This document discusses different types of muscle tone in infants. It describes active and passive tone, with active tone being the physiological resistance to movement and passive tone being the range of motion around a joint. It then defines the two kinds of tone that clinicians test - phasic tone, which is a rapid contraction in response to high-intensity stretch like a tendon reflex, and postural tone, which is a prolonged contraction of antigravity muscles in response to low-intensity stretch from gravity. Postural tone helps infants maintain their trunk and limbs against gravity, and depressed postural tone results in hypotonia where the infant appears floppy and unable to resist gravity.