Rate and Distribution of Body Movements during Sleep in Humans

Abstract

Body movements were measured during sleep with a mechanoelectrical transducer in 11 healthy adults. Also measured were the electroencephalogram (EEG), electrooculogram (EOG), and electromyogram (EMG). Each subject slept alone in a quiet room for 21 to 44 consecutive nights. Body movements were classified as minor movements (actogram signal or head leads artifact), major movements (actogram signal plus head leads artifact), or movement time (MT). There was a strong relationship between rate of body movements and sleep stages, with the rate decreasing along the following sequence of stages: W > S1 > REM > S2 > S (3 + 4). If the body movements for all nights are pooled per subject, the distribution of body movement rates shows hardly any overlap for the Stages 1, REM, 2, and (3 + 4). The relative frequency of body movements seems to be regulated by a stage-dependent mechanism. The reliability of the body movement rate was determined by computing correlations between pairs of adjacent nights, which resulted in a r = .69. When 2 to 9 nights were pooled stepwise according to a split-half procedure, the mean r increased and reached values between .80 and .90, which means that body movements are a reliable sleep measure especially if the time base is large enough.