Muscle Contractions

during these movements, the angles of those joints, as well as the muscles involved during the

Firstly, an isometric contraction is when the length of the muscle does not change and the angle of the joint does not change. The muscle is active during this contraction but it is in a static position. An example of this is when you stop halfway when doing a squat or push-up or holding yourself in an abdominal plank position. This type of muscle work is quite easy to do, however it can result in fatigue very quickly. Furthermore, this type of muscle work can cause a sharp increase in the blood pressure in the body because blood flow is reduced. Another type of muscle contraction is the concentric muscle contraction; this occurs when a muscle shortens against a resistance, an example of this is a bicep curl. The brachialis and bicep shorten, bringing your forearm towards your upper arm. These types of contraction are also known as the positive phase of muscle

Shoulder flexion/extension; Elbow flexion and extension; Use of the lower and upper back. Muscles involved include the latissimus dorsi, rhomboids, trapezius, deltoids and the pectorals.

2. In strength training and rehabilitation, emphasis should be given to both the concentric and eccentric phases of the movement. During the concentric phase, the muscle shortens from a lengthened position and during the eccentric phase the muscle lengthens from a shortened position. For example, in the execution of the

During an eccentric contraction, the muscle lengthens under tension due to an opposing force that is greater than the force being produced by the muscle (Lindstedt et al. 2001). Eccentric contractions require little metabolic energy, however they are characterized by a high production of force (Semmler 2014). Fick observed that a lengthening muscle contraction could exert more force than a shortening muscle contraction, while Hill later observed that the body has a lower energy demand when contracting eccentrically compared to concentrically (Lindstedt et al. 2001). When the force applied is larger than the force that is created, work is done on the lengthened muscle and mechanical energy is absorbed – this is called “negative work” (Lindstedt et al. 2001). This absorbed energy can either be dissipated as heat, or it can be temporarily stored as elastic recoil potential energy for later use (Lindstedt et al. 2001).

O B J E C T I V E S 1. To define these terms used in describing muscle physiology: multiple motor unit summation, maximal stimulus, treppe, wave summation, and tetanus. 2. To identify two ways that the mode of stimulation can affect muscle force production. 3. To plot a graph relating stimulus strength and twitch force to illustrate graded muscle response. 4. To explain how slow, smooth, sustained contraction is possible in a skeletal muscle. 5. To graphically understand the relationships between passive, active, and total forces. 6. To identify the conditions under which muscle contraction is isometric or isotonic. 7. To describe in terms of length and force the

Upright rows, when the barbell is raised, this movement is a concentric contraction. During this contraction, the trapezius are at its strongest in this point in the movement. As the weight is lowered back to its starting position, this movement downward is an eccentric contraction.

 1)Flexion happens when a decrease in the angle between two body segments happens like in the shoulder, elbow, hips and knee joints. An example could be when using a dumbbell of 10 pounds to curl the biceps, flexion takes place at the elbow.

First, before this assignment I had no idea of the levels involved in a muscle contraction. We can directly control or regulate the activity of our skeletal muscles. Striated muscle movement, produced by the interaction of filaments containing the proteins myosin and actin, is regulated by the proteins tropomyosin and troponin on the actin filaments. When an electrical signal passes down the motor nerve to a muscle it triggers a depolarization of the muscle membrane (sarcolemma). In results, triggers the sarcoplasmic reticulum to release calcium ions into the muscle interior where they bind to troponin, which causes tropomyosin to shift the actin filament to which myosin heads need to bind to produce contraction.

The shoulder is a ball and socket joint which allows it a flexion and extension motion.

This arrangement means that muscles are able to work together, allowing for one limb to be straightened by one muscle and to be bent by the other. Muscles that bend a limb are called flexors and muscles that straighten a limb are called extensors.

The musculoskeletal involves the muscles and skeletal system which consist of bones supporting the bodyweight. The muscles and bones help in movement and maintaining body position through the physiological process of contraction and relaxation, muscles pulling on the bones. The skeletal systems also consist of cartilages and ligaments important for bone connection and stability with connective tissue. The muscles get attached to the bone by the connective tissue enhancing contraction and relaxation in movement. The muscles contain long muscle fibers responsible for the contraction and relaxation. The fibers contain bundles some of which allow slow movement described as slow twitch and fast twitch which ensure fast movement. The process of movement involves coordination between the musculoskeletal system and nervous system. In the process of muscle contraction to enhance movement the following takes place. (Arthur Guyton, 2006)

Isometric contractions appear when there is no change in the length of the contracting muscle. This occurs when carrying an item in front of you. As the weight of the item is pulling your arms down, but your muscles are contracting to hold the items at the same level. Isokinetic contractions are really similar to isotonic, in that the muscle changes length during the contraction. Where they are different is that Isokinetic contractions produce movements of a constant speed. What you need to measure this is something called a isokinetic dynamometer. Concentric contractions are those which cause the muscle to shorten. An example is bending the elbow from straight to fully extended, causing a concentric contraction of the Bicep muscle. Eccentric

Eccentric muscle contraction can be defined as “muscle loading that involves an external force application with tension, increased during physical lengthening of the musculotendinous unit” (Albert, 1995, p.1). Eccentric exercise results in a greater amount of muscle damage than concentric training as the contracting muscle is forcibly lengthened; this also leads to a greater inflammatory response. There are two prominent signs of muscle damage after eccentric exercise,

The main movement which is exhibited when using a computer comes from the elbows, wrists and shoulder griddle. Due to the sitting position the majority of the body’s joints and muscles are dormant, except from the triceps and biceps.