S56 Abstracts / Gait & Posture 33S (2011) S1–S66 aids was allowed) and the femur length had to be at least 21 cm in order to properly use the DGO. Apparatus: Robotic-assisted locomotion training was per- formed using the commercially available DGO Lokomat ® [4] (Hocoma Inc, Zurich, Switzerland) at Casa di Cura “Habilita” (Zingo- nia, Italy). This system included a treadmill, a body-weight support system and two light-weight robotic actuators that have to be attached to the subject’s legs. Lokomat is fully programmable, including control of knee and hip range of motion, the amount of assistance the system provides to the patient, and the speed at which the patient ambulates [5]. Protocol: The children participating in the study were divided into two groups: Lokomat (LOKG) and Intensive Physiotherapy (IPTG) group. For all the children the trial consisted of 40 rehabili- tative sessions, each of 30 min, over a 10 week course. Children of LOKG had 20 sessions on the DGO and 20 of additional physiother- apy; for children of IPTG 40 sessions exclusively of physiotherapy were scheduled. The exercises of physiotherapy and the physio- therapist were the same for all children of LOKG and IPTG. Outcome Measures: Three clinical assessments were per- formed: pre (T0), post-treatment (T1) and 3 months after the end of treatment (T2). Gait endurance was assessed by measuring the walked distance (dist) with the 6-minute walking test (6minWT). The Gross Motor Function Measure (GMFM-88) and particularly the relative dimensions D (standing) and E (walking, running, jumping) were assessed by GMFM-certified therapists. The Ashworth scale was used to assess the muscle spasticity. 3D-Gait Analysis (3DGA, Elite, BTS Bioengineering, Italy) was used to quantitatively describe the gait pattern of children, who wore their usual orthoses and footwear, and utilized their regular walking aids during the test. Results Evaluating the data of clinical assessments (T0 vs T1 and T0 vs T2), both LOKG and IPTG children showed significant improve- ment in GMFM-88, in particular in the relative dimensions D and E, and in the Ashworth scale. In 6minWT children of LOKG increased their walked distance more than those of IPTG (T0: dist-LOKG = 298.7 ± 168.9 m, dist-IPTG = 301.7 ± 144.6 m, T2: dist- LOKG = 323 ± 156.4 m, dist-IPTG = 311.7 ± 145.7 m). 3DGA showed improvements in stance, step and stride length for both LOKG and IPTG. Discussion Our data suggested that DGO therapy is safe, feasible to imple- ment and well-accepted by children. DGO Lokomat seemed to be generally as effective as intensive traditional physiotherapy, with an additional slightly positive effect on gait endurance. Further studies are needed in order to evaluate the DGO effect in a larger number of children and to identify the most effective set of DGO training parameters. References [1] Mayr A, et al. Neurorehabil Neural Repair 2007;21:307–14. [2] Wirz M, et al. Arch Phys Med Rehabil 2005;86:672–80. [3] Meyer-Heim A, et al. Arch Dis Child Aug 2009;94(8):615–20. [4] Colombo G, et al. J Rehabil Res Dev 2000;37:693–700. [5] Hidler J. Conf Proc IEEE Eng Med Biol Soc 2004;7:4829–31. doi:10.1016/j.gaitpost.2010.10.068 P31 Pendulum model to calculate virtual time to contact in the assessment of balance disorders D. Cattaneo 1 , J. Jonsdottir 1 , A. Crippa 1 , A. Montesano 1 , M. Bove 2 1 LaRiCE: Gait and Balance Disorders Laboratory, Department of Neu- rorehabilitation, Found. Don C. Gnocchi Onlus, IRCCS, 20148 Milan, Italy 2 DIST: Department of Experimental Medicine Human Physiology, Uni- versity of Genoa, Italy Introduction It is generally recognized that in quiet standing the goal of postu- ral control is to keep the vertical projection of Centre of Mass (CoM) stable within a particular sub-area of the base of support (BoS); CoM sway around its mean position (stability point) is considered an index of balance performance. It has recently been stressed that the Central Nervous System does not only take into account the position of Centre of Pressure (CoP) with respect to the stability point but also the movement of the CoP toward the limits of BoS. To address this hypothesis the Virtual Time to Contact (VTC, [1]) has been defined as the virtual time taken by CoP to move from its actual position to the boundaries of BoS, as a function of its instan- taneous initial position, velocity and acceleration (Fig. 1). Based on Slobounov’s model we developed a new model to calculate VTC that takes into account the geometrical and inertial characteristics of the human inverted pendulum. Materials and methods 13 healthy subjects (HS), and 41 subjects suffering from mild to moderate form of multiple sclerosis (MS) were recruited. Subjects were tested in eyes open and eyes closed conditions for 30 s on a stabilometric platform. To calculate the new model of VTC (VTCnm) a simplified version of the inverted pendulum was implemented taking into account the following variables: the angle (˛) between the leg and the vertical (Fig. 1), the falling angle () between the Y axes of the platform and the initial position of the leg, its instan- taneous angular velocity and the body moment of inertia. For each CoP position a virtual vector was calculated in function of virtual time () using a recursive algorithm (Fig. 2). The algorithm provided the time necessary to reach the boundaries of BoS (Virtual Time to Contact). Results The virtual vectors of a healthy subject and a subject suffering from MS are represented in Fig. 2. Table 1 reports data regarding the two groups of subjects in the two experimental conditions. Statistical significant differences were found between HS and MS (P < 0.001) and between groups in eyes open (P < 0.001) and closed condition (P < 0.001). Fig. 1. Virtual vector and pendulum model.