International SportMed Journal - Volume 7, Issue 1, 2006
Volume 7, Issue 1, 2006
Author Peter GermonpreSource: International SportMed Journal 7, pp 1 –15 (2006)More Less
SCUBA diving carries with it not only the risks associated with any kind of adventurous outdoor activity, but also some hazards typical of the exposure to high environmental pressure while under water. Through a systematic overview of these hazards, the principles of barotrauma and decompression sickness are explained. <br>Some of the discussion looks at the fact that many, if not most, of the commonly used decompression aids (e.g. tables or computers) use algorithms that have been derived from rather crude observations, and so can only, at best, give an "educated guess" at how to decompress a diver in trouble safely. It is thus unwise to dive to the limits of these devices, as this may dramatically increase the risk of having a diving accident.
Seasonal changes and physiological responses : their impact on activity, health, exercise and athletic performance : review articleSource: International SportMed Journal 7, pp 16 –32 (2006)More Less
Changes associated with the seasons affect climatic and environmental conditions across the globe. Environmental temperatures, hours of daylight and precipitation vary according to latitude and the prevailing season. Biological and cultural adaptations have enabled humans to inhabit the major climatic regions. Environmental and climatic changes during the annual cycle often force humans to change their social behaviour and the range and amount of physical activity. Such seasonal changes can have a detrimental effect on human health. Seasonal adjustment in human activity and behaviour also influence the physical fitness levels of individuals which alter with the quality of training inputs. The competitive sports calendar determines the circannual variations in training of athletes and their performance peaks. Notwithstanding the seasonal variability observed in physiological variables, the major influences on circannual rhythms appear to be the dimensions of the training programmes employed by athletes. Specific sports are biased towards winter or summer peaks, whereas indoor facilities provide an environment sheltered from the forces of nature and thus promote all-year-round activity. Weather conditions and surface characteristics have consequences for injury risk and the quality of performance. It is concluded that activity and fitness levels are more a function of organisational and external factors than are endogenous circannual rhythms.
Source: International SportMed Journal 7, pp 33 –57 (2006)More Less
During extended heat exposure, humans can experience three phases of heat adaptation. These start with the cardiovascular, sudomotor and neuroendocrine reactions induced by an acute heat exposure, progressing to an amplification of these responses (Phase two: positive adaptation), and possibly ending with the more efficient negative adaptation (Phase three) seen in indigenes from hot climates, where skin blood flow and sweating are reduced. This review briefly describes these physiological changes and provides a theoretical background underpinning adaptation strategies. Gender differences in the acute and adaptation responses are not discussed. Using simple modelling, there is a development of the key principles that are essential to evaluating the need for heat adaptation in various sports, and there is discussion of the disadvantages of heat adaptation. Several adaptation practices are described and evaluated relative to the needs of the athlete. From these, it is concluded that living and training under hot conditions may best improve performance in the heat. However, since high-intensity training is invariably hard to sustain in the heat, it is recommended that athletes live in the heat, experience heat under the pressure of competition, acclimate for a specific climate and then undertake high-quality training in the cool. Athletes must not ignore the psychological aspects of preparing for competition in the heat, since inappropriate choices can undo years of physiological preparation.
Author Timothy D. NoakesSource: International SportMed Journal 7, pp 58 –74 (2006)More Less
A remarkable feature of the human species is our great capacity to lose heat and to regulate our body temperatures when exposed to heat. The Heinrich (Hunting) hypothesis theorises that this capacity evolved in early hominids and provided an extraordinary evolutionary advantage since it allowed our human ancestors to chase nutritionally-dense but non-sweating mammals like large antelope, to their (lesser) limits of thermoregulatory failure. In this fatigued state, the exhausted animals were more easily killed. It is further hypothesised that it was the consumption of the high protein / fat diet made possible by the capture of such animals that fuelled the development of the higher brain centres on which superior human intelligence depends. But the key physiological point is that during the hunt, early hominids had no access to fluid, the carrying of which would have hindered their ability to run. Thus for their evolutionary progress to have occurred, humans had to evolve a sweating mechanism to prevent overheating during exercise, as well as the capacity to continue exercising in the heat even though they were becoming increasingly dehydrated as the duration of the hunt increased and the environmental conditions likely became more severe. <br>Until 1969 the advice given to endurance athletes mirrored this understanding of our evolutionary biology. Thus human athletes were advised <I>not</I> to drink during exercise. But the development of the world's first "sports drink" in Florida in the 1960s led gradually, but perhaps inevitably, to the promotion of a novel dogma that humans need to drink "as much as tolerable" during exercise if they are to avoid heatstroke and to optimise their performances. <br>In this article this and three other dogmas that have evolved simultaneously over the past 35 years are analysed. These are: (i) that dehydration is the most important determinant of the body temperature during exercise; (ii) that athletes collapse after exercise because of a circulatory collapse caused by dehydration and hyperthermia; and (iii) that heatstroke always occurs in otherwise normal, healthy athletes who simply exercise too hard for too long in exceptionally hot conditions. <br>Rather, it is argued in this paper that (i) all the published evidence supports the belief that health and performance during exercise are optimised by drinking according to the dictates of thirst ("ad libitum"); (ii) the brain sets both the work rate and the rectal temperature during exercise specifically to insure that heatstroke will almost never occur in otherwise healthy humans. As a result, the rectal temperature is determined principally by the exercising work rate; (iii) that post-exercise collapse in athletes who remain conscious is due to a low peripheral vascular resistance to which dehydration makes essentially no contribution; and (iv) that heatstroke is more likely due to an exaggerated and explosive thermogenesis that develops in genetically-predisposed individuals on exposure to exercise and other triggering environmental factors. It is also suggested that the skeletal muscles are the site of this florid thermogenesis and that the leakage of toxic proteins into the circulation from damaged muscles, and not the hyperthermia, is the more likely cause of the multiple organ failure that typifies fatal heatstroke.