Body Mechanics: Matching Movement to Muscles and Bones
Repeat the simple jazz arm exercise shown in figure 1.3 until your muscles get tired. In this way you will be able to identify which muscles are doing the work in this exercise.
Do this jazz arm exercise until your arms get tired.
With a partner, take turns doing a similar movement with resistance (see figure 1.4). Note: One person does the movement while the other person carefully presses or pulls on the lower arm in the opposite direction (resistance).
With your partner, discuss which muscles you felt when you bent your elbow (flexion) and when you straightened your elbow (extension).
Flexion and extension of the biceps while bending and straightening the elbow joint.
- concentric contraction
- eccentric contraction
- prime mover
- synovial joint
The skeletal system has three major functions. It gives the body support and form. The bones and their attached muscles determine the body’s structure. The skeleton provides protection for internal organs. Consider what vital organs your skull (brain), rib cage (lungs and heart), and pelvis (reproductive organs) house and protect. The skeletal system also allows for movement. Bones play a passive role in movement, but their shapes, lengths, and places where muscles can attach dictate how the body moves.
Joints are where two bones meet. Movement occurs at the joints. Although there are various types of joints, dancers, athletes, and kinesiologists (those who study the principles of mechanics and anatomy in relation to human movement) are usually concerned with synovial joints. Synovial joints (such as the knee; see figure 1.5) include cartilage-covered bone endings (a form of connective tissue that is smooth and elastic), a capsule (also made up of connective tissue) that protects and strengthens the joints, and synovial fluid that lubricates the joint (like oil in an engine). Ligaments (tissues that connect bones to bones) and muscles also strengthen and protect the joints. The freedom and direction of movement possible at a joint are determined by how the ligaments are placed and the shape of the bone endings.
The muscular system contains muscles, tendons (which connect the muscles to the bones), and ligaments. The muscles actively work to produce movement. Simply put, the muscles shorten and lengthen while pulling on the bones, thereby creating motion. During a movement, one muscle shortens. This muscle is called the prime mover (a muscle that is mainly responsible for a motion). On the other side of the bone, its antagonist (a muscle that counteracts, or slows down a motion) lengthens in opposition. In this way, not only is movement created, but also the joints are protected from too sudden or too much force. For example, in the Move It! exercise the following occurred: To bend (flex) your elbow, the biceps did a shortening (concentric) contraction while the triceps did a lengthening (eccentric) contraction (see figure 1.4). In extending your elbow, the muscle groups reverse roles.
Put simply, other muscles, called synergists, often help the prime movers. Also, fixators (muscles that hold or fix a body part in a particular position to support the movement of another body part) hold other body parts in place so that a certain motion can be done efficiently.
Take the Stage
The following is a matching exercise for linking muscles, joints, and movements.
- Identify the two sets of muscles that are the prime movers and antagonists for the joints in figure 1.6: shoulders, wrists, fingers, hips, knees, and ankles.
- Write your predictions or guesses next to the name of the joint.
- While moving the joint, touch the muscles to see if your predictions are true. Make any needed corrections. Use the partner work that you did in this lesson’s Move It! to help you with your work. (Remember how your partner provided careful resistance.)
Muscles of the arms, hips, and legs.
Take a Bow
Compare your work with another student’s work. It would be preferable if this student were not your first partner. Discuss and defend your findings. Make any needed corrections on your prediction list.
- Check your results with your teacher.
- Make corrections on your prediction list as needed.
Irene Dowd (1946-)studied with and assisted Dr. Lulu Sweigard at the Juilliard School from 1968 through 1974. Irene has a BA in philosophy from Vassar College and studied anatomy and neuroanatomy at Columbia Presbyterian Medical School and neuroscience at Teachers College, Columbia University. Currently, she is on the faculty at the Juilliard School where she teaches classes in anatomy and kinesiology and dynamic trunk stabilization, and another course on understanding technique for summer high school students. She also teaches at the National Ballet School of Canada and conducts training programs for both faculty and students of the school. Irene has a private practice in neuromuscular training that she started in 1974. The focus of her private teaching practice is solving individual problems with the functioning of musculoskeletal and nervous systems, which can cause discomfort or the inability to achieve one’s potential in movement. In the third edition of her book, Taking Root to Fly, Ms. Dowd speaks of the process of seeing and touching her students as they go through movements in daily activities.
Did You Know?
Many resources can help you learn more about the human anatomy. One of the most popular is Gray’s Anatomy of the Human Body, by Henry Gray (1825-1861). In 1858, the first English edition of Gray’s Anatomy was published. Forty editions have been published, and it still serves as a primer for students of anatomy worldwide. You can visit your local library or bookstore to check out this valuable resource. For an interesting alternative, try using the Anatomy Coloring Book.