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The Benefits of Endurance Training
The fundamentals of exercise are
endurance, strength, and speed. Endurance provides the foundation or base for activities
of all durations. Once a foundation of endurance and speed is in place with all of its associated
adaptations, the other
energy systems can be trained to develop
muscular endurance, speed endurance, and power. It is important to note
that speed refers to the rate of muscular contraction, not the rate of
travel so performing endurance rides incorporating speed should be done
at low intensity. For cyclists that means a cadence of 90 or above in a
small gear.
The "PhysioFunnel" to the right depicts
the order of energy system development to maximize performance
potential. The gray top area of the funnel represents the capabilities
of a sedentary person to metabolize energy to perform muscular work. The
black arrows at the exit of the funnel represent work efficiency. The
blue area at the top of the funnel represents the additional capacity to
metabolize energy through endurance training. The increased opening size
at the bottom of the funnel depicted by the red area and red arrows
represents the increased efficiency of doing work through training of
the anaerobic energy systems. A solid foundation of endurance and some
low intensity speed work for about 3 months with twice weekly continuous
activities exceeding 2 hours will help to optimize fat oxidation and
maximize the blue adaptations from aerobic base work. Once the aerobic
foundation is in place, specific anaerobic exercises can be performed to
widen the opening of the PhysioFunnel. If the aerobic foundation is not
in place, the anaerobic systems can be developed, but the PhysioFunnel is
effectively drained before the fourth quarter, final hill, or final
sprint.
Endurance can be thought of as the base
of an equilateral triangle in an x-y coordinate system of Time vs. Performance
Potential. The longer the base is, the higher the peak can
be. The accompanying graph depicts a higher performance potential for
athlete b with a
greater base than that of athlete a. The athlete who chooses to limit
endurance foundation, progress too quickly, or increase intensity too
early effectively reduces the base and knocks the top off
the performance potential peak. Perhaps more importantly, a lower peak
results in a shorter period of competition level performance.
These are often referred to as "plateauing" or, worse, burnout.
Endurance training provides the base for training all energy systems.
Adenosine tri-phosphate (ATP) is the energy currency of muscles.
Macronutrient carbohydrates, fat, and protein combined with oxygen are
broken down into ATP which the muscle cell mitochondria use to contract muscles.
There are two basic anaerobic (do not require oxygen) energy pathways
and an aerobic pathway:
- ATP-Phosphocreatine (PC) pathway
(anaerobic). Primary energy system employed for the 100M dash or
the 200M match sprint. It produces very large amounts of energy within
the muscle cells for
periods of about 10 seconds, but is very inefficient. It's like a
dragster that uses 8 gallons of fuel to cover 1/4 mile in 8 seconds.
Only a couple seconds of ATP is stored in the muscles. One of the
products of ATP metabolism is ADP so for another couple seconds a
phosphate molecule can be taken from muscular PC to create more ATP. It uses large numbers of type II fast twitch muscle fibers
and is not as trainable as the other energy systems so genetics mostly
define short term performance potential.
- Glycolysis pathway (anaerobic).
Primary energy system employed for the mile run or the pursuit. Again,
large amounts of energy are produced for 1 to 3 minutes in the
muscle cells, but the process is inefficient. It's more like a V8 that
will accelerate well on the highway and climb well, but only get about
10MPG. Glycogen stored in the liver and
muscles is broken down into glucose, which is then oxidated into ATP.
One of the major by-products is lactic acid, which explains the burning
sensation in the muscles. It is trainable and more efficient after a
good warm up.
- Tricarboxylic Acid (TCA or Krebs
cycle) and oxidative phosphorylation pathway (aerobic). Primary
energy source for events lasting more than 6 minutes. It produces low
amounts of energy, but is very efficient - 15-20 times the
energy per ATP molecule compared to glycolysis. It's like the Honda
that gets you from Seattle half way to San Francisco on a tank of gas.
The good news is it is very trainable.
The ATP-PC system is used only for the
highest level of activity. To a small degree glycolysis is always
occurring and aerobic metabolism (oxidation of carbohydrates,
proteins and fat) always occurs.
Carbohydrate, Protein, and Fat
Oxidation by the Mitochondria
The mitochondria of muscle cells are
like the pistons and intake valves in an engine. They combine enzymes
and oxygen with carbohydrates, fat, and protein to form ATP, which the
muscles use to create mechanical energy. Protein, the building block for all
cells, is also used for a small amount of energy production. It accounts for about 5% of energy at rest
and about 10% during long endurance exercise. Carbohydrate oxidation
accounts for about 35% of energy at rest and nearly 100% of energy at
max intensity and following a meal. Fat oxidation accounts
for up to 30% of energy during exercise, 60% of energy at rest and
between meals (this is why dieting alone to lose weight doesn't work), and 80% of energy after fasting 24 hours.
Fat burning is maximized at about 45-50% of VO2 Max (this is why a
combination of exercise and diet to lose weight works). Fat oxidation
requires 75% more oxygen to create ATP than glycogen (carbohydrates). This is why it
feels so bad to "hit the wall", or "bonk."
The Adaptation Cycle is depicted at
right. Adaptation is the end result of recovering from stress we place
on the body. After a strain is placed upon the body to stress it, a
recovery period is required and then an adaptation may occur so that, in
subsequent cycles, equal strain results in less stress or more strain
results in the same amount of stress. Here's a way to put this into
perspective. It takes two weeks for a 20-something body (add ~half a
week per decade after 20) to rebuild after a workout. If you cut your
finger it gets sore and scabs up. After about two weeks it completely
heals, but if you pick the scab it never heals and may even get worse.
Body builders intentionally over train to make their muscles look
stronger. What they're getting, though, is bigger, weaker muscles.
Endurance athletes seek the inverse of this - smaller, stronger muscles.
Recovery is the key. Let the scabs heal. The art and science of getting
smaller, stronger muscles lie in applying the right amount of strain and
recovery so as to maximize adaptation. This is
where periodization applies to all micro-, meso-, and macrocycles, which
you could generally think of as weekly, monthly, and season time
periods. As can be seen in the Stress Adaptation "Onion" pictorial,
periodic adaptations of stress result in greater adaptation. The
foundation or base period accounts for the majority of the adaptations
and the potential for maximized adaptations in the anaerobic energy
systems. Here is a list of the specific adaptations from low
intensity endurance training:
- Increase in capillary density (number of capillaries per
muscle fiber) to supply oxygen and nutrients and
carry away carbon dioxide and other waste products. It takes about 3 months to increase and about the same
period to detrain.
- Increase in number and size of
Mitochondria - up to 5% in the number of mitochondria cells per week
for a 6 month period.
- More efficient transport of fatty
acids, lactate, oxygen, and Glucose. Adaptation of the latter occurs
after just 10 days of exercise.
- Increased
intramuscular fuel stores of Glycogen and intramuscular Triglycerides.
- Up to a two fold increase in enzyme
activities in mitochondrial pathways. It only takes 10 rides and degrades just as
quickly to 40% attained at peak.
- Hypertrophy - increase in the size of
fast twitch fibers.
- Improved circulation for increased
blood plasma volume and lactic acid buffering.
- Increased stroke volume to pump
more blood per heartbeat.
- Improved liver Gluconeogenesis. The
liver converts amino acids,
lactate, and glycerol into glucose where it is released to the blood or stored
as glycogen, which is necessary to provide fuel for the brain.
- Neuro-muscular facilitation or
teaching the muscles to contract and relax repeatedly.
- Strengthening of the joints,
ligaments, and tendons for injury prevention and increased strain.
- Increased cardio-respiratory and
circulatory development and efficiency.
- Improved thermoregulation.
Note that in the onion analogy the
beginning and end of the periods start at nearly the same level. At the
beginning of the season or training cycle is a point that is just about
the same for all athletes. After applying multiple layers, however, the
adaptation occurs more quickly and a higher level of adaptation is
achieved. This is why an athlete can start at about the same fitness
level at the beginning of each season, but in subsequent seasons can
attain greater adaptation. This is simply the Adaptation Cycle principle
applied over and over. When this is applied to all energy systems and
specificity of exercise it is known as periodization.
In summary, training for 2 or more
hours at an intensity to carry on a conversation teaches the body to use
fat as a primary energy source, preserving the less efficient, but
higher energy producing anaerobic energy pathways for the next hill,
sprint, bridge, or long breakaway. Applying that over a period of about
3 months results in development of a strong foundation on which to build
strength and develop the anaerobic energy systems for optimum
performance.
The primary references for this article
were the late Ed Burke's Optimal Muscle Recovery and Joe Friel's
Cyclist's Training Bible, both available in the
Library.
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