Biomechanics of the arm

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Biomechanics of the arm

Filed under Orthopaedics. Pronation and supination are rotational motions that exist exclusively in the forearm. The mechanical bases for these movements are the existence of two forearm bones and the presence of two coupled trochoid joints—the proximal and distal radioulnar joints PRUJ and DRUJ.

Furthermore, only two bones at the forearm provide a wide range of motion but stable and light construction. Hagert 5 compared the montages of the forearm with a ventral view of the leg. The proximal ulnar and distal radial segments create a unit similar to the tibia. The olecranon resembles the patella fused with the tuberosity of the tibia; the radial styloid resembles the medial malleolus at the ankle. The proximal radial and distal ulnar segments create a unit reminiscent of the fibula with the ulnar styloid resembling the lateral malleolus.

The DRUJ consists of two parts: the radioulnar articulation and the ulnoligamentous articulation. The border between these two components is defined as the ulnar extension of a line along the subchondral bone of the distal radius.

The articular surface of the distal radius toward the ulnar head is the sigmoid notch, and the corresponding surface of the ulnar head constitutes the seat of the joint. By convention, an ulnar-neutral variance is one in which the distal cortical surface of the ulnar pole is level with the cortical surface of the most proximal aspect of the lunate fossa.

This is measured perpendicular to the longitudinal axis of the forearm when the radiograph is taken with the forearm and wrist in neutral extension and neutral deviation and with the x-ray tube perpendicular to the plane of the radiocarpal joint. If the ulna is shorter than the radius ulnar negativethe ulnar head is cone shaped. If the ulna and radius are similar in length, the ulnar head is cylindrical ulnar neutral.

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If the ulna is longer than the radius ulnar positivethe ulnar head is spherical Fig. Aside from the seat, the ulnar head articulates with the TFC. The dorsal radioulnar ligament attaches to the dorsal rim of the distal radius at the level of the sigmoid notch and courses obliquely ulnarly and anteriorly to insert with the palmar radioulnar ligament into the fovea of the ulnar head and the styloid process.

The palmar radioulnar ligament attaches radially to the palmar rim of the distal radius at the level of the sigmoid notch and courses obliquely ulnarly and dorsally to attach with the dorsoulnar ligament to the fovea of the ulnar head and the ulnar styloid process Fig. The IOM is a quadrangular sheath that extends from the radius to the ulna, filling the interosseous space. It links both bones of the forearm and also separates the anterior and the posterior compartments of the forearm.

Proximally and distally the membrane is not continuous and is perforated by posterior and anterior interosseous vessels Fig. Fibers in the anterior plane run distally and obliquely from the medial border of the radius to the lateral border of the ulna.

Three bundles are distinguished: the proximal descending fibers are almost horizontal, the intermediate descending fibers follow a short oblique direction, and the distal descending fibers have a long, oblique trajectory. The proximal ascending bundle is short, oblique, and quite strong.

It arises from the interosseous tubercle of the radius and ends at the proximal ulna. The distal ascending bundle is inconstant. Its direction is long oblique. It arises from the distal radius and reaches the proximal ulna. In their cadaver study, they found a discrete central band or thickening. The tract of the IOM is taut in pronation and loose in supination. It strengthens the dorsal capsule of the DRUJ, forming a sling that protects the ulnar head during pronation.

The head is ovoid rather than circular and is offset approximately 15 degrees from the longitudinal axis of the radius. Cartilage covers degrees of the radial head, which articulates with the ulna at the PRUJ. The stability of the PRUJ is excellent because the radial head is enclosed in a very strong osteoligamentous cavity that is made of the radial notch of the ulna and the annular ligament, which is a very resistant ligament Fig.

There are rarely problems with the joint, except in fractures of the radial head. The ulnar head moves in a rolling and sliding motion from the dorsal to the palmar rim of the sigmoid notch as the joint moves from pronation to supination.Average 4.

Thank you for rating! Please vote below and help us build the most advanced adaptive learning platform in medicine. Just skip this one for now. An injury was most likely sustained to which of the following arteries labeled in Figure A? Review Topic Tested Concept. Prevents anterior translation of the humerus with the arm in 45 degrees of abduction.

Prevents anterior translation of the humerus with the arm in 90 degrees of abduction. Based on the radiographs shown in Figures 6a through 6c, what preoperative factor will most affect postoperative functional outcome? Anteriorly translated with the arm in 90 degrees of abduction and externally rotated. Anteriorly translated with the arm in 90 degrees of abduction and internally rotated. Inferiorly translated with the arm in 45 degrees of abduction and internal rotation.

Inferiorly translated with the arm in 90 degrees of abduction and neutral rotation. Glenohumeral Joint Anatomy, Stabilizer, and Biomechanics.

Colin Woon. Anthony Romeo. American Shoulder and Elbow Surgeons. Ligamentous Restraints in different Arm Positions. Arm Position. Posterior Res. Please rate topic. Please vote below and help us build the most advanced adaptive learning platform in medicine The complexity of this topic is appropriate for? L2 - PGY3. L3 - PGY4. L4 - PGY5.Baseball is widely known as America's favorite game and pastime. It's fun to watch two teams pit their skill and strategy against each other.

There are many factors that affect the score and which team wins the game. The teams need to hit the ball, field the ball, and run fast.

One of the most important factors is good pitching. If the pitcher is not in top form, then the opposing team has more chances to hit the ball, get on base, and score. Figure 1. This image shows a baseball game in progress at Wrigley Field in Chicago, Illinois.

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Wikipedia, Pitching a ball quickly and accurately is complicated. It is dependent on how the pitcher controls and uses his or her body to eject the ball from his or her hand. Biomechanics is the study of the human body in motion.

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Biomechanists apply principles from mechanics and engineering to study the forces that act on the body and the effects they produce. A pitcher needs to understand how to use his or her body and become familiar with all of its possible positions in order to pitch a ball as fast as he or she can.

In fact, pitchers can get injured if they don't know how to use their bodies properly. The American Sports Medicine Institute has separated the act of pitching into six phases. It is important for the pitcher to properly perform each step in order to prevent injury.

Calculate Muscle Force at the Elbow Joint When Holding a Dumbbell

These six phases are as follows:. Figure 2. Four of the different phases of pitching: a Windup, b Stride, c Arm cocking and d Follow-through. Pitching puts a great amount of stress on the throwing arm, especially at the elbow and arm. During pitching, there are both external and internal forces acting on the body. External forces include gravitational force and the ball's resistive force. Internal forces include how each part of the arm the hand, the wrist, the elbow act against each other.

There is a lot of physics that describes the motion of the throwing arm. In this sports science fair project, you will experiment with the biomechanics of pitching. You will determine if the stride step and the length of the stride affect the speed of a pitch. Remember to warm up your arm prior to starting this science fair project, and stop pitching if your arm starts to hurt.

You don't want to get injured as you perform your project. Have your coach or an adult standing by to help, if necessary. Batter up!It can be a touchy and controversial subject.

I will do my best to label what are just plain facts, and what is my opinion based on these facts. I invite you to question what you know, and my opinions. This technique probably differs the most within the volleyball world.

Elbow high or low? Hit with your shoulder or by rotating your hips? Focus on internal and external rotation, or elbow extension? Should I do pull ups or push ups to improve my arm swing? When do I get my elbow up? The list can go on an on, yet there is hardly any science telling us what do to specifically in regards to volleyball.

I hope to solve that within this series. The volleyball arm swing is a lot more complicated than it seems — there is way more to it than meets the eye.

First off, a volleyball arm swing is a rotation of the body. Think of your left scapula and left hip being the hinges on a door, and the rest of your body being a less rigid door. Believe it or not, a volleyball arm swing is only slightly different from a baseball throw, javelin throw, discus throw, some really big basketball dunks, or a tennis serve.

They are all ipsilateral rotations. See for yourself. One of the best dunkers and shot blockers in the NBA.

Meet Matt Anderson, one of the few players to leave college early for a big six figure contract in Korea. Meet David Lee, one of the best middles in the world. Was an invaluable part of the Gold medal team. Meet Andy Roddick, one of the best tennis servers in the world. Psst, his mechanics also happen to be phenomenal. Meet Greg Maddux, one of the best pitchers to ever play. Meet Ashton Eaton, recently won the Olympic decathlon by setting a new world record.

After viewing a photo of him coming out of the blocks for a race, our entire office came to a stand still because he is so biomechanically perfect.

This perfection is what ensured him such dominance. But no, he decides to be a boss and do them all. Have you noticed any similarities yet? First, look at their left arm. The position is nearly the same in every photo sorry for the backside of Matt Anderson. Look at their left legs. All of them are in some amount of hip flexion, those who are further along in the rotation have more hip flexion. All are slightly side bent to the left, this is not the best for their bodies, but it creates a mechanical advantage and thus improves their performance.Outline the biomechanics of reaching both in healthy individuals and in individuals with acquired brain injury ABIand to discuss the clinical implications for using valid biomechanical models to assess reaching.

A review of current literature, including a MEDLINE search using keywords of reaching, acquired brain injury, stroke, biomechanics and motor control. Current assessments of the upper extremity in acquired brain injury ABI are focused on single joint characteristics of range of motion, strength, and spasticity.

However, reaching is a functional multijoint task requiring interjoint coordination in addition to feedback and feedforward control to optimally position the hand at a desired location so that it may interact with the environment. From the literature, biomechanical measures of reaching such as movement time, movement distance and interjoint coordination have been shown to discriminate changes to hand path quality following brain injury.

The Role of Arm Swing in Sprint Biomechanics

These measures also have been shown to correlate with measures of sensorimotor function e. Further development of reliable and valid multijoint biomechanical evaluations is required, particularly for natural and goal-oriented reaching movements. The biomechanical assessment of reaching in ABI can provide an understanding of the specific deficits in physiological structures or motor planning underlying altered reaching ability, assist in the evaluation of new therapies, and characterize the recovery process following ABI.

The ability to reach is critical for virtually all activities of daily living such as grooming, toileting, feeding, transfers, and dressing. Although grasping 3 and postural control 4 actions often accompany a reach, these elements are controlled by distinct motor programs. Reaching ability following an ABI is generally assessed on an ordinal scale as one component of a standardized upper extremity function scale, e.

Furthermore, ordinal scales provide little information as to the underlying causes of the motor dysfunction. A full understanding of human movement requires the integration of kinematic movement and kinetic force analyses to identify the internal forces e.

Movement analysis of reaching can identify changes in interjoint coordination or the quality of the hand path e. In fact, kinematic measures of movement time, movement distance and interjoint coordination during a reaching task are strongly correlated to functional measures of upper extremity function e.

In addition, movement analysis of reaching may be useful for the evaluation of existing 17 and developing upper extremity therapies in acquired brain injury ABI such as the force use paradigm where the less affected arm is restrained to encourage use of the more affected extremity, 18 the use of neuromuscular blocks e.

Despite the fact that reaching is one of the major functions of the upper extremity and has poor recovery in ABI, 6 the biomechanics of this multijoint task are largely ignored in undergraduate rehabilitation curriculums relative to the emphasis placed upon the multijoint function of the lower extremity.

Therefore, the purposes of this paper are 1 to outline the biomechanics of reaching in healthy individuals, 2 to review the uses of current clinical assessments of reaching function in ABI, 3 to describe the findings of biomechanical investigations in ABI, and 4 to discuss the clinical implications and future considerations for the use of valid biomechanical models for the assessment of reaching.

Additional references were gleaned from the articles identified. Understanding the biomechanical and neuromotor control processes underlying reaching in the healthy population can help clinicians to identify where deficits may occur in persons with ABI.

Segments of the upper limb may move about seven possible degrees of freedom DOF i. This natural excess of joints affords the central nervous system CNS the ability to employ an infinite number of paths and when reaching to a specific target. Despite the many available degrees of freedom, joint motion during reaching is similar for a given start position, end position, and hand orientation across the healthy population.

Neuromuscular control of reaching is computationally complex and requires the synchronization of muscle activation at all the moving joints as well as all the muscles involved in postural stabilization. The acceleration of each joint during a reaching movement depends upon both the net joint torque i. Gravitational effects depend upon the weight and general orientation of the arm segments.

Viscoelasticity is the inherent mechanical property of passive tissues i. The central nervous system CNS planning of reaching movements may be considered as a hierarchical control in which spatial information is converted to motor patterns at the shoulder and elbow to move the hand through space. A series of transformations convert sensory signals into hand trajectories, then into corresponding joint trajectories, required muscular torques, and finally into the actual patterns of muscle activity.

The CNS uses both feedforward and feedback strategies to control reaching movements. Feedforward control is characterized by a profile of continuous movement that contains one acceleration and one deceleration phase. The second phase of reaching is feedback controlled and corrects for discrepancies between where and how one wants to place the arm versus the current position and speed of the arm. In feedback control, signals from peripheral receptors provide information back to the nervous system about the events occurring in the muscles, joints and other tissues.

Feedback control is characterized by a profile of discontinuous movement that contains multiple accelerations and decelerations of progressively shorter duration as the error between the hand and the target approaches zero.

Normal multijoint reaching is characterized by a smooth bell shaped velocity profile with a peak velocity approximately halfway between the start and endpoints see line LA in Figure 1. The peak velocity corresponds to the changeover from the acceleration and deceleration phases and its location within the velocity profile is an indicator of strategy.

As requirements for accuracy increase, the bell shaped velocity profile becomes skewed and the peak velocity occurs earlier in movement. Conversely, as requirements for speed increase, the peak velocity occurs later in movement.

Fingertip speeds for the more affected MA and less affected LA arms while during a reaching task.Learn something new every day More Info The shoulder is an intricate multidimensional joint complex consisting of four separate connection points of bones responsible for the movement of the hand, arm and shoulder.

The biomechanics of the shoulder is how the shoulder moves, as well as the scientific study of this movement. This can include intentional movements as well as movements in response to internal and external changes or forces acting upon the shoulder. The shoulder is made up of separate joints that link the arm to the torso, and includes bones in the trunk, including the shoulder blade and the collar bone — these are known as the scapula and clavicle, respectively.

These structures are attatched to the humerus, which is the body's upper arm bone. Due to its complex nature, the shoulder is one of the most mobile joints in the body.

biomechanics of the arm

This multi-faceted system gives the shoulder the ability to move in straight and rotational planes. Understanding the biomechanics of the shoulder makes it possible to prevent or treat injuries limiting the mobility of the shoulder area.

Having a basic knowledge of the structure of the shoulder is important to understanding the biomechanics of the shoulder. For example, the glenohumeral joint is the area where the upper arm bone connects to the shoulder blade by resting in a hollowed out area called the glenoid fossa. This type of joint is referred to as a ball-and-socket. This joint allows the shoulder to move in straight planes, forward or backward, and side to side. This kind of connection also lets the shoulder rotate so the arm can swing in a circular pattern without hitting against the sides of the bony connection point.

The circular or rotational components of shoulder movement are dependent on the ability of the shoulder blade to move unrestricted. The acromioclavicular joint is another important bony connection that gives the arm the ability to rotate. It also allows for protraction and retraction, or the movement of the arm in a forward and backward manner. Movement of the shoulder blade and the collar bone to position the glenoid fossa in the correct position for appropriate movement is necessary for smooth motion of the arm.

Understanding these biomechanics of the shoulder allows for better insight into shoulder problems resulting in movement restrictions. In other words, if the arm has lost the ability to move out away from the body and up towards the head, the movement of the shoulder blade as well as the collar bone must be evaluated in order to restore pain-free, unrestricted movement of the shoulder.

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Thank you for helping to improve wiseGEEK! View slideshow of images above. Watch the Did-You-Know slideshow. Follow wiseGEEK.Understanding this can help you make adjustments in form and sort out which variations of the basic curl are best for you. Since the discs and other spine structures become more vulnerable with injury and age, trainees returning from a back injury, older trainees in general, and the simply risk-adverse may find these techniques useful in avoiding further unnecessary wear and tear.

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Acquiring muscular arms is a classic motivation for fitness enthusiasts, and the curl is the obvious go-to option. The standing biceps curl has a special place for those of us who got started at home with a vinyl-covered barbell set.

We may not have had a squat rack or bench, but we could put the plates on the bar and start curling right out of the box. The standing curl is a perfectly adequate exercise, especially at the beginning levels of strength and effort.

Kicking biomechanics: Importance of balance

But as we get more experienced, push harder, and become stronger, we use more weight and the curl can put an unexpected strain on the back. The likelihood of problems increases if the spine is overloaded lifting weights when it is out of the neutral position.

The spine is designed to bear loads and stresses in neutral; if it is not aligned properly those loads and stresses are transmitted unevenly and transferred to structures that were not designed for load-bearing.

biomechanics of the arm

If improper posture or lifting is repeated continuously, this will fatigue or weaken the spinal structure increasing the chance of injury. The same continual exposure to force on the spine will cause general wear and tear on the spinal column as we age.

biomechanics of the arm

This decreases the space between the vertebral bodies and allow forces on the spine to affect the nerves and spinal column, ultimately resulting in increased pain and decreased function. But as you train with heavier weights or move deeper into fatigue, there is an inevitable lean away from the weight, especially as you approach the sticking point forearms horizontal.

This results in a sway back posture, a deviation from the neutral spine, which is discouraged as a postural condition, much less with an additional load and effort through the spine. With your feet parallel, in line with your shoulders and hips, your base of support is a straight line in the frontal plane. As you curl the weight forward, the weight moves your center of gravity forward of that base of support, the very definition of unstable.

What keeps us from face planting is the shoulders and head being drawn opposite the weight by the contraction of the deep back muscles, creating the sway back, but bringing stability to the body-barbell system. Notice, as you complete the curl, the sway back goes back to neutral. Instead of your head and shoulders moving back, your hips will move forward as your body tries to regain stability.

What Is the Biomechanics of the Shoulder?

A more effective fix is a staggered stance. By placing one foot in front of the other, you are rotating your base of support ninety degrees - front-back instead of side-to-side.

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Within the staggered stance, it also helps if you alternate curls rather than do both arms simultaneously. In effect, you reduce the total weight impacting the center of gravity. This curl creates a cantilever - a beam that projects beyond a fulcrum, supported by a larger weight on the other side of the fulcrum. Out of gym, this design is used to provide stability without a second support, like a shelf or balcony.

On the Scott bench or machine, your arm is the beam and the bench is the fulcrum. You may still find some mid-to-upper back discomfort with the Scott curl and the standing curl, or for that matter any exercise with the weight held in front, even with a neutral spine.

What keeps your spine from falling into flexion is enough of a contraction of the deep spine muscles to hold the posture. Add to that, any additional bodyweight you carry in front: a big chest, forward head, rounded shoulders, a big belly, plus whatever you carry in your hands. Then, you work out with the weight or kettlebell held in front of your body.


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