Mechanical work and power analysis in the joints of the lower extremity of adults with down syndrome during plane walking

Individuals with Down syndrome (DS) use a different motor gait strategy than healthy people. This study aims at analyzing plane walking differences between two groups of normally developed (ND) subjects and subjects with DS in terms of the generated mechanical power and work in the joints of the lower limb. Thirty-nine adults including two groups of 21 subjects with DS (age: 21.6 ± 7 years (mean ± SD)) and 18 ND subjects (age: 25.1 ± 2.4 years) participated in this study. Gait data and ground reaction forces were acquired using a quantitative movement analysis system composed of an optoelectronic motion analyzer (Elite2002, BTS) with eight infrared cameras, and two force platforms mounted in the middle of walkway. Mechanical power and work exchanges were computed during the stance phase by dedicated software, and then compared between the two groups (significance level: p-value = 0.05). Results showed that the mechanical power at the ankle joint was significantly larger in ND subjects compared to subjects with DS (0.084 ± 0.015 vs 0.027 ± 0.010 W/kg). The mechanical work of the ankle joint and the knee joint was significantly lower in ND compared to DS (0.015 ± 0.013 vs 0.028 ± 0.008 kJ/kg.m, and 0.066 ± 0.031 vs 0.109 ± 0.023 kJ/kg.m, respectively). For both groups, the mechanical work done by knee was less than that performed at the ankle and hip level, which might indicate that the knee muscles mainly absorb the energy, rather than generate it. Our results suggest that the subjects with DS walk with a different motor strategy than normal subjects in terms of mechanical power and work in the joints of the lower extremity. Further investigations are warranted to study the relation between these parameters and gait strategy in subjects with DS, which can lead to better rehabilitative strategies