Preserving trunk muscle strength and balance requires daily time spent in an upright position. Data for the length of time and number of times per day is needed. An adequate time can be determined by a sense of well-being that lasts for several hours in the absence of signs of sensory deprivation.
Sensory deprivation occurs in chairs that support their head and trunk while their body is horizontal to the floor because this does not provide opportunities for trunk control to preserve muscle strength or their sense of balance.