ROLUL INSULINEI IN PERFORMANTA SPORTIVA

Abstract

There are two keys to a better body: a solid exercise program and healthy meals. There's also another key that's just as important as proper workouts and wholesome meals but is often overlooked: the performance zone A number of recent studies have provided important insight into the role of insulin in facilitating recovery following exercise. Insulin and physical exercise are well-known regulators of both protein and glucose metabolism. Evidence indicates that the ability of insulin to stimulate glucose uptake in skeletal muscle is enhanced after exercise. The effect of insulin on glucose transport into the muscle cell has been extensively documented. Latest research has shown that insulin plays a multi-faceted role in the recovery process. [PUBLICATION ABSTRACT]

Lygia ALEXANDRESCU

Universitatea "Spiru Haret", Bucureçti, FEFS.

Cuvinte cheie: nutrice, cresterea performanci, carbohidrati, recuperare.

Rezumat

Un antrenament sustinut si bine orientât si o alimentatie sanatoasa sunt principalele instrumente de imbunatatire a performantei. Exista insa si un ait factor la fel de important ca antrenamentul si nutritia corespunzatoare si care de multe ori este neglijat: zona de performanta. O serie de studii recente au relevât faptul ca insulina are rolul de a usura recuperarea in perioada post-efort. Insulina si exercitiul fizic sunt doi reglatori esentiali in metabolismul proteinelor si glucozei. Rezultatele clinice releva faptul ca abilitatea insulinei de a stimula incarcarea muschilor striati cu glucoza este crescuta dupa efort. Efectul insulinei in transportai glucozei spre célula musculara a fost studiai in detaliu si ultímele cercetari arata ca insulina joaca roluri multiple in procesul de recuperare post-efort.

Introducere

Insulina este un hormón produs de pancreas si este eliberata atunci cand se consuma carbohidrato Principala functie a insulinei este de a usura transportai carbohidratilor, in special al glucozei, dinspre sange spre célula musculara, unde poate fi apoi metabolizata pentru a produce energie, care va permite muschiului sa lucreze. Cand organismul nu reuseste sa produca o cantitate suficienta de insulina, apare patologia numita diabet. Indivizii eu diabet trebuie sa ia medicatie orala sau sa isi injecteze insulina pentru a stimula producerea acestui hormón. Deoarece este implicata si in multe alte aspecte ale recuperarli si performantei musculare, insulina a fost denumita principalul hormón in recuperare. Astfel, ultímele cercetari au aratat ca insulina:

* imbunatateste reconstructia proteinei musculare aféctate de efort

* joaca un roi important in reducerea stresului muscular

* stimuleaza producila de glicogen in célula musculara

Mecanismul refacerii nivelului de insulina si glicogen

Insulina joaca doua roluri in stimularea sintezei glicogenului. In primul rand, faciliteaza transportul glucozei dinspre sange spre célula musculara, unde poate fi transformata in glicogen.

Producila glicogenului muscular din glucoza presupune prezenta unei enzime numite glicogen-sintetaza. Insulina stimuleaza aceasta enzima, facand posibila transformarea glicogenului la o viteza mult mai mare. Presupunand ca sunt suficiente cantitatile de carbohidrati, eu cat nivelul plasmatic al insulinei creste post-efort, eu atat transportul glucozei spre célula musculara va fi mai rapid, iar viteza de sinteza a glicogenului muscular va fi mai mare. Timpul in care se desfasoara acest procès este esential. Célula musculara are sensibilitate maxima la insulina in perioada 0-2 ore post-exercitiu. De fapt, sinteza glicogenului la doua ore dupa efort are loc de 2-3 ori mai rapid decat normalul. Dupa aceste 2 ore célula musculara devine practic rezistenta la insulina, efect care continua pentru mai multe ore. Asadar, depozitele de glicogen trebuie refacute imediat dupa exercitiu. Consumul a 50g de carbohidrati la 4 ore dupa exercitiu, va produce rezultate diferite comparativ cu situatia in care s-ar consuma aceeasi cantitate de carbohidrati la 30 de minute dupa exercitiu. Acest efect este adesea ignorât de sportivii de performanta.

Deoarece raspunsul insulinei este esential in procesul de recuperare musculara, cercetatorii au investigat felul in care insulina poate fi stimulata post-exercitiu. Aceste studii au importante implicatii pentru sportiv. Cercetatorii au aratat ca in momentul adaugarii proteinei la carbohidrat, raspunsul insulinei este aproape dublu. Astfel, ar fi normal ca orice bautura sportiva cu proteine si carbohidrati sa ofere un avantaj in procesul de recuperare. Tonisi, prea multa proteina poate incetini procesul digestiv, si atunci sa se incetineasca regenerarea hidrica si a glicogenului. Cand raportul carbohidrat:proteina este de 4:1 (de exemplu 56 g de carbohidrat si 14 g de proteina) actiunea de stimulare insulinica a proteinei nu interfera esential cu faza de rehidratare. Anumiti aminoacizi din structura proteinei, au fost determinati ca fiind favorizanti in procesul de refaceré a glicogenului. Studiile au aratat ca aminoacidul arginina creste viteza de refaceré a glicogenului in procesul de recuperare prin utilizarea excesiva a grasimii ca sursa de energie post-exercitiu. Prin utilizarea intensa a lipidelor, mai multa glucoza este disponibila in procesul de reconstruire a depozitelor de glicogen muscular.

Problema

Insulina si stresul muscular post-efort

Exercitiul exténuant poate cauza eliberarea de cortizol, hormón care influenteaza profund procesul de recuperare. Cortizolul este un hormón eliberat de glandele adrenale, organe mici atasate deasupra fiecarui rinichi. Principalul rol al cortizolului este de a ajuta mobilizarea energiei. Cortizolul afecteaza muschiul in mod direct prin cresterea vitezei catabolismului proteic. Acesta este motivul pentru care sportivii implicati in aireñamente de forta pot constata o scadere a masei musculare daca nu vor urma pasii necesari pentru refacerea proteinelor si pentru a reduce eliberarea cortizolului. De aceea, este esential pentru un sportiv sa-si reduca nivelul cortizolului. Studii recente au aratat ca o bautura care contine carbohidrati si proteine poate inhiba cresterea nivelului cortizolului prin stimularea eliberarii insulinei si deci favorizeaza cresterea sintezei proteinelor. Pe langa rolul pe care il joaca in reducerea catabolismului proteic si cresterea refacerii carbohidratilor, insulina este implicata in procesul de reconstructie a proteinelor. Insulina creste sinteza proteinelor prin usurarea transportului aminoacizilor spre célula musculara. Aminoacizii sunt parte structurala din proteina. Prin asigurarea unor cantitati suficiente de aminoacizi la nivel muscular, insulina ajuta célula sa produca proteinele necesare pentru mentinerea structurii si functionarii celulare.

Recent, doua grupuri de cercetatori au raportat rezultatele obtinute pentru o noua bautura sportiva creata special pentru a stimula insulina. Aceasta contine carbohidrati si proteine in raport de 4:1 si in plus arginina. Carbohidratul a constat initial din zaharuri cu indice glicemic superior. Aceasta bautura a fost testata concurential cu bauturile sportive de notorietate. Cercetatorii au descoperit o crestere a insulinei cu 70% in urma consumului acestei bauturi. Cel mai important din punct de vedere al sportivului, s-a dovedit ca rezistenta a crescut cu 55%, iar degradarea musculara post-efort a scazut cu 36%. Aceste rezultate indica faptul ca stimularea insulinei, in special la 2 ore imediat dupa exercitiu, poate avea un impact esential in procesul de recuperare si in performanta sportiva.

Solutie

Nutritia inainte de efort

Datorita impactului puternic si imediat al deshidratarii in sportul de performanta, este recomandat sportivilor sa consume 300-500 mi de bautura sportiva cu 30 de minute inainte de efort, antrenament sau competitie. prin consumul de fluide in aceasta perioada de timp, se va intarzia instalarea deshidratarii, se va grabi debutul procesului de transpiratie si se va produce o crestere mai mica a temperaturii corporale, bauturile sportive sunt preferate apei pure deoarece contin electroliti (in principal sodiu). acesti electroliti nu permit excretia apei prin rinichi (nevoia de eliminare), prin consumul de carbohidrati, impreuna cu un lichid cu o jumatate de ora inainte de exercitiu, se poate imbunatati regenerarea depozitelor de glicogen muscular si hepatic si poate creste nivelul glucozei in sange. acestea sunt principalele surse de energie ale organismului in timpul exercitiului. numeroase studii au aratat ca prin consumul de carbohidrati inainte de efort, se poate imbunatati semnificativ performanta aeroba. faptul ca bauturile sportive contin carbohidrati este un alt motiv pentru care trebuie alese eie in locul apei. cele mai bune bauturi sportive contin 6-8% carbohidrati (20-24 g / 300 ml de lichid). multe bauturi sportive nu contin proteine, insa cele care contin sunt preferate deoarece reduc degradarea musculara in timpul efortului.

Nutritia in timpul efortului

In timpul efortului, nutritia poate furniza urmatoarele beneficii:

1. Previne deshidratarea si aparitia crampelor musculare

2. Creste energia si rezistenta

3. Limiteaza degradarea musculara

4. Limiteaza scaderea sistemului immutar

5. Accelereaza recuperarea post-efort

Pentru a avea toate aceste beneficii, este important sa se foloseasca bauturi sportive bine formulate si care sa contina apa, electroliti, 6-8% carbohidrati, si aproximativ 2% proteine. Insulina stimuleaza transportul glucozei spre celulele sensibile la insulina ale organismului prin intermediul transportatorilor de glucoza (GLUT) dupa cum se arata in figura 2.

Apa si electrolitii din bauturile sportive sunt necesare pentru a inlocui lichidele pierdute prin transpiratie. Chiar si deshidratarea minora poate reduce performanta aeroba si poate cauza crampe musculare. Consumul de lichide in timpul efortului nu poate opri complet deshidratarea, dar o poate reduce considerabil, in acest fel crescand performanta si scazand riscul aparitiei crampelor musculare.

Din moment ce glucidele reprezinta principala sursa de energie in timpul efortului, este normal ca un consum adecvat de carbohidrati in bautura sportiva sa imbunatateasca semnificativ rezistenta in comparatie cu situatia in care s-ar consuma apa. Sistemul immutar are nevoie de asemenea de carbohidrati si de aceea, efortul excesiv tinde sa scada activitatea sistemului immutar, facand organismul susceptibil la infectii. Folosirea bauturilor sportive poate reduce de asemenea si acest rise.

Bauturile sportive care contin proteine, au avantajul suplimentar de a reduce degradarea musculara cauzata de efort. Intr-un studiu efectuat pe o bautura sportiva care contine carbohidrati si proteine (Accelerade), s-a observât o scadere a degradarli musculare cu 83% fata de o bautura sportiva obisnuita. Aceasta poate duce la o mai buna performanta in antrenamente si competitii si la o recuperare mai rapida dupa efort.

Pentru cele mai bune rezultate, este necesar sa se consume cantitati mici (100-200 ml) dintr-o bautura sportiva, in mod freevent (la flecare 10-15 minute) in timpul exercitiului fizic. Asadar, este important pentru un sportiv sa-si particularizeze strategia nutritionala in zona de performanta pentru flecare activitate particulara.

Nutritia post-efort

Un sportiv trebuie sa continue sa consume care sa contina carbohidrati si proteine dupa 15 minute de la terminarea efortului. Studiile au aratat ca portivii sunt capabili sa se recupereze mult mai repede daca au aport nutritional imediat dupa efort, comparativ cu situatia in care ar astepta si ar consuma aceiasi nutrienti mai tarziu.

In mod special, nutritia imediata post-efort accelereaza refacerea si reconstructia musculara si reincarcarea cu combustibil muscular. In timp, aceasta reduce riscul accidentarilor si imbunatateste forma fizica a sportivului. Spre exemplu, intr-un studiu, sportivii care au consumât suplimente care contineau carbohidrati si proteine imediat dupa efort, si-au imbunatatit forta eu 8% in 12 saptamani, in timp ce sportivii care au asteptat 2 ore dupa efort, nu au realizat nici o imbunatatire a fortei.

Concluzii

Zona de performanta este o oportunitate nutritionala care incepe la 30 de minute inainte de exercitiu, continua in timpul exercitiului si se termina la 15 minute post-efort. Studiile arata ca ceea ce sportivii realizeaza din punct de vedere nutritional in aceasta perioada are un impact major atat asupra rezultatelor, cat si a antrenamentelor in sine si a dietei lor in general. Prin consumul unei diete corespunzatoare in zona de performanta, sportivii pot obtine rezultate mult mai bune, farà sa se antreneze extenunat si farà sa- si restrictioneze dieta mai mult decat de obicei. In acelasi timp, este evident faptul ca stimularea insulinei, in special in primele 2 ore post-efort, poate avea un efect semnificativ asupra procesului de recuperare si asupra performantei sportive.

Bibliografìe

1 . Asker,.J., Sport Nutrition, Human Kinetics Publishers, Chicago, 2002

2. Buhociu, E., Kinetoterapia în afecjiunile endocrino-metabolice, Ed. Fundajiei Romania de Maine, Bucuresti, 2005

3. Rändle PJ, Garland PB, Newsholme EA & Hales CN 1965 The glucose fatty acid cycle in obesity and maturity onset diabetes mellitus. Annals of the New York Academy of Sciences 131 324-333.

4. Stroescu V., Farmacologie clinica, Editura Medicala, 200 1

THE ROLE OF THE INSULIN HORMONE IN THE EFFORT'S BIOCHEMISTRY

Lygia ALEXANDRESCU

University "Spiru Haret" Bucuresti, FEFS.

Keywords: nutrition, endurance enhance, carbohydrates, recovery

Abstract

There are two keys to a better body: a solid exercise program and healthy meals. There's also another key that's just as important as proper workouts and wholesome meals but is often overlooked: the performance zone A number of recent studies have provided important insight into the role of insulin in facilitating recovery following exercise. Insulin and physical exercise are well-known regulators of both protein and glucose metabolism. Evidence indicates that the ability of insulin to stimulate glucose uptake in skeletal muscle is enhanced after exercise. The effect of insulin on glucose transport into the muscle cell has been extensively documented. Latest research has shown that insulin plays a multi-faceted role in the recovery process.

Introduction

Insulin is a hormone that is produced by the pancreas and is released when we consume carbohydrate. A primary function of insulin is to facilitate the transport of carbohydrate, specifically glucose, from the blood into the muscle cell, where it can then be metabolized to produce energy that will enable the muscle cell to do work. When the body fails to produce sufficient quantities of insulin, a condition called diabetes results. Individuals with diabetes must take medication to stimulate insulin or take injections of insulin. Because it is involved in so many aspects of recovery and muscle performance, insulin has been termed "the master recovery hormone". The latest research has shown that insulin:

- Enhances the rebuilding of damaged muscle protein

- Plays an role in reducing muscle stress

- Stimulates glycogen manufacture in the muscle cell

Mechanism of Insulin and Glycogen Replenishment

Insulin plays two roles in stimulating glycogen synthesis. First, it facilitates the transport of glucose from the blood into the muscle where it can be manufactured into glycogen. The manufacture of muscle glycogen from glucose requires the presence of an enzyme called glycogen synthetase. Insulin stimulates this enzyme, enabling the glycogen manufacturing process to proceed at a faster rate. Assuming that sufficient amounts of carbohydrate are available, the greater the plasma insulin levels after exercise, the faster the transport of glucose into the muscle cell and the faster the rate of muscle glycogen synthesis. Timing of this process is key. The muscle cell is maximally sensitive to insulin 0-2 hours after exercise. In fact, glycogen synthesis in the two-hour period post-exercise proceeds two to three times faster than normal. After two hours, the muscle cell actually becomes resistant to insulin, an effect that continues for several hours. Thus, glycogen stores should be replenished immediately after exercise. Consuming 50 grams of carbohydrate four hours after exercise will produce very different results than consuming the same amount of carbohydrate 30 minutes after exercise. This effect is often ignored by the elite athletes.

Because the insulin response is vital in the muscle recovery process, researchers have investigated how insulin can be further stimulated after exercise. These studies have important implication for the athlete. Researchers have shown that when protein is added to carbohydrate, the insulin response is almost doubled. Thus it would appear logical than any sports drink with protein and carbohydrate would offer an advantage in the recovery process. However, too much protein can slow gastric emptying, thereby slowing fluid and glycogen replacement. When the ratio of carbohydrate to protein is 4 to l(for example, 56 grams of carbohydrate and 14 grams of protein), the insulin stimulating action of protein does not appear to interfere with the essential rehydration phase. Specific amino acids within protein have been found to also increase glycogen replenishment. Studies have shown that the amino acid arginine increases muscle glycogen replenishment in the recovery period by increasing the utilization of fat as an energy source after exercise. By increasing the utilization of fat, more glucose is available to help rebuild depleted muscle glycogen stores.

Problem

Insulin and Post-Exercise Muscle Stress

Vigorous exercise causes the release of Cortisol, which can severely influence the recovery process. Cortisol is a hormone released from the adrenal glands, small organs attached to the top of each kidney. The primary role of Cortisol is to help mobilize energy. Cortisol affects muscle directly by increasing the rate of protein breakdown. It is the reason individuals involved in strength training may experience a decrease in muscle mass if they do not take the necessary steps to replenish protein and reduce the release of Cortisol. So that it is very important for an athlete to reduce Cortisol levels. Recent studies have shown that a carbohydrate/protein drink can inhibit the rise in Cortisol by stimulating insulin release and thereby promote increased synthesis of protein.

In addition to playing a role in reducing protein breakdown and increasing carbohydrate replenishment, insulin is involved in the protein rebuilding process. Insulin increases protein synthesis by facilitating the transport of amino acids into the muscle cell. Amino acids are the building blocks of protein. By making sure the muscle cell has the necessary amounts of these essential building blocks, insulin enables the cell to produce proteins necessary for maintaining cell structure and function. Recently, two groups of investigators reported the results of studies of a new sports drink, specifically designed to stimulate insulin. It contained carbohydrate and protein in a 4 to 1 ratio and arginine. The carbohydrate consisted primarily of high glycémie index sugars. This drink was tested against the leading sports drink. The investigators found that the 4 to 1 drink increased insulin levels by 70%. Most importantly, from an athlete's perspective, it was also proven to increase endurance by 55% and reduce post-exercise muscle damage by 36%. These results indicate that stimulation of insulin, especially in the two hours immediately following exercise, can have a dramatic effect on recovery and athletic performance.

Solution

Nutrition before exercise

Because of the immediate and dramatic effects of dehydration on sports performance, it is recommended that exercisers consume 300-500 ml of a sports drink 30 minutes before practices, workouts, and competition. Consuming fluids during this time will delay the development of dehydration, speed the onset of sweating and cause a smaller rise in body temperature. Sports drinks are preferred over pure water because they contain electrolyte minerals (mainly sodium). These minerals prevent the excretion of water through the kidneys (the need to eliminate). Consuming carbohydrate along with fluid in the half-hour before exercise can help increase liver and muscle glycogen stores and raise blood glucose levels. These are the body's main fuel source during exercise. Many studies have found that consuming carbohydrate prior to exercise can actually improve aerobic performance. The fact that sports drinks contain carbohydrate is another reason to choose them over plain water. The best sports drinks contain 6-8% carbohydrate (20-24 grams per 300 ml serving). Most sports drinks do not contain protein, but the ones that do are preferable, because they reduce muscle damage during exercise.

Nutrition during exercise

During exercise, nutrition can provide the following benefits:

1. Prevent dehydration and muscle cramps

2. Increase energy and endurance

3. Limit muscle damage

4. Limit immune system suppression

5. Accelerate post- workout recovery

In order to have all of these benefits, it is a must to use a well-formulated sports drink containing water, electrolytes, 6-8% carbohydrate, and roughly 2% protein. Insulin stimulates glucose transport into insulin-sensitive cells of the body via glucose (GLUT) carriers as shown in Figure 2:

The water and electrolytes in sports drinks serve to replace the fluid lost through perspiration. Even mild dehydration can reduce aerobic performance and cause muscle cramps. Drinking throughout exercise can't halt dehydration completely but it can slow it considerably, thereby enhancing performance and lowering the risk of muscle cramps.

Since carbohydrate is the body's main energy source during exercise, it's no surprise that consuming carbohydrate in a sport drink has been shown to enhance endurance substantially as compared to water. The immune system also runs on carbohydrate, so hard exercise tends to suppress the immune system and opens the door for infections. Using a sports drink reduces this risk as well.

Sports drinks with protein have the added advantage of reducing muscle damage. In one study a carbohydrate-protein sports drink (Accelerade) reduced muscle damage by 83% more than a conventional sports drink. This results in better performance in the current workout or competition and a faster recovery afterwards.

For the best results, drink small amounts (100-200 ml) of a sports drink frequently (every 10-15 minutes) throughout exercise. Be aware that different activities present distinct sets of nutrition challenges and opportunities. For example, drinking on a bicycle is much easier than drinking while running. Therefore it's important for the athlete to customize her/his performance zone nutrition strategy to the particular activity.

Nutrition after exercise

The athlete should continue drinking a carbohydrate-protein sports drink for 15 minutes after exercise is completed. Research has shown that exercisers are able to recover much more quickly if they take in nutrition immediately after exercise than if they wait and take the same nutrition later.

In particular, immediate post-exercise nutrition accelerates muscle repair and rebuilding and muscle fuel replenishment. Over the long term this reduces the risk of injuries and enhances fitness gains. For example, in one study, exercisers who consumed a carbohydrate-protein supplement immediately after exercise improved their strength by 8% in 12 weeks, while those who waited two hours showed no improvement.

Conclusion

The performance zone is a nutritional window of opportunity that begins 30 minutes before exercise, continues throughout exercise, and ends 15 minutes afterward. Research shows that what exercisers do nutritionally during this period has as great an effect on their results as their workouts themselves, and their overall diet. By taking in the right nutrition within the performance zone athletes can get much better results without training harder or making their diet even more strict than it already is. In the same time it is obvious that the stimulation of insulin, especially in the two hours immediately following exercise, can have a dramatic effect on recovery and athletic performance.