EXERCISE PHYSIOLOGY: energy for exercise

by Mary & Christina on July 13, 2010 · 0 comments

Whether you are completely new to fitness or are already an avid runner, cyclist, swimmer, etc., it is important to understand how your body responds, adapts, and adjusts to exercise.  Understanding even the basics of exercise physiology will help you to train your body in the best way possible.   Since exercise physiology encompasses a WIDE range of topics, we decided to break it down into separate posts for you.  Enjoy!

Energy is stored in the body as CHEMICAL ENERGY (stored fat, carbohydrate, and protein stored in muscle tissue) and is converted to MECHANICAL ENERGY during work.  Glycogen (a chain of glucose) is a form of stored energy in the muscles and in the liver; it provides fuel when the body is in need of it.  Liver and muscle glycogen are a bit different from one another….Liver glycogen is broken down to help keep blood sugar levels steady between meals while muscle glycogen is only available to the working muscles.Pre-exercsie levels of stored glycogen is an important impact on endurance exercise performance. So when you wake up first thing in the morning and exercise, your muscle glycogen levels will be fine but your liver glycogen levels will be low…explaining why you may feel light headed and/or weak if you do not eat first.

The greater your glycogen stores, the longer and harder you will be able to go.  Carbohydrates are the MOST important fuel for exercise AND for the Central Nervous System (CNS) activity and mental performance. In fact, your brain required 125 g of carbs per day!  125 g of carbs amounts to:

  • 1/2 C pasta
  • 1/3 C rice
  • 2/4 to 1 ounce of cereal
  • 1 slice of bread
  • 1/2 of a small bagel
  • 1/2 C starchy vegetables (potatoes, corn, peas, etc.)
  • When you exercise for a long period of time (even moderate exercise) you need to take in carbs to maintain levels of stored muscle glycogen.  It is also important to consume carbs in the immediate post-exercise period (up to an hour after exercising) in order to restore muscle glycogen levels…during this time your body is best able to reload — after the hour has passed, it is more difficult to restore the glycogen levels.

    A good post recovery snack is a smoothie.  Smoothies are easy on the stomach (not to mention delicious). If you are a chocolate lover, the Chocolate Thunder is a great smoothie to try out but if you prefer vanilla, you can try the White Lightning! Both are delicious!

    Cellular Respiration is the aeorbic process of convering glucose into ATP (the energy currency of work in the body).  ATP is made in the Mitochondria (the powerhouses of the cell…the “factory” of energy production).  Regular aerobic training increases the number of mitochondria in the muscle cells, allowing the contracting muscles to produce energy more quickly and efficiently.

    The body can generate new glucose from non-carbohydrate sources.  However, this does not make up for or even maintain glycogen stores depleted by inadequate Carbohydrate consumption.  Limiting carbohydrate consumption limits your energy transfer capacity, depressing the intensity of aerobic exercise. We hope by now you are realizing just how important Carbohydrates are and why it is important not to skimp on them and follow those fad diets!!

    Fat is almost a HUGE source of energy in the body.  Fat metabolism is a slower process than glucose metabolism.  Because of this, the body requires adequate amounts of carbohydrates in order to BEGIN exercise, and fat is only available as fuel for aerobic exercise.  Higher intensity exercise is fueled almost exclusively by carbohydrate.  Regularly training at an aerobic pace will encourage your body to use available fat for fuel.

    Protein can also be used as fuel for exercise but is a last resort during high intensity exercise, once the body has run out of carbohydrates.  Protein comes from the  muscles... which is not a desirable situation; we want to train our bodies to increase the synthesis of muscle, not break it down! A HIGH PROTEIN, LOW CARB DIET IS NOT RECOMMENDED FOR ATHLETES...it will decrease glucose levels, increase cortisol levels, and increase breakdown of skeletal muscle tissue and decrease uptake of available glucose by muscle.

    There are three energy systems in the body: (1) ATP-CP (used to power short bursts of work and does not require oxygen), (2) lactic acid system (produces 2 ATPS per 1 glucose, the breakdown of glucose results in lactate which at high levels eventually causes fatigue, and (3) the aeorbic energy system (most effiecient of the three, can use fat as fuel).  These systems work together and overlap.

    The more fit you become, the harder it is to maintain a max aeorbic pace because that pace becomes faster and faster. (this explains why when you first start out running you can only go at a very slow pace but after training for awhile you find that you can go much faster while still training aerobically).  The goal of training is to strengthen the ability of each system to function as efficiently and effectively as possible and for the body to go as long as possible in the aeorbic state.

    RECAP:

    • The greater your glycogen stores, the longer and harder you will be able to go.
    • Pre-exercsie levels of stored glycogen is an important impact on endurance exercise performance.
    • Carbohydrates are the MOST important fuel for exercise AND for the Central Nervous System (CNS) activity and mental performance.
    • When you exercise for a long period of time (even moderate exercise) you need to take in carbs to maintain levels of stored muscle glycogen.  It is also important to consume carbs in the immediate post-exercise period (up to an hour after exercising) in order to restore muscle glycogen levels
    • Limiting carbohydrate consumption limits your energy transfer capacity, depressing the intensity of aerobic exercise.
    • Fat is almost a HUGE source of energy in the body.  It takes a long time to metabolize fat and so the body requires adequate amounts of carbohydrates in order to BEGIN exercise.
    • Higher intensity exercise is fueled almost exclusively by carbohydrate.  Regularly training at an aerobic pace will encourage your body to use available fat for fuel.
    • Protein can also be used as fuel for exercise but is a last resort during high intensity exercise.
    • A HIGH PROTEIN, LOW CARB DIET IS NOT RECOMMENDED FOR ATHLETES.
    • The more fit you become, the harder it is to maintain a max aeorbic pace because that pace becomes faster and faster.
    • The goal of training is to strengthen the ability of each system to function as efficiently and effectively as possible and for the body to go as long as possible in the aeorbic state.

    { 2 comments… read them below or add one }

    1 Matt July 13, 2010 at 10:28 am

    Great info! I actually learned a few things :)

    Reply

    2 BostonRunner July 14, 2010 at 12:12 pm

    This is a great, informative post! Thanks!

    Reply

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