Kinesiology (Education)

This article provides an overview of kinesiology, the study of human movement. This article describes the three major body systems that are involved in movement-the skeletal system, the muscle system and the nervous system. Kinesiology includes the study of how these body systems work, both individually and cooperatively to facilitate the full range of human motions. This article explains the basic components of the skeletal system, including the internal structure of bones, bone development and the major classifications of bones. The muscular system is also described. The muscular system includes various types of muscles that provide the ability to perform movement and exert force through the activation of various muscle groups throughout the body. The information system that connects and commands the various body systems and functions is the nervous system. This article describes the components of the central nervous system-including the brain, spinal cord and neurons-and the peripheral nervous system and motor unit. Finally, the article describes how kinesiology applies to various motor skills, such as the major motion patterns that are involved in the movement of external objects, the ability of the body to maintain balance and support itself and to stop the movement of objects. The following sections explain these concepts in more detail.

Keywords Anatomy; Balance; Bone; Equilibrium; Gravity; Muscle; Nervous System; Range of Motion

Overview

Every day, from the time we wake up in the morning until the time we lie down to sleep at night, our body is in motion. This motion may not be immediately obvious, but there are muscular contractions unseen to the human eye that are occurring at all times. Even during sleep, often thought to be a period of inactivity, respiration continues, the beating of the heart slows but never stops and the body changes positions during the course of sleep. Only in paralysis does muscular response cease to exist.

Kinesiology, at its most basic, is the study of movement. Kinesiology is not an isolated science. Instead, kinesiology involves the examination of many sciences as they relate to the human body and movement. This broad discipline brings together the fields of anatomy, physiology, physics and geometry, and examines their relationship to human movement. In addition, kinesiology includes the study of the interrelationship between the major body systems, including the skeletal, muscular and nervous systems. Kinesiology also examines how basic human movements are completed and supported through the cooperation of bone, muscle, neural transmissions and even thought. Thus, kinesiology is a broad field that includes the study of the human body in motion and the collaboration of the body systems that facilitate this process. The following sections provide a more in-depth explanation of these concepts.

Role of the Skeleton in Movement

The human skeleton is the framework of the body. Bones vary in size according to gender and ethnicity, and among individuals within these groups. It is the bones that primarily determine the characteristics of body build. For instance, bone development will determine whether a person will be tall or short, will have thick limbs or slender or whether their hands and feet will be stocky and wide or small and delicate. The bone structure also has a significant impact on the movements of the individual. Certain bone structures are ideal for performing short, quick motions while these same movements would tend to cause imbalance in other bone structures.

In addition to determining body structure, bones serve a number of important purposes. First, bones play a significant role in a person's movement and work. Bones provide not only the dimension of the levers for work in the length of the bones themselves, but also the axes on which these levers turn in the form of joints. Each bone must be rigid and strong to withstand both the force of the muscles which pull upon it, called tension forces, and also the stress of the load which the lever bears, known as compression forces. Likewise, bones must be dense and solid to protect other vulnerable organs and tissues such as the vascular centers within long bones or the heart and lungs enclosed by the thorax. Although all bones play a similar role in framing the body and facilitating movement, the structure and classification of bones vary significantly.

Internal Structure of Bone

The internal structure of bones are made up of two different forms of material—compact bone and cancellous bone.

• Compact bone is the dense, hard exterior of the bone. It has the color and texture of ivory and is exceptionally strong. Holes and channels are intertwined through it to carry blood vessels and nerves from the periosteum - the bone’s membrane covering - to its inner elements.

• Cancellous bone has the appearance of a sponge and develops inside the compact bone. It is comprised of a mesh-like network of miniscule pieces of bone called trabeculae, with marrow filling in the spaces between.

Bones are living tissue and contain various layers. The center of bones consists of a tiny canal known as the Haversian canal through which extends a supply of tiny blood vessels that transport blood and fluids for metabolic needs. Around this central canal lie concentric rings of calcification that also contain canals for tiny capillaries. These layers do not fit together perfectly, and the spaces between are filled with layers of deposits so that the compact bone appears uniform and solid. The cancellous bone shows the same basic system of calcium deposits around circulatory canals, but these layers are not as parallel in arrangement.

Both compact and cancellous bone responds to the pressure and tension forces acting on the bone. The compact bone generally provides strength and protection. The cancellous bone is designed to provide strength while still being lightweight. If stress on a bone is great, the bones become substantial and the holes are smaller and more widely spaced. As stress diminishes, the bones will become less dense over time.

Bone Development

The human body contains 206 bones that support and connect muscles and protect vital organs. At the center of the human skeletal system is the spine and vertebral column, made up of 25 bones that support upright carriage and enable movements such as standing, walking, running, sitting and engaging in all large-muscle movements. In addition, human hands and feet contain slender, finer bones that enable the performance of intricate tasks. Each hand contains 27 bones, including an opposable thumb that provides the ability to perform a wide range of movements such as maneuvering tools, performing meticulous actions or playing musical instruments.

As bones develop, they first emerge as cartilage and are similar in shape and proportion to the ossified, adult bone. The bone changes from this state as a result of ossification. Ossification is the process whereby cartilage is gives way in favor of hard deposits of calcium phosphate and stretchy collagen, which are the two major components of bone. This process is started before birth and is gradually continued until a person reaches the early to mid-30s. In longer bones, the process of ossification takes longer and thus these bones are the last to calcify.

Once bones develop and are calcified, they still remain dynamic and living tissue that can adapt to stress, heal from injury and repair from fractures. The repair process occurs when the cracks or separated ends of a fractured bone first fill in with cartilage and begin bonding together. Over time, they are transformed into a stronger bone than before the facture. This healing process requires the steady supply of blood. The blood supply to both the marrow and the bone itself is profuse, supported by an ample supply of capillaries and blood vessels that transport nutrients for metabolism, bone absorption and replacement and the production of red cells. Through their development and repair process, the bones reveal a great deal about an individual's growth process, reflecting nutritional deficiencies, general health status and even age.

Classification of Bones

Bones are classified according to shape and proportion. Long bones consist of a shaft of compact bone filled with marrow that fills in the spaces between the sections of the cancellous portion. Muscles and tendons attach directly into the membrane that covers bone ends, and in some cases the fibers of tendons reach deep into the bone. Short bones are of irregular shape but are generally equivalent in diameter. They too have cartilage inside and a membrane that covers the outside. Short bones are mostly cancellous bones with a thin outer layer of compact tissue.

Irregular bones vary greatly in their shape, with different parts or projections depending on their purpose. They always contain compact bone as a shell and are filled with cancellous bone if they are of any thickness. Finally, although flat bones are thin, they are seldom flat. The ribs and cranial bones are considered flat bones, but are actually thin and curved. Flat bones are usually made up of outer layers of compact bone or plates of compact bone with a cancellous layer in between for strength. The cross section of flat bones resembles that of a cardboard box, with corrugated layers in between sheets of paper.

Role of the Muscular System in Movement

All movements of the segments of the body are the result of muscle contraction or muscle tension, or of the application of some external force, such as gravity. In muscle contraction, energy is expended to create movement. In muscle tension, the movement is passive and the energy cost of this form of movement is different than muscle contraction. Whenever there is nervous stimulation, it causes contraction or causes the muscle to resist relaxation. This results in muscular tension, which tends to increase the resistance offered to antagonistic muscles, and to slow up or actually check movement. The muscles of the body are a vast and intricate system of cooperation and harmony. There are a number of important muscle groups that are engaged during movement.

Types of Muscles

There are three types of muscles-cardiac, smooth and skeletal or striated-which vary in accordance with their function. Cardiac and smooth muscles have similar functions and are also similar in structure. They both surround hollow organs. Cardiac muscle is the muscle of the heart, and smooth muscle is the power unit of blood vessels, the digestive tract and certain other organs of the viscera. Cardiac and smooth muscles contract slowly, rhythmically and involuntarily. Skeletal muscles are quite different. They contract voluntarily as well as reflexively, and their fibers contract with great rapidity. Skeletal muscles are also usually attached to bones and cartilages. Under an ordinary microscope, skeletal muscles appear to be crossed with striations, whereas the smooth muscles have no such striations.

Muscle Movement & Strength

Movement is produced when some of the over 600 muscles constituting 40% of the human body weight shorten, thereby exerting a pull on the bones to which they are connected. In addition, muscles usually do not produce movements by working individually, but rather by participating with as many as 20 or 30 other muscles. When some muscles contract, muscles on the reverse sides of the joints involved must relax if movement is to be produced. There are approximately 75 pairs of muscles that are directly involved in working in coordination to move the bones to maintain posture, exert force or activate movement.

Muscular contraction can be classified generally into three types: concentric, eccentric and static.

• Concentric contraction occurs when a muscle develops sufficient tension to overcome a resistance and shortens, such as when an individual picks up an object such as a glass. In such a movement, some of the muscles of the arm-the biceps, for instance-shorten as the glass is lifted and moved.

• Eccentric contractions occur when muscles are used to oppose a movement but not to stop it, as in the action of the bicep in lowering the arm gradually after curling a free weight. The main characteristic is that the muscle lengthens during the action. Concentric and eccentric contractions are both called isotonic because the muscle changes length during the movement.

• A static contraction occurs when a muscle that contracts is unable to move the load and retains its original length. The effort exerted by the muscle is insufficient to move the load it is opposing, either because the load is too heavy or because the opposing muscles also contract, thus preventing movement. This type of static muscle contraction is termed isometric because the muscle develops tension without changing length.

Muscles are capable of generating significant force. To do so, muscles are powered by energy, which comes from ingested food that is transformed by the digestive system into chemical energy through a complex metabolic process that requires oxygen for its completion. The primary source of energy for muscles is in the form of glycogen, a carbohydrate that the muscles store in limited quantities and which must be replaced if activity is maintained for a long time. Thus, physical activity is made possible by the action of the heart as it moves oxygenated blood through the circulatory system and by metabolic processes that convert food into energy.

Muscle Groups

Muscles of the Head & Neck

Humans have skilled muscles in the face that allow for a wide variety of facial expressions. Because the muscles are used to express a wide range of emotions, they are an important way to convey meaning in a nonverbal manner. The muscles that are activated in the formation of facial expressions include frontalis, orbicularis oris, laris oculi, buccinator, and zygomaticus. In addition, there are four pairs of muscles that control chewing movements or mastication and are some of the strongest muscles in the body. Finally, there are a number of muscles associated with the throat, neck and the vertebral column. One of the most important muscles, the trapezius, extends down and across the back.

Muscles of the Trunk

The muscles of the trunk are the muscles responsible for moving the vertebral column, forming the thoracic and abdominal walls and covering the pelvic girdle. The erector spinae group of muscles on either side of the vertebral column is a significant muscle mass that extends all the way from the lower end of the spinal cord up to the skull. These muscles are mainly responsible for supporting the vertebral column and maintaining correct posture. The muscles of the thoracic wall are involved primarily in the process of breathing.

Abdominal muscles consist of four major muscles. The transversus abdominus, which forms the deepest muscle layer, keeps the trunk stable while preserving internal abdominal pressure. The rectus abdominus, which is located between the ribs and the pubic bone at the front of the pelvis, has bumps or bulges that can be visible when contracted, and are often called a “six pack.” The external oblique muscles located are on either side of the rectus abdominus, and allow the trunk to twist in opposition to a contracted external oblique. An example is when the right external oblique is contracted, the body turns to the left. Finally, the internal oblique muscles are next to the rectus abdominus and are located just inside the hipbones. They are similar to the external oblique muscles, but operate in the opposite way. Thus, a motion twisting the trunk to the left requires the left side internal oblique and the right side external oblique to contract together.

Muscles of the Upper & Lower Extremities

The upper extremities are connected to the trunk by means of the shoulder girdle. The upper limbs include the shoulder girdle, which is connected to the shoulder blade and collar bone; the upper arm, connected to the humerus; the lower arm, attached to the ulna and radius bones; and the hand, which contains the carpus, metacarpus and fingers. The over 20 muscles that regulate most wrist, hand, and finger movements are located along the forearm. In the lower extremity, the muscles groups consist of the muscle and connective tissue of the iliac, or pelvis, region and the muscles of the thigh, leg, ankle and feet.

Role of the Nervous System in Movement

The command center for movement is the nervous system, made up of the brain, the spinal cord and a complex network of peripheral nerves. The nervous system coordinates all of the body's activities in response to signals from inside and outside of the body. In the larger nerves, those signals can be transmitted at 500 impulses per second and travel at 330 feet per second. When a person moves, the command center in the cerebral cortex, or the front part of the brain, forms a plan for the movement. The plan is relayed to the motor center in the cerebellum, the back of the brain at the base of the skull, where a final plan of action is determined that takes into account feedback transmitted from the various limbs about the movement that is already in progress. The plan is then put into action while signals are constantly being relayed to the command center to keep it informed about how the movements are progressing. Thus, control of the action of the muscles is maintained by various regions of the brain, although the cerebellum and the spinal cord primarily facilitate the coordination of sensory input and motor skills to produce coordinated movement.

Central Nervous System

The central nervous system includes the brain and the spinal cord and neurons. The brain and the spinal cord are protected by the surrounding bones, the skull and the vertebrae. The neuron is the functional unit of the nervous system. Neurons are electrically charged cells in the nervous system that can move into an excited state to process and transmit information. The central nervous system serves as the main information processing center for the entire nervous system and controls all the biological functions of the body.

Brain

The human brain is an amazing organ. It provides humans with the ability to think, plan, reason, speak, imagine and create. The brain also regulates important bodily tasks, such as controlling body temperature, blood pressure, heart rate and breathing; processing the information it receives about the environment and managing physical movement.

The brain consists of four regions. First, the brain stem regulates the reflexes and other automatic functions such as heart rate and blood pressure as well as limb movements and digestive functions. The brain stem consists of the medulla, which is a large portion of the upper spinal cord, the pons, and the midbrain. The cerebellum integrates the information it receives regarding balance, position and movement to coordinate limb movements. The hypothalamus and pituitary gland regulate functions such as body temperature and behavioral responses as well as sensory and emotional information. Finally, the cerebrum, also called the cerebral cortex, analyzes information from all of the sense organs, starts motor functions, regulates emotions and maintains memory and thought processes.

Spinal Cord

The spinal cord is a thin, tubular bundle of nerves about the same size as the diameter of a human finger and functions as an extension of the central nervous system. The spinal cord extends from the brain through the length of the spine and is located inside the bony vertebral column for protection. In addition, the spinal cord is surrounded by cerebral spinal fluid, a clear liquid that cushions the delicate nerve tissues so they are not damaged by banging against the inside of the vertebrae. The primary function of the spinal cord is the transmission of neural inputs between the nervous system and the brain.

The spinal cord itself is comprised of millions of nerve fibers which send information back and forth to the limbs, trunk and organs of the body and back to the brain. The brain and spinal cord are known as the central nervous system, while the nerves connecting the spinal cord to the rest of the body are known as the peripheral nervous system. Further, the nerves within the spinal cord transfer information to and from different levels within the spinal cord, which are called segments. There are 31 pairs of spinal nerves connected to the spinal cord in a branch-like structure. The terminal end of the spinal cord is called the conus medullaris.

Neurons

Neurons are highly specialized components of the central nervous system that channel information from the cells. Given the diversity of functions performed by neurons throughout the nervous system, neurons have many different shapes, sizes and electrochemical properties.

Neurons vary in type, generally according to their function. Afferent neurons send information from tissues and organs back to the central nervous system and are also known as sensory neurons. Efferent neurons convey signals from the central nervous system to the effector cells and are generally referred to as motor neurons. Interneurons connect neurons within individual regions of the central nervous system.

Peripheral Nervous System

The peripheral nervous system includes the cranial and spinal nerves and the peripheral portions of the autonomic nervous system. The functions of the peripheral nervous system are divided into two categories: the somatic nervous system and the autonomic nervous system. The somatic nervous system coordinates the body movements and receives external signals. It is the system that maintains activities that the body controls consciously. The autonomic nervous system consists of the sympathetic, parasympathetic and enteric systems. The sympathetic nervous system reacts to the threat of immediate danger or stress with physiological responses such as an increased heartbeat and blood pressure, and activates the fight or flight instinct that is associated with an increase of adrenaline in the body. Conversely, he parasympathetic nervous system is in charge when the body is at rest and is responsible for unconscious activities such as the constriction of the pupil, the slowing of the heart, the dilation of the blood vessels and the stimulation of the digestive and genitourinary systems. The enteric nervous system manages every part of digestion, from the passage of food through the esophagus to the stomach, small intestine and colon.

Motor Unit

A motor unit is the name for an individual alpha motor neuron and all the muscle fibers it controls. In the majority of skeletal muscles there are thousands of muscle fibers, but each is not supplied with a separate nerve fiber. Instead, the fibers divide and branches into many terminals, and each terminal activates a specific muscle fiber. Thus, the motor unit is an incredibly complex system of neurons and muscle fibers that together form the brain's smallest functional unit of development control over movement and the application of force.

Applications

Applying Kinesiology to Motor Skills

The three major body systems in the study of kinesiology-bones, muscles and the nervous system-are involved in any type of movement. Movement initiated within the body requires that nerve impulses reach muscle fibers. When this happens, the nerve impulses start a chemical reaction within the muscle fibers that results in contraction of the fibers. As the muscle shortens during contraction, it creates movement of the bones to which the muscles are attached. The moving bones act as levers, transmitting energy from the muscle to the object or force that the muscle is opposing. Thus, the study of kinesiology includes an examination of the full range of human motion, including the movement patterns that are involved in moving external objects, the balance skills that are essential for the body in supporting its own weight and the movement patterns that are activated in stopping a moving object. The following sections examine these common motor skills in greater detail.

Moving External Objects

There are five basic patterns of movement that comprise any effort to move external objects. These patterns are: The underarm pattern, overarm pattern, sidearm pattern, pushing and pulling pattern and kicking pattern.

Underarm Patterns

The underarm pattern is most frequently seen in skills that project an object by means of a throw or strike. Its outstanding characteristic is movement of the arm, usually with extended elbow, by shoulder joint action. The arm, at the height of the backswing, is approximately shoulder height; during the force-producing phase, the arm is moved rapidly downward and, at release or impact, reaches a position that is usually parallel with the line of the trunk or slightly beyond that line. All underarm movement patterns include some form of shoulder movement. However, the other levers within the upper arms, forearms and hands vary with the movement itself. Common underarm patterns are present in activities such as bowling, softball pitching, the golf stroke and the underhand badminton serve.

Overarm Patterns

The overarm pattern, like the underarm pattern, is commonly used in throws and strikes. Its distinguishing feature is action at the shoulder joint, which rotates the humerus, or the long bone in the upper arm, laterally-away from the body-during the initial phase of movement and medially, or toward the body, during the force-producing phase. Movements that involve overarm patterns are the overarm throw or pitch in football or baseball, tennis serve and javelin throw. Because the overarm pattern can produce a great deal of force from the shoulder through the fingertips, movements involving this pattern are prone to injury. Athletes who repeat these motions on a consistent basis must take create care to strengthen the muscles and to complete the movement properly so as to avoid strains, tears or injuries.

Sidearm Patterns

The sidearm pattern, like the underarm and overarm patterns, is usually used in throws and strikes. Unlike the latter two, the distinguishing feature of the sidearm pattern is not the type of shoulder joint action but the lack of action or the limitation of action at this joint. The main action in the sidearm pattern is pelvic rotation, with the arm held fairly stable in an abducted position. Sidearm patterns are evident in movements such as the sidearm throw, forehand and backhand tennis strokes, batting and discus throwing.

Pushing & Pulling Patterns

The pushing pattern is commonly used to project and move objects forward while keeping contact with them. Generally, both hands are used, and in some cases there may be no joint action in the upper limbs, with the arms held rigidly in front of the body. In such cases, these limbs serve as a connection between the body and the object, or they may not be used at all. For example, in a push, it may be the shoulder girdle that moves the object, and the force will be powered from action of the lower limbs. In general, pushing movements in the preparatory phase consist of the acting body segments moving toward each other. In pulling, many of the same principles of the push apply, but the direction of the movement is reversed. Pushing and pulling movements are used in many everyday activities as well as in such athletic movements as weight lifting, basketball, shotputting and wrestling.

Kicking Patterns

The kicking pattern, used to apply force to an object with the foot, is a modification of the walking pattern. It is also closely related to the running movement. The kick differs from the walk and run in that force is applied with the swinging limb rather than with the supporting limb. In the final force-producing phase, the primary action is knee extension. Though there is little or no hip action in the final phase, the hip joint nonetheless makes an important contribution in the force-producing phase in that as the thigh is swung forward by hip flexion, it carries the leg and foot with it. During this time, the knee flexes, a movement which moves the foot backward, which allows for more force as it is ultimately swung forward to contact the object. Kicking patterns are seen in many sports activities, including football, soccer and kickball.

Balance

Humans use motion not only to move external objects but also to move the entire body or its parts to maintain any desired position. Movement of the entire body occurs when the base of support is changed, as it is in walking, running and jumping. In these activities, the supporting surface is an important factor. It must be strong enough to resist the force exerted against it by the moving body. As the supporting surface resists the force of the body, the body's force is transferred back into it and the body is propelled forward or backward, up or down. The larger the base of support, the less resistance from the support base. For instance, humans cannot stand on quicksand because their entire weight pushes down on the small surface on which they stand. However, if people lie down on quicksand, their weight is distributed, and the downward push by each section of the body is more likely to be within the limits which the sand can resist.

One of the prime examples of the body supporting itself is in balance activities. To maintain balance, people must keep their center of gravity in an area that is within and directly above their supporting base. The larger the base, the greater the range in which the center of gravity can be moved without the body's falling. People can use many body segments as a base-the feet, one foot, the hands or even fingers. However, balance movements are most often done instinctively in everyday life, as people react to their environment and make the movements necessary for comfort, sport, safety or rest. For instance, carrying bags of groceries up a stairway engages almost every muscle group, including the ability to maintain balance. Most sports activities also require that athletes perform complicated movements while maintaining balance. Even walking down crowded streets or walking on icy or wet surfaces requires a significant balancing effort in addition to the physical efforts of the movement itself. Some movements, such as swimming, require a certain amount of balance although the resistance is not as great as that from hard surfaces.

Stopping the Movement of Objects

Many muscle groups are also involved in stopping the movement of objects. The object may be external, such as a ball, or it may be the individual's own body, such as when a person lands from a height. The common skills used to stop moving objects are catching, falling and landing from a height. The pattern of joint actions in these movements varies somewhat, but in all of these movements the mechanical principles remain the same. If the stop is skillfully made, the momentum of the moving object is decreased by joint actions.

Generally, these actions are such that the object is permitted to continue its motion as its velocity is gradually decreased. If the object is in contact with the hands, and if the arms are out to meet it, the joint actions are those of a pulling pattern. For instance, when a person catches an object that was thrown, the momentum of the oncoming object moves the arms in the same direction the object was moving. At the same time, the muscles within the arm are activated to resist that motion. As the upper arm is extended by the force of the object, the shoulder flexors resist and as the forearm is flexed, the elbow resistors resist. Ultimately, when the resistance of the muscles surpasses that of the object in motion, the object is brought to a halt. Likewise, when the body lands from a height, the center of gravity would tend to flex ankle, knee and hip joints, which resist the downward force of the body and bring it to a halt.

Conclusion

This article has provided an overview of the basic components of kinesiology, the study of human movement. Kinesiology is comprised of the interrelationships between complex body systems, including the skeletal, muscular and nervous systems. The skeletal system provides the framework of the human body. The study of the skeletal system includes understanding the internal structure of bones, bone development and the major classifications of bones. The muscular system is comprised of major muscle groups throughout the body that work in tandem to facilitate movement. The muscular system is made up of various types of muscles and muscle groups that provide the strength and force involved in human movements. The nervous system is an intricate, complex system of information processing and exchange that includes the central nervous system, which consists of the brain, spinal cord and neurons, and the peripheral nervous system and motor unit. Finally, application of kinesiology to various motor skills involves the study of the major motion patterns that are involved in the movement of external objects, the ability of the body to maintain balance and support itself and to stop the movement of objects.

Terms & Concepts

Balance: The mechanical (i.e., position of segments) and physiological (e.g., muscle forces/joint stiffness) prerequisites for beginning and continuing a purposeful movement.

Body Weight: The resultant force for all the segmental weights of a human or animal body.

Bone: The dense, semi-rigid, porous, calcified connective tissue that forms the largest portion of the skeleton of most vertebrates. It has two components: a dense organic matrix and an inorganic, mineral component.

Control: Producing a desired outcome by means of continual adjustment.

Conservation of Energy: The sum of the external kinetic and the external and internal potential energy of a system are constant if the external forces and the internal forces acting between the mass points are conservative.

Deformation: Change in size of a structure in response to external forces acting on it.

Drag: A resistive force imposed on an object, which is passing through a viscous medium.

Equilibrium: The state of a system (e.g., a body or position of segments) that is not being accelerated.

Isotonic Contraction: A muscle contraction against a constant external load.

Friction: The resistance of two surfaces to slide with respect to each other.

Mass: The amount of matter in an object.

Muscle: A tissue containing fibers with the ability to contract and create body movement.

Nervous System: The system of neurons and tissues that is responsible for the actions and responses of vertebrates and many invertebrates. The nervous system of vertebrates is comprised of the brain, spinal cord and autonomic and peripheral nerves.

Nutrient Requirement: Amount of nutrition necessary to elicit balance, i.e., when intake equals excretion.

Posture: The external visible relative arrangement of body segments in a given upright position representing a discrete event in the time-history of balance.

Work: Physical or mental effort or activity directed toward the production or accomplishment of something.

Bibliography

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Suggested Reading

Knudson, D. (2005). Evidence-based practice in Kinesiology: The theory to practice gap revisited. Physical Educator, 62 , 212-221. Retrieved January 23, 2008, from EBSCO Online Database Education Research Complete. http://search.ebscohost.com/login.aspx?direct=true&db=ehh&AN=19409779&site=ehost-live

Vincent, W.J. (1991). Kinesiology, the proper name for the discipline. Physical Educator, 48 , 119-123. Retrieved January 23, 2008, from EBSCO Online Database Education Research Complete. http://search.ebscohost.com/login.aspx?direct=true&db=ehh&AN=9609192485&site=ehost-live

Wenos, D. & Koslow, R.E. (1996). Employment trends in kinesiology/physical education higher education: 1988-1992. Physical Educator, 53 , 24-27. Retrieved January 23, 2008, from EBSCO Online Database Education Research Complete. http://search.ebscohost.com/login.aspx?direct=true&db=ehh&AN=9604024414&site=ehost-live