Introduction

Exercise and Environmental factors are the most common causes of heat related illness. However several other factors can play a part including medical illness (eg. infection), drugs/medication, dehydration, being overweight, lack of acclimatization and the extremities of age. In race situations many environmental factors such as heat, wind, and cloud cover are simply unavoidable if you choose to compete!

 

Preparation/Prevention

1. Acclimatization: Proper acclimatization takes at least 2 weeks and aims to increase the amount of sweating (at a lower temperature) and reduce salt loss from the kidneys/urine. This can be achieved by training under similar conditions to race day. It is important to get some respite from the heat for/during recovery.

2. Avoid Dehydration: Hydration in ultramarathons is a separate topic in itself. Briefly however it is important to note that both dehydration and overhydration (www.overhydration.org) can occur. Avoid ‘Blanket’ drinking/hydration guidelines such as those from the American College of Sports Medicine. Know through experience how much fluid you may need in certain conditions especially in races with minimal support. Many longer Ultramarathons such as the ones at Glasshouse will have ‘weigh stations’ so people can check for weight (loosely fluid) loss or gain. It is quite ‘normal’ to lose a kg or 2 by the end of an ultramarathon. It is important to note that whilst there is a correlation between >3% dehydration and a rise in core body temperature (CBT) the biggest determinant in CBT is effort/workload. Needless to say the ingestion of cold fluids can aid cooling.

3. Adequate clothing: (light, loose fitting, breathable) and sun protection is vital

4. Pre-cooling: some high performance athletes propose pre-cooling before an event eg. cold showers, pools.

5. Accept that sometimes you just need to slow down or even stop and cool down! The biggest determinant of core body temperature is your workload not hydration levels. You simply can’t run as fast in hot/humid conditions.

Minor Heat Syndromes (and Mis-nomers)

Heat syncope (fainting) is due to dilation (enlargement) of the veins and small blood vessels – blood can ‘pool’. This is obviously worsened by dehydration. A similar mechanism explains why runners can ‘faint’ in the post-race hot shower: lack of blood circulation due to the ‘calf pump’ stopping and dilation of veins from heat. Having said this many people who faint post-exercise have normal/expected CBTs. Obviously there can be other more concerning causes of syncope/fainting.

The best avoidance of cramps is adequate training – working muscles way past exhaustion will cause cramps despite CBT, adequate hydration and electrolyte levels.

The role of hydration and electrolyte replacement in cramp prevention is unclear and certainly there is evidence that ‘crampers’ and ‘non-crampers’ have similar hydration and electrolyte levels (http://www.sportsscientists.com/2007/11/muscle-cramps-part-ii.html).

Heat Exhaustion

Often used to describe people with heat syncope (above) but more correctly can describe a pre-heatstroke condition.

People can have a variety of symptoms including dizziness, feeling ‘unwell’, nausea/vomiting, headache, exhaustion, muscular aches/pains.

Keep in mind that many of these symptoms are relatively non-specific. Whilst CBTs can be elevated it is under 40 degrees C (the point at which most people involuntarily ‘stop’) and they have no Central Nervous System (Brain) symptoms (eg. Confusion). They are usually dehydrated and can have varying Sodium levels when tested. Depending on the level of dehydration and presence/absence of nausea runners may require intravenous fluid. The importance for runners is to firstly prevent heat exhaustion but if it occurs to recognize it early and slow down/stop (starts the cooling), check hydration and reassess.

Heat Stroke

Describes someone with a core temperature over 40 deg C who has Central Nervous System (CNS) effects (below) and may/may not still be sweating. The CNS effects include irritability, confusion, hallucinations, unsteadiness and even seizures and coma. This is a serious, life-threatening condition that requires management in hospital with intravenous fluid and electrolyte replacement and cooling. Simple ways of cooling pre-hospital include evaporation (removing clothes, fanning, water spray, keep in shade) and ice-packing (eg. Groin and arm pits). Another method is immersion eg. In a cool pond however this can be cumbersome, lead to shivering and risk drowning.