Author(s): MARCOLIN, G., BOZZATO, M., FAGGIAN, S., ZULLO, G., RIZZATO, A., PAOLI, A., Institution: UNIVERSITY OF PADOVA, Country: ITALY, Abstract-ID: 1626

INTRODUCTION:
The translation of the base of support represents a promising paradigm to assess dynamic balance control. Dynamometric platforms allow us to quantify postural adjustment objectively throughout the calculation of the Center of Pressure (CoP) displacements. Muscles are engaged to react to these postural perturbations to regain balance and avoid falling. This study aimed to investigate postural responses to unexpected perturbations of the support base through CoP displacements and lower limb muscle co-contractions.
METHODS:
Twenty-two healthy young adults (Females = 11) participated in the study. They were assessed on a force platform screwed over a servo-controlled, electrically driven supporting platform combining the following independent variables: direction (forward (FW) and backward (BW)), displacement (25mm, 50mm, and 100mm), and ramp rate (100 mm/s and 200 mm/s). The subjects underwent two sets of 12 trials, randomly combining the platform settings. The CoP anterior-posterior trajectory within the 2.5s time window after the perturbation occurred was considered to calculate the following parameters: mean velocity (UP), displacement (Area95), first peak (FP), maximal oscillations (ΔCoPMax), and standard deviation (PPV). The surface electromyography of the tibialis anterior, gastrocnemius lateralis, rectus femoris, biceps femoris, rectus abdominis, and erector spinae was recorded within the same time window to calculate the co-contraction index (CCI) of the shank, thigh, and trunk. Two-way ANOVAs were performed for CoP-related parameters and CCI. Bonferroni post hoc analysis was performed where appropriate.
RESULTS:
UP and Area95 were influenced by direction (p<0.05), displacement (p<0.01), and ramp rate (p<0.01) with higher values in FW than BW and values that increased with the increment of ramp rate and displacement. Similarly, FP and ΔCoPMax were affected by the direction (p<0.05) and negatively influenced by the increments of ramp rate (p<0.01) and displacement (p<0.001). PPV was not affected by platform direction. Interestingly, lower values of FP and ΔCoPMax occurred in the FW translations. Shank, thigh, and trunk CCI within the 2.5s time window showed no significant trends.
CONCLUSION:
UP and Area95 results indicated less efficient postural responses in the FW condition. The greater values of FP and ΔCoPMax in BW could depend on the foot-ankle anatomical complex that allows a greater CoP displacement toward the tiptoes. CCI findings did not account for the CoP behavior and warrant further analysis over a shorter time window after the unexpected translation of the platform occurred.

REFERENCES:
Rizzato et al., Sensors, 2023. doi: 10.3390/s23136203.
Brown et al., Gait Posture, 2001. doi: 10.1016/s0966-6362(01)00131-x.