Human body kinematic movements can be classified into two main types – voluntary and involuntary. Execution of daily activities and specialised activities with complete cognitive control causes voluntary movements and such movement is the expression of a thought through action. Almost all areas of the central nervous system are involved in the execution of voluntary movements and the main flow of information may begin in cognitive cortical areas in the frontal lobe or in sensory cortical areas in the occipital, parietal and temporal lobes. Ultimately, information flows from motor areas in the frontal lobe through the brain stem and spinal cord to the motor neurones [110].
Muscles are contracted due to the signals received throughout the central nervous system. The peripheral nervous system that is associated with the skeletal muscle voluntary control of the body is referred to as the somatic nervous system. There are 43 segments of nerves in the human body and associated with each segment is a pair of sensory and motor nerves. The spinal cord has 31 segments of nerves while the remaining 12 are in the brain stem. The electrical signals instigated from the brain are transmitted through the nerves and prompt the release of the chemical acetylcholine from the presynaptic terminals. This chemical is picked up by special sensors (receptors) in the muscle tissue. If enough receptors are stimulated by acetylcholine, the muscles will contract and force the specific part of the body to move. Almost all voluntary motor functions are controlled by the area referred to as the motor cortex in the brain. The primary motor cortex generates neural impulses to activate the muscle contractions and the nerves cross the body midline so that the left hemisphere of the brain controls the right side of the body and vice versa. Other areas of the motor cortex include the posterior parietal cortex, the premotor cortex and the supplementary motor cortex. The posterior parietal cortex is involved in transforming visual information into motor commands and transmits the information to the premotor cortex and the supplementary motor cortex. The supplementary motor cortex is involved in planning complex motions and also coordinating the two hands, whereas the premotor cortex is invoked in sensory guidance of movement and controls the more proximal muscles and trunk muscles of the body. According to Taga [345], the neural system indeed formulates structured sequences of signals or can even be considered as programs for the human motion via activation of muscles. Therefore, certain physiological conditions or injuries that affect the primary motor cortex (Figure 1.2) can adversely affect the functionality of the locomotor system.
Figure 1.1 The demonstration of the passive and active locomotor system. Sources: (a) https://commons.wikimedia.org/wiki/File:Human_skeleton_front_en.svg; (b) https://commons.wikimedia.org/wiki/File:1105_Anterior_and_Posterior_Views_of_Muscles.jpg.
Figure 1.2 Functional description of the brain motor cortex.
1.2 Musculoskeletal Injuries and Neurological Movement Disorders
Movement difficulties can be due to a number of causes and generally are classified as neuromuscular disorders. The causes of these abnormal movements can be classified into two main categories: musculoskeletal injuries and neurological movement disorders.
1.2.1 Musculoskeletal injuries
These injuries are normally observed in joints associated with certain degrees of movement, such as shoulder, elbow and wrists in the upper extremities and hips, knees and ankles in lower ones, which may eventually lead to abnormal movements or event disabilities. Some examples of disorders are shown in Tables 1.1 and 1.2.
1.2.2 Neuromuscular disorders
The disorders that can be associated with the nervous and muscular systems affect the movements and can sometimes exhibit characteristic movement patterns associated with certain conditions. Neuromuscular disorders affect the nerves that control the voluntary muscles – muscles that can normally be controlled by the individual. Such disorders include motor neurone diseases, neuropathies, muscular dystrophies and neurodegenerative disorders. These disorders can be classified according to the area of the neuromuscular system that is affected.
Table 1.1 Examples of musculoskeletal injuries in joints of the upper extremities. Inj is for injury and ST is for studies about using physical rehabilitation to treat the conditions or stimulate recovery (the same as that in Table 1.2).
| Shoulder | Elbow | Wrist | |
|---|---|---|---|
| Movements | Flexion, extension, abduction, adduction, internal and external rotation [84] | “Flexion and extension at the ulnohumeral and radiocapitellar articulations, while pronation and supination at the proximal radioulnar joint” [56] | Flexion, extension, radial deviation and ulnar deviation [271] |
| Inj1 | Shoulder impingement | Tennis elbow | Carpal tunnel syndrome |
| Description | It “occurs against the anterior edge and undersurface of the anterior third of the acromion, the coracoacromial ligament, and, at times, the acromioclavicular joint” [255] and deemed as one of the factors that lead to shoulder disability [254]. | Although it is not perfectly understood, it negatively influences “the attachment of the extensors of the forearm at the lateral side of the elbow”, thereby leading to pain [365]. | It usually is caused by the pressure on the median nerve on a wrist and leads to various conditions, such as pain, paraesthesiae, hypoaesthesia and so on [287]. |
| ST | [238] | [366] | [251] |
| Inj2 | Adhesive capsulitis | Scaphoid | |
| Description | The general cause leading to this condition is described as “progressive fibrosis and ultimate contracture of the glenohumeral joint capsule” [258]. |
It is usually caused by a hyperextended and radially deviated wrist and seen in patients aged between 15 and 40 [167].
|