Lower Extremity Support during Toddler Gait S.Potoczny 1, D.G.E. Robertson 1 & H. Sveistrup 1,2 1 School of Human Kinetics and 2 School of Rehabilitation Sciences,University of Ottawa Hypothesis: Hypothesis: Toddler support moments, net moments and powers will differ from adults and will develop to more adult like patterns over the first year of walking. Purpose: Purpose: To examine whether toddler lower extremity support moments, net moments of force and their powers differ from that of adults and to determine if and when these kinetic patterns develop within the first year of walking. Conclusion: Conclusion: Toddler support moments, net moments and powers all differ from that of adults. Toddler joint kinetics also develop over the first year of walking. There is a general trend in the lower limb joint kinetics to develop patterns closer to that of ?normal adult-like joint kinetics from ankle to hip?. Figure 2. Is “falling while walking” reflected in the toddler support moments? Do toddler support moments show increasingly greater control becoming more adult-like over the first year of walking? Support moment curves of individual steps for a one, two, four, five, nine and eleven month autonomous walker are plotted. Also plotted are adult (mean +/-sd; data from Winter, 1980) support moment curves for both natural and slow walking cadences. Note the different scalings for the adult support moments. Toddler support moments are approximately two-fold smaller than adults in relative amplitude. Also, the first twenty percent of stride for both the one and two month walker show negative support moments in approximately 50% of the trials indicating a controlled fall during the initial part of stance period. The number of steps with negative support moments then diminish for the four and five month walkers, while the nine and eleven month walkers’ support moments show minimal to no negative values. The amplitudes of the support moments increase over the first year of walking indicating greater contributions by the moments of force during stance. Figure 4. Does the progression observed in the toddler joint moments show similar progression in the moment power production? Is development of gait characterized by a sequential development of moment power production? Hip, knee, and ankle powers (mean +/-sd) for three toddlers (one, five and eleven month autonomous walkers) and adult slow walking (mean +/- sd; data from Winter 1991). All moments were normalized to body mass and to percent of stride. Note the different scalings of the adult slow ankle powers. The vertical dotted line represents the foot strike of the right foot and the beginning of stance phase. Despite the differences in toddler and adult ankle moment power amplitudes, a very similar pattern of power production occurs at the ankle throughout the first year of walking. This was evident in both the ankle moment powers as well as the correlation ranges of 0.37 to 0.87, 0.57 to 0.93 and 0.18 to 0.88 for the one, five and eleven month walkers respectively. The knee power production correlation ranges of to 0.36, to 0.44 and to 0.55 show that the increases in power production by the fifth month corresponds to a development into a more adult-like pattern. By the fifth month the hip also begins to exhibit a more adult like pattern as seen in the average correlations of 0.25, and 0.45 for the one, five and eleven month walkers, respectively, but begins to exhibit more adult-like power production amplitudes by the first year of walking as seen by the hip powers. Figure 3. Is the transition observed in the support moments reflected by a parallel transition in joint moments? Is the development of gait characterized by a sequential development of joint moments? Support, hip, knee, and ankle moments (mean +/-sd) for three toddlers (one, five and eleven months autonomously walking) and adult slow walking (mean +/-sd; data from Winter, 1980) are plotted. All moments were normalized to body mass and percent of stance. Extensor moments are plotted as positive values and flexor moments plotted as negative values. Note the different range on the y axis of the adult slow graphs. Pearson product-moment correlation ranges were also obtained for each toddler by comparing adult slow walking mean curves with each toddler walking step to obtain the range of correlations. Correlation averages were obtained by dividing the sum of the range correlation values by the number of steps (between 6 and 15) analyzed for that toddler. Although the amplitude of the joint moments remain approximately two-fold lower than that of adults, the pattern of joint flexor and extensor moments approaches that of the adult pattern over the first year. This transition in the pattern of extensor and flexor moments is characterized by a sequential development over the first year of walking beginning with the ankle, proceeding to the knee and then the hip. The pattern of ankle joint moment is adult-like after as little as one month of walking and remains consistent over the first year of walking as indicated by both the shape of the moment curves and the correlation ranges and (averages) of 0.78 to 0.95 (0.87), 0.68 to 0.98 (0.86) and 0.78 to 0.98 (0.89) for the one, five and eleven month autonomous walkers respectively. The patterns of knee moments develop over this first year as seen by the increase in the range and (average) correlation values from to 0.36 (0.04), to 0.47 (0.18) and 0.1 to 0.84(0.49) and the change in shape of the joint moment curve. Even with this development of the knee moment by 11 months, the knee has an inconsistent flexor moment that spans less of the stance phase then adults and is only present in approximately half of the trials. The hip also develops over this first year of independent walking as indicated by the correlation ranges and (averages) of to 0.74 (0.29), to 0.85 (0.61) and 0.09 to 0.84 (0.43) for the one, five and eleven month walkers, but even by the first year of walking the hip continues to remain in extension longer and lacks the shift to a flexor moment around midstance. These data suggest that joint moment development occurs from distal to proximal. It is hypothesized that this order of developmental occurs as a function of the increased resources utilized for posture control by toddlers with less walking experience. Methodology Acknowledgements: These experiments were funded in part through an operating grant from the Natural Sciences and Engineering Research Council of Canada. Stefan Potoczny holds a Ontario Graduate scholarship and a academic excellence scholarship. Heidi Sveistrup is a Career Scientist with the Ministry of Health and Long-term Care of Ontario. & References: Brenière Y, Bril B (1988) Why does the child walk in falling while the adult falls in walking? C. R. Acad. Sci. Paris, 111: Robertson DGE (2002) Schneider K, Zernicke R (1992) Mass, center of mass, and moment of inertia estimates for infant limb segments. J. Biomechanics, 25: Winter DA (1980) Overall principle of lower limb support during stance phase of gait. J. Biomechanics, 13: Winter DA (1991) The Biomechanics and Motor Control of Human Gait. Waterloo: Waterloo Biomechanics. Participants: Thirteen healthy toddlers autonomously walking for less than a year participated in this study. Procedure: Ground reaction forces were recorded (240 Hz) and video images (3 cameras; 60 Hz) as toddlers walked toddlers walked unsupported across two AMTI force platforms. Eight reflective surface markers were placed over the anterior superior iliac spine, sacrum, greater trochanter, knee, tibial tuberosity, ankle, heel and fifth metatarsophalangeal joint. Toddler body segment parameters (BSP) were recorded according to Schneider and Zernicke (1992) and were used in inverse dynamics calculations. Steps were included for analysis if all surface markers were visible in at least two cameras, if the right foot only was in full contact with a single plate, and if the toddler was not running or toe walking. Between six and fifteen steps were analyzed for each toddler. All calculations were done using the Biomech software (Robertson, 2002). Results Table 1. Subject Characteristics and Body Segment Parameters Table 2. Gait Characteristics IFS Figure 1. Illustration of a toddler with digitized segments and force signature overlaid for that trial. Support Moments % Stance Net and Support Moments Moment Powers % Stride Introduction Walking is one of the most purposeful and fundamental movement patterns for humans. The first two years of life are characterized by some of the greatest physical development and motor ability changes in a child including the acquisition of gait, yet there is little research available on the kinetic gait patterns of toddlers. Brenière & Bril (1988) proposed that children within their first few months of independent walking actually “walk while falling,” whereas adults “fall while walking.” The purpose of this study was to determine whether this transition was consistent with developmental changes resulting in increasingly adult-like support moments as well as net moments and powers. Moment / Body Mass (N.m/kg) Power / Body Mass (Watts/kg)