RESEARCH REPORT PLATFORM PRESENTATION

MUSCLE CO-CONTRACTION DURING WALKING: COMPARISONS BETWEEN YOUNG AND ELDERLY WOMEN. Dias J, Alencar M, Arantes P, Kirkwood R, Dias R; Physical Therapy Department, Federal University of Minas Gerais, Belo Horizonte, Brazil

PURPOSE: The objective of this study was to compare co-contraction levels between young and elderly women with regard to the vastus lateralis and biceps femoris (VL-BF) and the tibialis anterior and gastrocnemius (TA-GAS) muscles, 200 ms before and after initial contact (IC) during gait. Comparisons of gait velocity, knee and ankle angles at IC and work for body mass (W/BM) were also analyzed. RELEVANCE: An investigation into the presence of co-contractions as a possible strategy adopted by the elderly during this initial contact phase and its correlations with kinematics alterations in gait and muscle performance, may contribute to a better understanding of the mechanisms of dynamic joint stabilization. This evidence may also contribute with important information to the existing body of knowledge and assist in the elaboration of more efficient strategies for gait training. PARTICIPANTS: Forty women participated in this study: 20 young (20-27 yrs; 22.5±2.21 yrs) and 20 elderly (65-79 yrs; 71±4.23 yrs). The volunteers had to meet the following criteria: live independently in the community, be capable of walking without an assistance device and be sedentary in accordance with the classification of the American College of Sports Medicine (ACSM). This study was approved by the Federal University Ethics Committee-number 2004/579. METHODS: Muscle co-contraction was assessed through surface electromyography and kinematics parameters during gait. Gait velocity and knee and ankle joint angles at initial contact were obtained by motion analysis system. Work normalized by body mass was obtained through concentric contractions using isokinetic dynamometry. ANALYSIS: Distribution of data was tested by the Shapiro-Wilk and Lilliefors tests and the homogeneity of variance was tested by the Cochran and Bartlett tests. ANOVA with posterior average comparisons (Student-t test) was performed to compare groups regarding to variables of co-contraction levels, gait velocity, knee and ankle joint angles at initial contact and W/BM. The observed co-contraction levels, kinematics parameters and muscle performance in each group were analyzed by Pearson correlation test. The level of significance was set at 5%. RESULTS: The elderly women co-contracted VL-BF and TA-GAS more than the young women both before and after IC (p≤0.0005). Gait velocity and W/BM were lower for older women (p≤0.0003). No differences were observed with regard to joint angles (p≥0.493). For the younger group, moderate correlations were only observed between TA-GAS co-contractions before IC and dorsiflexor W/BM (r = 0.504; p = 0.024) and plantar flexors W/BM (r = 0.602; p = 0.005. CONCLUSIONS: Elderly women showed higher levels of co-contraction of the VL-BF and TA-GAS during the initial contact phase of the gait when compared with young women. This increase in co-contraction may be a strategy the elderly adopt to ensure dynamic joint stability and be better prepared for potentially unstable situations during gait. However, the possible factors associated to this phenomenon are not yet completely known and require future studies to elucidate this issue. IMPLICATIONS: It is likely that these adaptations are strategies to compensate for present limitations due to the aging process and a means of maintaining functionality. The results of this study suggest that physical therapy programs for elderly women might be beneficial to enhance these adaptations. KEYWORDS: elderly, young, co-contraction. FUNDING ACKNOWLEDGEMENTS: Financial support: CNPq – Brazilian Funding Research Agency. CONTACT: jmdd@ufmg.br

ETHICS COMMITTEE: Federal University Ethics Committee-number 2004/579.