Development of pendulum mechanism and kinematic coordination from the first unsupported steps in toddlers

Abstract

In addition, in the on-line version, the first sentence of the second paragraph of the subsection 'Relation with speed' in the Results (p. 3805) should read: Fig.·5A shows the R vs Fr function for our toddlers at the first unsupported steps, 1-5·months later, for children older than 2·years of age, and for adults.The print version of the article is correct.We apologise to authors and readers for any inconvenience these errors may have caused. 3797Spatiotemporal dynamics of normal walking in human adults is governed by general principles, including mechanisms of propulsion, stability, kinematic coordination and mechanical energy exchange (Alexander, 1989;Capaday, 2002;Dietz, 2002;Lacquaniti et al., 1999;Poppele and Bosco, 2003;Saibene and Minetti, 2003;Vaughan, 2003;Winter, 1991). One basic mechanism of walking is represented by the inverted pendulum model in which the centre of mass (COM) of the body vaults over the stance leg in an arc (Cavagna et al., 1963(Cavagna et al., , 1976. Kinetic energy in the first half of the stance phase is transformed into gravitational potential energy, which is partially recovered as the COM falls forward and downward in the second half of the stance phase. Recovery of mechanical energy by the pendulum mechanism depends on speed, amounting to a maximum of about 65% around the natural preferred speed (Cavagna et al., 1976).The principle of dynamic similarity states that geometrically similar bodies that rely on pendulum-like mechanics of movement have similar gait dynamics at the same Froude number, i.e. all lengths, times and forces scale by the same factors (Alexander, 1989). The Froude number (Fr) is given by Fr=V 2 g -1 L -1 , where V is the average speed of locomotion, g the acceleration of gravity, and L the leg length. Fr is directly proportional to the ratio between the kinetic energy and the gravitational potential energy needed during movement. Dynamic similarity implies that the recovery of mechanical energy in subjects of short height, such as children (Cavagna et al., 1983;Schepens et al., 2004), Pygmies (Minetti et al., 1994) and dwarfs (Minetti et al., 2000), is not different from that of normal sized adults at the same Fr. No overt violations of the pendulum mechanism have been reported so far for legged walking on land. It has been demonstrated not only in The inverted pendulum model in which the centre of mass of the body vaults over the stance leg in an arc represents a basic mechanism of bipedal walking. Is the pendulum mechanism innate, or is it learnt through walking experience? We studied eight toddlers (about 1 year old) at their first unsupported steps, 18 older children (1.3-13 years old), and ten adults. Two infants were also tested repeatedly over a period of 4 months before the onset of independent walking. Pendulum mechanism was quantified from the kinematics of the greater trochanter, correlation between kinetic and gravitational potential energy of the centre of body mass obtained from the force plate recordings, and percentage of recovery of mech...

Humans exploit the biomechanics of bipedal gait during visually guided walking over complex terrain

“…We also calculated energy recovery, which is a measure of the efficiency of the transduction between potential and kinetic energy during walking [31,[37][38][39][40][41][42]. Percentage energy recovery (%ER) refers to the amount of work done to increase the potential energy of the COM that is recovered in the form of kinetic energy, such that…”

Development of human locomotion

“…Unsupported walking is jerky and variable, with poor balance over the single support leg (while swinging the contralateral leg), the arms raised above the waist (as balance poles), legs splayed wide apart, and short variable steps [5 , 25,[54][55][56][57][58][59]. Double support is relatively prolonged, while swing is brief.…”

“…Also, non-plantigrade gait with a high foot lift represents a simple strategy to avoid stumbling and falling, while reducing foot drag owing to limited dorsiflexor activity. However, energy recovery by exchanging forward kinetic energy and gravitational potential energy of the center of body mass is very limited [55].…”

“…Moreover, walking experience rather than chronological age explains improvement in performance [5 ]. Indeed, onset of unsupported locomotion triggers the improvement of several gait parameters (speed, inter-step repeatability, trunk oscillations, tuning of planar covariance, energy recovery) relative to the previous supported locomotion [55,58]. These changes occur rapidly over the first 6 months after the onset of independent walking.…”

Changes in Step Variability of New Walkers With Typical Development and With Down Syndrome

“…By 5 months of walking experience, toddlers have combined the postural requirements for remaining upright with forward progression, leading to a decrease in step width and in lateral acceleration of the center of mass (Bril & Brenière, 1992). By 2−4 months after the onset of independent walking, toddlers begin to use their legs effectively as inverted pendulums (Hallemans, Aerts, Otten, De Deyn, & De Clercq, 2004;Ivanenko et al, 2004). That observation implies that the rhythmic pendular oscillations seen in adult walking are not innate and that before that pattern can emerge, active neural control and intersegmental coordination are required (Ivanenko et al).…”