  We investigate if known extrinsic and intrinsic factors fully account for the
complex features observed in recordings of human activity as measured from
forearm motion in subjects undergoing their regular daily routine. We
demonstrate that the apparently random forearm motion possesses previously
unrecognized dynamic patterns characterized by fractal and nonlinear dynamics.
These patterns are unaffected by changes in the average activity level, and
persist when the same subjects undergo time-isolation laboratory experiments
designed to account for the circadian phase and to control the known extrinsic
factors. We attribute these patterns to a novel intrinsic multi-scale dynamic
regulation of human activity.
