Definitions of terms that you will find in the Blog Post below

External rotation: Lateral rotation Biomechanics The act of turning about an axis passing through the center of the leg; ER of the leg occurs with closed chain supination; the talus acts as an extension of the leg in frontal and transverse planes.
Rotation: The process of turning around an axis. In obstetrics, the turning of the fetal head (or presenting part) for proper orientation to the pelvic axis.
Bat Lag:
Flexion: The bending of a joint between two skeletal members to decrease the angle between the members; opposite of extension.
Extension: The movement of a limb to increase the angle of the joint. Some joints (at the wrist, in the neck) are able to hyperextend.
Force: The energy or power; that which originates or arrests motion.
Ground Reaction Force: Refers generically to any force exerted by the ground on a body in contact with it.
Center of Pressure: Is the point on a body where the total sum of a pressure field acts, causing a force and no momentum about that point.
Center of Mass: Is the mean location of all the mass in a system. In the case of a rigid body, the position of the center of mass is fixed in relation to the body.
Momentum: Is the product of the mass and velocity of an object (p = mv).
Dynamic Balance: The ability to maintain and distribute balance evenly (refers to your stance).
Absorption of Force: The ability to absorb that force in a short amount of time (or impulse) is important in being elastic and loading the tendon for increase power output. If the athlete does not possess the strength to absorb the force in a short impulse time then they may have to flex deeper into the movement, thus increasing the risk of poor compensation patterns and injury.
Axis of Trunk: Sagittal motion.
Sagittal Plane: Is a vertical plane which passes from front to rear dividing the body into right and left sections.
Median Plane or Mid-Sagittal Plane: Sometimes used to describe the sagittal plane running through the midline. This plane cuts the body into halves (assuming bilateral symmetry),[1] passing through midline structures such as the navel and spine. It is one of the lines defining the right upper quadrant of the human abdomen.
Exertion: Is a concept describing the use of physical or perceived energy. It normally connotates a strenuous or costly effort related to physical, muscular, philosophical actions and work.

Break Down of a Baseball Swing

Many movements are involved in the proper technique of a baseball swing. Ground reaction force is the interaction of the body and the ground. As we all know a very important step in the baseball swing, it applies the force, distance, and location of where the ball will go on the field. Each individual foot will result in a different magnitude of force applied; a person’s body weight percentage also plays a major part in a person’s force of swinging. The more weight that is exerted on the feet the greater amount of force. The center of pressure or center of mass also plays a role of the force of a person’s swing. The relative movement of the center of pressure between the 2 feet and the body’s center of mass will result in dynamic balance which gives the batter their forward momentum. Flexion and extension of the left and right knee as well as the left and right elbows have to form the correct angle to get proper direction and absorption of force on our joints; should be about 90* at flexion to about 180* at extension. To properly utilize all of the above a batter also needs to remember you gain more bat speed by the proper rotation and interaction of the hips, shoulders, and arms. They rotate around a common axis of the trunk; hips rotate, shoulder rotate, then the arms and wrists. Next the batter should focus on “bat lag” which is the absolute angle formed between the bat from the handle to the barrel and from the mid-shoulders to the mid-wrists. When the bat is fully extended away from the arms and everything is in line the angle of your arms/wrists; the bat should be about 180*. Everything combined above in a step by step procedure, the swing is initiated with a weight shift toward the right (back leg), at about the same time, the upper body rotates in a clockwise direction around the axis of the trunk, initiated by the arms and shoulders, followed closely by the hips. Even though all this is broken down into steps when put together and implemented in a game/practice setting these steps will go will be done almost simultaneously they are just broken down for purposes of improving techniques or teaching new players.

Baseball Practice - Hitting Tips and Drills for Baseball Coaches & Players