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.

Training and competing in the Heat - what can you do to help?

As Britain enjoys one of the warmest summers I remember, I was asked the question, 'how does heat effect your training and what can you do to help your training and racing in the heat?'

One of the main effects of heat is an increase in perceived effort and the decreased motivation to go out and perform. Training or competing seem much harder and therefore times can suffer either in training or competition.

But what are the physiological effects of the heat?

The main ones are:

• Dehydration
• Increased Heart Rate
• Reduced Blood Flow (and subsequently oxygen) to the working muscles.

Dehydration - I have already covered dehydration and why and what we should drink in a previous posts. But why does the risk of dehydration increase as the environmental temperature increases? 

Thermoregulation is the body's way of maintaining a consistent internal temperature, vital for bodily functions which keep us alive.  One of the ways that the body looses heat is via sweating, with the rate of evaporation linked to how well the body is cooled and the atmospheric humidity. When humidity is low evaporation increases, when humidity is high the rate of evaporation decreases and less cooling occurs.

Sweating leads to fluid loss, and dehydration occurs from the inadequate replacement of fluids. It is thought that every 2% loss of body weight through sweat can lead to about a 4-6% decrease in performance.  If this fluid is not replaced an athletes blood volume decreases, less blood returns to the heart and less oxygen rich blood reaches the muscles. You produce less energy aerobically and you run slower for a given effort level.  As it gets hotter, this effect is increased. The more heat that needs to be dissipated, the greater the proportion of blood diverted to the skin.

What can you do?

Training in itself provides some adaptation to the heat. It increases the total plasma volume which is why the fittest athletes (and likely those with the highest plasma volume) typically adapt more easily to the heat and perform better.

Regular training in the heat can result in it becoming easier to maintain a faster pace and reduce perceived exertion by increasing blood plasma volume, increasing sweat rate, reducing heart rate at a given pace and speeding up the onset of sweating. These adaptations make it easier to perform in the heat and can be noticed after only a week or two of heat exposure.  Training in the same temperatures as you would be competing at can have a massive positive affect.

Heat also effects intensity. Some athletes may benefit from moving training focus away from a certain time goals to running at an equivalent efforts. Sessions could be moved away from a track, to make it easier to pay attention to feel and perceived exertion rather than split times

What can you do for racing in the heat?

• Adjust preparation - increase the layers in training to replicate warmer temperatures when you race. I have known triathletes preparing for Kona do bike sets next to a radiator with additional layers to prepare themselves for the heat they could expect when they race
• Increase fluid and electrolyte intake in the days prior to racing to make sure you are hydrated
• Stay as cool as possible before the race (sponges)
• Perhaps have a shorter warm up
• Pay more attention to perceived effort rather than race splits 

The other bit to recognise is the signs and symptoms of heat stroke:

• Headache
• Dizziness and light headedness
• Lack of sweating despite exercising in the heat
• Dry Skin
• Muscle weakness or cramps
• Nausea and Vomiting

If you do train in the heat and experience any of the above, try to get in a cool environment and drink plenty of water.

What should you drink?

Continuing the blog on hydration, I thought I would look at the different types of drinks and when they may be useful in different situations.

When training or exercising, athletes need to consider the intensity of their session, the duration of the activity and the environmental conditions, and how these may affect their sweat rates. For example, if their session is a light aerobic session in a cool environment, their sweat rates and energy needs are going to be lower than if they were training at a high intensity on a hot summer's day.

Some sports have very little change in environmental conditions such as swimming or indoor sports, whereas some sports involve varying conditions and therefore athletes need to understand how their body responds to different conditions and be prepared in order to ensure they maximise their training and recovery.

There are three different types of drinks, based on the solute concentration and their osmotic pressure. 

Hypotonic - generally contains less than 4g of carbohydrates per 100ml. It provides little energy, but will be taken up by the body quickly, and therefore ideal for recreational sports or shorter or less strenuous exertion.  Examples include:

• Water
• WeakCordial 

Hypertonic - this type of drink generally has more than 8g of carbohydrates per 100ml and greater osmotic pressure than bodily fluids. Its main aim is to supply energy and the fluid is taken up more slowly than water. Ideal use is 30-60 mins before exercise and immediately after sports.  They are also useful for athletes who find they need a bit more energy.

• Milkshakes
• Smoothies
• Concentrated Fruit Juices 

Isotonic - this type of drink contains between 4-8g of carbohydrate per 100ml and has about the same osmotic pressure as bodily fluids. An Isotonic drink is taken up by the body about as quickly as water and they are intended to help hydration and provide energy.

• Sports Drinks
• Squash

Also considering the different times athletes may need to choose different drinks. 

Before Exercise - The main aims are to ensure the athlete is hydrated before exercise, as athletes will be able to meet energy needs through solid foods, therefore a hypotonic drink such as squash or water will be adequate. If it is prior to competition, and athletes struggle to eat, then isotonic drinks can help meet energy requirements while making sure athletes are hydrated. 

During - This will be dependent on the training programme. Many athletes will be fine with a hypotonic sports drink replacing fluid loss and athletes should choose drinks which are palatable to encourage consumption. However, if the training session or competition is high intensity and longer than 90 min, some athletes may need to include some energy, therefore an isotonic drink will meet an athletes needs. Other ways to meet this need if athletes prefer to drink water is to take a high carbohydrate snack to have alongside training which can be consumed at an appropriate interval. 

After - The session type and environment conditions will influence the athlete's choice of drink. After a  high intensity session, it is going to be important to replace energy and fluid needs. If an athlete is able to eat immediately after a session, a high carbohydrate snack alongside squash or water should be sufficient to meet their needs. However, if an athlete struggles to consume any food following a training session, a hypertonic drink which is high in carbohydrate will be able to support this. This is why many athletes now choose to drink milk or milkshakes after a training session. Athletes should be aware of when their sweat rates are high and make sure they adequately replace their fluid intake in the hour after a training session.

Athletes can monitor their hydration by comparing to a pee chart, a simple indication of their hydration status, with the idea to be on the paler side of the chart.  One of the main things is to to be happy and comfortable with what you drink. It could be the best drink which will help performance, but if the athlete doesn't like the taste they probably won't consume as much as is needed. 

Are you drinking enough?

With one of the challenges of the World Cup being identified as the heat and hydration of the players, the recent warm weather we have enjoyed and the fact that I forgot my drinks bottle at my last training session, I thought it would be useful to include a topic on hydration.

Dehydration is caused by an athlete not sufficiently replacing fluid losses during exercise which is caused by sweating in order to maintain a constant core temperature and the body not over heating through exercise. Therefore sweat rates are naturally higher when athletes are exercising at higher temperatures. 

The main impairments are as follows, with the magnitude increasing as the level of dehydration increases: 

• Increased heart rate
• Impaired heat regulation- leading to the risk of heat stroke
• Exercise feels harder than normal
• Reduced mental function
• Reduced skill level
• Stomach upset

To prevent any of the above from occurring, athletes need to match their fluid losses with the amount of fluid they are drinking. The easiest way that athletes can do this is by taking their body weight before and after exercise, adding the amount of fluid they have taken in during the session and then this will give the total loss for the session. Once and athlete begins to understand their sweat losses, athletes can be prepared, taking into account the varying environmental conditions they may be training in.

To ensure that athletes maximise their rehydration, the most important thing is that drinks are palatable and are non-carbonated. The amount of carbohydrate and electrolytes will be linked to their palatability, the type of training and the environment the athlete is training in.