KinX Learning

Digital Products in the Kinesiology of Exercise

Muscular-Structural Arrangements in the Human Body

Posted by KinX Learning on January 23, 2018 . 0 Comments

Wheel and Axle

Wheel and axle-like arrangements in the body are needed for the transmission of force. A good illustration of this is shoulder joint medial and lateral rotation. For example, hold the upper arms in line with the shoulders, elbows bent 90 degrees, and the forearms vertical and holding a weight in the hands. Lower the forearm downward behind the head, maintaining the 90-degree angle (or greater) in the elbow to execute lateral rotation with the axis along the long shaft of the humerus.

When you raise the hand in the opposite action you execute medial rotation in which the humerus rotates in the opposite direction (forward) on its long axis. In this case, there is a short radius of rotation of the humerus, but with the forearm bent at a 90-degree angle you generate considerable speed or force at the end of the forearm (the hand).

Many strength exercises involve some rotation of the arms (or legs). To prevent injury to the muscles involved especially when executing medial and lateral rotation, you should not execute other actions in the same joint at the same time. This is often difficult to see but it typically happens quite naturally.

Pulley Systems

Another muscular-structural arrangement in the body is the pulley. Pulleys are very common in exercise machines such as in the lat pull-down to create a greater mechanical advantage and to move the limbs freely. In the body, we find a pulley type system in the knee joint, more specifically, with the patella. The quadriceps tendon (ligament) goes over the patella to insert on the tibia bone in the shin.

Because of the patella protrusion, the quadriceps tendon inserts at a greater angle to create more of a straight-line force when the knee is in the bent position. As a result, you generate greater force which goes around the patella to change the direction of pull. There are few such pulley type muscle arrangements in the body.

Most pulley (cable) systems (free weight machines) create the ability to guide and move the resistance handles in various directions, especially the free motion systems. Depending upon the configuration of the pulley or pulleys you can increase or decrease the amount of effective resistance. Some pulley machines even have an extremely strong negative component.

After you execute the lift in an exercise, the weight stack is raised. At this time the amount of force involved in lowering the weights can be extremely high. Thus care must be taken on different exercise machines. To prevent an injury you should become familiar with the exercise machine before using appreciable weight.