1. CONCLUSIONS Locally generated forces seem to have remote effects on the organization of movement, revealed in this study by overall increases in stiffness-nonlinearity and in local increments in stiffness-magnitude. These effects were observed along with increases in the amplitude of oscillation. The Biotensegrity Model of the Musculoskeletal System aids our interpretation of the data. This model predicts (1) force transfer across the body, which could account for the changes in amplitude observed, and (2) stiffening as a result of local stress. Stiffening of tensegrity structures occurs as a response to local stress because more members of the structure are aligned in the direction of the applied stress. Interpretation of the data based on other hypotheses cannot be ruled out. Remote effects of a locally produced force on the organization of rhythmic movement Paula L. Silva 1, Marisa C. Mancini 1,2, Sergio T. Fonseca 1,2, Miguel Moreno 1 1 Center for the Ecological Study of Perception and Action, University of Connecticut 2 Federal University of Minas Gerais Acknowledgments. This research was supported by grants from the National Science Foundation (SBR 04-23036), the University of Connecticut (Co-laboratory of Rehabilitation Research), and CAPES Awards from the Brazilian Ministry of Education. We thank Claudia Carello, Bruce Kay, and M. T. Turvey for suggestions about the design and analysis. RESULTS Amplitude and Period Amplitude was affect by pendulum length (p =.04;  2 =.10) and force level (p =.002;  2 =.43): The greater the length and the higher the force, the greater the amplitude. Period was affected only by pendulum length (p =.0001,  2 =.88): The produced period was close to the eigenperiod of the pendulums. There was no effect of force on period. The Experiment Seven participants were asked to swing a single hand-held pendulum at a comfortable tempo (with amplitude unconstrained) while continuously squeezing a dynamometer with their other hand. Experimental Manipulations: three levels of force (0, 10 and 20% of maximum strength) and three pendulums presenting distinct lengths and eigen-periods (36 cm/0.94 sec; 56 cm/1.10 sec, and 70 cm/1.45 sec). Stiffness: Linearity and Magnitude Analyzes Both the linearity (p =.0001;  2 =.58) and the magnitude (p =.0004;  2 =.388) of stiffness were affected by force level: As force was increased, the magnitude of linear stiffness also increased and the variance explained by a linear fit to the Hooke’s Portrait decreased. Nervous System Overflow of CNS activity as a result of afferent information from local muscular contraction. INTRODUCTION Rhythmic movements are assembled from a number of interacting resources. RESEARCH GOALS The objective of the present study was to describe the remote effects of a tonic force produced at one wrist on the observed kinematic pattern and underlying organization (parameter and oscillatory dynamics) of rhythmic movements produced by the opposite wrist. 20 15 10 5 0 Displacement 5 10 15 20 25 30 Time (sec) Two trials of 30 seconds were performed in each condition (combination of pendulum and force level), totaling 18 trials, fully randomized. The consistency of force production was monitored by the experimenter. The STIFFNESS PARAMETER was evaluated on Hooke’s plane (acceleration vs. position). For each trial we computed (i) the magnitude of the linear stiffness as the slope of the linear portion of the plots and (ii) the linearity as the variance explained by a linear fit to the entire plot. The R 2 coefficients were transformed into Z scores prior to analyses. The OSCILLATORY DYNAMICS was evaluated by the W-method (Beek & Beek, 1998). The goal of this analysis was to identify the non-linear functions underlying the rhythmic movements and their relative contributions to the observed pattern as force was changed. Oscillatory Dynamics: Non-linear functions The W-Analysis did not reveal any changes in the non-linear functions underlying the rhythmic movements as a function of force level. Rayleigh, Van Der Pol and Duffing were consistently identified as predictors of the W- function at the different force conditions. Descriptive Analysis of the Data MODEL: The results of the W-analysis suggest that the biological pendular motions under investigation were essentially hybrids of the van der Pol and Rayleigh oscillators (Kay et al., 1991) with the addition of a soft Duffing (cubic term). Equation (2) predicts increases in period associated with increments in amplitude: as amplitude increases, more of the non- linear portion of the spring is reached, leading to a decrease in period of oscillation as a result of diminished restoring torque. A decrease in period was not observed in the present study. Possible explanation The increases in linear stiffness observed as a function of force might have compensated for the slowing down due to the non-linearity (Equation 3) Research Question How does the oscillatory dynamics of the system changes so as to produce the observable changes in pattern? A motion-capture system (Polhemus Coorporation®) recorded movement trajectories of the pendulum. Mean AMPLITUDE and PERIOD were computed from the time-series obtained in each trial. Related Research There is evidence that muscular activity generated locally at the foot or hand is reflected in the degree of change in the temporal organization of rhythmic move- ments of other body segments. Frequency (  ) analysis Equation (2) Equation (3) REFERENCES Levin, SN. The Tensegrity-Truss as a model for spine mechanics: Biotensegrity. (2002). Journal of Mechanics in Medicine and Biology, 2(3-4), 375-388. Meijer, H.J.M., Baan, G.C., Huijing, P.A. Myofascial force transmission is increasingly important at lower forces. (2006) Acta Physiologica, 186, 185-195. Kugler, P.N., & Turvey, M.T. (1987) Information, natural law, and self-assembly of rhythmic movements. New Jersey: Lawrence Erlbaun Associates. Beek, P.J., Beek, W.J. Tools for constructing dynamical models of rhythmic movement. (1988). Human Movement Science, 7, 301-342. Kay, B.A., Saltzman, E.S., Kelso, J.A.S. Steady state and perturbed rhythmical movements: A dynamical analysis. (1991). Journal of Experimental Psychology Human Perception and Performance 17: 183-197. Circulatory System Level of heart activity enhanced by tonic force production, increasing the intensity of contraction of the muscles producing the movement (Bingham et al., 1991). Duffing x -  x +  x 3 +  x 2 x + kx -  x 3 =0 Rayleigh vdp Equation (1) Hence, there are mechanical, neural and physiological pathways through which a tonic force generated in one body segment may change the pattern of rhythmic movements produced at another limb, namely its period and amplitude. The present research will focus on remote effects of changing the tonic activation level at one limb on the organization of rhythmic movements produced at the contralateral limb. Musculoskeletal System Connective tissue (ligaments, capsules and fascia) and muscular tissues seem to be integrated in the musculoskeletal system, constituting pathways for force transmission across the body (Meijer et al., 2006). Such an integrative view is consistent with the BioTensegrity Model of the Musculoskeletal System (Levin,2002). In tensegrity structures, locally produced forces are immediately transmitted as tension to all structural members. Changes in any component are expected to reorganize the interaction dynamics, leading to modifications in the movement pattern. How might such remote effects be mediated?