Coordination modes in multi-segmented rhythmic behavior: The dynamics of hula hooping

In three experiments, the spatio-temporal patterns produced by the kinematics of the lower limbs while balancing a hula hoop were analyzed using the Karhunen-Loeve (K-L) decomposition. Two modes were identified to account for most of the variance seen in the spatio-temporal pattern. The amount of variance accommodated by the two modes, varied systematically as function of experimental manipulations of hoop size and frequency. The relative phase between the joints of the lower limbs obtained through a Hilbert transform was elected to be a candidate variable behind the qualitative changes seen in the modal structure. An inspection of the relative phase between the hip, knee and ankle joints revealed that while the hip-ankle relation remained fairly close to inphase (0 radians) the hip-knee and ankle-knee phasing relations drifted away from inphase over manipulations of hoop size and frequency. It was concluded that the coordinative structure for hula-hooping might involve the assembly of two subsystems that reflect the functional organization of the lower limb: a hip-knee-ankle subsystem (in charge of vertical suspension) and a hip-ankle system (in charge of sustaining fore-aft oscillations). The two subsystems would satisfy the requirements of imparting changes, respectively, to the vertical and horizontal components of the hoop\u27s angular momentum, ensuring its dynamical stability.