Home > Uncategorized > Exercise Physiology and How It Relates to Endurance Training

Exercise Physiology and How It Relates to Endurance Training

(Taken from the KET Training Manual)

A little Anatomy & Physiology
Let’s try to understand what exactly happens inside our bodies during all of this endurance training.

The transportation of oxygen and nutrients to the muscle starts with circulation. The delivery of oxygen and nutrients is what helps the muscles contract to produce movement. The circulation and delivery of the oxygen and nutrients to the muscles can be enhanced with training and good nutrition.

The Macro View:
We inhale the oxygen and consume the macronutrients(carbohydrates, fats, and proteins) to provide the muscles with energy. The oxygen moves into the lungs where the exchange of oxygen & carbon dioxide takes place. We exhale the carbon dioxide and the oxygen moves into the blood after leaving the lungs. While in the blood, the oxygen moves to the muscles carried by the red blood cells. The oxygen moves into the muscle with help from oxidative enzymes.

While this is happening in the blood the nutrients from the food and fluid we consume moves into the digestive system where it is broken down and transported into the blood as glucose, proteins, and fats. These macronutrients are then transported to the muscle. So the muscles use the oxygen and macronutrients for energy during endurance exercise.

The sequence goes like this:
Lungs to Heart to Arteries(lined w/muscle) to (oxidative enzymes)Muscle to CO2 Veins(not lined w/muscle-has valves) to Heart to Lungs to Exhale CO2 + H2O(another reason to hydrate).
Blood carries the O2 and nutrients to muscle.

There are also phytonutrients, nutrients found in plants(mainly fruits & vegetables), that also help with transportation of the oxygen and macronutrients by causing an opening of blood vessels(vasodilation)and increased blood flow.

The “Fick Equation”
The Fick Equation is a good example of how the system works during exercise and where the benefits from regular endurance training occur.

VO2(oxygen consumption by the muscle)= CO(Cardiac Output or the amount of blood leaving the heart per minute) x A(oxygen in the Arteries )-V(oxygen in the Veins)o2 difference in arteries and veins.
AND the AVO2 difference increases with increased activity from the oxidative enzymes in the muscle. This is where a large part of the benefit of training occurs.
Skeletal Muscle

The role of the skeletal muscle:
Skeletal muscles contract moving bones through the full range of motion at a joint and overcoming resistance by the generating force. There are different shapes of muscles allowing for different types of movement.

“Form follows Function”

Rectus Abdominus is used during sit-ups or “flexion of the spine” and the Transverse Abdominus is used when rotating the trunk.
How do Muscles Function?

Simply, the muscle contracts pulling on a tendon(tendons connect muscle to bone), the tendon then pulls the bone causing movement.
Now for the Micro view (hang with me!)
ATP(adenosine triphosphate)
In the muscle there are ATP molecules, when in the presence of O2, can multiply in volume to provide greater amounts of energy.

Hence, Oxygen in muscle forms large amounts of ATP which then causes greater amounts of energy for muscle contraction to move the body. Oxygen transported to the muscle is important to form the energy needed for endurance training.

But without O2 the only source of energy available to make ATP is glucose. When only glucose is available small amounts of ATP are formed. This energy does not last long. Just a few minutes. An example is the 100 m sprint.

Inside the fibers proteins Actin and Myosin slide passed each other from energy derived from the break down of CP(Creatine Phosphate) in the mitochondria(the powerhouse of the cell)
Calcium, Potassium, Sodium (electrolytes) move in and out of the cell
This is done in a fluid medium. This fluid medium is important. This is why drinking water and remaining hydrated is so crucial to effective endurance training.

The Power House of the Cell: Where the energy is generated

Anaerobic and Aerobic energy systems:
The 2 systems and differences in intensity and duration
The Anaerobic(without O2 and not a lot of ATP) and Aerobic(with O2 and high amounts of ATP) energy systems are the energy systems used during training. We constantly move in and out of these 2 systems during a training session. An example would be a bike ride where we are riding easily on a flat area of road (aerobic system) then we approach a hill. During our climb up the hill the intensity becomes greater. That is when we are moving into the anaerobic system. If we become so out of breath that we needed to stop and walk the bike up the hill we entered the anaerobic system to the greatest extent and exceeded the anaerobic threshold. More on that later. If we could make it to the top crest of the hill without walking we stayed mostly in the aerobic system.

There are differences in intensity and duration of the 2 energy systems. The anaerobic system is a high intensity, short duration(1-5 minutes)system. It uses primarily glucose as the immediate source of energy in the muscle and blood.

The aerobic system is the lower intensity and longer duration system.
During a comfortable, mostly steady, and flat training session you are primarily using the aerobic energy system.
Oxidative Enzymes and Nitric Oxide

Some physiologists would argue that the benefits of exercise are mostly derived from oxidative enzymes (increase with aerobic exercise)and NO(Nitric Oxide) which causes vasodilation of the arteries(greater blood flow) facilitating the movement of oxygen and nutrients into the active muscle.
There are Different Muscle Fibers

Fast Twitch, Slow Twitch Muscles and In-Between

Skeletal Muscle is composed of 3 types of muscle fibers:
Slow Oxidative(SO), Fast Oxidative Glycolytic (FOG), and Fast Glycolytic (FG)

SO: Is an endurance, long duration, oxygen dependent muscle fiber. Oxygen is utilized to generate high amounts of ATP. Exercise using predominantly slow twitch fibers can last a very long time. The SO fibers are the fibers that are working primarily during those comfortable sessions. At this level of intensity you can hold a conversation.

FOG: Is a fiber that uses oxygen for generation of ATP and also can generate a lot of speed. If you do speed work during the week the FOG fibers will become enhanced. These are the “lactate threshold fibers”. The fiber that can carry you through at a race pace or a good tempo session. This fiber is a hybrid of the slow and fast twitch. It can provide long durations and a higher intensity. Breathing is somewhat difficult at this level of intensity while using these muscle fibers.

FG: These fibers are for very high intensity and short duration activities. The kick at the end of a race. The climb up a very steep incline or 200m repeats on a track. These fibers provide very high intensities but can only be sustained for short periods of time.

Training the Different Systems

So how can we train those different muscle fibers?

• 1x/week of speed training is sufficient to engage the FG fibers during the base and build phases and working on the weak sport during the off-season period.

• 1x/week Tempo and hills engage the FOG fibers

• 1x/week of long slow distance in each sport in base/build phases of training-trains SO

High Intensity-Acids Increase

Lactic acid and Hydrogen:
During high intensity sessions hydrogen and lactate increase. This pushes the Ph to a more acidic range (<7.0). There are organs that can use lactate for energy. The heart muscle is an example. However, most can not. When the production of lactate exceeds the absorption of lactate this state is referred to as the “lactate threshold”. What many athletes are not familiar with is that hydrogen levels also rise causing a more acidic environment in the muscle. The combination of acids increasing cause stiffness, fatigue and soreness but the condition often only takes into account the lactic acid.

The endurance training goal is an increased lactate threshold. This increased threshold means the athlete can work at a higher intensity for a longer period of time.


-Mark Kotarski, MEd


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