Energy Demands of Muscles During Exercise!

Friday May 7, 2010

All forms of exercise require the activation of skeletal muscles.  To contract muscle fibers require many physiological conditions, such as energy, oxygen, and removal of lactic acid.

For very brief periods, the energy for muscle contraction can be provided by the energy stored within the muscle itself in molecules such as ATP, creatine phosphate (you may have heard of the supplement Creatine), glucose, and glycogen (storage form of glucose).

More prolonged activity requires increased delivery of oxygen and metabolic fuels (such as glucose and fatty acids) to the muscle from other sources.

Contracting muscle cells produce heat and metabolites, including lactic acid and carbon dioxide, which must be carried away in order for the muscle to continue functioning.  If these metabolites are not removed, muscle pain and fatigue can result.

The proportional use of fuels (carbohydrate, fat, and even protein) during exercise depends on the intensity and duration of the activity.  This means that mix fuels used at the beginning is different than the mix used later on (notice I say “mix fuels” because many have the assumption that during exercise we use either glucose, or fat as energy, in reality we use both but at different proportions depending on the duration and intensity of the exercise).

In a very high intensity, short durations, exercise such as sprints the main source of energy is ATP and glucose these are two sources of energy that can be called on quickly-that is, it does not require oxygen.  With longer durations of exercise a greater proportion of ATP is generated through the breakdown of fat (fatty acids)-involves oxygen.

If you are trying to burn more fat when exercising it is usually recommended to do aerobic activities longer than one hour in a moderate intensity.  The reason behind this is if the intensity is too high you will be using a greater proportion of glucose (from blood, muscle, or liver) rather than fatty acids.  In moderate intensity you will be using greater proportion of fatty acids, sparing glucose.  You should do cardio longer than one hour because the longer you work out the greater will be the switch from using glucose as energy to fatty acids.

After a prolonged aerobic activity you should always consume a high glycemic food (refer to my previous post “Sugar Rush”) to recover glycogen stores in the muscles.  By doing so, you will decrease muscle fatigue, as well as you will have more energy for the next time you exercise!

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1 Comment »

I love it, you explain it so well! I feel like I know exactly what’s going on while I am exercising. Now it all makes so much more sense! 8-]

May 7th, 2010 | 12:53 pm
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