indeterminate
adj
(a) not fixed or exact; vague; indefinite 不固定的; 不确切的; 未限定的; 模糊的
a sort of indeterminate colour, half-way between grey and brown 一种介於灰色与棕色之间说不清的颜色.
(b) (mathematics 数) of no fixed value 数值不定的; 未定元的
an indeterminate quantity 不定量.
If it is not a question of resting the body, then perhaps it is the brain that needs resting? This might be a plausible hypothesis were it not for two factors.