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This is your brain, this is your brain on exericse!!!

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  • This is your brain, this is your brain on exericse!!!

    It’s been a generally held belief that cerebral blood flow (CBF) remains relatively steady during exercise, but recent studies (see abstracts below) suggest that’s not the case. CBF appears to depend on a multitude of factors, including exercise intensity. With lower intensity steady state forms of exercise – all things being equal, such as hydration, etc, - CBF may increase, but during high intensity intermittent forms of exercise, appears to decrease. This may partially explain the cognitive decline people experience during high intensity exercise.

    This information very much applies to law enforcement and military. Under psychological stress, demand for CBF increases, while supply may decrease, resulting in additional cognitive decline.

    If a person has not experienced that cognitive decline under training conditions - and so has some experience and understanding of its effects - the results could prove fatal during a “real life” encounter.

    If one has not experienced some stress training, they often find even simple directions difficult to follow during their first exposure to it. For example, simple directions regarding which targets to engage in which order, or other simple simple instructions, fail to happen…

    Obviously, this will differ greatly with the persons experience, training, fitness, etc., but it’s well established that physical + psychological stress = decline in cognitive abilities and that’s old news for most and common sense.

    The specific effects of stress, physical and psychological, on cognitive abilities is a large topic and not my area of expertise as it pertains to LE or mil.

    I’m sure others here can comment on that.

    Basic take home: some form of stress training, where higher intensity, intermittent, training combined with firearms- hopefully following some job/task relevant movement patterns - will help best prepare those who are likely to face violent encounters that require an ability to function under physical and psychological stress simultaneously.

    Additionally, such training will add to an ability to physically deal with the effects of stress and will improve overall fitness and general physical preparedness (GPP) of law enforcement and mil populations.

    My article “Improving the Physical Preparedness and Operational longevity of the SWAT Operator” has some additional info on this topic, and although directed at tactical LE, has useful info for mil and the dedicated civi, interested in practical stress training and it’s potential benefits.

    Finally, although everyone in the “tactical community” is well aware of the negative impact of dehydration on performance, I thought these recent studies below looking specifically at the effects of dehydration on cognitive function, interesting.

    Studies of interest:

    J Appl Physiol. 2009 Nov;107(5):1370-80. Epub 2009 Sep 3.
    Cerebral blood flow during exercise: mechanisms of regulation.
    Ogoh S, Ainslie PN.
    Dept. of Biomedical Engineering, Toyo Univ., 2100 Kujirai, Kawagoe-shi, Saitama 350-8585, Japan. [email protected]
    Abstract
    The response of cerebral vasculature to exercise is different from other peripheral vasculature; it has a small vascular bed and is strongly regulated by cerebral autoregulation and the partial pressure of arterial carbon dioxide (Pa(CO(2))). In contrast to other organs, the traditional thinking is that total cerebral blood flow (CBF) remains relatively constant and is largely unaffected by a variety of conditions, including those imposed during exercise. Recent research, however, indicates that cerebral neuronal activity and metabolism drive an increase in CBF during exercise. Increases in exercise intensity up to approximately 60% of maximal oxygen uptake produce elevations in CBF, after which CBF decreases toward baseline values because of lower Pa(CO(2)) via hyperventilation-induced cerebral vasoconstriction. This finding indicates that, during heavy exercise, CBF decreases despite the cerebral metabolic demand. In contrast, this reduced CBF during heavy exercise lowers cerebral oxygenation and therefore may act as an independent influence on central fatigue. In this review, we highlight methodological considerations relevant for the assessment of CBF and then summarize the integrative mechanisms underlying the regulation of CBF at rest and during exercise. In addition, we examine how CBF regulation during exercise is altered by exercise training, hypoxia, and aging and suggest avenues for future research.

    ________________________________

    Sports Med. 2007;37(9):765-82.
    Regulation of cerebral blood flow during exercise.
    Querido JS, Sheel AW.
    Health and Integrative Physiology Laboratory, School of Human Kinetics, The University of British Columbia, Vancouver, British Columbia, Canada.
    Abstract
    Constant cerebral blood flow (CBF) is vital to human survival. Originally thought to receive steady blood flow, the brain has shown to experience increases in blood flow during exercise. Although increases have not consistently been documented, the overwhelming evidence supporting an increase may be a result of an increase in brain metabolism. While an increase in metabolism may be the underlying causative factor for the increase in CBF during exercise, there are many modulating variables. Arterial blood gas tensions, most specifically the partial pressure of carbon dioxide, strongly regulate CBF by affecting cerebral vessel diameter through changes in pH, while carbon dioxide reactivity increases from rest to exercise. Muscle mechanoreceptors may contribute to the initial increase in CBF at the onset of exercise, after which exercise-induced hyperventilation tends to decrease flow by pial vessel vasoconstriction. Although elite athletes may benefit from hyperoxia during intense exercise, cerebral tissue is well protected during exercise, and cerebral oxygenation does not appear to pose a limiting factor to exercise performance. The role of arterial blood pressure is important to the increase in CBF during exercise; however, during times of acute hypotension such as during diastole at high-intensity exercise or post-exercise hypotension, cerebral autoregulation may be impaired. The impairment of an increase in cardiac output during exercise with a large muscle mass similarly impairs the increase in CBF velocity, suggesting that cardiac output may play a key role in the CBF response to exercise. Glucose uptake and CBF do not appear to be related; however, there is growing evidence to suggest that lactate is used as a substrate when glucose levels are low. Traditionally thought to have no influence, neural innervation appears to be a protective mechanism to large increases in cardiac output. Changes in middle cerebral arterial velocity are independent of changes in muscle sympathetic nerve activity, suggesting that sympathetic activity does not alter medium-sized arteries (middle cerebral artery).CBF does not remain steady, as seen by apparent increases during exercise, which is accomplished by a multi-factorial system, operating in a way that does not pose any clear danger to cerebral tissue during exercise under normal circumstances.
    ________________________________________

    J Am Coll Nutr. 2007 Oct;26(5 Suppl):604S-612S.
    Exercise, heat, hydration and the brain.
    Maughan RJ, Shirreffs SM, Watson P.
    School of Sport and Exercise Sciences, Loughborough University, Leicestershire LE11 3TU, United Kingdom. [email protected]
    Abstract
    The performance of both physical and mental tasks can be adversely affected by heat and by dehydration. There are well-recognized effects of heat and hydration status on the cardiovascular and thermoregulatory systems that can account for the decreased performance and increased sensation of effort that are experienced in the heat. Provision of fluids of appropriate composition in appropriate amounts can prevent dehydration and can greatly reduce the adverse effects of heat stress. There is growing evidence that the effects of high ambient temperature and dehydration on exercise performance may be mediated by effects on the central nervous system. This seems to involve serotonergic and dopaminergic functions. Recent evidence suggests that the integrity of the blood brain barrier may be compromised by combined heat stress and dehydration, and this may play a role in limiting performance in the heat.
    _________________________________________________
    Int J Psychophysiol. 2001 Nov;42(3):243-51.
    Effects of fluid ingestion on cognitive function after heat stress or exercise-induced dehydration.
    Cian C, Barraud PA, Melin B, Raphel C.
    Centre de Recherches du Service de Santé des Armées, Unités de Psychologie et de Bioénergétique et Environnement, 38702 La Tronche Cedex, France. [email protected]
    Abstract
    This study investigated the effects of heat exposure, exercise-induced dehydration and fluid ingestion on cognitive performance. Seven healthy men, unacclimatized to heat, were kept euhydrated or were dehydrated by controlled passive exposure to heat (H, two sessions) or by treadmill exercise (E, two sessions) up to a weight loss of 2.8%. On completion of a 1-h recovery period, the subjects drank a solution containing 50 g l(-1) glucose and 1.34 g l(-1) NaCl in a volume of water corresponding to 100% of his body weight loss induced by dehydration. (H1 and E1) or levels of fluid deficit were maintained (H0, E0). In the E0, H0 and control conditions, the subject drank a solution containing the same quantity of glucose diluted in 100 ml of water. Psychological tests were administered 30 min after the dehydration phase and 2 h after fluid ingestion. Both dehydration conditions impaired cognitive abilities (i.e. perceptive discrimination, short-term memory), as well as subjective estimates of fatigue, without any relevant differences between the methods. By 3.5 h after fluid deficit, dehydration (H0 and E0) no longer had any adverse effect, although the subjects felt increasingly tired. Thus, there was no beneficial effect of fluid ingestion (H1 and E1) on the cognitive variables. However, long-term memory retrieval was impaired in both control and dehydration situations, whereas there was no decrement in performance in the fluid ingestion condition (H1, E1).
    Last edited by WillBrink; 10-03-2010, 04:39 AM.
    - Will

    Performance/Fitness Advice For the Tactical Community

    www.OptimalSWAT.com

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    www.BrinkZone.com

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