Through his observations of patients with neurological disorders and chronic musculoskeletal pain, Janda found that the typical muscle response to joint dysfunction is similar to the muscle patterns found in upper motor neuron lesions, concluding that muscle imbalances are controlled by the CNS (Janda 1987). Janda believed that muscle tightness or spasticity is predominant. Often, weakness from muscle imbalance results from reciprocal inhibition of the tight antagonist. The degree of tightness and weakness varies between individuals, but the pattern rarely does. These patterns lead to postural changes and joint dysfunction and degeneration.
Janda identified three stereotypical patterns associated with distinct chronic pain syndromes: the upper-crossed, lower-crossed, and layer syndromes. These syndromes are characterized by specific patterns of muscle weakness and tightness that cross between the dorsal and the ventral sides of the body.