Von Holst (1939/1973) parsed intersegmental coordination into relative and absolute to distinguish moderate and extreme forms. Kelso and DeGuzman (1992) discussed an interpretation of relative coordination in terms of the chaotic phenomenon of intermittency. The data of concern (DeGuzman & Kelso, 1991) do not, however, exclude a stochastic interpretation, which is detailed here following earlier suggestions. The key difference is modeling relative coordination by stochastic variability about weak attractors rather than by deterministic variability about remnants of attractors (”ghost attractors”). The intermittency interpretation is not robust in the presence of noise and, therefore, is not well disposed to account for uncertainty in detailing a model of behavioral data or its parameters. In contrast, the stochastic interpretation is based upon an approximation of unknown underlying processes in the form of Gaussian white noise. A stochastic method for estimating model parameters from a stationary probability distribution and a mean first passage time is illustrated using experimental and simulated data.
David R. Collins, Hyeongsaeng Park and Michael T. Turvey
Jack R. Engsberg, Richard E. A. Van Emmerik, Sandy A. Ross and David R. Collins
This investigation developed a measure of motor control at the ankle for persons with CP using relative phase. Twenty-nine subjects, 14 with spastic diplegia cerebral palsy (CP group) and 15 without disability (WD group) were tested once. Video data were collected as a seated subject performed four full range of ankle plantar and dorsiflexion movement tasks (right ankle, left ankle, ankles in-phase with each other, and ankles antiphase to each other) at four different frequencies (self-paced, 0.5, 0.75, 1.0 Hz). The relative phase measure was able to discern the differences between the two groups of children. The CP group had poorer motor control than the WD group, based upon the measure. Both groups had more difficulty performing the antiphase than the in-phase movements. The investigation adds to the body of knowledge in that the concept of relative phase was used as a measure of motor control at the ankle in persons with CP. Results indicated that the measure was adequately sensitive to quantify differences between a group with CP and a group without disability. Clinically the measure could eventually be used as both an assessment and outcome tool.
David R. Lubans, Philip J. Morgan, Robin Callister and Clare E. Collins
The purpose of this study was to examine the relationship between pedometer step counts and estimated VO2max as determined by a submaximal exercise test. Participants (N = 115; 65 girls, 50 boys) wore pedometers for five days and completed the Queen’s College Step Test (QCST). Based on these results participants were classified as HIGH, MOD, or LOW cardiorespiratory fitness. Boys accumulated more steps per day (p < .05) than girls (12,766 ± 4,923 versus 10,887 ± 2,656). The relationship between estimated VO2max and mean steps/day was moderate (r = .34, p < .01). Participants classified as having HIGH fitness levels accumulated more steps/day than LOW-fit adolescents (p < .05). The results from this study suggest that estimated VO2max as determined by a submaximal exercise test is moderately associated with mean steps/day in adolescents.