Physiological Limits to Performance.docx

Physiological Limits to Performance ***3.0 Physiological Limitations to Performance*** There are several reasons why it is important for us to understanding the factors responsible for limiting sport performance. This may include an ability to overcome or mitigate the limiting factor(s) with appro...

Physiological Limits to Performance ***3.0 Physiological Limitations to Performance*** There are several reasons why it is important for us to understanding the factors responsible for limiting sport performance. This may include an ability to overcome or mitigate the limiting factor(s) with appropriate training and (legal) supplementation or it may be used a tool to identify talented (genetically gifted) individuals within a large cohort of potential athletes. If we understand the biological limitations, or limitations based on a specific genotype we can leverage this information to make important strategic decisions about how to train and how to compete. As exercise intensity increases, muscle fibre recruitment progresses from type I → type IIa → type IIx. This means that the ATP supply needed for tension development becomes more and more dependent upon anaerobic pathways. Suggesting, fatigue is specific to the type of task undertaken. If a task requires only type I fibre recruitment, then the factors limiting performance will be very different from those associated with tasks requiring type IIx fibres.   ***3.1 Factors limiting all out anaerobic performances*** All out performances fall into 1 of 2 categories: 1. Ultra short term (less than 10 seconds): eg: 100m sprint, weightlight, 50m freestyle etc. 2. Short term (10-180 seconds) Ultra Short Term - Events less than 10 seconds - Dependent on type 2 muscle fibres - Large amount of force is needed - Motivation, skill and arousal are important - Primary energy systems are ATP-PC and glycolysis, with a focus on phosphocreatine. The energy release necessary for performance is generated by the demand generated by neuromuscular drive. Intramuscular energy supply isn\'t a limitation. - Creatine supplements may improve performance. - Fibre type distribution and recruitment: the ratios will vary between individual but in this area, we want to focus on the recruitment of type 2. - Recruitment of fibres will rely on the athletes level of motivation and arousal. It plays an integral part in our ability to develop power. - Skill and technique can affect fatigue and performance.   Short Term - Events lasting between 10-180 seconds - Shift to aerobic metabolism - 70% energy supplied anaerobically at 10 seconds - 60% supplied aerobically at 180 seconds - Fuelled primarily by anaerobic glycolysis - Results in elevated lactate and hydrogen ion levels. - Interferes with calcium binding to troponin and glycolytic ATP production - Ingestion of buffers may improve performance     ***3.2 factors limiting all out aerobic performances*** Energy fuelling bouts of exercise longer than 3 minutes comes from aerobic sources. These longer duration bouts are subject to environmental and dietary factors having a direct influence on fatigue. Exercise is split into (little diagrams on PP): - Moderate length, 3-20 minutes - Intermediate length, 21-60 minutes - Long term performance, 1-4hrs   Moderate - 3-20 minutes - 60% ATP generated aerobically at 3 minutes - 90% of ATP supplied aerobically at 20 minutes - High VO2max is advantageous - Higher stroke volume and high arterial oxygen content (haemoglobin and inspired oxygen) - requires expenditure near VO2max, this leads to a recruitment of type 2 fibres in additional to type 1 and thus, a build up of the by products   Intermediate - 21-60 minutes - Mostly aerobic - Performing just below 90% vo2max - High VO2max is important - High % of type 1 fibres (important for running economy or exercise efficiency) - Environmental factors: heat and humidity, hydration status and lactate threshold of the athlete - VO2max and running economy is a good indicator for performance - Biomechanics and bioenergetics both influence running economy - Higher proportion of type 1 fibres gives someone a high lactate threshold - Races aren\'t run at 100% of VO2. - Performance is determined by the % of VO2max that a runner can maintain as well as their running economy.   Long - 1-4hrs - Aerobic fuel only - Environmental factors more important - Maintaining rate of carbohydrate utilisation: muscle and liver glycogen stores decline so ingestion of carbohydrates are needed to help maintain carbohydrate oxidation in the muscle - If we can\'t maintain carb utilisation and stores, performance will end up in the bin. - Consumption of fluids and electrolytes are important. If only drinking water and heavy fluid loss occurs, it can result in hyponatremia which is when your blood sodium levels get too low. - Diet also influences performance     ***3.3 acid base balance*** - The concentration of H+ in the body is expressed as pH, normal is 7.4 - Abnormal pH levels can effective enzymatic reactions and can lead to negative impacts of physiological function and performance - Acids: molecule that can liberate H+, increases H+ concentration, eg: lactic acid - Bases: molecules that combine with H+ and decreases their concentration, eg: bicarbonate. - High intensity exercise around 45 sec produces large amounts of H+ - Some sports have a higher risk of acid base disturbance, a spring finish in distance/endurance event increases the risk of acidosis - Acidosis can impair performance - Failure to maintain acid base homeostasis can lead to impairments in ATP production and interfere with calcium binding sites - Type 2 fibres have a higher muscle buffering capacity. This means that those with more type 2 have the greater ability to buffer. - Diets low in acids can decrease plasma pH but doesn\'t affect buffering capacity. Some sports ban some buffers. - Supplementing with sodium bicarbonate can have the side effects of nausea and vomiting and large doses can lead to alkalosis - Supplementing with sodium citrate. Improves extracellular buffering capacity and can improve performance during high intensity exercise. Large doses have the same effect as bicarbonate - Supplementation with beta alanine. Precursor to carnosine synthesis. Carnosine serves as in intracellular buffer and can increase time to exhaustion during high intensity exercise. Only know side effect is skin tingles. - H+ production depends on exercise intensity, amount of muscles involved and the duration of exercise. - Blood pH declines as exercise intensity increases and muscle pH declines with increase intensity and it\'s pH is lower than blood. - Whilst the kidneys have a role in the long term regulation of acid base balance, they don\'t have a major role in exercise.   Sources of H+ during exercise: - Production of CO2: end product of oxidative phosphorylation - Production of lactic acid: glucose metabolism via glycolysis - ATP breakdown during muscle contraction: results in a release of H+   Sources of H+ in Contracting Skeletal Muscles - Aerobic metabolism \> carbonic acid - Anaerobic metabolism \> lactate   Acid Base Buffer Systems: 1. Acid base balance maintained by buffers - Release H+ when pH is high - Accept H+ when pH is low 2. Intracellular buffers (these work collectively) (table showing action on PP) - Proteins - Phosphate groups - Bicarbonate - Histidine-dipeptides 3. Extracellular buffers - Bicarbonate: supplementing with this has shown some improvements in some sports. - Haemoglobin - Blood proteins   Buffering of H+ in the muscle. - 60% by intracellular proteins. - 20 to 30% by muscle bicarbonate. - 10 to 20% by intracellular phosphate groups. Buffering of lactic acid in the blood. - Bicarbonate is major buffer. - Increases in lactic acid accompanied by decreases in bicarbonate and blood pH. - Haemoglobin and blood proteins play minor role.   ***3.4 pulmonary function and performance*** - This is an area that has been deliberated for a while - It\'s not clear the role that it plays in exercise performance. - In low to moderate intensity, the pulmonary system doesn\'t limit exercise tolerance. - In high intensity exercise, it\'s not a limit for healthy people at sea level. However respiratory fatigue can occur during high intensity exercise at 90-100% VO2max levels in prolonged bouts of high intensity. This is due to the fatigue of the respiratory muscles - If there is incomplete pulmonary gas exchange, it may limit athletes in some performances.   ***3.5 genetic limitations*** - Genetics has a role in determining our training response. - Some people will be naturally more athletic than others. - 97 different genes contribute to training improvements and responses in VO2max - The average person has improve in VO2max between 15-20% - High responders can have upward of 50% improvement with appropriate training. - Low responders may only see a 2-3% improvement. - Anaerobic capacity is more genetically determined than aerobic. - Training in anaerobic performance can only improve to a small degree, due to the % of type 2 fibres that you are born with. - Genetics will have a role in a high VO2max, superior exercise economy and lactate threshold and critical power.   Low responders - Genotype A - Have low, untrained VO2max - Exhibit limited exercise training response High Responders - Genotype E - Those with ideal genetic make up - Have a untrained yet high VO2 max - Often increase VO2max by 50% with training.