Category Archives: Exercise Physiology

Energy and Work

We are now moving on to exercise Physiology…

Energy is what makes our body go, There are several kinds of energy that exist in the biological systems.

Energy in Biological Systems-

Electrical Energy-Nerves, muscles, cardiac rhythms.

Chemical energy: Synthesis of molecules, hormones.

Mechanical Energy: Muscle contraction (actual movement)

Thermal Energy: Regulation of body temperature.

The ultimate sourse of energy in all biological systems is Radiant Solar Energy  Captured in plants to convert simple molecules into fats, carbohydrates and protein. Trapped within the chemical bonds of food molecules.

“Energy cannot be created or destroyed, it can only  be changed from one form to another”. ~Albert Einstein

Use of Energy- The body must break down food to a usable form, the final product must be a molecule the cell can use (ATP) “YOU MUST EAT FOOD”

ATP- (Adenosine Triphosphate) is your main source of energy, electrical, mechanical, or chemical. In ATP, three phosphates are linked by high-energy state, becoming adenosine diphosphate (ADT) and inorganic phosphate (P).

Three phosphates linked by high energy bonds. When a bond is broken, energy is released.

ATP and Activity-

ATP is constantly converted to energy and must be replaced as fast as it is used in order for muscles to continue to generate force. Muscle cells have the capacity to regenerate ATP under a variety of work conditions, using multiple sources.

Immediate sources of energy: ATP and Creatine Phosphate

Short-term sources of energy: Glycolysis (anaerobic)-does not require oxigen and Glucose

Long-term sources of energy: Aerobic metabolism of glucose and fat, produced in the cells mitochondria.

Anarerobic energy Sources (Short-term): Cellular energy produced in the absence of oxygen, sources of anaerobic energy are:

ATP-Small amount already available, good for about 1 second.

Phosphocreatine (PC)– Stored in muscle cells, good for about 3-5 seconds

Glycolysis– glucose obtained from teh muscles glycogen stores, good for about 2 minutes.

Aerobic Sources of Energy (long-term): Oxygen must be present in the cell to create long-term energy.

Sources of long-term energy are muscle glycogen, blood glucose, fatty acids and intramuscular fats.

Aerobic Energy is used for activities lasting more that 2 minutes and up to 2 hours or more.

Exercise Intensity and Duration and Energy Production:

Energy from both anaerobic and aerobic sources is on-going. Short duration, high-intensity activity relies on a greater proportion of anaerobic energy and long duration, lower-intensity exercise relies on a greater proportion of aerobic energy.


** Disclosure- Everything from this article was found in the book Fitness Professional’s handbook Sixth Edition**