The 7 Biomechanical Principles PDF

The 7 Biomechanical Principles  These seven principles have been set forth by the Coaching Association of Canada’s National Coaching Certification Program (NCCP). Biomechanical principles help Kinesiologists and The...

The 7 Biomechanical Principles  These seven principles have been set forth by the Coaching Association of Canada’s National Coaching Certification Program (NCCP). Biomechanical principles help Kinesiologists and The Seven other movement professionals provide meaningful feedback to their students, athletes, Principles of or clients to help improve their movement Biomechanics patterns Understanding Static and Dynamic systems and how they relate to human movement patterns will be better understood once learning the 7 Biomechanical Principles Static Systems The seven principles of biomechanics are best understood in the context of static and dynamic systems. Statics is the branch of mechanics that deals with objects or bodies in a state of constant, unchanging motion. In static systems, the rate of change of motion of an object or body is unchanging over time (e.g., a gymnast holding a stationary pose on a balance beam or a high diver in free fall). If an external force is applied to a body and the rate at which the body is moving changes, the system is now said to be dynamic in nature. Dynamic Systems The branch of mechanics that studies changes in the motion of objects or bodies as a result of the actions of forces is known as dynamics. A dynamic system is one that experiences a change in the rate at which it is moving as a result of forces applied to it (e.g., a rugby player weaving his or her way down the field). Changes in our movement patterns are the product of multiple internal as well as external forces. The seven biomechanical principles involve the interactions of static and dynamic systems  1: Stability 2: Production of Maximum Force 3: Production of Maximum Velocity The Seven 4: Impulse-Momentum Relationship Principles 5: Direction of Application of the Applied Force 6: Production of Angular Motion (Torque) (Short Form) 7: Conservation of Angular Momentum Pg 190-191 of Workbook  Overview/Grouping Chart Concept Biomechanical Principle Stability 1. Stability Maximum 2. Production of Maximum Force Effort 3. Production of Maximum Velocity Linear Motion 4. Impulse-Momentum Relationship 5. Direction of Application of the Applied Force Angular 6. Production of Angular Motion (Torque) Motion 7. Conservation of Angular Momentum Biomechanical Principle 1: Stability Principle #1: “The greater the mass, the lower the centre of mass to the base of support, the larger the base of support, and the closer the centre of mass is positioned to the base of support, the more stability increases.” Key Concepts To Help Understand Mass: The quantity of matter contained within an object or body. Centre of mass: The imaginary middle point around which the mass of an object or person is balanced. Base of support: The supporting area beneath an object or body; its limits are defined by the points of contact with the supporting surface. Stability: The quality, state, or degree of being stable and capable of resisting a change in motion. Balance: An even distribution of mass enabling someone or something to remain steady.  Principle #1: The Concept of “Mass” Because football linemen have large mass, and therefore, more inertia, it is more difficult for their opponents to push or pull them out of position (i.e. destabilize them) The Concept of “Centre of Mass” The centre of mass is the imaginary point around which an individual’s or object’s mass is concentrated. When an individual stands upright, with their arms hanging at their sides, the centre of mass is located in the middle of the body at about the level of the navel. The concept of the centre of mass is important in the context of resistance to rotation.  The Concept of the “Base of Support” In a sports context, the base of support refers to the supporting area beneath the limbs of an athlete. - The stability of gymnasts is enhanced when they broaden their base of support. - Likewise, the stability of a football lineman is enhanced when he broadens his base of support. Intentional Instability In some sports, an athlete intentionally puts himself or herself in an unstable or potentially unstable position. The narrow base of support in combination with the high centre of mass of the football player in front tells us that this is not a very stable situation at all. A slight shift in the person’s centre of mass will lead to complete instability and likely a fall—which is what the player intends to happen.  Exit Question “What factors affect how stable an individual is while performing a physical task?” Biomechanical Principles 2&3: Principles of Maximum Effort In many activities, we must exert maximum effort, or “go all out” in order to accomplish a specific task. Two biomechanical principles are related to maximum effort: Principle 2: Production of Maximum Force Principle 3: Production of Maximum Velocity Focus Question “How can we produce maximum effort in performing a physical task?” Principle 2 The Production of Maximum Force: “The production of maximum force requires the use of all possible joint movements that contribute to the task’s objective.” Interpreting Principle 2 When people lift heavy objects, or perform other such tasks, they must make slow, controlled, and simultaneous high intensity movements. These movements are best produced by sequenced joint rotations. If the full joint range of motion (ROM) is restricted at any one of the joints involved in the movement, perhaps due to injury or disease (e.g., arthritis), fewer muscles are able to contribute to the movement Principle 2 in Action When we attempt to run as fast as we can, we are demonstrating biomechanical principle 2. When we run, we necessarily rely on joint rotation at the ankle, knee, and hip joints. Full rotation at each joint is achieved through the contraction of multiple muscles. These movements begin at the ankles and are followed by similar sequenced joint rotations at the knees and hips. Another example of biomechanical principle 2 is the awkward action of a four year-old ball player’s swing of a bat (with that of a professional baseball player). A young T-ball player will often stand very upright, with feet planted, and swing the bat using only the arms to make contact with the ball. The player has the potential to use more joints during the swing, but may not do so due to lack of experience. Over time, with practice and good coaching, the T-baller will become more proficient at this task. Principle 2 in Action Professional baseball player hitting a ball also demonstrate principle 2 in action. They typically flex their knees and hips while waiting for the ball to be delivered by the pitcher. As the ball is released by the pitcher, the batter will step toward the oncoming ball, extending previously flexed hip and knee joints, while rotating the hips (the core/trunk remains stiff). At the same time, the batter swings the bat fully using the shoulders, arms, and wrists. Principle 3 Production of Maximum Velocity “The production of maximum velocity requires the use of joints in order— from largest to smallest” Interpreting Principle 3 Activities requiring the production of maximum velocity (e.g., tennis serve, golfing, or pitching a baseball) are performed most successfully if the larger, slower joints begin the movement, and the smaller joints come into action later. Example of Principle 3 in Action When a baseball is thrown, the player’s joint actions are sequenced. Joint movement in the legs is followed closely by rotation of the hips. Rotation of the hips is followed by rotations of the arms, the elbows, and the wrists. By engaging more muscles and joints in a pitching motion, and sequencing them correctly, a professional baseball pitcher is able to generate maximum velocity. (See next slide.) Example of Principle 3 in Action Example of Principle 3 in Action Sequencing of joint rotation is particularly important when performing activities in which an object is being thrown or being struck by an implement. For example, a fly fisher can cast her line more effectively by using sequenced joint rotations. She first rotates at the trunk, followed by the shoulder, then the elbow, and finally the wrist. If her movements are sequenced correctly, the fly fisher will be able to cast her line with the attached fly a fair distance downstream. Example of Principle 3 in Action A proficient golfer relies on biomechanical principle 3. An experienced golfer performs a precisely sequenced swing. Leg, hip, and arm action are sequenced to produce a slower, more controlled swing of the club.  Exit Question “How can we produce maximum effort in performing a physical task?” Biomechanical Principles 4 &5: Linear Motion Two biomechanical principles are related to linear (or translational) motion: Principle 4: “The Impulse-Momentum Relationship,” Principle 5 :“The Direction of Application of the Applied Force” Principle 4 The Impulse-Momentum Relationship “The greater the applied impulse, the greater the increase in velocity.” When an object such as a cricket ball, field hockey ball, or tennis ball is in motion, it is said to have momentum. The momentum of the ball or any other object in motion is equal to its mass multiplied by its velocity. To get a ball moving, a cricket, field hockey, or tennis player will use a striking implement to apply a pushing force to the ball over a period of time. The greater the pushing force, and the greater the amount of time over which it is applied to the ball, the greater the impulse. This is a restatement of biomechanical principle 4. Imparting High Velocity to a Cricket Ball  Elite athletes and their coaches often rely on biomechanical principle 4 to improve their techniques and performance. For example, today’s high jumpers commonly use a technique called the Fosbury Flop. As jumpers near the bar, they arch their neck and back and push against the ground to create a powerful impulse force. An equal and opposite ground reaction force is generated, which propels the high jumper into the Example of Principle 4 in air. Action Principle 4 in Action The “jump serve” in volleyball provides another good example of biomechanical principle 4. Players begin well back behind the service line, lob the ball forward, and run and jump into the air in order to “spike” the ball to the opposing team. The forward running motion of the server’s body transfers momentum to the ball, making it move through the air at a high velocity. This increase in velocity, combined with a high flight path, makes it difficult for the ball to be returned by the opposing team. Applying Impulse in a Bobsled Race Principle 5 THE DIRECTION OF APPLICATION OF THE APPLIED FORCE “Movement usually occurs in the direction opposite that of the applied force.” The fifth biomechanical principle is closely related to Newton’s third law of motion, which states that for every action there is an equal and opposite reaction. People at work and at play rely on this principle constantly. For example, when a person sitting in an armchair stands up, the individual will place his or her hands on the armrests and push down. A reaction force that is equal in magnitude but opposite in direction will be generated by the chair arms. Principle 5 and Aquatic Events Biomechanical principle 5 is evident in many aquatic events. When completing a length of a pool, for example, free-style swimmers turn and push against the wall of the pool with their legs. The swimmers’ bodies are propelled forward—in the direction opposite that of the applied force. Example of Principle 5 in Action Example of Principle 5 in Action Biomechanical principle 5 can be seen in action in many team sports. In making a cut, for example, an ultimate player or a soccer player will push his or her foot against the ground to make a change in direction away from an opponent. Similarly, an ice hockey player will push off using the edge of the skate blade to make the same type of movement to either avoid a hit or make one.  Exit Question “How can we optimize physical movements that involve linear (or translational) motion?” Biomechanical Principle 6&7: Angular Motion Two biomechanical principles are related to angular (or rotational) motion: Principle 6: Production of Angular Motion, or Torque Principle 7: Conservation of Angular Momentum Focus Question: “How can we optimize physical movements that involve angular (or rotational) motion?” Principle 6 PRODUCTION OF ANGULAR MOTION (TORQUE) “Angular motion is produced by the application of a force acting at some distance from an axis; that is, by torque.” If an eccentric (or “off-centre”) force is applied to a body, the force tends to make the body rotate about its axis. This “turning effect” is known as torque. The magnitude (size) of the torque depends on three factors. Factors That Affect the Amount of Torque The amount of toque that is generated is affected by three factors: The applied force, The length of the lever arm, and The angle of application of the force, as shown in the diagram. Example of Principle 6 in Action In the generation of torque, the length of the lever arm and the angle at which the force is applied are very important. As might be expected, it is easiest to initiate rotation when the force is applied as far away as possible from the axis. It is also easiest to initiate rotation when the force is applied perpendicularly to the lever arm (e.g., when unfastening a bolt with a socket wrench). Generation of Torque at Human Joints  Principle 7 THE CONSERVATION OF ANGULAR MOMENTUM “Angular momentum is constant when an individual or object is free in the air.” (Angular momentum is the quantity of motion contained within an object or a body.) Principle 7 in Action Many physical activities—trampoline, gymnastics, tumbling, aerial skiing, aerial snowboarding, and diving—require individuals to be airborne and in a state of free fall. Angular momentum is the product of the rate at which the athlete is rotating— or her angular velocity—and the extent to which her body resists angular motion. This resistance to angular motion is known as the “moment of inertia.” The farther a body’s distribution of mass from the axis of rotation, the greater is the body’s moment of inertia. Adjusting the Moment of Inertia Successful rotational maneuvers in many sports involve adjusting (i.e., either minimizing or increasing) the moment of inertia. The moment of inertia is minimized, for example, when a trampolinist’s arms and legs are brought close to the athlete’s axis of rotation in what is commonly referred to as a tuck position. In this position, the trampolinist rotates rapidly. To slow the rate of rotation, she simply needs to extend her arms and legs away from her axis of rotation. In other words, she can adjust her moment of inertia by controlling how far her mass is distributed from her axis of rotation. Principle 7 in Action A high diver and a figure skater can adjust her moment of inertia by controlling how far her mass is distributed from her axis of rotation. By pulling her arms and legs close to her body, the diver can decrease her moment of inertia. As the moment of inertia changes, angular velocity also changes—by speeding up. As the diver approaches the water, she straightens out, which reduces the rate of rotation just before entry into the water. The same angular forces are at play in the case of a figure skater’s spin.  The Law of Conservation of Angular Momentum The principle underlying the angular forces at play in a diver’s rotation or a figure skater’s spin is known as the law of conservation of angular momentum. This law states: “THE TOTAL ANGULAR MOMENTUM OF A ROTATING BODY REMAINS CONSTANT IF THE NET TORQUE ACTING ON IT IS ZERO.” A rigid spinning object continues to spin at a constant rate and with a fixed orientation unless influenced by the application of an external torque.  The Law of Conservation of Angular Momentum  Exit Question “How can we optimize physical movements that involve angular (or rotational) motion?” Homework Complete pg 190-199 of Workbook