Heart and Vasculature Complications

Exercise-cold stress alters sympathetic nervous activity such that it causes an increase in vascular resistance, mean arterial pressure, and strain on the heart because of increases in stroke volume to compensate for lack of peripheral blood flow and increase in heart rate to meet the demands of oxygenated blood to working muscle, peripheral tissue and visceral organs (Doubt, 1991). Knowing this should prove to be obvious that athletes that are hypertensive or have heart conditions, such as angina, should be extremely carefully when exercising at high intensities (>70% of VO2 max).

Prospective in Future Research Majority of this research has been tested on rats, but provides a great deal of insight on ways to describe certain physiological occurrences that we currently cannot explain in great depth in humans, or need more plausible data to support any claims that we have at this point in time. The first study of concern looks at the effects of the catecholamine epinephrine on cold tolerance and brown adipose tissue.

Catecholamines have been described to have a major role in non-shivering thermogenesis through adrenergic receptors (Schonbaum et al., 1966). In humans, infusion of epinephrine is highly thermogenic (Jequier et al., 1992) and has the ability to aid in metabolic heat production during circumstances of thermal debt. Epinephrine, a “fight or flight” hormone is released into the blood stream during times of stress to provide sufficient energy for the body to get out of a potentially life threatening situation, such a cold stress, for example. Epinephrine therefore reduces the need for vasoconstriction and allows for heat generation to occur, while maintaining peripheral blood flow to tissue and potentially working skeletal muscle.

Brown adipose tissue (BAT) is fat that generates heat via non-shivering thermogenesis in newborns and mammals, but in some studies has proven to be present in small quantities on adults as well and related to skeletal muscle (Nedergaard, Bengtsson, and Cannon, 2007). These results have not been replicated in enough studies to produce any solid claims. But it is proven that BAT is present in mammals and that gene expression of BAT mitochondria requires the presence of epinephrine (Sharara-Chamia et al., 2010). Therefore, if it is possible to isolate for the process or mechanism responsible for the removal of BAT, and halt its occurrence, then another door for heat maintenance can be opened in adult humans.

The next study of interest was conducted by Bruton et al. (2010) addressing the similarities between adaptations made in skeletal muscle of mice during cold exposure and adaptation during endurance training. They believed that increased myoplasmic free calcium is necessary for these adaptations to take place. Experiments were performed on flexor digitorum brevis (FDB) muscles, which are not effecting by the involuntary contractions of a shivering response, of cold acclimated mice.

They had noticed that muscle fibres showed considerable increases in calcium levels, compared to fibres from the room-temperature control group mice. The cold-acclimated mice had an increased expression of genes and enzymes that imitate an enhanced production of mitochondria. As a result, muscle fibres had shown an improved resistance to fatigue (Figure 4). Bruton and his colleagues attribute their results to the presence of calcium during these adaptations. This shows that perhaps through calcium supplementation in cold acclimation, we can also produce more mitochondria to make work during the cold more efficient.

Experiment Experimental Hypothesis: Acclimation induced by long term exposure to moderate cold conditions should illicit hypothermic habituation. This will result in a more stable, efficient, and effective adaptation to sport performance in a cold environment, than that of acclimation induced from chronic short term exposures of severe cold that produce metabolic and insulative inclined acclimation. But athletes with combined approach will show a greater overall performance due to more thorough adaptation to the environment, equipping them with better means of performing, while the unacclimated group will perform the worst in comparison to other group.

Proposed Methods to Test Hypothesis Twenty endurance trained runners of ideally same or similar body composition, age, sex, and aerobic fitness will be split equally into four groups. One group will be exposed to a moderate cold climate, intended to alter the athlete’s core temperature to 36.7°C for 10 hours per day, 4 days per week for a total of 3 weeks. The second group will be exposed to a severe cold climate to alter their core temperature to 35.5°C in order to induce a state of near hypothermia (provoking sub-maximal shivering) for 10 minutes straight per day, 5 days per week for a total of 3 weeks.

The third group will receive a combination of moderate cold and sever cold conditions. On every odd day (day 1,3,5,7) athletes will experience the moderate cold climate for 10 hours, while on even days (day 2,4,6) athletes will experience the severe cold climate for 10 minutes and this will go on for 3 weeks. The fourth group will be a control group, not undergoing any form of acclimation. Athletes will be warmed up appropriately after time spent in cold room with vitals being constantly monitored to ensure that nothing goes wrong. At the end of the 3 week period, all athletes will compete in 3 trials (on 3 separate days) of a 10 km run in -10°C weather (without any wind chill). Ideally control over any nutritional difference across individuals will be made to remove any controllable bias. At the end of the run, mean times from each trial and group will be calculated and compared to see which group performed better during the run.

Predicted Results The group that is predicted to perform the best during the run will be the athletes that went under the combined method of acclimation. Coming in a close second place will be the hypothermic habituation group that was in the moderate cold climate. Next, in a close third place should be the group that was in severe cold climate. Finally, the unacclimated group will perform the worst coming in last place.

Applying Knowledge to Support Hypothesis The logic behind the combined acclimated group coming in first is simply because as stated in the hypothesis will have an advantage and be more prepared than the other groups during multiple trials of runs. The group that would come in second place would be close, but would be the moderate cold group. This is because the habituated group would have a blunted shiver response and decreased vasoconstriction of the periphery meaning that they would have a greater efficiency of blood flow to skeletal muscle. Because of this however, they are at a greater risk of cold-related injury, but considering they are competing for better times, they will be going at high intensities ensuring that body temperature is maintained throughout the race. In third place is the metabolic and insulative acclimated group.

The increase in metabolic heat production might help them to generate more energy early on during the race, but this could predispose them to fatigue earlier in the race. Also these athletes might not find a heightened shivering response to be very useful when they are constantly moving for the race, but they put up a good fight. Finally, the unacclimated group performed the worst simply because their bodies went into shock during the run and were be unable to adapt to the cold efficiently enough in time to catch up or to outperform any of their counterparts from other groups.

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