As temperatures rise during the summer, it is necessary to assess the impact of heat on military orienteering activities in line with JSP 375.

Orienteering is an individual activity, racing the clock, not other people.  Participants range in age from 18 – 60+.  Different length courses are provided at every event and individuals select a course for different personal reasons, some (45 year olds) racing around hard in c 60 minutes, some (young and old) taking a much more leisurely approach to the navigational challenge over 2+ hrs.  Most courses lie within forested areas, although open areas in the full sun will be encountered.

Those competing hard will be voluntarily exercising at a Rate of Perceived Exertion (RPE) of 8, in the upper reaches of Hard Work (“borderline uncomfortable, short of breath, cannot maintain a conversation”).  At the other end of the scale, and results, individuals will be exercising at only moderate intensity (RPE of 6 – “quite comfortable but challenging, breathing heavily, can hold a short conversation”) as their mental effort to navigate takes priority.  Both groups’ performances need to be taken into account when assessing the potential impact of heat on the event.  

Table 1 (below) from JSP 375 Ch 41 indicates the maximum continuous exercise duration that is to be permitted for actual WBGT temperatures and can be used to confirm that Expected Winning Times (under Hard Work) and thus maximum expected running times (under Moderate Work) will not be exceeded by the planned courses.  Generally, for standard military orienteering events a WBGT of below 32°C will be acceptable.

Prior to the event, Organisers are to use the ‘feels like’ temperature forecast from the Met Office ( to assess that the event is going to be safe.  On the day, actual open sun WBGT readings must be checked to confirm that the parameters will not be exceeded on the planned courses.  If necessary, courses can be shortened by amending the course maps.

In periods of known high temperatures, short courses can be planned in advance, including loops that can be run separately with a rest between each short exercise period.

In all circumstances, the Event Risk Assessment must take into account the impact of the expected weather, in particular ameliorating the impact of likely heat stress.  Organisers must know how to recognise and have a plan to treat any symptoms.  The provision of hydration to those affected will take priority over any COVID transmission risks.

AOA Chairman