D6 - Excessive Cold

• When humans are exposed to a cold environment at rest, the body attempts to prevent heat loss, as well as to increase heat production.
• Methods of reducing heat loss during sport and exercise performance:

  The three main methods a person uses to reduce their heat loss are:

  • Vasoconstriction
  • Shivering thermogenesis
  • Non-shivering thermogenesis
• Vasoconstriction:

  • First of all, the  body will decrease the blood supply to the peripheral circulation by vasoconstriction of the peripheral blood vessels.
  • The purpose of this is to keep the blood close to the body core and redirect the blood away from the body’s extremities and skin surface, where it would be cooled down by the environment.
  • In humans, vasoconstriction can reduce heat loss by up to a third.
  • The presence of subcutaneous fat also aids in maintaining the heat of the blood as fat is a very good insulator.
• Shivering thermogenesis:

  • A person will experience a rapid involuntary cycle of contraction and relaxation of skeletal muscles, which is called shivering.
  • The process of shivering can actually increase metabolic rate to four to five times above resting levels.
• Non-shivering thermogenesis:

  • Secondly, a person will experience an increase in their metabolic rate, which is brought about by an increased release of the hormones thyroxine and adrenaline.
  • An increased metabolic rate will generate body heat.
  • This process is called non-shivering thermogenesis.
  • A person can also conserve heat by adding clothing, which is a behavioural mechanism for minimising heat loss.
• Effects of cold on the body during sport and exercise performance:

  • The effect of a cold environment on exercise performance depends largely on the severity of the cold and the type of exercise performed.
  • Exposure to a moderately cold environment may actually have a positive effect on performance, as the cardiovascular system no longer has to divert blood to the periphery for heat loss in addition to supplying the exercising muscles with blood.
  • This results in less stress being placed on the heart than when exercising in the heat. 
• Exposure to a very cold environment may cause frostbite or hypothermia:

  • Hypothermia is defined as a drop in the body’s normal core temperature to 35’C or below. 
  • The condition usually comes on gradually and its severity varies in relation to how low the body core temperature drops - if it drops to 30’C or below, this can lead to cardiac and respiratory failure that is soon followed by death.
• Exposure to a very cold environment may cause frostbite or hypothermia:

  • Frostbite usually occurs in a person’s fingers or toes.
  • It happens when a part of the body becomes extremely cold, significantly reducing blood supply to the area, which results in the body tissue freezing.
  • The ice crystals that form will rupture and destroy the body’s cells.
  • The involved region turns a deep purple or red colour and has blisters, which are usually filled with blood.
  • This tissue will then have to be amputated to prevent infection spreading to other parts of the body.