Affected muscles typically show multiple signs, with severity depending on the degree of damage and other factors that influence motor control.
Health professionals' understanding of impairments in muscles after an upper motor neuron lesion has progressed considerably in recent decades.
The commonly quoted definition by Lance (1980) describes "a motor disorder, characterised by a velocity-dependent increase in tonic stretch reflexes with exaggerated tendon jerks, resulting from hyper-excitability of the stretch reflex as one component of the upper motor neurone (UMN) syndrome".
Assessment is needed of the affected individual's goals, their function, and any symptoms that may be related to the movement disorder, such as pain.
Impaired muscles typically demonstrate a loss of selective movement, including a loss of eccentric control (decreased ability to actively lengthen); this decreased active lengthening of a muscle is a key factor that limits motor control.
Impaired motor control also typically features a loss of stabilisation of an affected limb or the head from the trunk, so a thorough assessment requires this to be analysed as well, and exercise to improve proximal stability may be indicated.
For muscles with mild-to-moderate impairment, exercise should be the mainstay of management, and is likely to need to be prescribed by a physical therapist or other health professional skilled in neurological rehabilitation.
Also, in previous decades there has been a strong focus on other interventions for impaired muscles, particularly stretching and splinting, but the evidence does not support these as effective.
[3] One of the challenges for health professionals working with UMNS movement disorders is that the degree of muscle weakness makes developing an exercise programme difficult.