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Current aspects regarding the correlations that might exist between physical exercise and cognitive status/ Aspecte actuale privind corelatiile ce se pot stabili intre exercitiul fizic si starea cognitiva.

INTRODUCTION

As we will show in the present mini-review, lately, there has been an increased awareness regarding the connections that might exist between physical exercise and the cognitive status. In this way, fundamental publications such as "Nature Journal" and "Cochrane Database of Systematic Reviews" focused more and more lately on this subject.

Thus, in 2008, the research group of Prof. Hillman published a comprehensive review (which already achieved almost 1 000 citations until now) describing the so-called "be smart, exercise your heart" initiative, focused, of course, on the correlations that might exist between exercise performing and the brain and/or cognition (1).

In this way, it became clear that an emerging body of multidisciplinary literature proved the important influence of physical activity on various aspects of the brain superior functions, by using both human and non-human animal studies, as we will immediately show by also using some original research data of our group.

Another important aspect in this matter is represented by the fact that the lack of physical activity, particularly, among children in the developed world, is one of the major causes of obesity, which represents another very important and modern pathology (2).

In fact, there is also a very modern current stating that there is growing evidence for physical activity to be healthy for students and more importantly to improve their academic performance (3).

As a matter of fact, there are also some very comprehensive meta-analysis in this area of research, such as the one by Sibley et al (as cited by Sattelmair) (3) which did manage to demonstrate a positive correlation between physical activity and several subcognitive domains, such as perceptual skills, intelligence quotient, achievement, verbal tests, mathematics tests, developmental level/academic readiness on normal school-aged children (3, 4).

Moreover, a study performed by the Dwyer group, in 2001, also cited by Sattelmair (3) reported a significant correlation between the academic ratings versus the exercise levels/performance on physical fitness tests on an impressive number of almost eight thousand schoolchildren (3, 5).

However, there are still many controversies also in this area of research, especially since in other independent studies, such as the one of Ahamed group from 2002, it was reported that physical exercising interventions neither increased nor decreased standardized test scores, when compared to other control schools (the study School was a Canadian one which implemented a sixteen-month special physical program) (3).

Still, there are good evidences that exercising might not only help to improve the physical health, but might also improve the academic performance (1).

Moreover, these positive effects of exercise performing can be extremely varied and could include effects at the molecular or cellular level systems, as well as at the behavioural levels (1).

In addition, in 2008, another extensive review was published in the famous "Cochrane Database of Systematic Reviews" regarding the relevance of this subject in older people (6). Thus, the group leaded by Angevaren et al did manage to demonstrate that physical activity and enhanced fitness improve cognitive function in older people without known cognitive impairment (6).

Moreover, the aforementioned authors demonstrated the positive effects for the physical activity on the healthy ageing, concluding that exercising could preserve good cognitive function in older age. In this way, they analyzed eleven relevant studies which only used participants that were older then 55 years, mentioning that eight from this studies suggested improved cognitive status. In fact, the sub-cognitive domains which were facilitated by the physical exercising were represented by cognitive speed, delayed memory functions and auditory, visual attention and motor function. It is also important to mention that the aforementioned authors are concluding that although they found a very significant temporal association, the existing data is still insufficient to show that the improvements in cognitive function that can be attributed to physical exercise are due for sure the to improvements in cardiovascular fitness and larger studies are still require to confirm this, especially since some cognitive subdomains are not affected at all by the exercise performing (6).

Moreover, there are even more recent studies, such as the one of the Chapman group from the University of Texas, from 2013, which are reporting that aerobic exercise could represent indeed a true low cost prevention therapy to reduce the cognitive declines including memory, executive function, visuospatial skills and processing speed in normally aging adults (7). In addition, these aspects were also confirmed, in fact, by previous studies, such as the one conducted by Erickson et al. in 2011, which showed that exercise training increases size of hippocampus and improves memory processes (8).

As a matter a fact, there are also reports showing that six months of aerobic exercise could result in facilitated cognitive performing, improved executive function and attention, as well as increased task-related superior activity correlated to the anterior cingulated cortex (inhibiting activity in this cortical area) (9).

Also, there were previous studies performed on longer periods, such as one to two years, which showed an amelioration in the hippocampal volume loss, which is associated with aging, after various types of exercising (8). This could be extremely relevant, especially considering that the hippocampus is very well known for its implication on memory processes and storage (10).

Moreover, the aforementioned group of Chapman (7) found that even shorter term aerobic exercise (three months) can facilitate neuroplasticity and, additionally, to reduce both the biological and cognitive consequences of aging (as studied through various cognitive tests such as "Trails B--Trails A" (switching), California Verbal Learning Test, Wechsler Memory Scale, Delis-Kaplan Executive Function System--Color Word Interference subtest and Backward Digit Span) to benefit brain health in sedentary adults, as well as various hippocampal positive effects, as studied through very advanced MRI studies (7).

Various other reports stated also positive effects in this area of research, with exercising promoting from general adaptation and growth, preserving brain function, or enabling the brain to respond to future challenges (3), to specific and mechanistical aspects, such as increasing central perfusion (11), increased blood volume into hippocampus (with the aforementioned facilitatory effects on memory functions) (12) or other indirect improved memory-related processes (7, 8).

In addition, as we will also show in the present report, the animal studies are also important in this area of research, with previous studies describing that exercise causes gross structural and vascular plasticity (or adaptive brain modifications), enhances brain activity, and modulates important neurotransmitter systems (3).

In fact, mechanistically speaking, some of these effects can be explained by the positive effects exerted though the exercising on the cognition, with special focus on the immediate or delayed memory, as well as on the general brain function (e.g., increased flow), but also some specific factors, such as cardiovascular fitness aspects (e.g., [VO.sub.2max]). Moreover, physiological effects including the growth of new neurons in the hippocampus (the so-called neurogenesis) were also reported (1, 3).

There are a lot of evidences suggesting that exercise could affect slow wave sleep (13), with positive effects, of course, on the superior functions or could also enhance the general mood state (14), while there are evidences that it could help in ADHD (Attention Deficit Hyperactivity Disorder) (15).

The positive effects of exercising on inflammation are also cited (strong anti-inflammatory effects) (16). This could lead us to some of our group's original results regarding the relevance of oxidative stress metabolism (which is, of course, cited for its very close correlation to the inflammatory status) (17) and the performing exercise.

Therefore, as we showed in the paper published this year in the "Central European Journal of Medicine" (18), today it is well established that there is an important correlation between the physical exercise performance and the oxidative stress process, which is defined as the imbalance between the organism antioxidant capacity on one side and the overproduction of the reactive oxygen species (ROS) on the other side (19).

Thus, there are previous reports describing a direct relationship between the muscle oxidative stress status and the isometric force production (20) and it seems that a perfectly balanced equilibrium between ROS production and the enzymatic/non-enzymatic antioxidants will result in an ideal skeletal muscle force (21).

However, while some authors demonstrated an increase in the oxidative stress status as a result of physical exercise (22), there are also reports describing a so-called adaptation of the antioxidant system to physical exercise and training (23), which will result in an increase of the various types of antioxidant defences. These aspects led to numerous contradictions in the current literature regarding the levels of some oxidative stress markers after physical training.

So, back then, we were interested to study the modifications of some oxidative stress markers (two antioxidant enzymes--superoxide dismutase and glutathione peroxidase, a lipid peroxidation parameter--malondialdehyde, the Total Antioxidant Status--TAS and protein carbonyl levels), from the serum of rats that were subject to one bout of five minutes exercise on a treadmill. In this way, our original data showed additional evidences regarding the increase in the oxidative stress status as a result of a five minutes bout of treadmill exercising and expressed through a decrease in the SOD specific activity and the total antioxidant status and also an increase of the lipid peroxidation and protein oxidation processes (18).

Thus, when it comes to the exact mechanism governing the interaction between the contracting skeletal muscles and the oxidative metabolism, there are many controversies in the present literature, considering that some authors reported that intense and prolonged exercise can result in free radical generation and oxidative damage (21, 22), while on the other side, there are reports clearly stating that exercise performing will result in decreases oxidative stress and inflammation (as we mentioned earlier) (24) or in vivo experiments demonstrating that regular exercise is a very effective way to reduce oxidative stress, especially in old rats (25).

Moreover, there are many contradictions in this area of research regarding the levels of some oxidative stress markers after the exercise performing with increased (26), decreased (27) or no modifications at all (21) for the specific activity of the various antioxidant enzymes (e.g., superoxide dismutase--SOD, glutathione peroxidise--GPX and catalase--CAT), which have the role to counteract the harmful effects of the reactive oxygen species (ROS).

Additionally, despite some recent opinions stating that exercise-induced oxidative stress might be prevented by some antioxidant interventions (28), there is still insufficient knowledge about the interactions that could appear between the possible usage of antioxidants and their possible protective effect against exercise-induced oxidative damage.

In this way, in another paper which was just got accepted in the "Archives of Biological Science Journal" (29), we decided to investigate the effects of a 40 minutes bout of bicycle exercise on the main serum oxidative stress markers of some young untrained subjects, as well as the effects of vitamin C administration, 12 hours before the same kind of exercise, on these markers.

As follows, we demonstrated an increased oxidative stress status as a result of exercising, as demonstrated especially by the increased levels of malondialdehyde, as a marker of the lipid peroxidation processes and also by the decrease in the specific activity of some antioxidant enzymes, such as glutathione peroxidase, when compared to baseline.

More importantly, we also showed that the oxidative stress levels are reduced by the pre-administration of vitamin C, as demonstrated by the decreased levels of malondialdehyde and the increase in the activity of glutathione peroxidase, when compared to both baseline and effort without antioxidants administration groups.

These aspects suggested that it could be possible for the physically active subjects to consider increasing their daily dietary vitamin intake and we especially highlight here the possible reinforcement of the antioxidant defence system with vitamin C before physical training.

Coming back to the exercise and cognition, as we will discuss immediately, it is also important to mention, that although it is becoming increasingly clear that animal models and human research seem to confirm the relevance of the aerobic exercising on enhancing the superior functions, the quality of physical education it also seems very important for the cognitive/ memory outcome (this aspect could also perhaps explain some of the controversial and different results from this area of research, which were also presented in this report).

CONCLUSIONS

Therefore, it seems that human and non-human animal studies have shown that aerobic exercise can improve a number of aspects of cognition and superior functions. In this way, physical exercise could be considered a lifestyle factor that might lead to increased physical and mental health throughout life (1). However, there are still many unknowns and controversies in this area of research as we have shown in the present mini-review. In this way, one possible solution to solve this could be represented by a mutual agreement on a reduced battery of cognitive tests to use, in order to increase the reproducibility of results for future research (6).

Thus, perhaps a modern approach physical exercise should move away from its competitive-sports approach to one that refers to a wide range of play involving strenuous physical activity adapted for every participant (3).

ACKNOWLEDGMENTS AND DISCLOSURES

This paper is supported by the Sectoral Operational Programme Human Resources Development (SOP HRD), financed from the European Social Fund and by the Romanian Government under the contract number POSDRU/I5911.5151133675.

REFERENCES

(1.) Hillman, Charles H., Erickson, Kirk I., Kramer, Arthur F., Be smart, exercise your heart: exercise effects on brain and cognition, Nature Reviews Neuroscience 9, 58-65 (January, 2008)

(2.) Pujanek, M., Bronisz, A., Malecki, P., Junik, R., Pathomechanisms of the development of obesity in some endocrinopathies--an overview, Endokrynol Pol., 2013; 64(2):150-5

(3.) Sattelmair, Jacob, Ratey, John J., Physically Active Play and Cognition. An Academic Matter?, American Journal of PLAY, 2009, 365-374

(4.) Sibley, Benjamin A., Etnier, Jennifer L. (2003), The relationship between physical activity and cognition in children: A meta-analysis, Pediatric Exercise Science, 15:243-56

(5.) Dwyer, Terry, Coonan, Wayne E., Leitch, Donald R., Hetzel, Basil S., Baghurst, Peter A. (1983), An investigation of the effects of daily physical activity on the health of primary school students in South Australia, International Journal of Epidemiology, 12:308-13

(6.) Angevaren, M., Aufdemkampe, G., Verhaar, H. J., Aleman, A., Vanhees, L., Physical activity and enhanced fitness to improve cognitive function in older people without known cognitive impairment, Cochrane Database Syst Rev., 2008, Apr. 16;(2):CD005381

(7.) Chapman, S. B., Aslan, S., Spence, J. S., Defina, L. F., Keebler, M. W., Didehbani, N., Lu, H., Shorter term aerobic exercise improves brain, cognition, and cardiovascular fitness in aging Front Aging Neurosci., 2013, Nov 12; 5:75

(8.) Erickson, K. I., Voss, M. W., Prakash, R. S., Basak, C., Szabo, A., Chaddock, L. et al. (2011), Exercise training increases size of hippocampus and improves memory, Proc. Natl. Acad. Sci., U.S.A., 108, 3017-3022

(9.) Colcombe, S. J., Kramer, A. F., Erickson, K. I., Scalf, P., McAuley, E., Cohen, N. J. et al. (2004), Cardiovascular fitness, cortical plasticity, and aging, Proc. Natl. Acad. Sci., U.S.A., 101, 3316-3321

(10.) Eichenbaum, H., Cohen, N., Memory, amnesia, and the hippocampal system, MIT Press, 1993

(11.) Pereira, A. C., Huddleston, D. E., Brickman, A. M., Sosunov, A. A., Hen, R., McKhann, G. M. et al. (2007), An in vivo correlate of exercise-induced neurogenesis in the adult dentate gyrus, Proc. Natl. Acad. Sci., U.S.A., 104, 5638-5643

(12.) Burdette, J. H., Laurienti, P. J., Espeland, M. A., Morgan, A., Telesford, Q., Vechlekar, C. D. et al. (2010), Using network science to evaluate exercise-associated brain changes in older adults, Front. Aging Neurosci., 2:23

(13.) Horne, J. (2013), Exercise benefits for the aging brain depend on the accompanying cognitive load: insights from sleep electroencephalogram, Sleep Med., 14, 1208-1213

(14.) Blumenthal, J. A., Babyak, M. A., Moore, K. A., Craighead, W. E., Herman, S., Khatri, P. et al. (1999), Effects of exercise training on older patients with major depression, Arch. Intern. Med., 159, 2349-2356

(15.) Panksepp, Jaak (2008), Play, ADHD, and the construction of the social brain: Should the first class each day be recess?, American Journal of Play, 1:55-79

(16.) Kadoglou, N. P., Fotiadis, G., Athanasiadou, Z., Vitta, I., Lampropoulos, S., and Vrabas, I. S. (2012), The effects of resistance training on ApoB/ApoA-Iratio, Lp(a) and inflammatory markers in patients with type 2 diabetes, Endocrine 42, 561-569

(17.) Khansari, N., Shakiba, Y., Mahmoudi, M., Chronic inflammation and oxidative stress as a major cause of age-related diseases and cancer, Recent Pat Inflamm Allergy Drug Discov., 2009 Jan.; 3(1):73-80

(18.) Trofin, Florin-Petrut, Ciobica, Alin, Cojocaru, Dumitru, Chirazi, Marin, Honceriu, Cezar, Trofin, Laurentiu, Serban, Ionela Lacramioara, Cojocaru, Sabina Ioana, Anton, Emil, Increased oxidative stress in rat after five minutes treadmill exercise, Central European Journal of Medicine, 2014

(19.) Sies, H., Oxidative stress: oxidants and antioxidants, Experimental Physiology, 1997; 82: 291-295

(20.) Reid, M. B., Khawli, F. A., Moody, M. R., Reactive oxygen in skeletal muscle. III. Contractility of unfatigued muscle, J Appl Physiol., 1993; 75: 1081-1087

(21.) Powers, S. K., Jackson, M. J., Exercise-induced oxidative stress: cellular mechanisms and impact on muscle force production, Physiol Rev, 2008; 88: 1243-76

(22.) Reid, M. B., Shoji, T., Moody, M. R., Entman, M. L., Reactive oxygen in skeletal muscle. II. Extracellular release of free radicals, J Appl Physiol, 1992; 73: 1805-1809

(23.) Ji, L. L., Antioxidants and Oxidative Stress in Exercise, Exp Biol Med, 1999; 222: 283-292

(24.) Asghar, M., George, L., Lokhandwala, M. F. (2007), Exercise decreases oxidative stress and inflammation and restores renal dopamine D1 receptor function in old rats, Am J Physiol Renal Physiol, 293, 914-9

(25.) Goto, S., Radak, Z., Nyakas, C., Chung, H. Y., Naito, H., Takahashi, R. et al. (2004), Regular exercise: an effective means to reduce oxidative stress in old rats, Ann N Y Acad Sci, 1019, 471-4

(26.) Ohno, H., Suzuki, K., Fujii, J., Yamashita, H., Kizaki, T., Oh-ishi, S., Taniguchi, N. (1994), Superoxide dismutases in exercise and disease., Exercise and Oxygen Toxicity, 1, 127-161

(27.) Tiidus, P. M., Pushkarenko, J., Houston, M. E. (1996), Lack of antioxidant adaptation to short-term aerobic training in human muscle, Am J Physiol, 271, 832-836

(28.) Araujo, M., Pereira de Mour, Leandro, Ribeiro, Carla, Dalia, Rodrigo, Voltarelli, F. A. (2011), Oxidative stress in the liver of exercised rats supplemented with creatine, International Journal of Nutrition and Metabolism 3, 58-64

(29.) Trofn, Florin-Petrut, Chirazi, Marin, Honceriu, Cezar, Drosescu, Paula, Gradinariu, Gabriela, Vorniceanu, Alin, Anton, Emil, Cojocaru, Dumitru, Ciobica, Alin, Ciornea, Elena, Cojocaru, Ioana Sabina, Pre-administration of vitamin C reduces exercise-induced oxidative stress status in untrained subjects, Archives of Biological Sciences Belgr., 66, 3 (2014)

Florin Petrut Trofin--Ph. D. Fellow, Romanian Academy Iasi Branch, SOP HRD/159/1.5/S/133675 Project

Correspondence:

FLORIN PETRUT TROFIN

Bd. Carol I, nr. 8, Iasi, Romania

Tel./Fax: +40 754 288 343

E-mail: fiorintrofin@gmail.com

Date of Submission: May, 30, 2014/ Acceptance: August, 14, 2014

INTRODUCERE

Asa cum vom arata in prezenta mini-retrospectiva, in ultima vreme, se observa o accentuare a constientizarii conexiunilor care ar putea exista intre exercitiul fizic si starea cognitiva. In acest fel, publicatii fundamentale cum ar fi "Nature Journal" si "Cochrane Database of Systematic Reviews" s-au axat din ce in ce mai mult in ultima vreme pe acest subiect.

Astfel, in 2008, grupul de cercetare al Prof. Hillman a publicat o analiza cuprinzatoare (care deja a adunat aproape 1 000 de citate) descriind asa-numita initiativa "fii inteligent, antreneaza-ti inima", focusata, bineinteles, pe corelatiile care ar putea exista intre exercitiul fizic si creier si/sau cognitie (1).

In acest fel, este evident ca literatura multidisciplinara in curs de dezvoltare a demonstrat influenta importanta a exercitiului fizic asupra diferitelor aspecte ale diferitelor functiilor superioare ale creierului, prin utilizarea atat a studiilor pe oameni, cat si a celor pe animale, asa cum vom arata in continuare si prin folosirea unor rezultate originale ale grupului nostru.

Un alt aspect important in aceasta problema este reprezentat prin faptul ca lipsa activitatii fizice, in particular la copiii lumii dezvoltate, este una dintre cauzele majore ale obezitatii, o alta patologie moderna foarte importanta (2).

De fapt, exista, de asemenea, un curent modern care stipuleaza ca numarul dovezilor este in crestere in ceea ce priveste faptul ca activitatea fizica ar fi sanatoasa pentru studenti, dar, mai important, si ca imbunatateste performanta lor academica (3).

Ca o chestiune de fapt, exista si cateva metaanalize foarte cuprinzatoare in aceasta arie de cercetare, cum ar fi cea scrisa de Sibley et al. (asa cum a fost citata de Sattelmair) (3), care a reusit sa demonstreze o corelatie pozitiva intre activitatea fizica si cateva domenii sub-cognitive, cum ar fi: abilitatile perceptuale, coeficientul de inteligenta, atingerea unui scop, testele verbale, testele matematice, nivelul de dezvoltare/promptitudine academica a copiilor normali de varsta scolara (3, 4).

Mai mult, un studiu realizat de grupul lui Dwyer, in 2001, de asemenea, citat de Sattelmair (3), a raportat o corelatie semnificativa intre evaluarile academice si nivelul exercitiilor fizice/perfor mantei obtinute la testele fizice la un numar impresionant de aproape opt mii de scolari (3, 5).

Totusi, mai exista inca multe controverse in aceasta arie de cercetare, in special de cand, in alte studii independente, cum ar fi cel al grupului lui Ahamed din 2002, a fost raportat faptul ca interventiile in antrenamentul fizic nici nu au crescut, nici nu au scazut notele testului standardizat prin raportare la scoli-control (scoala din cadrul studiului a fost una canadiana care a implementat un program special de exercitii fizice in saisprezece luni) (3).

Exista insa dovezi bune ca antrenamentul ar putea nu doar sa ajute la imbunatatirea sanatatii fizice, dar si sa imbunatateasca performanta academica (1).

Mai mult, aceste efecte pozitive ale exercitiului fizic pot fi extrem de variate si pot include efecte la nivelul sistemelor molecular sau celular, precum si la cel comportamental (1).

In plus, in 2008, a fost publicata o alta lucrare vasta in faimoasa "Cochrane Database of Systematic Reviews" privind relevanta acestui subiect la persoanele in varsta (6). Astfel, grupul condus de Angevaren a reusit sa demonstreze ca activitatea fizica, ca si conditia fizica, de altfel, imbunatatesc functia cognitiva la persoanele adulte fara a provoca dereglari cognitive cunoscute (6).

Mai mult, autorii mentionati mai sus demonstreaza efectele pozitive ale activitatii fizice asupra imbatranirii sanatoase, concluzionand ca practicarea exercitiului fizic poate conserva functiile cognitive in stare buna la varste inaintate. In acest fel, ei analizeaza unsprezece studii relevante, in care singurii voluntari utilizati au avut peste 55 de ani, mentionand ca opt dintre aceste studii au sugerat o stare cognitiva imbunatatita. De fapt, domeniile subcognitive care au fost facilitate de exercitiul fizic au fost reprezentate de viteza cognitiva, de functiile de memorie intarziate, de atentia auditiva, de cea vizuala, precum si de functia motorie. Este, de asemenea, important de mentionat faptul ca autorii mai sus amintiti concluzioneaza ca, desi ei au gasit o corelatie temporala foarte semnificativa, datele existente sunt inca insuficiente pentru a arata ca imbunatatirile functiei cognitive care pot fi atribuite exercitiului fizic sunt datorate, cu siguranta, imbunatatirilor fitnessului cardiovascular, fiind necesare, prin urmare, studii mai ample pentru a confirma acest lucru, in mod special atunci cand unele domenii cognitive nu sunt afectate deloc de practicarea exercitiului fizic (6).

Mai mult, exista studii si mai recente, cum ar fi cel al grupului lui Chapman de la Universitatea din Texas, din 2013, care raporteaza ca exercitiile aerobice pot reprezenta, intr-adevar, o terapie preventiva ieftina pentru a reduce declinul cognitiv, incluzand memoria, functia executiva, abilitatile vizualo-spatiale si viteza de procesare a adultilor care imbatranesc normal (7). In plus, aceste aspecte au fost confirmate, in fapt, de studii precedente, cum ar fi cel condus de Erickson, in 2011, care a aratat ca antrenamentul fizic creste marimea hipocampului si imbunatateste procesele memoriei (8).

Ca un fapt de drept trebuie sa mentionam ca exista studii care arata ca sase luni de exercitiu aerob pot facilita performanta cognitiva, imbunatati functia executiva si atentia, precum si cresterea activitatii superioare referitoare la sarcini, corelate cu girusul cingular anterior (inhiband activitatea in aceasta zona corticala) (9).

De asemenea, exista si o serie de studii efectuate pe parcursul unor perioade mai lungi, cum ar fi unul de doi ani, care subliniaza o ameliorare in volumul hipocampal pierdut, care este asociat cu imbatranirea dupa diferite tipuri de exercitii (8). Acest lucru ar putea fi extrem de relevant, in special considerandu-se ca hipocampul este bine cunoscut pentru implicatiile sale in procesele memoriei si stocarii informatiilor (10).

Mai mult, grupul Chapman mentionat mai sus (7) a gasit ca exercitiile aerobe pe un termen mai scurt (trei luni) pot facilita neuroplasticitatea si, in mod aditional, reducerea atat a consecintelor biologice, cat si a celor cognitive ale imbatranirii (asa cum a fost studiat prin diferite teste cognitive, cum ar fi "Trails B--Trails A"--cu schimbare, California Verbal Learning Test, Wechsler Memory Scale, sub testul Delis-Kaplan Executive Function System--Color Word Interference and Backward Digit Span) pentru a beneficia de sanatatea creierului adultii sedentari, la fel ca si de alte variate efecte pozitive ale hipocampului, asa cum au fost acestea cercetate prin studii MRI foarte avansate (7).

Diferite alte studii arata, de asemenea, efecte pozitive in acest domeniu de cercetare, promovand exercitiul fizic pentru dezvoltarea generala, conservarea functiei creierului sau permiterea creierului de a raspunde la provocari viitoare (3), la aspecte specifice si mecanice, precum cresterea perfuziei centrale (11), cresterea volumului de sange in hipocamp (cu efectele mentionate mai sus care faciliteaza functiile memoriei) (12) sau alte imbunatatiri indirecte referitoare la procesele memoriei (7, 8).

In plus, asa cum vom arata in aceasta analiza, studiile pe animale sunt importante in acest domeniu de cercetare, studiile precedente descriind faptul ca exercitiile cauzeaza plasticitate vasculara si structurala bruta (sau modificari ale adaptarii creierului), stimuleaza activitatea creierului si regleaza sistemele neurotransmitatoare importante (3).

De fapt, din punct de vedere mecanic, cateva dintre aceste efecte pot fi explicate de rezultatele pozitive exercitate prin antrenament asupra cognitiei, cu o concentrare speciala asupra memoriei imediate sau intarziate, la fel ca si pe functia generala a creierului (de exemplu: cresterea fluxului), dar, totodata, si asupra catorva factori specifici, cum ar fi aspectele fitnessului cardiovascular (de exemplu: [VO.sub.2max]). Mai mult, au fost raportate efecte fiziologice incluzand cresterea de noi neuroni in hipocamp (asa-numita neurogeneza) (1, 3).

Exista, totodata, si multe dovezi care sugereaza ca exercitiul fizic poate, de asemenea, influenta undele lente ale somnului (13), cu efecte pozitive asupra functiilor superioare sau care ar putea, de asemenea, imbunatati dispozitia generala (14); in acelasi timp, exista si dovezi care ar putea ajuta in ADHD (deficitul de atentie) (15).

Efectele pozitive ale exercitiului fizic asupra inflamatiilor sunt, de asemenea, citate (puternice efecte antiinflamatorii) (16). Acestea ne pot conduce spre unele rezultate ale grupului nostru in ceea ce priveste relevanta stresului oxidativ metabolic (care este citat pentru corelatiile puternice stabilite cu starea inflamatorie) (17) si practicarea exercitiului fizic.

In acest fel, asa cum am aratat in lucrarea publicata in "Central European Journal of Medicine" (18), in prezent, este bine stabilit faptul ca exista o importanta legatura intre capacitatea de efort fizic si procesele stresului oxidativ, care este definit ca un dezechilibru intre capacitatea antioxidanta a organismului, pe de o parte, si productia de specii reactive ale oxigenului (SRO), pe de alta parte (19).

Cu toate acestea, studii anterioare descriu relatia directa dintre stresul oxidativ muscular si producerea fortei izometrice (20), rezultand faptul ca un echilibru perfect stabilit intre productia de SRO si antioxidantii enzimatici/neenzimatici va duce la producerea unei forte musculare ideale (21).

In acest context, in timp ce unii autori au demonstrat o crestere a stresului oxidativ, ca urmare a practicarii exercitiului fizic (22), in alte cercetari se descriu asa-zisele adaptari ale sistemului antioxidant la efort fizic si antrenament (23), rezultand astfel o crestere a diferitor sisteme defensive antioxidante. Aceste aspecte conduc la numeroase contradictii in literatura curenta privind nivelul unor markeri ai stresului oxidativ determinat dupa antrenamentul fizic.

Asadar, revenim la modificarile pe care dorim sa le studiem la cativa markeri ai stresului oxidativ (doua enzime antioxidante--superoxid dismutaza si glutation peroxidaza, un parametru al peroxidarii lipidice--malon dialdehida, Capacitatea Antioxidanta Totala--CAT si nivelul proteinelor carbonilice), din serul sobolanilor care au fost utilizati pentru efectuarea unui efort fizic de cinci minute pe banda de alergare. In acest sens, datele noastre au evidentiat accentuarea stresului oxidativ in urma unui efort fizic de cinci minute pe banda de alergare, acest lucru fiind exprimat prin scaderea activitatii specifice a SOD si a capacitatii antioxidante totale si, de asemenea, cresterea peroxidarii lipidice si a proceselor de oxidare proteica (18).

Totusi, atunci cand vine vorba despre mecanismul exact care guverneaza interactiunile dintre contractiile musculaturii scheletice si metabolismul oxidativ, exista multe controverse in literatura actuala, unii autori considerand ca eforturile intense si prelungite pot duce la generarea radicalilor liberi si la daune oxidative (21, 22), iar, pe de alta parte, unele studii demonstreaza clar ca practicarea exercitiului fizic conduce la reducerea stresului oxidativ si a inflamatiei (asa cum am precizat mai sus) (24) sau experimentele in vivo au demonstrat ca exercitiul fizic regulat este o cale foarte eficienta pentru a reduce stresul oxidativ, in special la sobolanii in varsta (25).

Mai mult, exista multe contradictii in aceasta arie de cercetare privind nivelul unor markeri ai stresului oxidativ dupa efort fizic, cercetarile raportand cresteri (26), reduceri (27) sau modificari nesemnificative (21) pentru activitatea specifica a unor antioxidanti enzimatici (de exemplu: superoxid dismutaza--SOD, glutation peroxidaza--GPX si catalaza--CAT), care au rolul de a contracara efectele distructive ale speciilor reactive ale oxigenului (SRO).

In plus, in ciuda unor opinii de actualitate, conform carora stresul oxidativ indus de efortul fi zic poate fi prevenit prin intermediul interventiei antioxidante (28), exista, totusi, insuficiente informatii cu privire la interactiunile ce pot sa apara intre posibilele utilizari ale antioxidantilor si efectele protective impotriva daunelor oxidative induse de acesta.

In acest sens, in alt articol care tocmai a fost acceptat la "Archives of Biological Science Journal" (29), am decis sa evaluam efectul a 40 de minute de efort pe cicloergometru asupra catorva markeri ai stresului oxidativ la subiecti tineri neantrenati, precum si efectul administrarii vitaminei C cu douasprezece ore inaintea aceluiasi tip de efort fizic, asupra acelorasi markeri.

In acest sens, am demonstrat o crestere a stresului oxidativ ca urmare a depunerii efortului fizic, lucru demonstrat de cresterea nivelului malondialdehidei, ca un indicator al proceselor de peroxidare lipidica si, de asemenea, prin reducerea activitatii specifice a unor enzime antioxidante, precum glutation peroxidaza, prin raportare la valorile bazale.

Mai important, am demonstrat ca nivelul stresului oxidativ este redus prin preadministrarea vitaminei C, lucru demonstrat de reducerea nivelului malondialdehidei si intensificarea activitatii glutation peroxidazei prin raportare la valorile obtinute in conditii bazale, cat si dupa efortul fizic fara administrare de antioxidanti.

Aceste aspecte sugereaza ca subiectii activi din punct de vedere fizic pot lua in considerare cresterea ratiei zilnice de vitamine, evidentiind astfel, in special, posibila intarire a sistemului antioxidant cu vitamina C inainte de efortul fizic.

Revenind la efortul fizic si cognitie, despre care vom vorbi imediat, este, de asemenea, important de mentionat--chiar daca este din ce in ce mai clar faptul ca modelele animale si umane de cercetare par sa confirme relevanta efortului fizic aerob asupra imbunatatirii functiilor superioare--calitatea educatiei fizice care pare a fi foarte importanta pentru cognitie si memorie (acest aspect poate, probabil, explica cateva dintre controversele si rezultatele diferite din aceasta arie de cercetare, care sunt prezentate in prezenta lucrare).

CONCLUZII

Asadar, se pare ca studiile pe modele umane si animale au aratat ca efortul fizic aerob poate imbunatati un numar de aspecte ale cognitiei si functiilor superioare. In acest sens, practicarea efortului fizic poate fi considerat un factor al stilului de viata ce poate conduce spre imbunatatirea sanatatii fizice si mentale de-a lungul vietii (1). Cu toate acestea, exista si multe necunoscute si controverse in acest domeniu de cercetare, dupa cum am aratat in prezentul material. In acest sens, o posibila solutie pentru a rezolva acest lucru poate fi reprezentata de un acord mutual pentru reducerea bateriei de teste cognitive utilizate in scopul cresterii reproductibilitatii rezultatelor in cercetarile viitoare (6).

Cu toate acestea, probabil insusi modul modern de abordare a efortului fizic ar trebui sa se transfere din sfera abordarii sporturilor in cea care se refera la o scara mai larga a activitatii care implica activitate fizica adaptata fiecarui individ (3).

MULTUMIRI SI DEVOALARI

Aceasta lucrare este sustinuta de Programul Operational Sectorial de Dezvoltare a Resurselor Umane (SOP HRD), finantat din Fondul Social European si de Guvernul Romaniei, sub contractul cu numarul POSDRU/ 15911.5151133675.

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(29.) Trofn, Florin-Petrut, Chirazi, Marin, Honceriu, Cezar, Drosescu, Paula, Gradinariu, Gabriela, Vorniceanu, Alin, Anton, Emil, Cojocaru, Dumitru, Ciobica, Alin, Ciornea, Elena, Cojocaru, Ioana Sabina, Pre-administration of vitamin C reduces exercise-induced oxidative stress status in untrained subjects, Archives of Biological Sciences Belgr., 66, 3 (2014)

Florin Petrut Trofin--bursier doctorand, Academia Romana, Filiala Iasi, Proiectul SOP HRD/159/1.5/S/133675

Corespondenta:

FLORIN PETRUT TROFIN

Bd. Carol I, nr. 8, Iasi, Romania

Tel./Fax: +40 754 288 343

E-mail: fiorintrofin@gmail.com

Trimis: 30 Mai 2014 / Acceptat: 14 August 2014
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Date:Sep 1, 2014
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