials can compare rewarming methods without shivering variability. Prehospital surveys in 2024 also show wider availability of active external warming equipment, which has practical implications for clubs that partner with local EMS. These data encourage explicit rewarming plans rather than ad hoc decisions at the finish line (Hara et al., Crit Care Med July 2025; Helland et al., Scand J Trauma Resusc Emerg Med 2025; Barsten et al., Scand J Trauma Resusc Emerg Med 2024).
Cardiac risk signals during exit and rewarming
Cold shock on immersion produces an immediate hyperventilatory and adrenergic response that raises drowning risk within the first minute of exposure and can challenge the cardiovascular system. During exit and early rewarming, moderate to severe hypothermia increases the risk of hypotension and arrhythmias, so careful handling and rhythm or blood pressure monitoring are recommended where available. Peer reviewed reviews advise extended pulse checks in severe hypothermia and caution that vasodilation during rewarming can unmask circulatory instability. This risk profile informs why elite events screen for red flags while progressing most athletes through supervised but routine rewarming steps (Tipton, Exp Physiol 2017; Paal et al., 2016).
Swimming induced or immersion pulmonary edema is a separate hazard that sometimes coexists with cold exposure. Recent summaries and position statements describe acute dyspnea, cough, hypoxemia, and occasional hemoptysis during or soon after swimming, with recurrence risk in those with a prior episode. Cold water, high exertion, hypertension, tight wetsuits, and rapid intensity changes are among factors discussed as contributors. Athletes with symptoms should be removed from the water, kept warm, and medically evaluated, and those with prior episodes merit pre race screening and conservative pacing plans (Moon, Chest Nov 2023; Banham et al., Diving Hyperb Med 2024; Barouch et al., JACC Case Reports 2022; Hageman, StatPearls 2023).
What elite coaches and lifesaving teams actually do on deck
Practical steps used by elite squads and event medics mirror core elements of wilderness and lifesaving guidance. Wet layers are removed promptly, the trunk is insulated first, wind is blocked, and warm sweet drinks are provided when the athlete is fully alert and not hypothermic. Many programs stage heated tents, insulated jackets or changing robes, hats, and warm footwear to reduce skin heat loss. A 2024 study in BMJ Open Sport and Exercise Medicine found that wearing a long post swim jacket improved thermal status and comfort after cold water immersion, lending objective support to this common practice. Athletes are typically observed through the first 20 to 45 minutes to capture the expected timing of any afterdrop (Read et al., BMJ Open SEM 2024; Nuckton et al., 2000; RNLI safety pages 2015 and 2024 summaries).
Coaches also plan the training cycle around acclimatization, conservative exposure in very cold water, and clear handover criteria to medical teams when warning signs appear. Handling remains gentle for obviously hypothermic or unstable athletes, consistent with medical cautions about arrhythmia risk in profound hypothermia. Where equipment permits, trunk focused active warming is added inside an insulating package rather than relying on shivering alone. These steps operationalize guideline principles in time constrained, outdoor environments (Wilderness Medical Society guidelines update 2019; Paal et al., 2016).
Where protocols and evidence diverge
Older teaching sometimes warned that any external heat would worsen afterdrop, but modern data support targeted heat to the torso within insulation when the athlete is alert and monitored. Guidelines caution against hot showers or baths for patients with hypothermia because rapid peripheral vasodilation can precipitate shock, yet that prohibition should not be generalized to all mildly cold but normothermic swimmers changing in a supervised setting. Evidence from randomized trials and reviews shows forced air and other active warming measures can be used safely when matched to severity, and a 2025 trial indicates that low to moderate intensity movement during rewarming did not exacerbate afterdrop in healthy participants. The resulting picture is nuanced rather than absolutist and supports graded rewarming scaled to symptoms, vital signs, and resources (Steele et al., 1996; Williams et al., 2005; WMS 2019; Hara et al., 2025; Peterson et al., Mil Med 2025).
Myths vs facts grounded in citations
Myth: Hot showers are dangerous for everyone after a cold swim
Fact: Hot showers are not universally dangerous for every swimmer, but they are not recommended for patients with hypothermia because rapid peripheral vasodilation can precipitate cardiovascular instability. For alert athletes with mild cold stress but without hypothermia, coaches sometimes allow brief, supervised warm water after trunk first insulation and screening, and no high quality evidence shows that careful use in this specific scenario routinely causes harm. The key is severity assessment, monitoring, and avoiding unsupervised hot baths or showers when hypothermia is suspected. This distinction appears in wilderness and lifesaving guidance and aligns with emergency medicine reviews that contextualize afterdrop risk (WMS 2019 summary; RNLI guidance 2015; Paal et al., 2016).
Myth: Any movement during rewarming will trigger fatal arrhythmias
Fact: Gentle handling is essential in moderate to severe hypothermia because the myocardium can be irritable, but ambulant, mildly cold athletes are commonly walked to shelter in organized events. Reviews specify prolonged pulse checks and careful positioning for severe cases, not a blanket ban on all movement. A 2025 study in healthy participants found that moderate intensity exercise during rewarming did not worsen afterdrop compared with low intensity movement. The practical takeaway is graded, symptom led movement with a low threshold for stretcher transfer when instability is suspected (Paal et al., 2016; Peterson et al., Mil Med 2025).
Myth: Afterdrop is always large and unavoidable
Fact: Afterdrop magnitude depends on how cold the person became, how rewarming is done, and individual factors. Classic and modern studies show that in many mild cases, core afterdrop is small when insulation, wind protection, and trunk focused heat are applied promptly. Field data from open water events confirm that the post exit nadir exists but can be managed with staged recovery and observation. Larger afterdrops occur with severe cooling, prolonged exposure, minimal insulation, or in very lean athletes, which argues for conservative exposure and structured recovery on deck (Webb 1986; Nuckton et al., 2000; Paal et al., 2016).
A pragmatic, evidence aligned checklist for clubs
Remove wet layers quickly, insulate the trunk first, block wind, and provide warm sweet fluids only to fully alert athletes. Add trunk focused active warming within insulation where equipment permits and escalate early for those with confusion, hypotension, wheeze, or persistent cough suggestive of immersion pulmonary edema. Observe through the first 20 to 45 minutes to catch the expected timing of any afterdrop and document rewarming responses to refine protocols over the season. Build preseason acclimatization plans, screen athletes with prior immersion pulmonary edema, and coordinate with EMS on handover criteria and rewarming rate targets supported by recent studies (WMS 2019; Read et al., 2024; Steele et al., 1996; Watanabe et al., 2019; Banham et al., 2024).
Selected peer reviewed sources with publication dates
Webb, J Appl Physiol, 1986; Romet, J Appl Physiol, 1988; Nuckton et al., Am J Emerg Med, 2000; Paal et al., Br J Anaesth, 2016; Tipton, Exp Physiol, 2017; Dow et al., Wilderness Environ Med, 2019; Watanabe et al., Scand J Trauma Resusc Emerg Med, 2019; Williams et al., Emerg Med J, 2005; Steele et al., Ann Emerg Med, 1996; Hara et al., Crit Care Med, July 2025; Helland et al., Scand J Trauma Resusc Emerg Med, 2025; Read et al., BMJ Open Sport Exerc Med, 2024; Banham et al., Diving Hyperb Med joint position statement on immersion pulmonary oedema, 2024; Hageman, StatPearls IPE chapter, 2023; Peterson et al., Mil Med, 2025.