Kinesiology: The Study of Human Motion
As athletes it is important for us to have a basic understanding of kinesiology and biomechanical principles. We should know how movements impact posture, body mechanics, our muscle system, and the sports and training that we participate in.
Kinesiology is the study of human motion and mainly focuses on muscles and their functions. It is the study of human movement, performance, and function by applying the sciences of biomechanics, anatomy, physiology, and neuroscience. It looks at movement and which muscles are involved to create movement relating to strength exercising and sports technique.
Biomechanics is the study of movement involved in strength exercise or in the execution of a sport skill. Biomechanics focuses on the physical factors with movement by applying scientific laws. With these applications, it looks at what takes place during an exercise and the role that each key joint and muscle plays. The scenic laws incorporate such physical factors as speed, mass, acceleration, levers, and force of the particular movement. Biomechanics explains the “why” of a movement and “how” the movement can be improved through science-based modifications.
Together, kinesiology and biomechanics can help you determine what exercises are appropriate, how to create a workout plan, the effectiveness of your execution of the exercise, and how safe they are for the sports that you participate in. Biomechanics is the execution of doing an exercise most effectively, while kinesiology tells which muscles are involved in the particular actions.
The Three Types of Muscle Contractions
There are three types of muscle contractions: 1) Concentric Contraction, 2) Eccentric Contraction, and 3) Isometric Contraction. Lets take a look at each.
1) Concentric Contraction: In a concentric contraction the muscles shorten to produce movement. Motion takes place by the muscle contracting and overcoming a resistance which sets the resistance in motion. The typical way it is measured is by the amount of weight that can be overcome in one repetition. An example of a concentric movement is doing a bicep curl with a weight. The upward motion is the concentric muscle action.
2) Eccentric Contraction: In an eccentric contraction the muscle lengthens as it contracts. The eccentric contraction plays the important role of controlling and stopping movement and prepares the muscle for an explosive type of contraction. An eccentric contraction can generate up to 50 percent greater tension than the concentric contraction. An example of a concentric movement is doing a bicep curl with a weight. The downward motion is the concentric muscle action.
3) Isometric Contraction: In an isometric contraction there is strength exhibited but no movement of the limb. The muscle does develop tension and some contraction of the fibers and tendons, but there is no movement. Isometric contractions play a large roll in the stabilization in the joints of our body. Two examples of an isometric contraction are: 1) Doing a bicep curl but just holding the weight with your elbow bent at 90 degrees (there is no movement), and 2) Doing a standing overhead press. Your back and oblique muscles tighten up to stabilize your body while performing the exercise. Although the muscles used in isometric contractions and stabilization can become pretty well developed, it it not as effective as a concentric contraction in developing muscle mass and strength.
An interesting fact about isometric contractions is that there is no work being done. Work is defined and measured by the formula W = F x D. W = work, F = force, and D = distance. And since in an isometric contraction there is no movement, there is no work being done. For work to be done there must be movement. It is not to say that energy is not being used. Energy is more physiological, while work is more mechanical.
The Roles Muscles Play (in terms of kinesiology)
There are five major roles that our muscles play relating to kinesiology and they are: 1) Prime Mover or Agonist, 2) Assistant Mover, 3) Antagonist, 4)Stabilization, and 5) Synergy.
1) Prime Mover or Agonist: Relates to the main muscle involved in a concentric contraction.
2) Assistant Mover: Usually assists the the prime mover muscles. It can play a main roll in certain ranges of motions or exercises.
3) Antagonist: It has an action that is directly opposite to that of the agonist. When an agonist muscle is undergoing a concentric contraction, the antagonist is undergoing a eccentric contraction. This eccentric contraction helps guide the movement and stabilize the joint. The antagonist contraction helps slowdown movement before an injury can occur to a joint.
During exercise, when the weight is especially heavy there is a co-contraction that take place where both agonist and antagonist undergo contraction. Again, this is needed to stabilize the joint during motion.
4) Stabilizer Muscles: These are the muscles that steady or hold a body part in place. It anchors the bone so that the prime mover has a firm base against which to contract. Stabilizer muscles help with all movements so that we have precise movements of our limbs and body parts. As mentioned earlier, stabilization muscles undergo a isometric contraction to hold the bone in place.
5) Synergy: In kinesiology there are are two types of synergy: 1) helping synergy: is when two muscles contract simultaneously to produce one movement, and 2) true synergy: is when a different muscle contracts to stop the secondary action of another muscle.
Types of Body Movements
Our body’s muscle movements can be classified into four types of movement: 1) Sustained Force Movement, 2) Ballistic Movement, 3) Guided Movement, and 4) Dynamic Balance Movements. I will explain each.
1) Sustained Force Movement: is a movement where there are continuous muscle contractions to keep moving a weight. The primary muscles apply force throughout the range of motion of the movement. A sustained force can also involve no movement such as in an isometric contraction.
2) Ballistic Movement: Movements that are performed with maximal velocity and acceleration.
3) Guided Movement: in this movement both the agonist muscle and the antagonist muscle contract to control the movement. The eccentric contraction of the antagonist muscles do most of the guiding work, while the prime movers are responsible for putting and keeping the limb in motion.
4) Dynamic Balance Movements: these are movements where there are constant agonist and antagonist muscle contractions to maintain a certain position or posture.
Planes of Motion and Movements within the Planes
Human movements are divided into the planes and the movements that occur in those planes. There are three imaginary planes the pass through the human body that divide the body into segments: left/right (sagittal), anterior/posterior (frontal), and the top/bottom (transverse).
The Major Movements and there Definitions
Abduction: is a movement of a body segment away from the midline of the body.
Adduction: is the movement of a body segment toward the midline of the body.
Rotation: the circular motion of a body segment about a long axis.
Circumduction: is the movement of a body part that outlines the geometric shape of a cone.
Flexion: is a decrease in the angle of two body segments.
Extension: is an increase in the angle between two body segments.
Hyperextension: is the increase in the angle beyond the anatomical point of normal joint movement.
Eversion: turning outward as in the sole of the foot.
Inversion: turning inward as the sole of the foot.