A. Aerobic Energy Substrates

 

Activity that raises the resting heart rate to 70% of maximum (220 - age = MHR), and is performed at this heart rate for a minimum of 20-30 minutes per session, thereby achieving what is commonly known as a ‘steady state’ of accelerated metabolic function. Activity must satisfy the above requirements in order to technically be considered aerobic. It is under these conditions that aerobic energy pathways (fatty acids & oxygen) are functioning optimally.

It is suggested the above aerobic activity be performed 3-4 times per week in order to maintain cardiorespiratory health and efficiency. Unlike during low level activity, which requires fatty acids and very little in the way of oxygen, it takes time for aerobic metabolism (oxygen and fatty acid use for energy provision), to kick in. Initially then, the aerobic activity participant is calling upon liver glycogen, muscle glycogen and blood sugar, with the gradually increasing assistance of oxygen, for energy.

The common physiological phenomena known as “catching your second wind” can be technically referred to as the aerobic threshold. This “threshold” is crossed at a point unique to the individual dependent upon the level of aerobic conditioning (the better the conditioning, the sooner the occurrence). This commonly experienced “second wind” occurs when the energy pathway has in effect, progressed through the first and second stages of energy provision, anaerobic glycolysis (the use of sugar in the absence of oxygen), and then metabolic oxidation (the use of sugar in the presence of oxygen), and then finally on to aerobic metabolism (the use of oxygen and fatty acids). The undisputable value in performing regular aerobic exercise is the conditioning of the cardiovascular as well as the respiratory systems.

There are no substitutes for aerobic activity when it comes to the maintenance of cardiorespiratory health. Moreover, cardiorespiratory efficiency leads to enhanced cellular uptake and exchange of oxygen, carbondioxide, nutrients and wastes. And, make no mistake, these are survival functions. It was once considered a given that aerobic exercise raised the metabolism and was the most widely prescribed method of exercise for eliminating bodyfat. Now it is the contention of the majority of health and fitness professionals that low level activity is superior in the pursuit of fat loss (even given its demanding time requirements), while moderate to intense resistance exercise is far superior to aerobic exercise in raising the metabolism (stimulates lean weight gain which in turn increases energy needs and metabolism.) Simply put, aerobic activity maintains the health and efficiency of the body’s most crucial “support systems” which provides for long life and lays the foundation necessary enabling us to comfortably, enjoyably and efficiently perform all other lifelong activities.

- The Aerobic system supplies the energy needed for continuous rigorous exercise which lasts for more than three minutes.
- Jogging, long distance running, swimming, cycling, cross-country skiing are some aerobic exercises.
- Oxygen is the key to the aerobic system.
- Glycogen (carbohydrates) and fat are systematically broken down or oxidized by a series of enzymes and finally combine with oxygen to form carbon dioxide and water.
- Energy released is used to form ATP.
- Aerobic system delays fatigue and is more efficient than Anaerobic system.
- Provides much more ATP (38) than Anaerobic system (2) which is why it can sustain moderate exercises for a long period of time.
- However, it takes 2-3 minutes for oxygen consumption to increase to the higher level, which is needed during exercise. During this time, there isn't enough oxygen to provide ATP through the Aerobic system, so the body relies on the Anaerobic system.

Uses Oxidative Phosphorylation Please refer to this link for further information.

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B. Anaerobic Energy Systems

Anaerobic Activity - (Resistance Exercise) Basically, when an individual muscle fiber contracts, it is blind to the amount of resistance the muscle group is being asked to move or the type of activity that is being performed. It simply does as it’s told and responds to the nerve impulse with all of its might whenever it is told, and for as long as it can before reaching failure or being told to stop. As a muscle fiber starts to fail, or as the resistance becomes greater, other muscle fibers are called upon to help. The harder the work, the more fibers that will be stimulated.

Failure of muscles to contract, under normal conditions, results from #1-exhaustion of energy and build up of intercellular wastes; #2-the resistance being so great that the fibrous cords (myofibrils), become damaged and fail under an extreme amount of resistance.

Since muscle fiber contractions occur during all forms of activity to include low level activity and aerobic activity, at what point does an activity become anaerobic? The answer to this question lies in the question itself. The definition of anaerobic is essentially, “in the absence of oxygen”. Therefore, the definitive answer is that whenever energy is produced for muscle activity without the use of oxygen, energy is said to be produced through the process called anaerobic glycolysis, inside the muscle fibers themselves. Your complete understanding of the following exercise induced physiological occurrence will improve your abilities as an effective educator and personal fitness trainer.

During a muscle fiber contraction the muscle fiber cell membrane becomes impermeable. This simply means that during this contractile state nothing can move into or out of the cell, to include oxygen and nutrient intake as well as lactic acid and cellular waste removal. Fully understanding this single physiological occurrence truly holds the key to identifying and/or differentiating between the three major classifications of activity as well as to identifying their unique pathways of energy provision. The more actual fibers there are contracting simultaneously (as stimulated during resistance exercise), in a given muscle group, the less oxygen this muscle group is receiving. Hence, anaerobic glycolysis would be the energy pathway used during the performance of heavy weight training since a maximal volume of fibers in a muscle group are contracting, and the contraction is sustained for a significant period disallowing the uptake of oxygen until the relaxation phase. At the extreme other end of the continuum, during aerobic activity, the volume of fibers contracting and the duration of these contractions are so insignificant as to cause only a brief interruption of movement across muscle fiber membranes, hardly enough to prevent oxygen uptake and waste removal. Hence, aerobic metabolism. Armed with only an understanding of the aforementioned principles of muscle fiber permeability, and consequent energy provision, you can better reason to your clients the effects exercise. The absence of labored breathing during the performance of heavy work may serve as an indicator of anaerobic energy provision.

- Anaerbic system involves short term but high intensity exercise, which lasts for 1-3 minutes.
- Includes weight lifting, sprinting, tennis, handball, and volleyball

ATP-PC (Phosphagen System) (click this link for a glance of the Phosphagen System diagram)
- Energy rich compounds like ATP (Adenosine Triphosphate) and PC (Phosphocreatine) are store directly in the muscle tissue.
- Simultaneous breakdown releases immediate energy for muscle contraction
- Energy from and ATP and PC are limited to 3-10 seconds only because only very small amounts of these compounds are stored in the muscle.

Lactic Acid Sytem or Glycolytic System (click this link for a glance of the Glycolytic System diagram)
- Supported by sugar in the form of glycogen
- When glycogen is burned in the absence of oxygen, it gives off lactic acid as its end product.
- Energy from this system is limited to activities that last approximately 1-2 minutes only.

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