Part 1: Nutrition.

Macronutrients and micronutrients.

A major source of the world population’s energy is provided by carbohydrates. This is a macronutrient, along with fat and protein. The function of carbohydrate, once digested, is to be stored in the muscles and liver as many linked molecules of glucose, called glycogen. The carbohydrate stored is used at the start of exercise and, as exercise intensity increases, the glycogen’s contribution to energy metabolism also increases. Carbohydrate exists in simple and complex forms; sources of simple carbohydrates consist of refined sugars and contain energy but lack nutrients, whilst complex carbohydrates are found in whole-grain products; beans, rice, bread and pasta include fibre and nutrients.

The rate of carbohydrate digestion and effect on the rise of blood glucose is described as the ‘glycemic index’. Food sources with a high glycemic index cause a rise in blood sugar levels and digest quickly. These foods are commonly white breads, bananas, potatoes and foods containing glucose and sucrose. Low glycemic index foods include nuts, peas, beans and milk, whilst foodstuffs such as spaghetti, corn and oatmeal are of moderate glycemic index. The NHS Advises that ‘Starchy foods such as potatoes, bread, cereals, rice, pasta should make up about a third of the food you eat’.

Another primary source of energy is fat. This is also the most efficient at storing energy, having 9.3 calories per gram compared to carbohydrate and protein which each have around 4 calories per gram. Fat is an essential component of cell walls and vital insulation in the nervous system, it acts as a shock absorber for internal organs and is used as fuel in sustained physical activity. However, excess dietary fat can contribute to heart disease, hypertension, diabetes, obesity and other illnesses. Energy can be acquired from the conversion of excess protein and carbohydrate which is stored as fat in adipose tissue, as well as through dietary fat. Fat is present in different forms and these include cholesterol and triglycerides. Triglycerides comprise of three fatty acid molecules which are attached to a molecule of glycerol. A fatty acid can be unsaturated or saturated and is the smallest component of a fat. Saturated fats are found in dairy products and meats, whilst a fatty acid, omega 3 is known as a polyunsaturated fat which is present in oily fish and green vegetables.

Proteins are described as ‘the building blocks of the body’. A vital dietary component required for the maintenance and growth of the body’s tissues and cells. Proteins consist of a long chain of twenty amino acids, of which eight are essential and can only be obtained through dietary sources. Providing all eight essential acids are present, the remaining amino acids can be synthesised by the liver. Foods which will provide all eight essential amino acids include dairy products, meats, fish, eggs and poultry. However, protein present in wheat, rice, oats, pulses and nuts may not.

Vitamins and minerals are only required in small amounts daily, these are known as micronutrients. Vitamins C and E are antioxidants that can stimulate and enhance the immune response. Vitamin C is found in citrus fruits, peppers and broccoli, and Vitamin E is present in vegetable oils, whole grain foods and wheat germ. Vitamin B, contained in nuts, spinach and potatoes has been found to promote white blood cells, whilst Folate is a vitamin which increases the activity of these cells. Folate is obtained from salmon, peas and lettuce. Carrots and sweet potatoes contain Beta-carotene which stimulates the immune system cells which fight infections. Minerals such as selenium; found in tuna and eggs, and zinc; present in eggs, whole grains and oysters, have also been found to aid the immune response. A particularly important mineral is Iron, as this transports and stores oxygen when used in muscle myoglobin and helps produce haemoglobin which transports oxygen in red blood cells from the lungs to the working muscles. Iron can be found in prunes, apricots, dates, beans and meats. 

One major component of teeth and bones is calcium, it is also involved in enzyme activity, blood clotting, nerve transmission and muscle contraction. Calcium is present in milk, cheese and other dairy foods, in soya and tofu, some oily fish and in anything made with fortified flour.

Alongside energy and nutrients found in foods, the body also requires an appropriate supply of water. The human body’s weight is made up of 55%-60% water, which is contained in cells and glands, extracellular fluids like saliva, tears and blood, and is present in the gastrointestinal tract. Water has many important functions which include temperature regulation through perspiration, lubrication of surfaces and membranes, the transportation of hormones, antibodies, waste products, energy and gases and is involved with the regulation of the acid-base balance in the blood. Even an inactive person will require around 2.5 litres of water per day to replace fluids lost in faeces, urine, skin and exhalation of the lungs.

Electrolytes (potassium, chloride and sodium) are minerals which help facilitate muscle contraction and relaxation, and play a key role in regulating fluid balance, both inside and outside the cells. Water alone will not replace electrolytes lost through exercise. All drinks contain an amount of water and count towards the daily requirement but pure water, milk and fruit juices are recommended as the healthiest.

 

Cycling specific nutrition.

David Brailsford, British Cycling’s performance director, (2003-2014) described the importance of lifestyle discipline for the young riders on the Olympic academy program. The need for appropriate and effective nutrition is likely to be particularly important to these cyclists, as their training regime consists of 2-5 hours every day, often riding 100 miles or more. The Performance Diet recommends that 55-60% of calories should come from carbohydrates. However, as the academy riders compete in endurance cycling events such as the individual pursuit, they will often be competing at an exercise intensity between VO2max (the maximal capacity to take in and use oxygen in exercise) and the second lactate threshold, where blood lactate levels rise to the point of excess anaerobic effort and exhaustion. This indicates the efforts will place a particular demand on the rider’s muscular endurance as well as the aerobic system, therefore the muscle’s glycogen supplies will rely on carbohydrate to provide sufficient fuel. The dietary recommendations of carbohydrate for elite cyclists is considered by British Cycling to be around 60-70%, which places even more importance on carbohydrate than the typical performance diet.

The recommendations in both the performance diet and British Cycling’s Level 3 coaching handbook indicate a 10-15% amount of total calories should come from protein, therefore to avoid muscle loss and to ensure repair of muscle tissue after training it is important for the riders, as endurance athletes, to intake 1.2-1.4 grams of protein per kilogram of body weight. It should be noted however, that when engaging in strength training and very high intensity programmes, cyclists may need to take in up to 2 grams per kilogram of bodyweight.

Although fat has been described as a primary source of energy, it is suggested that dietary fat should fall between 20-25% of daily intake and that no more than a third should comprise of saturated fats. For the academy cyclists, as their training and competition places demands on muscle glycogen, the importance of ensuring they can take on adequate amounts of carbohydrate would mean a recommendation for avoidance of excess dietary fat. During an aerobic endurance training phase however, it would be reasonable to consider that the cyclists may use fat stores when undertaking longer rides of low intensity and to ensure their diet is monitored appropriately.

Dehydration can result in poor performance for cyclists, as much as 20% if there is a loss of 2% of the body’s total weight, consequently, for the cyclists in our study to perform at their optimal level, attention to effective hydration is of maximum importance. Included with the loss of fluids during exercise, the riders will also lose electrolytes, for example, 1.5 grams of salt can be lost per litre of sweat lost. Therefore attention to the replacement of these minerals is essential. When in competition or periods of training, it is important that the academy riders are not susceptible to germs and infections and will rely on vitamins and minerals, which can be found either in food or supplements, to help maintain a healthy immune system.

Recommendations for pre- and post-training/competition nutrition and hydration.

David Brailsford explains that an ‘all or nothing’ approach is taken with the riders on the academy programme and they are looking for ‘a 1% improvement in 20-25 areas’. Therefore, it would be important to consider how much of a difference in performance the correct approach to nutrition and hydration would make. A recommended pre-training diet would be likely to include carbohydrates with a low to moderate glycemic index, this would ensure that a steady stream of glycogen is supplied during the exercise. This may follow the performance diet guideline of 55-60% of calories, but during intense training/competition may need to be increased. It is also necessary to ensure adequate hydration before training, depending on the temperature conditions, 500-750ml of water should be consumed. For cyclists, it is also likely that there is a need for hydration during activity, and depending on intensity, this may include an Isotonic sports drink, (containing 5-8% carbohydrate per 100ml of water) to maintain glycogen levels.

 

Immediately after exercise, it is suggested that consumption of high glycemic index carbohydrate is best. However, Ivy et al (2002, cited in Sharkey and Gaskill, 2007, p. 311) suggest this should also include protein, at a ratio of 1 grams to every 4 grams of carbs in order to speed muscle recovery and maximal replacement of muscle glycogen. This ‘refuelling’ process should ideally take place within 20 minutes of completing training or competition, as the sooner the nutrition is absorbed by the liver and muscles, the more effective the recovery process. Again, hydration is particularly important, and replacement of vital fluids and micronutrients is desirable. In order to ensure fluid replacement, recommendations to drink both water and fruit juices, which can contain a variety of vitamins, are made by both British Cycling and Sharkey and Gaskill. Alcohol would function as a diuretic, hindering the rehydration process, therefore should be avoided.

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References:

Sharkey, B. J. and Gaskill, S. E. (2007) Fitness & Health (6th edn), Leeds, Human Kinetics

The Open University (2008) E112 Introduction to Sport, Fitness and Management DVD, Milton Keynes, The Open University

Donnelly, J. (2008) 'Study topic 6: Eating to win’, in E112 Introduction to Sport, Fitness and Management, Milton Keynes, The Open University 

NHS (2011a) ‘Vitamins and minerals – Calcium – NHS Choices’ [online], http://www.nhs.uk/Conditions/vitamins-minerals/Pages/Calcium.aspx (Accessed 24th May 2012)

NHS (2011b) ‘Water and drinks – Live well – NHS Choices’ [online], http://www.nhs.uk/livewell/goodfood/pages/water-drinks.aspx (Accessed 24th May 2012)

NHS (2011c) ‘Starchy foods (carbs) – Live well – NHS Choices’ [online], http://www.nhs.uk/Livewell/Goodfood/Pages/starchy-foods.aspx (Accessed 24th May 2012)

Stanners, C. (ed.) (2008) British Cycling Coaching Handbook, Coaching for Performance, Level 3. Coachwise, Leeds.