UMass Amherst KIN 470 - Lab 2 Handout Submax VO2_adjusted (8 pages)

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Lab 2 Handout Submax VO2_adjusted



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Lab 2 Handout Submax VO2_adjusted

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Pages:
8
School:
University of Massachusetts Amherst
Course:
Kin 470 - Exercise Physiology
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LABORATORY 2 SUBMAXIMAL EXERCISE ENERGY EXPENDITURE AND RECOVERY IMPORTANT TERMS 1 2 3 Steady state oxygen consumption Oxygen deficit Excess post exercise oxygen consumption EPOC IMPORTANT CONCEPTS 1 2 3 Economy METS Work on the cycle ergometer INTRODUCTION This laboratory will investigate energy expenditure during submaximal cycle ergometry and recovery The concepts of steady state exercise oxygen deficit excess post exercise oxygen consumption and exercise economy will be covered in this lab Investigations of exercise frequently measure energy expenditure We are usually interested in comparing the energy cost of the same activity between individuals While performing exercise tasks that require some measure of skill or precision in execution experienced individuals will require less energy to complete a given task than unfit or less trained individuals Often it is said that the participant who uses less energy is the more efficient participant but this is a misuse of the term efficient Efficiency is defined in a physical sense as the amount of energy produced divided by the amount of energy consumed While efficiency would be an excellent tool for making comparisons in a practical sense it is impossible to measure efficiency in the lab as there is really no good method of determining work output exactly The best example of this is the case of a participant running on a treadmill While it is clear that the participant is expending a lot of energy and performing work to accelerate and decelerate in a strict sense no external work has been done because the participant s center of mass is in the same location as it was at the beginning of the test Devices such as the cycle ergometer provide a better estimate of work done but they still fail to measure internal work joint friction hemodynamic work etc as well as any energy lost in the driveline of the machine Therefore we are not actually measuring efficiency in the lab A more contemporary expression describing the difference in energy cost of an activity between individuals is economy Economy is often defined as the rate of oxygen use per unit work rate This may be expressed in many ways including ml kg Watt running or L Watt rowing In this lab we will express economy as ml kg Watt O2 body weight Power or L Watt O2 Power during cycle ergometry CLASSIFICATION OF WORK Different work tasks may be rated in terms of resting energy requirements With this system moderate work is defined in terms of the oxygen uptake that is three to six times the resting requirement while vigorous work is from six to nine times and very vigorous work is nine times and above the resting level These values are referred to as METs metabolic equivalents Another system of grading work is based on the energy required kcal per minute with guidelines for men and women based on average body weights 65 kg for men 55 kg for women 1 Table I Classification of work by caloric expenditure Light Moderate Heavy Very heavy Maximal Males 2 0 4 9 kcal min 5 0 7 4 kcal min 7 5 9 9 kcal min 10 0 12 4 kcal min 12 5 kcal min Females 1 5 3 4 kcal min 3 5 5 4 kcal min 5 5 7 4 kcal min 7 5 9 4 kcal min 9 5 kcal min Because 5 kcal is approximately equivalent to one liter of oxygen consumed it is possible to represent this 5 stage classification of energy expenditure either in terms of oxygen consumed l min or ml kg min or in METS One MET is equal to approximately 3 5 ml kg min which is considered the resting metabolic rate for the general population METs therefore are defined as multiples of this resting metabolic rate STEADY STATE OXYGEN CONSUMPTION Submaximal exercise as its name implies is performed at a workload below a participant s maximal oxygen consumption While there are a range of intensities that could be considered submaximal it is typically accepted that it corresponds to a work rate that can be maintained for a prolonged period with a corresponding steady state oxygen consumption Lactic acid is produced during steady rate exercise but its production rate is slow enough such that it can be either oxidized or reconverted to glycogen in the liver rate of lactic acid production equals rate of lactic acid removal Thus under true steady rate conditions lactate accumulation is minimal Steady rate oxygen consumption is a condition in which the energy expenditure provided during exercise is balanced with the energy required to perform that exercise aerobic energy supply equals aerobic energy demand GROSS AND NET EXERCISE OXYGEN CONSUMPTION In examining exercise energy expenditure and economy it is necessary to partition out the absolute oxygen requirements of the exercise or net oxygen consumption from the total oxygen consumption baseline oxygen consumption oxygen consumption required to perform the exercise Net exercise oxygen consumption is the total gross oxygen consumption during the exercise period minus the oxygen used at baseline rest By using net oxygen consumption it is possible to obtain a more accurate measure of the energy requirements of the exercise task OXYGEN DEFICIT Regardless of the intensity of the exercise at the onset of exercise there is an immediate need for additional energy above resting levels All three systems ATP CP system anaerobic glycolysis or lactic system and aerobic oxidation or O2 system will be involved in this response and their relative contributions are proportional to the intensity and duration of the activity Aerobic energy production contributes minimally to the energy required at the onset of exercise due to 1 a delay in circulatory delivery of oxygen to the working muscles 2 aerobic metabolism is stimulated by the presence of excess ADP in the mitochondria Therefore until ADP accumulates as a result of ATP breakdown anaerobic sources of ATP will make up for this discrepancy in oxidative supply and energetic demand The delay in the aerobic energy production at the onset of all exercise is known as the oxygen deficit It may be defined as the difference between the oxygen required during exercise and the oxygen supplied at exercise onset An individual who reaches steady state faster will have a smaller oxygen deficit This is generally seen in endurance trained individuals as compared to untrained individuals Trained individuals will reach steady state faster because they have a better developed aerobic system due to cardiovascular and muscular adaptations As a result the aerobic ATP production occurs earlier during the onset of exercise


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