Center Of Gravity
A natural application of angular kinetics and anthropometrics is the determination of the center of gravity of the body. The center of gravity is the location in space where the weight gravitational force of an object can be considered to act. The center of small rigid objects pencil, pen, bat can be easily found by trying to balance the object on your finger. The point where the object balances is in fact the center of gravity, which is the theoretical point in space where you could replace...
Optimal Projection Principle
For most sports and human movements involving projectiles, there is a range of angles that results in best performance. The Optimal Projection Principle refers to the angle s that an object is projected to achieve a particular goal. This section will outline some general rules for optimal projections that can be easily applied by coaches and teachers. These optimal angles are rules of thumb that are consistent with the biomechanical research on projectiles. Finding true optimal angles of...
Principle Of Balance
We have seen than angular kinetics provides mathematical tools for understanding rotation, center of gravity, and rotational equilibrium. The movement concept of balance is closely related to these angular kinetic variables. Balance is a person's ability to control their body position relative to some base of support Figure 7.13 . This ability is needed in both static equilibrium conditions e.g., handstand on a balance beam and during dynamic movement e.g., shifting the center of gravity from...
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Figure 3.2. Orthopedic and pediatric medicine often calls the lower extremity deviation in a genu knee valgus because the distal segment lower leg deviates laterally from the midline of the body. Normal leg orientation in the frontal plane is illustrated in b . The use of valgus and varus terminology is often inconsistent in the literature and should be clearly defined when used Houston amp Swischuk, 1980 . see that this little problem of anatomical description is very similar to the multiple...
Qualitative And Quantitative Analysis Of Vectors
Before moving on to the next kinetic approach to studying the causes of movement, it is a good time to review the special mathematics required to handle vector quantities like force and acceleration. The linear kinetics of a biomechanical issue called muscle angle of pull will be explored in this section. While a qualitative understanding of adding force vectors is enough for most kinesiology professionals, quantifying forces provides a deeper level of explanation and understanding of the...
Review Questions Ris
1. Which has more inertia, a 6-kg bowling ball sitting on the floor or one rolling down the lane Why 2. What are the two ways to express Newton's second law 3. When might it be advantageous for a person to increase the inertia used in a movement 4. Do smaller or larger muscle angles of pull on a distal segment tend to create more joint rotation Why 5. What are strategies to increase the friction between a subject's feet and the floor 6. What two things can be changed to increase the impulse...
Neuromuscular Control
The mechanical response of muscles also strongly depends on how the muscles are activated. The neuromuscular control of movement is an active area of study where biomechanical research methods have been particularly useful. This section will summarize the important structures and their functions in the activation of muscles to regulate muscle forces and movement. The Functional Unit of Control Motor Units The coordination and regulation of movement is of considerable interest to many scholars....
Torque
The rotating effect of a force is called a torque or moment of force. Recall that a moment of force or torque is a vector quantity, and the usual two-dimensional convention is that counterclockwise rotations are positive. Torque is calculated as the product of force F and the moment arm. The moment arm or leverage is the perpendicular displacement d from the line of action of the force and the axis of rotation Figure 7.1 . The biceps femoris pictured in Figure 7.1 has moment arms that create...
The Limitations Of Functional Anatomical Analysis
Anatomy classifies muscles into functional groups flexors extensors, abductors adductors, etc. based on hypothesized actions. These muscle groups are useful general classifications and are commonly used in fitness education, weight training, and rehabilitation. These hypothesized muscle actions in movements and exercises are used to judge the relevance of various exercise training or rehabilitation programs. This section will show that such qualitative estimations of muscle actions are often...
Review Questions Vbc
1. What are the major kinds of mechanical loads experienced by muscle, tendon, and bone 2. What are the mechanical variables that can be determined from a load-deformation curve, and what do they tell us about the response of a material to loading 3. Compare and contrast the mechanical strength of muscle, tendon, ligaments and bone. How does this correspond to the incidence of various musculoskeletal injuries 4. How does the passive behavior of the muscletendon unit affect the prescription of...
What Is Biomechanics
Biomechanics has been defined as the study of the movement of living things using the science of mechanics Hatze, 1974 . Mechanics is a branch of physics that is concerned with the description of motion and how forces create motion. Forces acting on living things can create motion, be a healthy stimulus for growth and development, or overload tissues, causing injury. Biomechanics provides conceptual and mathematical tools that are necessary for understanding how living things move and how...
Forcemotion Principle
Another way to modify human movement is to change the application of forces. The Force-Motion Principle states that it takes unbalanced forces and the subsequent torques they induce to create or modify our motion. To know what size and direction of force to change, recall that a free-body diagram of the biomechanical system is usually employed. A major limitation of functional anatomical analysis was the limited nature of the forces and structures being considered. We are not in a position to...
Review Of Key Anatomical Concepts
This section reviews several key concepts from human anatomy. A course in gross anatomy macroscopic structures is a typi cal prerequisite for the introductory biomechanics course. This section does not review all the bones, muscle, joints, and terms. Students and kinesiology professionals must continuously review and refresh their knowledge of anatomy. Anatomy describes the human body relative to the anatomical position. The anatomical position is approximated in Figure 3.1. The three spatial...
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Figure 2.6. A free-body diagram of a person quietly standing. The major vertical forces acting on the person gravity and ground reaction force are illustrated, while horizontal forces are small enough to ignore. Figure 2.6. A free-body diagram of a person quietly standing. The major vertical forces acting on the person gravity and ground reaction force are illustrated, while horizontal forces are small enough to ignore. body is our first example of what in mechanics is called a free-body...
Forcetime Principle
The Force-Time Principle for applying bio-mechanics is not the same as the Force-Time Relationship of muscle mechanics. The Force-Time Principle states that the time available for force application is as important as the size of the forces used to create or modify movement. So the Force-Time Principle is concerned with the temporal strategy of force application in movements, while the Force-Time Relationship electromechanical delay states a fact that the tension build-up of muscle takes time....
Qualitative Analysis
The examples that illustrate the application of the principles of biomechanics in the solution of human movement problems in this book will be based on qualitative analyses. Research has shown that general principles of biomechanics provide a useful structure for qualitative analysis of human movement Johnson, 1990 Matanin, 1993 Nielsen amp Beauchamp, 1992 Williams amp Tannehill, 1999 Wilkinson, 1996 . Quantitative biomechanical analysis can also be used, but most kinesiology professionals will...
Nine Fundamentals Of Biomechanics
Biomechanists measure all kinds of linear and angular mechanical variables to document and find the causes of human motion. While these variables and studies are extremely interesting to biomechanists, some kinesiology students and professionals may not find them quite so inherently stimulating. Most kinesiology professionals want to know the basic rules of biomechanics that they can apply in their jobs. This section proposes nine such principles of biome-chanics and demonstrates how they...