Table 2.

Circadian Rhythms Variables Derived from Actigraphy

Variables	Definition	Meaning
Amplitude	The height of the rhythm. Value = maximum activity – minimum activity	Lower amplitude suggests a dampened circadian rhythm.
Acrophase (h)	Time of day of the peak of the curve	A later time suggest more phase delay.
Mesor	The mean of the rhythm; Value = Minimum + 1/2 amplitude Half-way between minimum and maximum activity	Mean activity level
Up-Mesor (h)	The time of day when the women switched from low activity to high activity, i.e., from below the mesor to above the mesor	Higher value suggests a later starting time of activity; the time the women “got going” in the morning.
Down-Mesor (h)	The time of day when the women switched from high activity to low activity, i.e., from above the mesor to below the mesor	Higher value suggests a later time of decline of activity; the time the women “settled down” for the evening.
R-Squared	The reduction in squared error from using a model to summarize data (and predict future values) compared to using the mean	Higher value suggests a more rhythmic or robust rhythm.