Energetics of Skeletal Muscle Contraction.

2. Sources of Energy for Skeletal
Muscle Contraction
 In the skeletal muscle ATP is required for:
 muscle contraction
 NaK ATPase pump
 Calcium pump in sarcoplasmic reticulum for relaxation
 There are three sources of energy for Skeletal Muscle
 Phosphagen System
 Glycogen Lactic acid system
 Aerobic System

3. Phosphagen System
 It is the immediate source of energy and it includes ATP and
Creatin Phophate.
 ATP + H2O  ADP + H3PO4 + 7.3Kcal Enzyme ATPase
 ADP  AMP + 7.3 Kcal
 The ATP available in the skeletal muscle can maintain
contraction only for few seconds
 After that Creatin Phosphate help to reconstitute ATP
 ADP + CP  ATP + C Enzyme is creatin phosphokinase

 Creatin Phospahte can’t supply energy directly.
 It must first be converted to ATP.
 So currency for energy in body is ATP.
 Energy from Phosphagen system can maintain contraction only
for 8 to 10 seconds.
 So it supplies energy for 100 m race.

4. GLYCOGEN LACTIC ACID SYSTEM
 It is anaerobic.
 Glycogen is broken down to glucose 6 phosphate by glycolysis
into Pyruvate
 If oxygen is available then pyruvate will become acetyl Co A and
enters citric acid cycle.
 During exercise there is anaerobic conditions and pyruvate is
converted into Lactic Acid.
 When oxygen becomes avalaible, it is converted back into
pyruvate.
 Lactic acid can not be metabolized in muscle.
 So it enters the blood and reaches liver and enters CORRI’s cycle
where it is used for gluconeogenesis.
 Heart can also utilize Lactic acid.
 This second system provides energy to maintain contraction for
1.3 to 1.6 minutes.
 So it provides energy required for 400m race.

5. AEROBIC SYSTEM
 It includes the complete oxidation of nutrients.
 Acetyl Co A enters the mitochondria where it enters citric
acid cycle.
 Aerobic system can provide energy for muscle contraction
for unlimited period as long as the nutrients are available.

6. CONTRACTION
 It is the %age of the energy input which is converted into
work instead of heat.
 Normally maximum efficiency is 20 to 25 %.
 Efficiency is maximum when muscle contracts at a
moderate rate.
 And if there is too slow or too rapid contraction, efficiency
decrease.