Energy systems

Energy systems produce adenosine triphosphate (ATP) which provides muscle contraction allowing skeleton movement.

ATP is simply adenosine (a protein) plus 3 phosphate. When chemical bonds are broken they release energy. When a phosphate is broken off ATP it creates ADP (adenosine + 2 phosphate) and this energy allows for muscle contraction. 

ATP is only stored in the muscles in small amounts therefore allowing muscle contraction for a short duration only. Therefore, it has to be resynthesised to allow the muscles to continue contracting, this is where the energy system plays its role. Energy sources such as phosphocreatine, blood glucose, fatty acids, glycogen will produce ATP, but this is dependent on the energy system been used which in turn will depend on the duration and intensity of exercise.  

The 3 energy systems that supply ATP are:

1) Phosphagen (aka alactic) explosive activites e.g 50-100m sprint, provides energy immediately for short duration, up to 10 seconds 

Predominantly anaerobic, requires no oxygen  

Creatine phosphate is the fuel source 

At least 3 min to resynthesise or a work:rest of 1:12-1:20

E.g., 2x3x30m sprints with about 90 sec rest between reps; 3-5 min between sets

2) Glycolysis (aka lactate) e.g 400m sprints, provides energy for up to 3 min

Not as powerful as the first system but has a larger supply of ATP

Fuel source comes from the breakdown of carbs, blood glucose or stored glycogen

Work:rest of 1:3 for tolerance work or 1:5 for greater removal of lactate acid

E.g., 2x4x400m runs with about 270 sec rest between reps; 4-5 min between sets

3) Oxidative (aerobic) long slow distance running e.g 5k run. Provides energy for 2-3 hours 

Produces more ATP than the first two systems

Stored fats and carbs are used to fuel this system

Work:rest 1:1 or 1:3

E.g., 2x6x150m shuttles with 45 sec rest between shuttles; 2-3 min between sets