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During walking, falling is most likely to occur towards the side of the supporting lower limb during the single stance. Timely lateral redirection of the centre of mass (CoM) preceding the no-return position is necessary for balance. We analysed the curvature peaks (the inverse of the radius of curvature) of the three-dimensional path of the CoM during the entire stride. Twelve healthy adults walked on a force-sensorized treadmill at constant velocities from 0.4 to 1.2 m s -1 , in 0.2 m s -1 increments. The three-dimensional displacements of the CoM, the muscular power sustaining the CoM motion with respect to the ground, and the efficiency of the pendulum-like transfer of the CoM were computed via the double integration of the ground reaction forces. The curvatures of the CoM trajectory were measured (Frenet-Serret formula). During the single stance, the curvature showed a bell-shaped increment, lasting a few tenths of a millisecond, and peaking at 365-683 m -1 (radius of 2.7-1.4 mm, respectively), the higher the walking velocity. The CoM was redirected towards the swinging lower limb. The curvature increment was sustained by muscle-driven braking of the CoM. Smoother increments of curvature (peaking at approximately 37-150 m -1 ), further orienting the CoM towards the leading lower limb, were observed during the double stance. The peaks of the curvatures were symmetric between the two sides. The high curvature peaks during the single stance may represent an index of dynamic balance during walking. This index might be useful for both rehabilitation and sports training purposes., (Copyright © 2021 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Few studies have investigated the kinematic aspects of the body centre of mass motion, that is, its three-dimensional path during strides and their changes with child development. This study aimed to describe the three-dimensional path of the centre of mass in children while walking in order to disentangle the effect of age from that of absolute forward speed and body size and to define preliminary pediatric normative values. The three-dimensional path of the centre of mass during walking was compared across healthy children 5-6- years (n = 6), 7-8 years (n = 6), 9-10 years (n = 5), and 11-13 years of age (n = 5) and healthy adults (23-48 years, n = 6). Participants walked on a force-sensing treadmill at various speeds, and height normalization of speed was conducted with the dimensionless Froude number. The total length and maximal lateral, vertical, and forward displacements of the centre of mass path were calculated from the ground reaction forces during complete strides and were scaled to the participant's height. The centre of mass path showed a curved figure-of-eight shape. Once adjusted for speed and participants' height, as age increased, there was a decrease in the three-dimensional parameters and in the lateral displacement, with values approaching those of adults. At each step, lateral redirection of the centre of mass requires brisk transient muscle power output. The base of support becomes relatively narrower with increasing age. Skilled shortening of the lateral displacement of the centre of mass may therefore decrease the risk of falling sideways. The three-dimensional path of the centre of mass may represent maturation of neural control of gait during growth.

Gait analysis (GA) typically includes surface electromyographic (sEMG) recording from several lower limb muscles, optoelectronic measurement of joint rotations, and force recordings from ground-based platforms. From the latter two variables, the muscle power acting on the lower limb joints can be estimated. Recently, gait analysis on a split-belt force treadmill (GAFT) was validated for the study of adult walking. It showed high reliability of spatiotemporal, kinematic, dynamic, and sEMG parameters, matching those obtainable with GA on the basis of ground walking. GAFT, however, still needs validation in children. Potential differences with respect to adult GAFT relate to (a) possible high signal-to-noise ratio, given the lower forces applied; (b) higher differences between treadmill and over-ground walking; and (c) limited compliance with the experimental setup. This study aims at investigating whether GAFT provides results comparable with those obtainable from ground walking in children and consistent with results from GAFT in adults. GAFT was applied to three groups of healthy children aged 5-6 years (n=6), 7-8 years (n=6), and 9-13 years (n=8) walking at the same average speed spontaneously adopted overground. The results were compared with those obtained from another study applying GA to an age-matched and speed-matched sample of 47 children, and with those obtained from GAFT in adults. The reliability (as indicated by the SD) of both spatiotemporal and dynamic parameters was higher in GAFT compared with GA. In the 5-6-, 7-8-, and 9-13-year-old groups, at average speeds of 0.83, 1.08, and 1.08 m/s, step length was shorter by 9.19, 3.57, and 2.30% compared with GA in controls at comparable speeds, respectively. For the youngest group, a lower power generation from the plantar flexors (peak power: 1.35±0.32 vs. 2.11±1.02 W/kg) and a slightly more flexed posture of the hip, knee, and ankle joints were observed during GAFT compared with GA in controls. The other gait parameters were very similar between the GAFT and the GA groups. The shortening of step length during GAFT, relative to GA at superimposable speed, was on average of all children 6.8%, in line with the 8% decrease found in adults. The profiles of sEMG and joint rotations, and all of the weight-standardized joint power parameters, matched those recorded in adults. The entire experimental session lasted about 1 h. All children complied with the experimental setting and easily completed the requested tests. In conclusion, GAFT seems to be a promising alternative to conventional GA in children.

In healthy adults, the step length/cadence ratio [walk ratio (WR) in mm/(steps/min) and normalized for height] is known to be constant around 6.5 mm/(step/min). It is a speed-independent index of the overall neuromotor gait control, in as much as it reflects energy expenditure, balance, between-step variability, and attentional demand. The speed independence of the WR in patients with multiple sclerosis (MS), and its capacity to discriminate (a) across patients with MS and controls and (b) among disability levels in MS were tested. The WR was computed in 30 outpatients with MS [20 women, 10 men; Extended Disability Status Scale (potential range: 0-10, observed median 3.5, range 2.5-5.0)] walking at free speed (range: 0.43-1.67 ms), and in 30 healthy controls (20 women, 10 men) at free and slow speed (range: 0.55-1.67 ms). The WR was 6.38±0.66 in controls versus 5.36±0.86 in patients with MS (P<0.000), independent of age, sex, and walking speed. The WR was 5.95±0.69 and 4.90±0.70 in patients with an Extended Disability Status Scale score (P<0.001) below or above the median, respectively, independent of the disease duration (P<0.000). In patients with MS, the WR is a disability-sensitive index of neuromotor control of gait, and thus a promising outcome measure for treatments aimed at improving motor coordination.

During straight walking, the body centre of mass (CM) follows a 3D figure-of-eight ("bow-tie") trajectory about 0.2 m long and with sizes around 0.05 m on each orthogonal axis. This was shown in 18 healthy adults walking at 0.3 to 1.4 ms⁻¹ on a force-treadmill (Tesio and Rota, 2008). Double integration of force signals can provide both the changes of mechanical energy of the CM and its 3D displacements (Tesio et al., 2010). In the same subjects, the relationship between the tangential speed of the CM, Vt, the curvature, C, and its inverse--the radius of curvature, r(c), were analyzed. A "power law" (PL) model was applied, i.e. logVt was regressed over logr(c). A PL is known to apply to the most various goal-directed planar movements (e.g. drawing), where the coefficient of logr(c), β, usually takes values around 13. When the PL was fitted to the whole dataset, β was 0.346 and variance explanation, R², was 59.8%. However, when the data were split into low- and high-curvature subsets (LC, HC, arbitrary cut-off of C=0.05 mm⁻¹, r(c)=20mm), β was 0.185 in the LC (R² 0.214) and 0.486 in the HC (R² 0.536) tracts. R² on the whole dataset increased to 0.763 if the LC-HC classification of the forward speed and their interaction entered the model. The β coefficient, the curvature C, and the pendulum-like recovery of mechanical energy were lower during the double foot-ground contact phase, compared to the single contact. Along the CM trajectory, curvature and muscle power output peaked together around the inversions of lateral direction. Non-zero torsion values were randomly distributed along 60% of the trajectory, suggesting that this is not segmented into piecewise planar tracts. It is proposed that the trajectory can be segmented into one tract that is more actively controlled (tie) where a PL fits poorly and another tract which is more ballistic (bow) where a PL fits well. Results need confirmation through more appropriate 3D PL modelling., (Copyright © 2010 Elsevier Ltd. All rights reserved.)

Three-dimensional (3D) path of the body centre of mass (CM) over an entire stride was computed from ground reaction forces during walking at constant average speed on a treadmill mounted on 3D force sensors. Data were obtained from 18 healthy adults at speeds ranging from 0.30 to 1.40 ms(-1), in 0.1 ms(-1) increments. Six subsequent strides were analyzed for each subject and speed (total strides=1296). The test session lasted about 30 min (10 min for walking). The CM path had an upward concave figure-of-eight shape that was highly consistent within and across subjects. Vertical displacement of the CM increased monotonically as a function of walking speed. The forward and particularly lateral displacements of the CM showed a U-shaped relationship to speed. The same held for the total 3D displacement (25.6-16.0 cm, depending on the speed). The results provide normative benchmarks and suggest hypotheses for further physiologic and clinical research. The familiar inverted pendulum model might be expanded to gyroscopic, "spin-and-turn" models. Abnormalities of the 3D path might flag motor impairments and recovery., (Copyright (c) 2009 Elsevier Ltd. All rights reserved.)

Objective: Gait analysis (GA) is usually performed during overground walking, with ground reactions being recorded through force platforms embedded in the floor. Body kinematics and surface electromyography (EMG) are also recorded. GA on treadmills resting on force sensors (GAFT) is rather uncommon and has been criticized on various grounds (less reliability of force records; biomechanical differences in walking kinematics and dynamics). On the other hand, the treadmill allows very fast recording of data from many successive strides, at known and constant average speeds. The goals of this study were (a) to validate a system for GAFT based on a commercially available "split-belt" force treadmill, (b) to provide evidence that data can be compared with established norms from overground GA, and (c) to lend support to the potential clinical validity of the GAFT approach., Design: The treadmill adopted here allows subjects to walk on two parallel independent treadmills. Each of them is mounted on four 3D force sensors. Eight healthy adults (four women; ages 22-35 yrs) were tested on the treadmill, each at the average walking speed he or she adopted overground (average across subjects: 1.35 +/- 0.05 m x sec(-1)). Ground reactions, hip, knee, and ankle sagittal rotations, torques, power, and surface EMG from four thigh and leg muscles were recorded simultaneously., Results: Results were compared with those relating to a sample of 40 healthy adults (20 women; manufacturer's data, replicating published data) walking on floor-embedded force platforms (age 20-40 yrs; speed 1.33 +/- 0.06 m x sec(-1)). An 8% shorter stride length was adopted on the treadmill. All of the other results matched those obtainable overground., Conclusions: The results suggest that GAFT performed on the tested treadmill is a promising method of GA in a clinical setting.