Pubudu N. Pathirana - Human Motion Capture and Identification for Assistive Systems Design in Rehabilitation

Figure 1.2 Functional description of the brain motor cortex.

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.

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 1.1and 1.2.

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).

Conditions such as a cerebrovascular accident (stroke), Parkinson's disease, multiple sclerosis, Huntington's disease (Huntington's chorea) and Creutzfeldt‐Jakob disease are examples of upper motor neurone diseases.

Lower motor neurones are located in either the anterior grey column, anterior nerve roots (spinal lower motor neruones) or the cranial nerve nuclei of the brain stem and cranial nerves with a motor function (cranial nerve lower motor neurones) [1]. All voluntary movement relies on spinal lower motor neurones, which innervate skeletal muscle fibres and act as a link between the upper motor neurons and muscles [2, 3]. Cranial nerve lower motor neurones control movements of the eyes and tongue, and contribute to chewing, swallowing and vocalisation [4]. Damage to the lower motor neurone can lead to flaccid paralysis.

Table 1.2 Examples of musculoskeletal injuries in joints of the lower extremities.

Neuropathies involve dysfunction of the peripheral nerves, which consist of: motor neurones, that carry the electrical signals directly from the spinal cord and brain stem to activate muscle movement; the sensory neurones, which convey sensory information such as pain, temperature, light touch, vibration and position to the brain; and the autonomic neurons, which go to the internal organs and control blood vessel reflexes.

Myasthenia gravis and Lambert-Eaton syndrome are examples of neuromuscular junction disorders. Muscular dystrophies and inflammatory myopathies such as polymyositis are examples of primary muscular (myopathic) disorders.

Neurodegenarative classification encapsulates the progressive loss of structure or function of the neurone and a number of conditions exhibit this form of progression. Hence, amyotrophic lateral sclerosis (ALS), Parkinson's and Huntington's are classified as neurodegenerative diseases that affect movement. These conditions exhibit characteristically slower movement compared to healthy people – hypokinesis – or excessive and abnormal involuntary movements – hyperkinesis [156]. Some common examples of hypokinesis include bradykinesia, freezing, rigidity and stiff muscles, while those belonging to hyperkinesis are chorea, dyskinesia, myoclonus, tics and tremor [242].