{"id":1466,"date":"2022-09-28T17:45:38","date_gmt":"2022-09-28T15:45:38","guid":{"rendered":"http:\/\/madebydiet.com\/?p=1466"},"modified":"2025-03-04T10:13:40","modified_gmt":"2025-03-04T09:13:40","slug":"carbohydrate-loading-or-how-to-outsmart-fatigue","status":"publish","type":"post","link":"https:\/\/madebydiet.com\/eu\/carbohydrate-loading-or-how-to-outsmart-fatigue\/","title":{"rendered":"Carbohydrate loading, or how to outsmart fatigue?"},"content":{"rendered":"
[vc_row][vc_column][vc_column_text uncode_shortcode_id=”562930″] Authors: Klaudia Buczek, MSc Eng., and Micha\u0142 Mi\u015bta, MSc Pharm.<\/p>\n Contents<\/strong><\/p>\n Watching reports of athletes approaching the finish of a marathon we often see moving scenes, when staggering athletes unexpectedly fall down. With no strength to continue the race, they cover the last meters on all fours, and cross the finish line with the utmost effort. This phenomenon, manifested as extreme fatigue and sudden energy cut-off, accompanied by slowing the pace during exercise, is defined as \u201chitting the wall\u201d, \u201cbonking\u201d or \u201cblowing up\u201d. The term originates from cycling, but it equally refers to other endurance sports. The causes of \u201chitting the wall\u201d are complex, but one of the most important causes is undoubtedly depletion of body energy reserves.<\/p>\n Adenosine triphosphate, known as ATP, is a direct substrate supplying energy to the working muscles, and playing a role of a universal energy carrier. ATP reserve accumulated in the muscle cell is very small and allows for only a few contractions. In spite of this, even during intense exercise, its resources are depleted only by 20% to 30% of the initial content. The body does not allow depletion of ATP resources, since that would cause permanent connection of actin and myosin threads, i.e. protein filaments, whose physical interaction enables the function of a muscle cell (myocyte). This condition occurs after life processes are stopped, with resulting rigor mortis.<\/p>\n However, let us return to ATP. As already mentioned, its resource in the cell is very limited; therefore, it must be constantly regenerated. This process happens constantly with surprising efficacy: a working muscle cell recovers its all ATP pool in less than a minute, and the total amount of ATP undergoing recirculation in 24 hours is approximately equal to the body weight! This effective ATP regeneration certainly requires significant amounts of energy. In cell muscles, this energy is derived in the first place from another high-energy compound, called phosphocreatine.<\/p>\n The phosphocreatine supply in the muscle cells enables maintenance of high rate of ATP regeneration within several seconds of the start of exercise. Although this is a key energy source for athletes practising disciplines where the energy demand is immediate and short-term, e.g. weight-lifters, in the case of runners, the phosphocreatine pool stored in the muscles is sufficient for a 100 metre sprint. In order to continue exercise, the body would have to reach for other energy substrates, which may come from intramuscular sources (endogenous substrates -glycogen and triacylglycerols) and from blood (exogenous substrates, such as glucose, free fatty acids, plasma lipoproteins, ketone bodies or some amino acids). The degree of consumption of particular energy substrates depends on the type of muscle fibres, and on the intensity and duration of exercise. The awareness of their diversity, and the ability of their optimal regeneration is crucial for the selection of an optimal nutrition strategy. This will also affect the effectiveness of the exercise. In the case of endurance sport disciplines, one endogenous substrate is of special importance, i.e.\u2026<\/p>\n Glucose is a basic and very productive source of energy for body cells. Suffice it to say that complete oxidation of one glucose molecule results in the formation of about 30 ATP molecules. For a certain type of cells, such as red blood cells (erythrocytes), glucose is the only available source of energy.\u00a0Brain and nerve cells are especially sensitive to glucose absence. In the light of the above-mentioned information, it seems surprising that the total amount of circulating glucose of a person with a body weight of 70 kilograms is only 4 grams. This amount corresponds to a flat teaspoon, and its caloric content is only 16 kilocalories.<\/p>\n Glucose cannot be stored in an unchanged form, since its high concentration would disturb the osmotic balance of the cells, causing their damage. For this reason, human body has developed a complex system based on e.g. antagonistic activity of two hormones \u2013 insulin and glucagon, which maintains a relatively constant, standard blood glucose level of 4.0 – 5.5 mmol\/l, which corresponds to 70 \u2013 100 mg\/ 100 ml (dl), and is defined as euglycaemia in scientific literature. Glucose reserves are stored in the form of osmotically inactive and easy-to-use polymer – a polysaccharide called glycogen. Glycogen is a large molecule, whose core contains protein (glycogenin) surrounded by a high number of branched chains composed of glucose residues (monomers). Their ends form a complex surface of a glycogen particle, which, if necessary, may be quickly degraded, leading to effective release of required amounts of glucose.\u00a0 A two-dimensional model of a glycogen molecule is presented in the picture below.<\/p>\n A vast majority of glycogen is located in muscle cells – approx. 500 g on average (1% – 2% of the myocyte volume) and hepatic cells – approx. 80 g on average (5% – 6% of the hepatocyte volume), where it forms numerous granules of various sizes dispersed in the cytoplasm and containing different amounts of glucose monomers. The primary role of hepatic glycogen is to maintain constant blood glucose level and to react to the glucose need of the body, as a whole. And muscle glycogen is used only as a local glucose reservoir, available for the needs of a given muscle fibre (constituting a single, multinucleated cell). Due to physiological conditioning, glucose originating from glycogen accumulated in a given muscle fibre cannot be released to blood becoming a source of energy for other cells (or even for the neighbouring muscle fibres). This makes glycogen remain in the muscles for a longer time, and this fact may be used in practice, which will be discussed further in the text.<\/p>\n Muscle glycogen is mainly distributed in three specific regions (compartments) of the cell, in close proximity to the sites where energy supplies are required. It should also be added that glycogen granules are not only \u201ccontainers\u201d of condensed fuel, like glucose molecules, but have also another significance. To make it simple, they may be said to have a role of \u201csensors\u201d.\u00a0 Among other things, glycogen causes transmission of impulse leading to a muscle twitch (release of calcium ions from the sarcoplasmic reticulum) and takes part in the regulation of metabolic pathways related to the processes of exercise adaptation. Moreover, it is a part of the system regulating the intracellular osmotic pressure. Due to this varied role of glycogen, its decreasing resources during exercise may not only disturb energy transformations, but also complex signalling and regulatory processes. From the athlete’s point of view, it is important that they impair generation of muscle strength. This is probably why, during highly intense exercise, when the amount of muscle glycogen is much depleted, the body does not decrease its contents below 10% in relation to the initial amount.<\/p>\n Although the amount of glycogen accumulated in the liver and muscles is only 4% of the total energy reserves of the body, it is muscle glycogen that is a basic source of energy for working muscles in the case of exercise of moderate and high intensity.\u00a0 This results from the involvement (recruitment) of various types of skeletal muscle fibres which have various structural, functional and metabolic characteristics, depending on the type of exercise, which is illustrated in the table below.<\/p>\n Skeletal muscles are built of three types of fibres: type I fibres, i.e. slow-twitch or oxidative, and type IIa and IIx fibres, i.e. fast-twitch, called oxidative-glycolytic and glycolytic fibres, respectively.<\/p>\n During low intensity exercise, even such lasting a few hours, the use of glycogen is relatively low and primarily affects well vascularised and fatigue-resistant type I fibres, which are recruited by the body first. These fibres are naturally poor in glycogen and their chief source of energy is degradation of lipids (triacylglycerols). Lipids are a high-energy form of energy storage, although the process of ATP production therefrom is slower than the production of ATP from glycogen. This fact, combined with low transmission rate of axons innervating type I fibres, translates into their low speed of contraction. That is why they are called slow-twitch fibres. The presented characteristics predispose this type of fibres to be involved in long-term exercise, such as running a marathon or maintaining an extended body position.<\/p>\n Increased burden involves recruitment of glycogen-rich type IIa fibres (oxidative-glycolytic), which may derive energy from both aerobic and anaerobic processes. This results in an increased consumption of glycogen, which is a basic source of energy for these fibres.<\/p>\n In the case of the highest burden, type IIx (glycolytic) fibres are recruited last. They are characterised by \u201cpower burst\u201d, typical of sprints or weight-lifting. Their primary source of energy are anaerobic processes. These fibres are able to generate the highest amounts of energy, but they use much of their glycogen reserves for that purpose, rapidly showing fatigue.<\/p>\n It is interesting that in the case of oxidative (type I) fibres, the use of glycogen during intense exercise is reduced with an increased burden. For example, after stopping exercise of very high intensity (due to complete fatigue), there is almost complete glycogen utilisation in type IIx fibres, 70% decrease in the glycogen content in type IIa fibres, and only 25% decline in glycogen in type I fibres.<\/p>\n The proportions in which particular types of muscle fibres occur in a given muscle are genetically determined. Indeed, the proportion of type I fibres in the vastus lateralis muscle (constituting the strongest element of the quadriceps femoris) may range from 5% to 90%! This phenomenon partially accounts for natural predisposition of a given person to a specific type of activity. Therefore, it should not be surprising that athletes prepared in terms of endurance disciplines show a particularly high proportion of type I fibres, while groups of muscles crucial for sprinters and weight-lifers are primarily composed of type IIa and IIx fibres. There is an exception, however, the soleus muscle of the calf, which, regardless of an individual, is characterised by a high content of type I fibres, which is a great example of adaptation to the function it serves.<\/p>\n The recovery of glycogen resources utilised during training takes place in two phases.\u00a0 A rapid phase of glycogen resynthesis lasts 30-60 minutes after stopping exercise, and is related e.g. to transfer of glucose transporter type 4 proteins (GLU4) on the myocyte mucosa without the participation of insulin, which fosters glucose absorption by the muscle fibre. Glycogen resynthesis is then the fastest. In the subsequent slow (insulin-dependent) phase, glycogen resynthesis is much slowed down to approx. 10 \u2013 30% of the initial value.\u00a0 Available studies clearly indicate that consuming a portion of absorbable carbohydrates (with high glycaemic index) immediately post training initiates the process of rapid glycogen recovery, lasting for the first 2 hours post exercise. During this time, the so-called \u201cgarage door of opportunity\u201d is closed. These data show that if we wish to achieve quick recovery, we must not delay carbohydrate consumption after the training. In this case, the sooner, the better! If we then have a high-carbohydrate diet, i.e. such where carbohydrates constitute at least 70% of the caloric value, a complete glycogen resynthesis occurs within 24 hours.<\/p>\n Continuation of a high-carbohydrate diet in the next 24 \u2013 48 hours significantly increases the glycogen level in relation to pre-exercise content, but one must remember than any muscle injuries suffered during training may prolong this process. If the training volume is significantly reduced during this period, or, even better, complete rest is introduced, this may lead to a phenomenon called hypercompensation (or supercompensation) of glycogen. It has a very practical use in sport.<\/p>\n
\nEndurance sports, such as marathon, cycling, triathlon, cross-country running, long distance swimming, kayaking, rowing or cross-country skiing are highly popular. These activities require selection of an adequate type of training and complex preparation. One of its pillars is development of an individualised nutrition strategy, which not only enables the body to handle intense training, but also ensures optimal regeneration, prevents gastrointestinal problems or helps maintain well-being. Adequately selected nutrition, especially in the period around the event, will also have a great impact on performance.<\/strong><\/p>\n\n
Wall<\/h2>\n
Energy for working muscles<\/h2>\n
Phosphocreatine<\/h2>\n
Glycogen<\/h2>\n
<\/p>\nUse of glycogen in various types of muscle fibres<\/h2>\n
\n\n
\n Traits<\/strong><\/td>\n Types of muscle fibres<\/strong><\/td>\n<\/tr>\n \n Type I
\n(SO, ST)
\noxidative<\/strong><\/td>\nType IIa
\n(FOG, FTA)
\noxidative-glycolytic<\/strong><\/td>\nType IIx
\n(FG, FTX)
\nglycolytic<\/strong><\/td>\n<\/tr>\n\n Structural<\/td>\n Diameter<\/td>\n Low<\/td>\n High<\/td>\n Medium<\/td>\n<\/tr>\n \n Vascularity<\/td>\n High<\/td>\n Medium<\/td>\n Low<\/td>\n<\/tr>\n \n Fibre colour<\/td>\n Red<\/td>\n Reddish<\/td>\n White<\/td>\n<\/tr>\n \n Mitochondrial density<\/td>\n High<\/td>\n Medium<\/td>\n Low<\/td>\n<\/tr>\n \n Metabolic<\/td>\n Type of metabolism<\/td>\n Aerobic<\/td>\n Aerobic
\nand anaerobic<\/td>\nAnaerobic<\/td>\n<\/tr>\n \n Glycogen content<\/strong><\/td>\n Low<\/strong><\/td>\n High<\/strong><\/td>\n High<\/strong><\/td>\n<\/tr>\n \n Fat (triacylglycerol) content<\/td>\n High<\/td>\n Medium<\/td>\n Low<\/td>\n<\/tr>\n \n Myoglobin content<\/td>\n High<\/td>\n High<\/td>\n Low<\/td>\n<\/tr>\n \n Functional<\/td>\n Order of recruitment<\/strong><\/td>\n 1<\/strong><\/td>\n 2<\/strong><\/td>\n 3<\/strong><\/td>\n<\/tr>\n \n Speed of contraction<\/td>\n Low<\/td>\n High<\/td>\n High<\/td>\n<\/tr>\n \n Twitch strength<\/td>\n Low<\/td>\n Average<\/td>\n High<\/td>\n<\/tr>\n \n Resistance to fatigue<\/td>\n Very high<\/td>\n High<\/td>\n Low<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n Two phases of glycogen resynthesis<\/h2>\n
Glycogen hypercompensation<\/h2>\n