Wehrmedizinische Monatsschrift

Military training in cold or moderate climates: The often unknown or underestimated hazards of exertional heat illness

Karl Jochen Glitz a, Ulrich Rohde a, Kai Nestler b, Emanuel Vits a, Claus Piekarski c, Dieter Leyk a, d

a Bundeswehr Institute for Preventive Medicine – Division A -Health and Performance Promotion-, Germany

b Bundeswehr Central Hospital, Germany

c University of Cologne – Institute & Policlinic for Occupational Health, Environmental Medicine & Prevention Research, Germany

d German Sport University Cologne – Research Group Epidemiology of Performance, Institute for Physiology and Anatomy, Germany



It is well -known that soldiers deployed in hot climates are at higher risk of suffering from both heat stress and exertional heat illness (EHI). Substantially less attention has been paid to potential heat stress/ EHI during physically demanding training in moderate or even cold climates (figure 1). This poster focusses on the presence and the influence factors of heat stress/ EHI in cold or moderate climates.

Fig. 1: Physically demandig military training in cold or moderate climates


A selective literature research was conducted in PubMed for heat illness associated with the topics climate, mild climate, moderate climate, cold climate, cold weather, and cold. In addition, current guidelines, guidance sets and expert recommendations were considered.


Only little information on heat stress/ EHI in cold or moderate climates could be identified including a note from UK: In the British Army 66.5 % of 361 reported cases of EHI (2007 - 2014) occurred in temperate climates or during colder months [3].

Body heat balance mainly depends on the conversant influence factors climate, thermal insulation and workload (figure 2).

According to this prediction (figure 2) soldiers´ physical performanc e combined with prolonged high workload (>230 W/m2 ) will result in a remarkable thermal burden at moderate ambient temperatures due to the restricted heat exchange by high thermal insulation of protective clothing and equipment (>1.5 clo, e.g., combat suit and body armour).

Fig. 2: Predicted thermal insulation (clo) to maintain a compensated body heat balance at different ambient temperatures (-50 to + 10 °C) and workloads (resting to very high, W/m2; adapted from Rintamäki and Rissanen [2])

Even in cold climates, a balanced ratio of the influence factors is often impaired. This may be fatal since no protecting acclimatization can be developed by ambient climate exposure. Hence, compensation of heat stress is aggravated:


With the experience of heat stress in the cold and the intense physical performance demands, the risk of EHI in moderate climates may be frequently underreported and underestimated. This is contributed by the appropriate guidelines and guidance sets, which were initially intended for acclimatized persons in warmer climates (e.g.,[1]: ≥ 25.6 °C WBGT (table 1)).

Tab. 1: Fluid replacement and work/ rest guide [1]
Note: These recommendations are only valid for warm and hot conditions (≥ 25.6 °C WBGT) and do not include cold or moderate climates.

There is a necessity to enlarge the climatic range of these recommendations (e.g., [4]: 20 °C WBGT) to prevent an excessive body heat storage in cold or moderate climates under specific military challenges.

Operational Relevance

Awareness for heat stress and exertional heat illness (EHI) beyond hot climates should be promoted in instructors and military leaders: Before performing hard physical work even in cold or moderate climates a risk assessment is required with the objective of a flexible adjustment of workload and thermal insulation of clothing. This applies particularly to the military training of inexperienced recruits with a lower physical fitness level.


  1. Federal Ministry of Health: Inability to work: cases and days after diagnoses. Results of the disease type statistics of the statutory health insurance, years 2012-2016., last access 14 June 2020 mehr lesen
  2. Robert Koch-Institute/Destatis: Health reporting. Interactive table deaths, death rates (since 1980). , last access 14 June 2020 mehr lesen
  3. World Health Organization: Fact sheets on sustainable development goals: health targets: Noncommunicable Diseases. WHO Europe, 2017; , last access 14 June 2020. mehr lesen


For the authors

Dr. Karl-Jochen Glitz

Bundeswehr Institute for Preventive Medicine

Division A -Health and Performance Promotion-

Andernacher Str. 100, D-56070 Koblenz

E-Mail: karljochenglitz@bundeswehr.org

Posterpresentation at the ICSSP 2020 in Quebec, ­Canada (11 to 14 February 2020)