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Relationship Between Work and Energy

Bioenergetics - The degradation of fuel resulting in the production of heat and chemical energy, which is either used instantaneously or stored in a usable form. GENERAL PROCESS Fats Carbohydrates ATP Proteins (energy yielding metabolic pathways)

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Relationship Between Work and Energy

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  1. Bioenergetics- The degradation of fuel resulting in the production of heat and chemical energy, which is either used instantaneously or stored in a usable form. GENERAL PROCESS Fats Carbohydrates ATP Proteins (energy yielding metabolic pathways) In a general sense, bioenergetics deal with the formation of ATP and the use of its energy for physiological processes. ATP is a universal energy donor (recognized by all cells). It can donate energy to processes that require it, and ATP can accept energy from molecules which contain an amt. In excess of its own (more later)

  2. Relationship Between Work and Energy The performance of any type of work requires energy, and (with a constant mechanical efficiency) the amt. of energy required to do a given amt. of work is always the same. Thus, we must pay energetically for any work that we do. WORK & ENERGY 1 Kilocalorie = a) 426.85 Kpm b) 3087.4 ft. lbs. c) 4,186 joules ATP  ADP + Pinorganic Synthesis of ATP within metabolism (an energy requiring process) is accomplished by coupling other energy liberating reactions with ATP formation. ATP  + Pi + 7 Kcals liberated ADP + Pi  + 7 Kcals required

  3. Example of Coupling in Reactions • Compound A + ADP +Pi  Compound B + ATP + Heat • Compound A gives up its energy to synthesize ATP. Enough of the free energy is captured by the rxn to accomplish this task (free energy is that available to perform work). • Heat escapes because the efficiency of energy capture is not 100% • Compound B now has less energy stored in it than Compound A had. • The energy that is released by the high energy compound A is referred to as free energy (G), or that which is capable of performing work. • In order for a molecule to be able to resynthesize ATP, it must possess a greater G than ATP itself (>7 Kcal/mol) • Energy transfer can only be accomplished “downhill” • Example: • Creatine Phosphate (G = 10-12 Kcal/mol) • CP + ADP  ATP • Rxn is feasible as G for CP degradation >> that for ATP synthesis

  4. Source of Energy for Critical Biological Systems • Although the primary source of energy used in chemical rxns is ATP, other high energy phosphates do exist e.g. GTP, CTP • Present in muscle cell at about 4-6 mM of ATP/kg muscle • This is a very low concentration, but the turnover rate is very high (mol x s-1) -At rest + 40 Kg/24 hr (88 lbs) -Heavy Exercise = .5 Kg/min (1.1 lbs) • This fact indicates that ATP is not a storage form for energy. Rather, it is a transmitter or carrier of energy. • The concentrations of ATP, ADP, and AMP vary only slightly in normal cells under steady state conditions. This is an extremely critical aspect of cell life, and cells have very elaborate processes to ensure that this remains true under most, if not all conditions. • Nevertheless, a sudden increase in demand slightly decrease ADP and slightly increases ADP, resulting in the acceleration of metabolism (more later). A new “steady state” is formed. • Relevant Terms: • Steady State: A condition where energy created in the form of ATP equals breakdown. • Energy Charge: An indication of the availability of energy in a cell, characterized by the mathematical relationship of the concentrations of ATP, ADP, and AMP.

  5. Work = Force x distance traveled • Note: Force is not mass, it is mass x acceleration of gravity (distance in an exercising subject is not the length of the run) • Work is a mathematical relationship that does not have a psychological component. It is the same for all subjects no matter what their demographics, and its cost must be paid by some type of energy. • In exercise, thye largest component is done in the vertical plane, e.g. raising the the center of gravity. This makes it a very difficult to calculate in an exercising subject. • There are also other types of work e.g. pressure-volume. • Power = F x d x t-1 • Work done per unit time • Thus, to increase power, one must: • Exert a greater force in a given time • Move over a greater distance in a given time • Perform the same work in a given time • 1 Watt = a. 6.12 Kpm x m-1 • b. 0.73756 ft-lbs x s -1

  6. Quantifying Work and Power • Maximum Aerobic Power = maximum capacity to take up and consume 02 per unit time • Limitations lie either in the circulation (delivery) or in the muscles (utilization) • This is NOT maximum work capacity, as this issue deals with factors that result in fatigue. • Max aerobic power can be reached at low levels of muscle force output. • Power/Work can be measured in “relative terms”. 50% of maxVO2 or” absolute work” /power e.g. 900 Kpm or 3 liters. • Absolute is the same for all subjects no matter if they are trained, untrained, young, old, female, or male. • Relative varies considerably as the same % of max aerobic power can represent large differences in work done due to variations in size and state of training. • Nothing mentioned here alters the mathematical relationship between work • and energy.

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