Physiological Determinants of Endurance Performance - Essay Example

Discuss the Physiological Determinants of Endurance Performance Introduction Endurance performance of an individual is the measure of the ability ofthe individual to sustain an activity that makes demands on the generation of power or velocity for an extended period of time. Performance endurance in an individual is typically measured over time periods that range from thirty minutes to four hours. Performance endurance in individuals varies and is dependent on the ability to maintain the high energy demands required for the sustained effort. There are individual physiological determinants that influence an individual’s endurance performance. An understanding of these determinants and the manner in which they can be influenced is particularly useful in the field of sports, where better endurance performance is the difference between success and failure in competitive activities that place a demand on the endurance capacity of an individual (Coyle, 1999). Physiological Determinants of Endurance Performance According to Bouchard et al, 2000, the ability to cope with the demands made during a performance of endurance activity is influenced by many determinants. These determinants are physique, body composition, maximal oxygen consumption (VO2 max), biochemical factors, nutritional status, thermoregulation, sub-maximal exercise tolerance and efficiency, social factors and psychological traits. Furthermore there is realization that each of these determinants is in reality a host of several factors instead of being a single characteristic (Bouchard et al, 2000). This paper restricts itself to the evaluation of maximal oxygen consumption, lactate threshold, exercise economy and thermoregulation as these factors constitute the physiological determinants of endurance performance. Such a view is supported by Tanaka and Seals, 2008, who give maximal oxygen consumption, lactate threshold and exercise economy as the main physiological determinants of endurance performance and Coyle 1999, who contends that thermoregulation is a physiological determinant of endurance performance, due to the intense and prolonged oxidative metabolism that is characteristic of an endurance performance. Maximal Oxygen Consumption (VO2 Max) For the performance of physical activity the body requires energy. In performance sports the physical activity involves aerobic energy production means, where oxygen is a key component. In other words oxygen is used up during physical activity and for sustained physical activity at high intensity higher levels of oxygen requirement and utilization there is a high demand for oxygen. The greater the levels of oxygen that are taken up the more are the energy that is produced and sustained over more lengths of time. Shave and Franco, 2008, pp.62-63, define Maximal oxygen uptake (VO2 max) as “ the highest rate at which oxygen can be extracted, transported and consumed in the process of aerobic ATP synthesis”. VO2 max is usually expressed as the ration in millimeters per kilogram of body weight per unit of time (Shave & Franco, 2008). The body of an individual derives energy requirements from the aerobic and anaerobic metabolic pathways. However, the capacity in each individual for each form of energy transfer is not the same. This variance between individual capacities underscores the understanding of individual variances in metabolic capacities and through that endurance in performing physical activities (McArdle, Katch & Katch, 2007). There is greater reliance on the anaerobic metabolic pathway for energy requirements in the case of short bursts of movements and physical activity. Sustained energy demands for physical activity rely more on the aerobic metabolic pathway. At the start of physical activity the high-energy phosphate adenosine triphosphate (ATP) and phosphocreatine (PCr) present in the muscles meet the immediate energy demands by supply through the anaerobic pathway. The continued physical activity causes the glycolytic pathways to take over and meet most of the energy demands from the muscles. Thus sustained physical activity progressively places greater emphasis on the aerobic metabolic pathways and the need for oxygen (McArdle, Katch & Katch, 2007). Evidence from studies of athletes demonstrates that excellence in endurance sports is associated with a better capability for aerobic energy transfer in the muscles and the relevance of VO2 max to endurance performance. However, there are several factors besides VO2 max that are associated with capacity for aerobic energy transfer and these include capillary density, enzyme activity, size and quantum of the mitochondria and the type of muscle fiber. The importance of VO2 max lies in its ability to predict endurance performance of the individual and has physiological significance due to the integration of high levels of pulmonary, cardiovascular and neuro-muscular functioning for attaining higher levels of VO2 max. These features make VO2 max a significant physiological determinant of endurance performance by an individual (McArdle, Katch & Katch, 2007). The link between VO2 max and the other systems of the body involved in oxygen delivery can be seen from the argument of Bassett and Howley, 2000, that VO2 max has limitation, which is the ability of the respiratory and cardio-vascular system to deliver oxygen to the exercising muscles. Support for their line of reasoning comes from the changes in oxygen delivery due to blood doping, hypoxia or beta-blocking demonstrating a similar alteration in VO2 max levels; the increase in VO2 max as a result of training that can be attributed to the increased cardiac output and the finding that on over perfusing a small muscle through exercise causes the small mass of muscle to develop a high capacity for consuming oxygen. Thus the delivery of oxygen to the exercising muscles and not the extraction of oxygen by skeletal muscles should be considered as the primary limiting factor for Vo2 max in human beings (Bassett & Howley, 2000). The significance of VO2 max in endurance performance and the role of the respiratory system in making oxygen available in the body suggest that the respiratory system plays a role in endurance performance. Though there is limited clarity on the mechanisms by which respiratory training assists in endurance performance, anecdotal experiences of individuals associated with endurance sports activities supports the perception that improvements to respiratory functioning assist in enhancing endurance performance (Boutellier, 1998). Further support for the role of the respiratory system comes from the evidence of the role of respiratory training in enhancing the strength and endurance in exercise for individuals with compromised respiratory functioning, like individuals with chronic obstructive pulmonary disease (COPD). Individuals with COPD find it difficult to perform physical activities and respiratory training is recommended for improving their strength and endurance in indulging in physical activity (Weiner & McConnell, 2005). There are several exercise tests that can evaluate VO2 max in an individual. These tests activate the large muscle groups present in the body of an individual through the intensity and duration of the exercise and maximize the energy transferred aerobically (McArdle, Katch & Katch, 2007). Metabolic adaptations of the skeletal muscles are a key component in improving the endurance performance of an individual. Endurance training in an individual results in enhanced mitochondrial enzyme activities leading to better performance through increased fat oxidation and reducing the accumulation of lactic acid at VO2 max. (Bassett & Howley, 2000). Training individuals for increase in VO2 max can lead to enhanced capacity for better performance over extended periods of time. Subsequent exercise testing for VO2 max in the individual will show the impact on the increase in VO2 max and the capability of the individual for enhanced endurance performance (McArdle, Katch & Katch, 2007). Lactate Threshold The body of knowledge on the human physiology involved in the capability of individuals for performance of physical efforts associated with sports and games has enhanced greatly from the numerous studies that have evaluated this aspect. This enhanced knowledge has provided an understanding of the involvement of the lactate threshold in limiting the ability for endurance performance (Joyner & Coyle, 2008). Controversy exists over the definition of lactate threshold, its measurement and the exact mechanisms involved in lactate threshold. Without stepping into the controversial arena of definition, it can be safely said that the lactate threshold is reached through the accumulation of lactate in the blood as a result of enhanced exercise intensity. This build up of lactate in the blood in incremental steps during exercise may be a reflection of the inability of the oxidative metabolic pathways to remove or re-synthesize the lactate produced (Seraganian, 1993). Lactic is a product of the anaerobic oxidative pathway employed when there is a significant demand for energy as occurs in the case of intense physical exercise, which builds up in the blood. The presence of lactic acid in the blood hinders the ability in the skeletal muscles to use oxygen to create the required energy to meet the energy demands from physical activity. During physical activity when there energy demands are met by energy production through the oxidative pathway, very little lactate is produced and as a result the levels of lactate in the blood are low. Increased demand for energy as a result of prolonged or intense physical activity causes the anaerobic oxidative pathway to kick in with its accompanying increased production of lactate. This results in the build up of lactate in the blood and its limitation on the capability of an individual for endurance performance. The build up of lactate in the blood is related to the VO2 max of an individual. In an untrained individual lactic acid begins to accumulate in the blood when about 55% of the individual’s VO2 max is attained. In individuals that have undergone endurance training there is a marked change at which lactic acid begins to accumulate. In such trained individuals it is not uncommon to see the build up lactate starting as late as attaining 80% to 90% of the individual’s VO2 max (Seraganian, 1993). The percentage of VO2 max that an individual can maintain over sustained and intense physical activity is determined by the lactate threshold. The lactate threshold thus becomes a physiological determinant of endurance performance. The lactate threshold is measured by drawing blood and analyzing the lactate content over a continuous protocol of physical exercise. The method is expensive and requires skills in drawing blood and blood analysis. A simpler though not as accurate means to assess lactate threshold is to determine the ventilation threshold, which is a reflection of the lactate threshold (Seraganian, 1993). Exercise Economy Physiological responses of an individual during physical activity are largely dependent on the amount of energy expended in the physical activity. Energy expenditure during physical activity depends on the kind of physical, the intensity of the physical activity and the duration of the physical activity. There is a limit to human endurance of physical activities and conserving energy makes it possible to extend these limits of endurance. Increase in duration of physical activity as in endurance performance for a physical of a same type, means that either the intensity of the activity has to be moderated or the energy expended in a more conservative manner and with greater economy to maintain the activity within over time within human limits. It is this impact of the economic use of energy that makes the economy of exercise a physiological determinant of endurance performance (Brown, Miller & Eason, 2006). The energy that is expended for a given physical activity can be estimated quite accurately and this makes it possible to calculate the amount of energy different individuals expend for a physical activity of the same physical intensity. Efficiency of movement during physical activity can be taken as the ratio of work out put to the energy input. Greater efficiency of movement during physical activity lessens the energy input required for the same work output. Translating this into the relationship of energy expended in physical activity involving endurance performance, greater efficiency of movement in the execution of the physical activity means lesser energy expended and less stress on the body to generate the needed energy. This would enable an individual with better efficiency of movement or economy in expending energy during exercise to demonstrate better endurance performance. An individual having the same VO2 max as another individual and able to complete the endurance performance with the same percentage of VO2 max, will demonstrate better endurance performance than the other individual, if the individual has a better economy in expending energy during the endurance performance. For example the economy in expending energy in long distance running can be improved through training, which will enable the runner to perform better in the endurance race (Brown, Miller & Eason, 2006). Thermoregulation Intense and prolonged oxidative metabolism as required to meet the energy demands in endurance performance produces two main by products namely the accumulation of hydrogen ion or lactic acidosis and heat or hyperthermia. Both these byproducts limit endurance performance. The influence of the lactate threshold on endurance performance has already been discussed and hyperthermia has a similar effect on reducing the ability for endurance performance at a threshold level of temperature. It is not possible to ascertain this threshold level of temperature during the actual endurance performance, but tests conducted during simulated in the laboratory have shown that fatigue expresses itself at oesophageal temperature reaches forty degrees Celsius. The aetiology of fatigue from hyperthermia is still not completely clear, but there is a high probability of the involvement of the central nervous system in the aetiology of fatigue due to hyperthermia. Profuse sweating is normal in endurance performance, which can lead to dehydration. Dehydration during physical activity is a hyperthermia promoter due to the reduction in the blood flow in the skin, sweating rate and lowered dissipation of heat generated in the body. Dehydration in combination with hyperthermia as a result of the physical activity involved in the endurance performance brings about a severe reduction in the cardiac output and through that the flow of blood to the skeletal muscles involved in the physical activity. This means reduced oxygen availability within the muscles with a high demand for energy. The lack of oxygen availability causes the anaerobic metabolic pathway to be used in a larger proportion and thereby increasing the lactate in the blood and hindrance to the capacity for endurance performance (Coyle, 1999). Conclusion Evidence from studies on individuals involved in endurance sport activities shows that there are four main physiological determinants of endurance performance. These physiological determinants of endurance performance are maximal oxygen consumption, lactate threshold, exercise economy and thermoregulation. All these physiological determinants have an influence on the pathways involved with meeting the energy demands of endurance performance and through that place limitations on the capacity of an individual for endurance performance. Literary References Basett, D. R. & Howley, E. T. (2000). Limiting factors for maximum oxygen uptake and determinants of endurance performance. Medicine and science in sports and exercise, 32(1), 70-84. Bouchard, C. Wolfarth, B. Rivera, M. A. Gagnon, J. & Simoneau, J. (2000). Genetic Determinants of Endurance Performance. In Roy J. Shephard & Per-Olof Astrand (Eds.), Endurance in sport (pp.223-244). Chichester, U.K: Blackwell Publishing. Boutellier, U. (1998). Respiratory muscle fitness and exercise endurance in healthy humans. Medicine and science in sports and exercise, 30(7), 1169-1172. Brown, S. P. Miller, W. C. & Eason, J. M. (2006). Exercise Physiology: Basis of Human Movement in Health and Disease. Baltimore, U.S.A: Lippincott, Williams & Wilkins. 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