Wednesday, 6 August 2014

Nutritional Considerations for Ultra-Endurance Events

Participation in ultra-endurance events has been increasing as cycling, Ironman triathlons and running events are all becoming popular challenges for people to test their physical limits. So when my partner asked for nutrition advice for his 12hr Time Trial event, I thought this could be a good topic to blog about.  I have split the topic into two sections - the first will look at the physical challenges the body faces when being put through ultra-endurance events and the second will look at the nutritional strategies that athletes can use to ensure they achieve their goals.

By definition, an ultra-endurance is an event which last over 6hrs in duration, and the athletes who are successful are those who have the ability to sustain higher absolute speed for a given distance than the other competitors. The three main demands which are placed on the body during this time are:
  • Meeting energy demands
  • Maintaining body temperature
  • Replacing fluid and electrolyte loss
Alongside that, there are increased injury and immune function risk after the event has taken place, and these have to be managed.

Hyperthermia - Maintaining Core Body Temperature

As well as supplying oxygen-rich blood to the body, the heart helps control body temperature by pumping warm blood to the skin where body heat is lost through the evaporation of sweat. During prolonged periods of exercise, heat is produced and increased heat loss needs to occur through sweating to maintain a constant body temperature and body functions.

There are certain factors which can prevent or reduce sweating and heat loss - high humidity can reduce evaporation and dehydration can impair the ability to transfer heat from muscles to the skin. In both situations, the increase in the core body temperature will increase the risk of heat problems. Muscle weakness and disorientation can develop with smaller increases in body temperatures with more serious effects occurring as the body temperature rises. Ways in which an athlete can maintain a constant body temperature will be looked at in the next blog.

Hyponatremia - Fluid and Electrolyte Loss

In recent years, it has been suggested that dehydration in marathon runners is over emphasised and results in some runners suffering with hyponatremia. During exercise, electrolytes, as well as fluids, are also lost in sweat.  Sodium and potassium are the main two electrolytes lost and need to be replaced at some point, depending on the duration and intensity of the event. 

Hyponatremia is the dilution of sodium levels in the blood often caused by the consumption of too much fluid and not replacing the lost electrolytes in sweat. This eventually causes swelling of the brain which can be fatal and has been reported during marathon events in recent years.  This is more common in slower runners who have more time to drink, and are often encouraged to do so. Ways in which athletes can maintain their electrolyte levels will be discussed in the next blog. 

Glycogen Depletion

Carbohydrates are the main energy source during endurance events and provide energy to the muscles at a rate which can sustain a fast pace optimal for performance. Carbohydrates are found as glycogen in the muscles and liver and as blood glucose. As blood glucose is used up, the body converts glycogen into glucose and releases it into the bloodstream to maintain a constant supply of energy. However, glycogen stores are and can only sustain a high work rate for about 60-90mins. If carbohydrates are not replaced at or before the point of glycogen depletion, the body must turn to other energy sources to maintain this work rate. The main alternative source is fats which can sustain exercise for much longer than glycogen, but at a much slower rate. It is much harder to maintain the same pace following the shift in fuel source, a point which is often known as ‘bonking’ or ‘hitting the wall.’ It is important to maintain levels of muscle glycogen and blood glucose for as long as possible. Ways to do this will be discussed in the next blog.

Injury and the Immune System

Due to the length of time an athlete will be performing the same activity and the same action over and over again, there is going to be a considerable amount of stress placed on certain muscles, bones and other soft tissues. Muscle damage and inflammation can remain for several days after completion of the event, and tissues can take much longer than normal to fully repair. Even while the athlete may be celebrating completing the event or achieving their goal, there are a number of things which they can do to aid recovery and prepare for the next training session or event.

As well as the muscle damage, as part of the repair process, cytokines are released from the injured area to promote an influx of white blood cells from the immune system, and these remain elevated following prolonged exercise.  However, there are other markers of immune function which are lower after completing an endurance event, leaving the immune system less able to protect the body from infections. This is why many athletes become ill after endurance events or high intensity training. There are certain practices athletes can do to ensure that both injury and muscle soreness can be reduced and this will be looked at next time.

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