My post to FeldyForum (discussion group for Feldenkrais teachers)
Q: What is your thinking about movement during sleep?
A: We certainly do move while we sleep. People shift body position from a minimum of 8 to a maximum of about 30 times during a night. Those who shift position fewer times generally report more restful sleep than those who report more. Sleep movement may be necessary to prevent blood-pooling and lactic-acid build-up in muscles during the nightly sedentary period. It reflects changes in arousal level during the sleep cycle.
Though some people insist that they always go to sleep in one position and stay in it all night, that is highly unlikely. Sleep is marked by all kinds of subjective phenomena which are not in accord with objective observation, and this is one of them.
According to Harvard sleep-researcher J. Alan Hobson, body movements during sleep typically occur during phase transitions, for example during the transition from REM to non-REM sleep or vice versa. Movements may also signal that dreams have just occurred, or are about to begin, according to Hobson.
It's also interesting to note that couples who sleep together, especially when they go to bed at the same time, tend to synchronize their REM/non-REM sleep cycle and therefore their sleep-related movements. Talk about togetherness!
As I have mentioned before on this forum, the late Mark Reese was of the opinion that the quality of body movements during sleep is one of the keys to sound sleep. His reasoning was: When people sleep, they move. To the extent that those sleep movements are rendered easy, light, and effortless, the person will sleep more deeply and restfully.
Mark created a beautiful ATM lesson called "The Wheel" that clarifies the movements needed to "roll in place" from supine, to side lying, to prone, to the other side, to supine again, with minimum effort and maximum pleasure. I am currently working on reconstructing the lesson, and I am eager to hear from anyone who knows it.
Reflexive Movements
In addition to these gross body movements, there are smaller, reflexive movements that occur during both REM and non-REM sleep. Slow-rolling eye movements (SEMs) with respiratory-like periodicities occur with increasing frequency and duration at sleep onset, and decline during later stages of non-REM sleep. Clonic jerks, those fast jerky movements of the body that occur at sleep onset, often accompanied by feelings that one is falling, are thought to reflect sudden shifts in the physiological arousal level. Their cause is unknown.
During REM sleep the cortex produces significant motor output, but the spinal motoneurons are completely shut down--so there is "postural atonia," a kind of a temporary paralysis. But smaller, more distal movements do occur during REM, for example the rapid eye movements for which this sleep-stage is named, as well as rapid tongue movements and movements of the extremities.
Sleep talking can occur during either REM or non-REM sleep; during REM talking is more comprehensible and often comprises clear words or sentences and recall of sleep mentation.
Finally, there are the movements of respiration that occur throughout the sleep cycle. Respiration becomes unstable at sleep onset with oxygen consumption, as well as rythm and amplitude of respiratory movement, going up and down in synchrony with the fluctuations between alpha and theta EEG activity that characterize early sleep onset. During non-REM sleep, oxygen demand is at its lowest, oxygen consumption is highly regulated, and respiratory movement tends to be slow, or of low amplitude, or both.
During REM sleep the brain is highly activated, thus requiring more oxygen, so there tend to be spikes in oxygen consumption and respiratory movements tend to be more more varied and more vigorous.
Pathological sleep-related movements, like sleep walking, restless leg syndrome, sleep disordered breathing, and sleep apnea, are another story for another day....
