Table Of ContentThe Science of Running
Factors Affecting Distance Running Performance
Steve Magness
George Mason University
Table of Contents
Chapter 1: How Running Happens
Motor Programming
Sending and Receiving the signal
Muscle Contraction
Energy Needed
Muscle Fiber Types
A Recruitment Issue
Passive Mechanics
Chapter 2: Fatigue: Friend or Foe?
How Fatigue manifests itself
How Fatigue occurs
Oxygen’s role
Chapter 3: An Oxygen Problem
The measurement: VO2max
Oxygen intake
Oxygen Transportation
Oxygen utilization
The VO2max limiter
Chapter 4: The Fallacy of VO2max
How the VO2max concept developed
Efficacy of basing training paces off of VO2max
Should we train to improve VO2max?
Chapter 5: Lactate, Acid, and other By-products
Buffering/Dealing with high acidosis
The Lactate Threshold Maximum
Lactate Steady State
Lactate Testing
Chapter 6: Efficiency
The Measurement: Running Economy
Biomechanical Efficiency
Neuromuscular Efficiency
Metabolic Efficiency
Problems with Running Economy
Chapter 7: The Brain-Muscle Connection
Neuromuscular and Anaerobic factors in performance
Fatigue and the CNS
Temperature Regulation
The Psychology of it all
Chapter 8: The Genetics of Training
Steps of Adaptation
Long Term Adaptation
Training Applications
Chapter 9: Theories of Training Adaptation
General Adaptation
Syndrome and Dose-Response
Individuality of adaptation
Chapter 10: Volume and Intensity of Training
Volume of Training
Intensity of Training
Interaction of Volume and Intensity of Training
Training in the Real World
Supplemental training
Training Frequency
Chapter 11: Periodization
Periodization in Endurance Sport
Individualization
Chapter 12: Training Models- Example of Integration of Theory and Practice
Chapter 13: Where do we go from here?
References
Introduction
The sport of distance running has a long history that has been closely tied with the rise of sports
science. The founder of modern physiology Nobel Peace Prize winner A.V. Hill chose running as his
platform to develop the concept of oxygen consumption (Bassett & Howley, 2000). Even with this long
history of investigating the mechanisms behind performance and ways to enhance it in sports science,
many questions remain unanswered and the exact factors that govern performance are still debated.
In addition, unlike other activities such as weight lifting, the optimal way to train distance runners,
including both the effects of training at different intensities and how to periodize that training,
remains unknown. The current function of science in training is not to be used as a way to prescribe
training, but instead as a way to explain why training used by coaches or athletes works.
The purpose of this review is two fold. First, it is to establish the variety of mechanisms that control
and limit performance in the sport of distance running. Secondly, it is to look at the current training
methods used by trained athletes and evaluate their impact on the physiological factors that govern
performance. By analyzing the factors that affect performance and the current training trends,
limitations in the training of competitive distance runners will become apparent. I’ll take you through
how we run, from the nervous system down to what happens on the muscular level. Additionally,
a sub goal is to bridge the gap between the Sports Scientists/Physiologists of the world and the coaches
of the world. Both groups do outstanding work, but it is as if a gap exists with each group going about
their business with an air of superiority while completely ignoring or dismissing the other group. This
has resulted in two completely different ways of training endurance athletes, with the coaches
prevailing up to this point in superiority of performance, in my opinion. This strange battle should
not be against each other, but rather a cooperative one aimed at finding out how to optimize
performance. Once egos are put aside and everyone acknowledges that we do not have all the
answers, then I feel that new performance levels will be met.
Chapter 1: How Running Happens
When broken down in its simplest form, running is nothing but a series of connected spring like hops
or bounds. A certain amount of energy needs to be imparted into the ground to propel the runner
forward, continuing the running movement. The amount of energy needed depends on the pace that
the athlete is running; as the pace increases a greater amount of energy is needed. This energy comes
about through two primary mechanisms called active and passive mechanics. Active mechanics refers
to what we all think about when it comes to what drives running, actively recruiting muscles that
generate force via muscle contraction. On the other hand, the body, namely the muscles, tendons,
and ligaments, act in a spring like manner temporarily storing the energy that comes about from the
collision of the foot with the ground. During the subsequent push off, or propulsion, phase of
running, this energy is utilized and released, contributing to forward propulsion. These two
mechanisms combine to provide the necessary force and energy to power the running movement. In
simplistic terms a runner can keep going at the same pace as long as they can produce the necessary
kinetic energy, whether this comes from force production or passive mechanical energy. Once they
cannot impart enough energy, the pace has to slow as they are not able to cover the same amount of
ground with the same stride rate. Simply stated, they fatigue. Before looking at performance and
fatigue, it’s important to grasp the intricacies of the running movement. While the previous
description provides the framework, lets delve into each step of how running actually occurs from
the Central Nervous System all the way down to a single muscle contraction. Once this has been
done, the potential limiters along the route can be identified.
Motor Programming
The brain, or to be more exact the Central Nervous System (CNS), is where movement starts. The
simple act of moving one finger is an incredibly complex task involving multiple systems, so
completely understanding a complex dynamic movement like running is a daunting task. What we
do know is that movement originates in the nervous system. The nervous system consists of higher
levels of organization, such as the brain itself, and lower levels of organization, such as the spinal cord
and brainstem. These two levels of the nervous system combine to decide how movement takes place.
Movement occurs with a combination of pre-conceived motor programs and slight tweaks or
alterations based on sensory information. Essentially, the body has a gross general plan of how to go
about doing a certain movement, and then tweaks that plan based on the sensory information it is
constantly receiving, such as the ground surface, the position and length of your limbs, and a whole
load of other sensory sources. The movement pattern serves as the rough basis for how that particular
movement should take place. The sensory information provides for the on the go adjustment like that
seen when running on a road versus the sand, or if an unexpected root pops up in front of you. If the
body simply worked of pre-determined motor programming without the ability to use feed forward
or feedback information to adjust, we’d all be in trouble.
On the higher level, the brain works in an integrated way in that several areas of the brain combine
to work dynamically to create the running pattern, using feedback and feed forward information to
provide the details on what the muscles should do. At the lower spinal cord level, movements that
occur reflexively or without the need for sensory feedback or feed forward information are developed.
At the spinal cord level, Central Pattern Generator’s (CPG) guide movement patterns and muscle
activity without the need for sensory input (Molinari, 2009). These two processes integrate using both
active and passive mechanics to decide how movement ultimately takes place.
In establishing the movement pattern, what muscles to activate, how often to activate them, and in
what order activation takes place is all determined. While running, the CNS uses a complex amount
of sensory information including; external stimuli such as the ground surface, limb movement and
position, such as how the foot is striking, and internal stimuli such as the length of various muscles
throughout the movement or even the buildup of fatiguing products in the muscles themselves. All
of this information, combined with the basic motor programming, results in an on the fly adjustment
of how you are moving. A variety of adjustments are made including: what type of motor unites
(groups of muscle fibers) are recruited, the recruitment pattern, how long a rest to work cycle a motor
unit has, the relaxation of opposing muscles, and the manipulation of nonpropulsive fibers to
minimize the effect the impact with the ground has. The CNS is constantly using all of the sensory
information, comparing the intended movement with the actual movement and making slight tweaks
or adjustments. Not only does it make adjustments based on the movement, but also on what to alter
when fatigue is building up. While this will be covered in depth in the next chapter, how the body
deals with fatigue is ultimately a motor control issue. Have you ever wondered why you might start
leaning back, swing your arms wildly, or reach out with your foot during the end of an exhausting
race? This happens because of a combination of conscious and subconscious control in which you are
trying to compensate for fatigue by a variety of biomechanical adjustments. Part of training is
teaching the body how to accurately adjust the movement pattern to fatigue. From a motor
programming standpoint, doing all out workouts where form is broken down completely might lead
to negative motor programming, or in laymen terms bad habits.
At first the movement pattern is rough, uncoordinated and inefficient, but as a person becomes better
trained, this process is refined and improved. Initially, the exact recruitment pattern or how to relax
the opposing muscle is not known or refined. Slowly, the body becomes more efficient at determining
exactly what muscles need to be working and for how long. This refinement results in a smoothing
out of the movement and is an improvement in neuromuscular control which creates an efficient
movement pattern that enhances performance via improving efficiency. This process is called motor
learning, and contrary to popular belief, running is a skill that needs to be learned and refined.
While previously it had been thought that improvement in motor learning only occurred at the
higher levels such as in the motor cortex in the brain, recent evidence has demonstrated that even at
a spinal cord level, the movement pattern can be refined (Molinari, 2009). The movement pattern is
generally improved by a better coordination of activating just the right amount of motor units to do
the work, improving the cycling of motor unit activation, and decreasing the level of co-activation
(when the opposing muscle is active at the same time as the main muscle). Additionally, as a
movement becomes well refined, it is believed that the CNS becomes better at using all of the sensory
information that is receiving, essentially weeding out the pertinent versus inconsequential
information better than when first learning how to move.
Running Around with your head cut off:
The phenomenon of chickens running around after their heads cut off shows that a general
movement pattern for running is available at the spinal cord level. Studies with other animals
and even historical reports with humans when the guillotine was in use, have confirmed this
phenomenon. This points to the conclusion that activities like running and walking might
have an ingrained motor program that has developed through evolutionary process.
Sending and Receiving the Signal:
The actual process of activating muscles occurs via the nervous system sending neural signals called
action potential. Action potentials work as the communication system between the nervous system
and the muscles. Both Neurons, which are nerve cells, and muscle cells create action potentials. In
neurons, the action potentials serve as a communication device, and in the case of movement send the
signal to contract all the way to the muscles. An action potential works via differences between the
electrical charge inside the cell and outside the cell. A cell has a resting voltage called the resting
membrane potential. In its resting state, a cell is polarized in that inside the cell has a negative charge
compared to the outside of the cell. This happens because of a greater concentration of negative ions
inside the cell and/or a greater concentration of positive ions outside the cell.
When this charge is reversed, or depolarized, to a significant enough degree so that now the inside of
the cell has a positive charge, an action potential arises (Brooks & Fahey, 2004). Full depolarization
has to occur for an action potential to be generated. This means that a significant enough stimulus
needs to be received to change from a negative to a positive electrical balance inside the cell. Once
the action potential is generated, repolarization occurs, returning the membrane potential to resting
levels. The action potential flows down the cell and communicates to the next cell in line via
neurotransmitters. This process occurs over and over as the signal makes its way from its origin
through the nervous system and down to the muscles.
The manipulation of the electrical charge inside and outside of the cell occurs mainly from differences
in sodium and potassium inside and outside of the cell. The Potassium maintains the negative internal
charge, while the sodium keeps the positive external charge. The manipulation of the sodium and
potassium levels inside and outside of the cell creates the differences in charges. The primary
mechanisms for controlling these two substances are the Sodium-Potassium pump, and a greater ease
of movement through the cell membrane of potassium (Brooks & Fahey, 2004). For depolarization to
occur, sodium gates open which causes the shift in electrical charge to occur. The opening of the
sodium gates in motor units is caused by the neurotransmitter Acetylcholine (ACh).
Neurotransmitters are chemicals that allow for communication between cells. Following the action
potential creation, the potassium gates open causing potassium to exit the cell, which causes
repolarization, returning the cell to normal. As we become better trained, the signaling via the
neurons can improve. A change in the excitability of a neuron is one possibility, as is a change in the
speed of the signal being sent.
Muscle Contraction
The nerve signal eventually reaches an α motoneuron, which is a neuron that innervates a group of
muscle fibers. The entire α motoneuron and connected muscle fibers make up what is called a motor
unit. The action potential travels down the neuron until it reaches the gap between the neuron and
the actual muscle fiber and is called the neuromuscular junction. This junction is where
communication between the neuron and the muscle takes place. As previously mentioned, this occurs
via the releasing of neurotransmitters (in this case ACh) that travel across a small gap between the
neuron and the muscle and bind to special receptors on the muscle. The binding of the
neurotransmitter causes an action potential to occur in the muscle cell, which can lead to the
depolarization process described previously.
In the muscle cell, the depolarization causes Calcium that is stored in a structure called the
sarcoplasmic reticulum to be released. The Calcium quickly spreads throughout the muscle fiber with
the goal of eventually reaching the actual contractile parts of the fiber. Deep within the cell is its basic
unit the myofibril. The myofibril consists of two main filaments, actin and myosin. Actin is referred
to as a thin filament while myosin is the thick filament because it has myosin heads on it which can
attach to the actin. At rest, the myosin heads cannot attach to the actin because the attachment site is
blocked. However, the calcium released frees up the attachment site and allows the myosin head to
attach to the actin. When it does this, it essentially pulls on the actin, causing contraction. The
repeated pulling and releasing that goes on is what causes muscle contraction. Without calcium
release this interaction cannot occur. To help conceptualize this process, think of a stationary person
(the myosin) pulling on a rope (the actin) to try and drag a heavy object towards them. The person’s
hand represent the myosin head as they grab the rope, pull it some, let go, and then grab it again to
pull the object closer.
But that’s not the entire story. This whole contraction process requires energy. Energy in the form
of ATP is required so that the myosin head can pull on the actin. This movement requires the release
of energy. However, in terms of supplying energy, ATP needs to be supplied once the myosin head
has completed its pull to allow for it to release and be ready for the next pulling cycle. Thus, the
process of supplying energy is one of replenishment. Without the resupplying of ATP after the myosin
head’s pulling has occurred, the continual process of attaching, dragging, and releasing can not occur.
In our conceptualization, without energy, the actual pulling of the rope takes energy, but if we did
not supply energy at the end of a single pull, then our person would not be able to move his hands
further up the rope and pull again. This is the process of a single contraction of a muscle fiber. Once
the contraction occurs, relaxation has to occur before a subsequent contraction occurs. Relaxation is
dependent on the calcium being transported back into its holding site, the sarcoplasmic reticulum.
Until the calcium returns, another contraction can not occur.
Energy Needed
As you can see from the process of contraction, chemical energy needs to be generated in the form
of ATP to resupply the myosin heads during the contraction process. We only have a limited amount
of stored ATP in the muscle, so instead we have several processes to recycle ATP. These processes
are a series of chemical reactions that take the various products left over from the energy release that
occurs when contraction takes place and recycles them into ATP. When energy is used by the myosin
head, the ATP, which consists of an Adenosine molecule and three Phosphates (Pi), is broken down
to ADP (Adenosine + 2 Pi) and a Pi. The releasing of one of the Pi is what causes energy release. In
the end we are left with ADP and Pi floating around, or in some cases AMP (Adenosine + 1 Pi) and
Pi. The energy systems work to use these and other building blocks to recreate ATP.
The energy systems all use a series of chemical reactions to produce ATP. With each chemical
reaction, enzymes are required to convert the initial products into the final products. Enzymes
accomplish this by speeding up the rate of the reaction. Therefore the quantity of certain enzymes is
one trainable factor that can enhance performance, as the ability to perform certain essential chemical
reactions is improved.
Each energy system differs in complexity in terms of how many reactions are needed to finally get to
ATP, and on what the initial fuel source is. Obviously, with a greater number of reactions, it takes
longer to go through the entire process. Additionally, there are more steps involved, which means
more chances of slow down, and more substances needed for each reaction. On the other hand, the
supply of the products used during the energy systems matters. With our simple, one or two step
reaction systems they can produce ATP very quickly, but the fuel supply is limited and thus used
quickly. On the other hand, the complex multi reaction systems have fuel supplies that are much
larger which means while they cannot produce ATP as quickly, they can do so for a much longer time.
Lastly, one other difference is in the by-products that are produced with each system. Each system
