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Exercise Physiology

We will give a brief overview of what actually happens in the human body during exercise.  We will not go into the details, for there is an entire course in exercise physiology.  We will discuss some of the metabolic pathways and the adaptations that the body makes during training over a period of time.  Some of these points are very beneficial, especially when trying to design a training program for your particular sport.

  1.  Glycolysis (anaerobic)

• occurs without the presence of oxygen and only uses CHO as a substrate for energy
• used for quick bursts of energy; provides immediate energy for the body, but can only last for 1-2 minutes
• produces lots of lactic acid, the product that leads to fatigue in the muscles and hinders performance
• uses fast-twitch muscle fibers which fatigue rapidly; do not utilize oxygen and can not get rid of the lactic acid

  2.  The Krebs Cycle and the Electron Transport System (aerobic)

• occurs in the presence of oxygen
• uses CHO, fats, and proteins as substrates for energy
• more efficient process than glycolysis and does not produce as much lactic acid; allows the athlete to perform longer
• used for moderate to intense exercises lasting anywhere from 2 minutes to hours
• uses oxidative (slow-twitch) muscle fibers and can use the oxidative/glycolytic muscle fibers

***The intensity of the exercise is going to dictate which process you use.  If you need rapid energy for short duration, glycolysis will most likely be used.  If you are going to run a marathon, the aerobic processes will fuel the exercise.  While you are seated in class, your body is burning mostly fats.  If you are running at a maximum speed for 30 minutes, your body will be using CHO. The lower the intensity, the more fat is utilized.  The higher the intensity, the more CHO is utilized. However, as the exercise progresses and the duration is longer, the greater the utilization of fatty acids as energy.  As already stated, the body stores of CHO may be depleted during prolonged exercise.  It is at this point that the body will begin to use fatty acids so it can store the remaining CHO as a fuel source, if needed later on. There are some physiological adaptations that occur in the body with prolonged training that allows these things to occur.  We will discuss them next.

Metabolic Adaptations to Endurance Training

  1.  Increase in the size and the number of the mitochondria (mitochondria help with the aerobic energy process)

• the more mitochondria means there is less of a need for glycolysis, which means less fatigue

  2.  Increase in the electron transport system capacity

• due mainly to the increase in the size and number of the mitochondria

  3.  Increase in the Type IIA (oxidatve/glycolytic) fibers and a decrease in the Type IIB (glycolytic) fibers

• Type IIA use oxygen and don't fatigue as quickly; Type IIB are anaerobic and do not use oxygen

  4.  Increase in the enzymes necessary for the breakdown of fats as an energy source

• allows the body to use fats as an energy source and spares the CHO for later use during prolonged exercise

  5.  Increase in CHO storage

• helps increase the amount that may be stored during "CHO loading"

  6.  The trained person produces less lactic acid

• less lactic acid produced during exericse, the slower the rate of fatigue

All of these adaptations allow the athlete to perform longer and at a greater intensity.  This is going to lead to an increase in performance.  The trained individual will also have a lower resting heart rate and a lower exercising heart rate.  The body will not have to work as hard to keep up with the intensity of the exercise.  The stroke volume, the amount of blood pumped out by the heart, will also increase.  This will also allow the body to function at a lower energy demand, even at higher intensities.  The trained individual will also be able to divert blood flow to the working muscles more efficiently during exercise.  This will allow for the removal of lactic acid from the muscle and lead to less fatigue.  It will also increase the amount of oxygen being delivered to the muscles during exercise.  The perfusion in the lungs will also become more efficient, allowing for greater performance.  

These adaptations will all increase performance, but they will take a few months to occur. These are some of the metabolic adaptations that occur with exercise.
These are the reasons that trained individuals can perform better than the untrained people.  

Factors that affect strength:

1. Cross-sectional area of the muscle
   --the greater the area, the stronger the muscle
2. Fiber type composition
   --greater type II fibers, the greater the strength
3. The angle of pull
   --the strength of contraction will be different throughout the entire range of motion
4. Muscle length
   --you want to stretch a muscle slightly to get the most force produced
5. Speed of contraction
   --increase the speed, decrease the force
6. Aging
   --strength increases until about 30-40 years of age, then begins to decline; dramatic decline between 60-75 years of age
7. Gender
   --little differences until puberty; men surpass women by 20% after puberty (may be only 10-15% in the lower body)
8. General body warm-up
   --by warming up, you will increase the body temperature which will increase the efficiency of the enzymes of the required reactions; also improves nerve and conduction velocity; a warm muscle has less resistance to change in length

Adaptations That Accompany These Factors

     1.  Increased muscle mass (hypertrophy)

     2.  Increased protein structure

The hypertrophy is due to the increase n fiber size.  There is an accelerated protein synthesis and a diminished protein degradation with strength training.  This will occur with the recruited muscle fibers that you are training.  The increased protein synthesis will lead to an increase in protein structure.  Both males and females can have the same relative muscle growth when exposed to the same training stimulus.  Their % increases will be about the same.  These adaptations will cause an increase in bone density and connective tissue strength.  It will also maintain muscle mass, which may help with performance.

General Principles for Strength Training:

1.  Progressive, heavy overload of specific muscles

• do this by changing the # of reps, sets, exercise choice, or the load

2.  Keep the training interesting and motivational

3.  Train the large muscle groups before the small ones

• studies show that if you do the small groups first you can only do 40% of the load with the larger groups

4.  Make sure you leave adequate recovery between sets and repetitions

• 2-3 minutes between sets might be the time needed to do the same # of reps at that same weight as you did previously
• this should stimulate optimal muscle growth

5.  Rest between days of exercise

• wait at least 48 hours before using the same muscle groups
• this should optimize muscle strength
• you want a net protein gain so you must allow for adequate muscle protein synthesis

Acclimitization may take 7-10 days in the same environment to occur.

     1.  Increase in stroke volume; decrease heart rate

     2.  Decrease core temperature and skin temperature

     3.  Increase capacity for sweating --3 times more in quantity and in distribution

     4.  Decrease the threshhold for sweating

     5.  Increase in plasma volume

     6.  Decrease in sodium loss

When you acclimate, you sweat sooner and sweat more.  If you are trained, this will be more efficient than in the untrained person. Acclimitization will allow for an increase in exercise capacity.

***This is just a brief overview of what can happen in the body during training.  I hope this was helpful and now maybe you realize why you are able to perform better than the out-of-shape competitor.  Even though you may be able to train and make these adaptations possible, if you stop, you will also lose them.  Make sure you keep that in the back of your mind.  As we grow older, things become more difficult so you need to keep the motivation strong and you will still succeed.***

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