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Eric James, Charles S. Layne, and Karl M. Newell

Studies of bimanual coordination have typically estimated the stability of coordination patterns through the use of the circular standard deviation of relative phase. The interpretation of this statistic depends upon the assumption of a von Mises distribution. The present study tested this assumption by examining the distributional properties of relative phase in three bimanual coordination patterns. There were significant deviations from the von Mises distribution due to differences in the kurtosis of distributions. The kurtosis depended upon the relative phase pattern performed, with leptokurtic distributions occurring in the in-phase and antiphase patterns and platykurtic distributions occurring in the 30° pattern. Thus, the distributional assumptions needed to validly and reliably use the standard deviation are not necessarily present in relative phase data though they are qualitatively consistent with the landscape properties of the intrinsic dynamics.

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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.

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Patrick Ippersiel, Richard Preuss, and Shawn M. Robbins

Continuous relative phase (CRP) is an analysis technique used to study joint coordination and variability in human movement. 1 CRP is based in dynamic systems theory and quantifies the phase relationship between 2 body segments. 2 A recent review suggests that the most robust approach of

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Jeffrey M. Haddad, Richard E.A. van Emmerik, Jonathan S. Wheat, Joseph Hamill, and Winona Snapp-Childs

A variety of kinematic and kinetic measures are typically used to examine gait symmetry. Here we make the argument that gait asymmetries may be most clearly revealed through higher-order coordinative measures such as continuous relative phase (CRP). Participants walked on a treadmill with a load attached to their nondominant limb. Gait symmetry was then assessed using spatial (angular), temporal (velocity), and higherorder (CRP) symmetry measures. It was found that higher-order measures were most sensitive at assessing asymmetries due to load manipulation at both the distal and proximal segments. Symmetry measures derived from velocity variables were more sensitive than angular measures at detecting asymmetries, but were less sensitive compared with CRP. Asymmetries were also more readily detected using segmental angles compared with joint angles. These results suggest that gait asymmetries that emerge from changing constraints manifest along both spatial and temporal dimensions.

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Kentaro Kodama, Hideo Yamagiwa, and Kazuhiro Yasuda

synergies of novice young participants ( Mildren, Zaback, Adkin, Bent, & Frank, 2018 ). They reported that participants improved their performance rapidly and coordinated upper body synergies after training ( Mildren et al., 2018 ). They also conducted relative phase analysis on multijoint pairs and found a

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Ross H. Miller, Stacey A. Meardon, Timothy R. Derrick, and Jason C. Gillette

Previous research has proposed that a lack of variability in lower extremity coupling during running is associated with pathology. The purpose of the study was to evaluate lower extremity coupling variability in runners with and without a history of iliotibial band syndrome (ITBS) during an exhaustive run. Sixteen runners ran to voluntary exhaustion on a motorized treadmill while a motion capture system recorded reflective marker locations. Eight runners had a history of ITBS. At the start and end of the run, continuous relative phase (CRP) angles and CRP variability between strides were calculated for key lower extremity kinematic couplings. The ITBS runners demonstrated less CRP variability than controls in several couplings between segments that have been associated with knee pain and ITBS symptoms, including tibia rotation–rearfoot motion and rearfoot motion–thigh ad/abduction, but more variability in knee flexion/extension–foot ad/abduction. The ITBS runners also demonstrated low variability at heel strike in coupling between rearfoot motion–tibia rotation. The results suggest that runners prone to ITBS use abnormal segmental coordination patterns, particular in couplings involving thigh ad/abduction and tibia internal/external rotation. Implications for variability in injury etiology are suggested.

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Joseph F. Seay, Jeffery M. Haddad, Richard E.A. van Emmerik, and Joseph Hamill

Increases in movement variability have previously been observed to be a hallmark property of cooraination changes between coupled oscillators that occur as movement frequency is scaled. Prior research on the walk-run transition in human locomotion has also demonstrated increases in variability around the transition region, supporting predictions of nonequilibrium phase transitions (Diedrich & Warren, 1995). The current study examined the coordinative patterns of both intra- and inter-limb couplings around the walk-run transition using two different temporal manipulations of locomotor velocity as a control parameter in healthy young participants (N = 11). Coordination variability did not increase before the transition. The nature of the change in continuous relative phase variability between gait modes was coupling-specific, and varying the time spent at each velocity did not have an overall effect on gait transition dynamics. Lower extremity inter-limb coordination dynamics were more sensitive to changes in treadmill velocity than intra-limb coordination. The results demonstrate the complexity of segmental coordination change in human locomotion, and question the applicability of dynamical bimanual coordination models to human gait transitions.

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Viviane Kostrubiec, Régis Soppelsa, Jean-Michel Albaret, and Pier-Giorgio Zanone

This study investigates how motor coordination undergoes the passage from a discrete to a continuous movement régime. Participants repeated concatenated discrete movements with each hand such that one hand was lagging the other by a quarter of a cycle (i.e., with a 90° phase difference). As movement frequency increased, the tendency to persist in this relative phase competed with a progressive effect of the interlimb coupling favoring 0° and 180°. In 61% of the participants, a switch from a discrete to a continuous motion régime was accompanied by a shift toward the 0° or 180°. The 0° was more often favored than 180°. The remaining participants sustained a relative phase close to 90° even at the highest movement frequency and proved to be more accurate at the initial lowest frequency. These findings indicate that a priming effect may circumvent the tendency to produce preferred patterns and favor the production of nonpreferred patterns and that initial individual differences affect how motor coordination evolves with changing constraints.

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Nicole Wenderoth, Otmar Bock, and Rainer Krohn

The present study investigates whether the acquisition of a rhythmical bimanual coordination pattern is influenced by existing intrinsic coordination tendencies. Participants were required to learn 1 of 5 new coordination patterns, whose relative phase ϕ was either 36, 60, or 90° away from the 0° and 180° attractors, respectively. They performed 35 trials, each consisting of 2 conditions: In the augmented feedback condition, continuous visual guidance was provided, while in the normal feedback condition participants were required to rely on normal vision of their arms. We found that all to-be-learned patterns were performed with higher accuracy in the visually guided condition, whereas interference with pre-existing coordination tendencies was more pronounced in the normal vision condition. Comparing the learning progress of the 5 groups, we found for patterns close to anti-phase, a smaller improvement and significantly larger phase errors than for patterns close to in-phase. This indicates that the acquisition of a new phase relationship is influenced by existing attractors and that the 180º attractor interfered more strongly with the to-be-learned pattern than the 0º attractor.

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Dennis E. Dever, Kellen T. Krajewski, Camille C. Johnson, Katelyn F. Allison, Nizam U. Ahamed, Mita Lovalekar, Qi Mi, Shawn D. Flanagan, William J. Anderst, and Chris Connaboy

the lower extremity (ie, foot, shank, and thigh) interact in state space through the entirety of a stride. Continuous relative phase (CRP) determines the angular position–velocity segment orientation relationship between 2 segments in regard to their movement through state space. 23 , 24 Visual