Energy Sources For Muscular Contraction Worksheet printable pdf download

Energy Sources for Muscular Contraction

Introduction:

Energy is released when adenosine triphosphate (ATP) is split into adenosine

diphosphate and phosphoric acid. The energy given up in this reaction is what powers

muscular contractions. Since there is no store of ATP in the body, it must be synthesized

continuously. This resynthesis of ATP from ADP and phosphoric acid is supplied by the

energy released in the splitting of creatine phosphate (CP). But creatine phosphate is also

in short supply and must be resynthesized continuously. There are two sources of energy

for the resynthesis of ATP and CP. These two sources are (1) the combustion of food as

measured by the consumption of oxygen, and (2) glycolysis, the breakdown of glycogen

resulting in the formation of lactic acid. Lactic acid can be reconstituted to glycogen with

energy input from food combustion.

Thus there are three reactions which produce energy;

1. splitting of ATP and CP

2. food combustion

3. glycolysis,

and two reactions which require energy;

1. ATP and CP resynthesis

2. glycogen resynthesis.

For moderate muscular energy requirements, the combustion of food can supply the

energy requirements for the ATP and CP synthesis, and this can be measured by the

consumption of oxygen (oxidation). Tests have shown that energy yield from oxidation

is about five calories per milliliter of oxygen consumed. The rate of the heart beat has

been shown to be a good measure of the rate of oxygen consumption.

For moderate steady exercise, the energy supplied to the muscles can be provided by

oxidation up to a maximum of about 220 calories per minute per kilogram of weight.

When this energy requirement is exceeded, then energy must be supplied by glycolysis,

and the resulting formation of lactic acid. The energy supplied by glycolysis is about 230

calories per gram of lactic acid produced, up to a maximum of about 50 grams. From this

information, one can calculate the rate at which work (work per unit time is defined as

power, measured in Watts) can be performed by the muscles if the energy is supplied

only by oxidation or by both oxidation and glycolysis. If one exceeds the power supplied

by 220 calories per minute per kilogram of weight, then lactic acid formation will occur,

and it will take time to resynthesize the glycogen after the work is complete. Thus more

rest is required after strenuous exercise because the lactic acid that has been built up must

be resynthesized to glycogen. In strenuous exercise you build up an energy deficit

(oxygen debt) that must be repaid by rapid breathing. The larger the oxygen debt

incurred, the longer it will take to recover.

In this experiment you will calculate the rate at which you can perform a particular type

of exercise, and how much lactic acid will be produced for different exercise rates.

Energy Sources For Muscular Contraction Worksheet