During workout, you gasp your breath for air & afterwards look to refuel with carbs & fats to balance the glycogen lost during workout. It boils down to ATP-adenosine triphosphate, the compound which is responsible for providing energy to your cells.
When you are doing workout, your muscles consume a lot of energy to keep them contracting & relaxing. The carbs, protein & fat you got from the protein bar you just ate is not going to be used instantly by your working muscle fibers. Through long & complex processes, the energy from the good you consume & your body’s existing glycogen & fat stores are processed into substrates that help generate energy for cellular processes: ATP. It is ATP that provides energy for our bodily processes right from cell development to muscle contractions & growth. The largest volume of ATP is produced in the presence of oxygen & that is the reason we breathe heavily when we exercise.
ATP is the energy carrying molecule that consists of one adenosine & three phosphate groups. To prevent ATP’s energy being released as heat, the energy is only released when it is hydrolysed by enzymes called ATPases. All our cells & specifically our muscle fibre contains these enzymes. During hydrolysis, ATP releases one phosphate & converts into ADP- one adenosine & two phosphate groups whereby energy is released. At some occasions ATP is further broken down into AMP- adenosine & one phosphate group. In most of the cases ADP is recharged in a process called phosphorylation. In this process, one phosphate group is attached back to the ADP molecule to reform & recharge ATP which can be used again.
Let us discuss in detail mechanisms muscles use to generate ATP
- Phosphagen system: When a muscle starts to contract, it quickly uses the energy released by ATP & this free moving ATP is depleted fast. The cell quickly starts to run ATP by a phosphagen system which does not last long but provides a good amount of energy during the first few seconds of exercise. The phosphagen system is an energy reservoir that buffers ATP’s energy by use of molecules known as Creatine forming phosphocreatine.. The system is in equilibrium during rest however during intense the reaction is pushed breaking down into more phosphocreatine & producing ATP thereby providing muscles with energy.
- Glycolytic system: No doubt, Glycolysis is slower than phosphagen system but it is beneficial during the first period of exercise. The system consists of a chain of enzymatic reactions producing ATP from glucose which is taken from blood or through hydrolysis of glycogen which is muscle’s carb store. Besides ATP, another product of glycolysis is pyruvate which can be processed & used in the final energy system or converted into lactic acid. Lactic acid is further converted into lactate which is energy source for some other cell types
- Oxidative Phosphorylation: Slowest but the most efficient energy system. This provides muscle fibre with a great amount of ATP under the consumption of oxygen. This process takes place in cell compartments called mitochondria. Muscle fibres are rich in mitochondria specifically in case of slow twitch muscle fibre known for endurance workout( Genomics testing will help you identify your muscle fibre type & accordingly structure your workout schedule). This process takes place in the internal membrane of mitochondria. This is the place where oxygen, fatty acids & pyruvate come into picture. The mitochondrial membranes are charged by hydrogen ions thereby forming hydrogen potential. This enables production of ATP from ADP & inorganic phosphate( phosphorylation). In order to charge this membrane, oxygen is required & hence is referred to as oxidative phosphorylation. Besides, molecules that develop hydrogen ions are also used. These molecules are developed through a chain of chemical reactions called a Kreb cycle.Kreb Cycle does generate a few ATP molecules but also CO2 which enters our blood & leaves our lungs when we exhale.
Oxidative Phosphorylation uses metabolites derived from carbohydrates. However, fatty acids are the most important fuel for prolonged activities . It is important to note that when carbs are depleted & fats are minimal, our body, amino acids shall be used as fuel for Oxidative Phosphorylation
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