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Generalized hypotonia refers to a pathologically decreased postural tone that involves the four extremities, the trunk, and the neck. Facial involvement is not a requisite for the diagnosis of generalized hypotonia.
In this book, postural tone refers to: (1) the resistance that the striated muscles and the tendons offer when stretched by a sustained low-intensity force either by an examiner or by gravity; and (2) the recoil capability of the striated muscles and the tendons once they are fully extended by a sustained force for a few seconds. Postural tone is not the same as dynamic tone. Dynamic tone refers to the resistance that the striated muscles and the tendons offer when stretched by a brief high-intensity force by an examiner's maneuvers.
Postural tone results from the spring-like properties of the striated muscle fibers and the tendons. The spring-like properties of the striated muscle fibers are a function of the intrinsic resistance of its contractile elements (actin and myosin), intrinsic resistance of the collagen fibers in the endo-, peri-, and epimysium, and the effects of the nervous system upon the contractile elements. The spring-like properties of the tendon are a function of the intrinsic resistance of the collagen fibers.
Postural tone is determined by observing the resistance muscles offer to the force of gravity, by testing the resistance of the limbs to limb extension by slow motion maneuver performed by the examiner, and by testing the passive recoil of the limbs after such maneuvers. Clinically, the resistance muscles offer to the force of gravity is evaluated by observing the angle of the upper and lower limbs while the neonate is resting during quiet wakefulness, the angle of the lower limb and shoulder muscle resistance during vertical suspension, and the angle of the limbs, and trunk and neck curvature during vertical suspension.Facial tone is judged by facial expression.

Pathologically low postural tone
Generalized hypotonia or pathologically low postural tone is a subjective diagnosis given by an examiner based on experience. The diagnosis of generalized hypotonia in neonates should take into account: (1) gestational age, and (2) behavioral state. The diagnosis of generalized hypotonia should be reserved for neonates whose postural muscle tone is less than what is expected for their gestational age. Normal premature neonates should not be diagnosed with generalized hypotonia because their postural tone is not that of full term-neonates.
The assessment of postural tone during sleep is unreliable because muscle postural tone is physiologically decreased during sleep and especially during active sleep.