Obstacle stepping in children: task acquisition and performance

"Walking selectivity" in the occipital place area in 8-year-olds, not 5-year-olds

A recent neuroimaging study in adults found that the occipital place area (OPA)-a cortical region involved in "visually guided navigation" (i.e. moving about the immediately visible environment, avoiding boundaries, and obstacles)-represents visual information about walking, not crawling, suggesting that OPA is late developing, emerging only when children are walking, not beforehand. But when precisely does this "walking selectivity" in OPA emerge-when children first begin to walk in early childhood, or perhaps counterintuitively, much later in childhood, around 8 years of age, when children are adult-like walking? To directly test these two hypotheses, using functional magnetic resonance imaging (fMRI) in two groups of children, 5- and 8-year-olds, we measured the responses in OPA to first-person perspective videos through scenes from a "walking" perspective, as well as three control perspectives ("crawling," "flying," and "scrambled"). We found that the OPA in 8-year-olds-like adults-exhibited walking selectivity (i.e. responding significantly more to the walking videos than to any of the others, and no significant differences across the crawling, flying, and scrambled videos), while the OPA in 5-year-olds exhibited no walking selectively. These findings reveal that OPA undergoes protracted development, with walking selectivity only emerging around 8 years of age.

Dynamic stability during level walking and obstacle crossing in children aged 2–5 years estimated by marker-less motion capture

In the present study, dynamic stability during level walking and obstacle crossing in typically developing children aged 2–5 years (n = 13) and healthy young adults (n = 19) was investigated. The participants were asked to walk along unobstructed and obstructed walkways. The height of the obstacle was set at 10% of the leg length. Gait motion was captured by three RGB cameras. 2D body landmarks were estimated using OpenPose, a marker-less motion capture algorithm, and converted to 3D using direct linear transformation (DLT). Dynamic stability was evaluated using the margin of stability (MoS) in the forward and lateral directions. All the participants successfully crossed the obstacles. Younger children crossed the obstacle more carefully to avoid falls, as evidenced by obviously decreased gait speed just before the obstacle in 2-year-olds and the increased in maximum toe height with younger age. There was no significant difference in the MoS at the instant of heel contact between children and adults during level walking and obstacle crossing in the forward direction, although children increased the step length of the lead leg to a greater extent than the adults to ensure base of support (BoS)-center of mass (CoM) distance. In the lateral direction, children exhibited a greater MoS than adults during level walking [children: 9.5%, adults: 6.5%, median, W = 39.000, p < .001, rank-biserial correlation = −0.684]; however, some children exhibited a smaller MoS during obstacle crossing [lead leg: −5.9% to 3.6% (min–max) for 4 children, 4.7%–6.4% [95% confidence interval (CI)] for adults, p < 0.05; trail leg: 0.1%–4.4% (min–max) for 4 children, 4.7%–6.4% (95% CI) for adults, p < 0.05]]. These results indicate that in early childhood, locomotor adjustment needed to avoid contact with obstacles can be observed, whereas lateral dynamic stability is frangible.

Effects of Practice on the Control of Whole-Body Momentum in Active Children and Adults

The purpose of this study was to determine the effects of practice on performance of a running task requiring maximal speed and accurate termination. Physically active pre-pubertal boys and men ran as fast as possible and stopped at a pre-determined target location. Twenty-five trials were collected and comparisons made between first five (early) and last five (late) trials. Approach velocity, normalized approach velocity (percent of maximal sprint velocity, %Vmax), stopping distance from target, and success rate were calculated. Self-efficacy for task performance and fatigue reports were collected prior to trials. Children ran more slowly than adults in absolute terms but performed at higher relative velocity. Both groups displayed similar accuracy and percentages of successful trials across early and late practice. Adults increased approach velocity and %Vmax from early to late; children, already higher in relative maximal velocity, did not change. Self-efficacy paralleled performance findings and correlated with %Vmax and success rate; both groups reported higher self-efficacy for late compared with early. With practice, adults increased approach velocity and children did not; however, children appeared to be performing at a higher relative level from the beginning, perhaps reflecting their more substantial recent histories of similar physical activity and limiting further effects of practice.

Different neural substrates for precision stepping and fast online step adjustments in youth

Humans can navigate through challenging environments (e.g., cluttered or uneven terrains) by modifying their preferred gait pattern (e.g., step length, step width, or speed). Growing behavioral and neuroimaging evidence suggests that the ability to modify preferred step patterns requires the recruitment of cognitive resources. In children, it is argued that prolonged development of complex gait is related to the ongoing development of involved brain regions, but this has not been directly investigated yet. Here, we aimed to elucidate the relationship between structural brain properties and complex gait in youth aged 9–18 years. We used volumetric analyses of cortical grey matter (GM) and whole-brain voxelwise statistical analyses of white matter (WM), and utilized a treadmill-based precision stepping task to investigate complex gait. Moreover, precision stepping was performed on step targets which were either unperturbed or perturbed (i.e., unexpectedly shifting to a new location). Our main findings revealed that larger unperturbed precision step error was associated with decreased WM microstructural organization of tracts that are particularly associated with attentional and visual processing functions. These results strengthen the hypothesis that precision stepping on unperturbed step targets is driven by cortical processes. In contrast, no significant correlations were found between perturbed precision stepping and cortical structures, indicating that other (neural) mechanisms may be more important for this type of stepping.

Slow maturation of planning in obstacle avoidance in humans

Complex gait (e.g., obstacle avoidance) requires a higher cognitive load than simple steady-state gait, which is a more automated movement. The higher levels of the central nervous system, responsible for adjusting motor plans to complex gait, develop throughout childhood into adulthood. Therefore, we hypothesize that gait strategies in complex gait are likely to mature until adulthood as well. However, little is known about the maturation of complex gait from childhood into adolescence and adulthood. To address this issue, we investigated obstacle avoidance in forty-four 8- to 18-yr-old participants who walked at preferred speed along a 6-m walkway on which a planar obstacle (150% of step length, 1 m wide) was projected. Participants avoided the obstacle by stepping over this projection, while lower body kinematics were recorded. Results showed that step length and speed adjustments during successful obstacle avoidance were similar across all ages, even though younger children modified step width to a greater extent. Additionally, the younger children used larger maximal toe elevations and take-off distances than older children. Moreover, during unsuccessful trials, younger children deployed exaggerated take-off distances, which resulted in obstacle contact upon the consecutive heel strike. These results indicate that obstacle avoidance is not fully matured in younger children, and that the inability to plan precise foot placements is an important factor contributing to failures in obstacle avoidance.

Dynamic stability during running gait termination: Differences in strategies between children and adults to control forward momentum

Rapid deceleration during running is key for successful participation in most childhood activities and sports; this requires modulation of body momentum and consequent challenges to postural equilibrium. The purpose of this study was to investigate the strategies employed by adults and children to control forward momentum and terminate running gait. Sixteen young adults and 15 pre-pubertal children completed two tasks as fast as possible: an unobstructed run (RUN) and a run and stop (STOP) at a pre-determined location. For STOP, center of mass (COM) approach velocity and momentum prior to deceleration and spatiotemporal characteristics and COM position during deceleration were compared between groups. Position and velocity variables were normalized to height and maximum velocity during RUN, respectively. Children used fewer steps with relatively longer step length to decelerate over a relatively longer distance and longer time than adults. Children approached at higher relative velocity than adults, but adults approached with greater momentum. Adults positioned their COM lower and more posterior than children throughout deceleration. Our results suggest that pre-pubertal children and young adults employ different strategies to modulate body momentum, with adults exhibiting mechanics characteristic of a more stable strategy. Despite less stable mechanics, children and adults achieved similar success.

Influence of sex and maturation on knee mechanics during side-step cutting

INTRODUCTION

Females have been reported to have a three to five times greater incidence of noncontact anterior cruciate ligament injury when compared with their male counterparts. Previous research suggests that physical maturation is one factor that is associated with the development of potentially injurious lower extremity biomechanics in female athletes.

PURPOSE

The study's purpose was to determine whether lower extremity biomechanics differ between male and female soccer athletes during a cutting maneuver across different stages of maturational development.

METHODS

One hundred fifty-six soccer players (76 males and 80 females) between the ages of 9 and 23 yr participated. Subjects were classified on the basis of maturation as prepubertal, pubertal, postpubertal, or young adult. Lower extremity kinematics, kinetics, and ground reaction forces (GRFs) were obtained during a 45° side-step cutting maneuver. Differences between sex and maturation were assessed for peak knee valgus angle, knee adductor moments, and GRFs (vertical, posterior, and lateral) during weight acceptance using a two-factor ANCOVA (controlling for approach velocity).

RESULTS

No sex × maturation interactions were found for any variable of interest. On average, females exhibited greater knee abduction and adductor moments than males. Prepubertal athletes demonstrated greater knee adductor moments and GRFs than all other groups.

CONCLUSIONS

Biomechanical differences between males and females were evident across all stages of maturation. On average, less mature athletes exhibit biomechanical patterns during cutting that may place them at greater risk for injury than their more mature counterparts.

Child temporal-spatial gait characteristics and variability during uphill and downhill walking

PURPOSE

Gait maturation, evidenced in, for example, the ability to walk over nonlevel surfaces, is an important indicator of typical development in children. Therefore, the purpose of this study was to compare the walking strategies used by children and adults during hill walking.

METHODS

Temporal-spatial gait parameters and trial-to-trial coefficient of variation of these parameters were compared between 30 children (aged 3.5-5.5 years) and 30 adults during level and 15° hill walking.

RESULTS

Compared with the adult group, the child group coefficient of variation was greater during all conditions. Furthermore, unique to the child group, there was a significant increase in variability during downhill walking.

CONCLUSION

It is evident from the current results that children aged 3.5 to 5.5 years do not yet exhibit a mature gait and that downhill walking may increase fall risk. Attention should be given to gait variability and nonlevel walking when investigating or training children's gait.