The effect of a Microgravity environment on autonomic cardiovascular control, energy expenditure and muscle characteristics

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The decision of Mark Shuttleworth to travel to space has provided South Africa with a unique opportunity to promote and share our unique scientific research and technology with the rest of the world. The Exercise Science and Sports Medicine Department of the University of Cape Town together with Body iQ have proposed a study entitled “The effect of a microgravity environment on autonomic cardiovascular control, energy expenditure and muscle characteristics”. The rationale, aims and methodology of the study are discussed below.

Both heart rate and blood pressure are controlled by the autonomic nervous system. This nervous system is an unconscious, or “automatic” nervous system, which consists of 2 parts – the parasympathetic nervous system and the sympathetic nervous system. These 2 systems have opposing roles and are activated according to the different needs of the individual. The parasympathetic nervous system is activated during rest and assists in energy restoration by means of the digestion and absorption of food. This system also acts to decrease heart rate. The sympathetic nervous system, on the other hand, prepares the body for an emergency and counteracts the parasympathetic nervous system in order to maintain the required energy supply. During any emotional or physical stress, adrenaline is released by the sympathetic nervous system, which acts to increase heart rate and blood pressure.

Accordingly, heart rate is controlled by the balance between parasympathetic (PNS) and sympathetic nervous system (SNS) activity. On a beat-to-beat basis, however, it has been observed that heart rate is not constant and there are periodical fluctuations indicative of the relative contributions of each of these 2 components of the autonomic nervous system. There have been various methods employed in an attempt to quantify the relative contributions of each of these systems. One of the most commonly used methods is the frequency domain analysis of heart rate variability. This method uses highly sophisticated techniques to determine different frequencies of heart rate and from this analysis can identify which nervous system is predominantly active during both rest and exercise.

There have been very few studies conducted during space flights that have measured this component of physiology, and those that have been done have yielded conflicting results. Therefore, the first aim of this study will be to determine whether the relative contributions of the parasympathetic and sympathetic nervous system remain the same in space when compared to earth and in this way we hope to provide additional information to the scientific literature to either support or refute the notion that heart rate variability is different between the 2 conditions. Heart rate will be measured using an on-board electrocardiograph (ECG), after which, the collected heart rate data will be transmitted to earth, via satellite, where it will be analysed and interpreted.

A second aim of the study will be to provide Mark with a number of specifically designed exercises that he will be able to do both before he leaves for space as well as while he is in space. Previous research has shown that although there is no muscle damage that occurs during space flight, predominantly because there is no gravity to load the muscles, as soon as the astronauts arrive back to earth they experience muscle pain and stiffness. This muscle pain is similar to that which we experience on earth after participating in any unaccustomed or strenuous exercise, and is caused by miniature tears to the muscle fibres. This pain usually occurs a little while after the exercise, and hence it has been referred to as delayed onset muscle soreness (DOMS). Other studies have shown that if an exercise causes this kind of response, it is likely that there may be some protective effect on that muscle and that if the same exercise is performed on a second occasion, this pain and muscle damage may be slightly less.

A component of space travel that has been extensively studied is that of energy balance and energy expenditure. The use of the doubly labeled water technique, a very accurate means of measuring total daily energy expenditure (TEE), has previously been validated in space with highly accurate results. It has been found that astronauts lose a significant amount of body weight during space flight. This is attributed to the maintenance of energy expenditure while dietary intake is significantly reduced, resulting in a negative energy balance.

Another method for measuring TEE is the heart rate monitoring (HRM) method. Heart rate monitors provide relatively inexpensive, non-invasive tools that allow for the accurate measurement of energy expenditure, provided the person has been individually calibrated so that they have created their own heart rate-energy expenditure curve. If HRM is proved to be an accurate measure of TEE, when compared to the doubly labeled water technique, in micro-gravity, then this should strengthen the accuracy of this method on Earth and further encourage the use of this relatively inexpensive method amongst Africans in group based population studies.

Practical relevance and importance to South Africa

The practical importance of these different studies has direct relevance to South Africa and to South African technology. Our previous and current research of health and fitness parameters in the general South African public has illustrated a need for scientific communication and expertise outside of the boundaries of our building. Accordingly, we have aimed to develop technology that will enable South African scientists to evaluate both athletes and the general public at a distance and to provide them with new and relevant information specific to their sport and well being. By studying Mark Shuttleworth in Russia and aboard the ISS, we will begin both to demonstrate and develop the capacity for this distance coaching and evaluation, using data such as heart rate. We believe that this experience will provide the necessary impetus and opportunity to develop the capacity for distance coaching and evaluation, throughout South Africa and, in due course, the rest of the world.

South Africa has one of the highest recorded incidences of chronic diseases of lifestyle, which include heart disease, hypertension, diabetes and obesity. The fundamental underlying factor contributing to most of these diseases has been shown to be physical inactivity, as expressed by total daily energy expenditure. Heart rate and blood pressure are both practical measurements of health that the South African, and international, public are able to relate to. This research project aims to promote the understanding and importance of these variables and how they are affected during physical activity. Both heart rate and blood pressure will be broadcast via the Internet to a South African based web site, driven by Body iQ. This company, who have developed a novel methodology both designed and engineered in South Africa to measure and promote health, will analyse and interpret the information that is received directly from Mark in space. This will be a world first. As a result, the exposure of Mark’s heart rate, blood pressure and total daily energy expenditure variables to the public will create maximal awareness of health, as well as aiding in the promotion of the use of physical activity in the improvement of health in South Africa.

Ultimately, the international exposure of South African science may interest international funding sources and collaborative relationships. This will further strengthen our investigative capabilities as well as our standing in international research.