Use it or lose it? Effects of age, experience, and disuse on crawling

Reevaluating the energy cost in locomotion: quadrupedal vs. bipedal walking in humans

This study examines the energy expenditure and physiological responses associated with short-term quadrupedal locomotion compared to bipedal walking in humans. It aims to support evolutionary theory and explore quadrupedal locomotion's potential for enhancing fitness and health. In a randomized crossover design, 12 participants performed quadrupedal and bipedal walking on a treadmill at identical speeds. Physiological responses, including energy expenditure, carbohydrate oxidation rates, respiratory rate, and heart rate, were measured during both forms of locomotion. Quadrupedal walking significantly increased total energy expenditure by 4.15 Kcal/min [95% CI, 3.11 - 5.19 Kcal/min], due to a rise in carbohydrate oxidation of 1.70 g/min [95% CI, 1.02 - 2.24 g/min]. It also increased respiratory and heart rates, indicating higher metabolic demands. The exercise mainly activated upper limb muscles and the gluteus maximus in the lower limbs. Ten minutes of quadrupedal walking at the same speed as bipedal walking resulted in a 254.48% increase in energy consumption. This simple form of locomotion offers a strategy for enhancing physical activity, and supports the idea that energy optimization influenced the evolution of efficient bipedal locomotion.

Forecasting motion trajectories of elbow and knee joints during infant crawling based on long-short-term memory (LSTM) networks

BACKGROUND

Hands-and-knees crawling is a promising rehabilitation intervention for infants with motor impairments, while research on assistive crawling devices for rehabilitation training was still in its early stages. In particular, precisely generating motion trajectories is a prerequisite to controlling exoskeleton assistive devices, and deep learning-based prediction algorithms, such as Long-Short-Term Memory (LSTM) networks, have proven effective in forecasting joint trajectories of gait. Despite this, no previous studies have focused on forecasting the more variable and complex trajectories of infant crawling. Therefore, this paper aims to explore the feasibility of using LSTM networks to predict crawling trajectories, thereby advancing our understanding of how to actively control crawling rehabilitation training robots.

METHODS

We collected joint trajectory data from 20 healthy infants (11 males and 9 females, aged 8-15 months) as they crawled on hands and knees. This study implemented LSTM networks to forecast bilateral elbow and knee trajectories based on corresponding joint angles. The data set comprised 58, 782 time steps, each containing 4 joint angles. We partitioned the data set into 70% for training and 30% for testing to evaluate predictive performance. We investigated a total of 24 combinations of input and output time-frames, with window sizes for input vectors ranging from 10, 15, 20, 30, 40, 50, 70, and 100 time steps, and output vectors from 5, 10, and 15 steps. Evaluation metrics included Mean Absolute Error (MAE), Mean Squared Error (MSE), and Correlation Coefficient (CC) to assess prediction accuracy.

RESULTS

The results indicate that across various input-output windows, the MAE for elbow joints ranged from 0.280 to 4.976°, MSE ranged from 0.203° to 59.186°, and CC ranged from 89.977% to 99.959%. For knee joints, MAE ranged from 0.277 to 4.262°, MSE from 0.229 to 53.272°, and CC from 89.454% to 99.944%. Results also show that smaller output window sizes lead to lower prediction errors. As expected, the LSTM predicting 5 output time steps has the lowest average error, while the LSTM predicting 15 time steps has the highest average error. In addition, variations in input window size had a minimal impact on average error when the output window size was fixed. Overall, the optimal performance for both elbow and knee joints was observed with input-output window sizes of 30 and 5 time steps, respectively, yielding an MAE of 0.295°, MSE of 0.260°, and CC of 99.938%.

CONCLUSIONS

This study demonstrates the feasibility of forecasting infant crawling trajectories using LSTM networks, which could potentially integrate with exoskeleton control systems. It experimentally explores how different input and output time-frames affect prediction accuracy and sets the stage for future research focused on optimizing models and developing effective control strategies to improve assistive crawling devices.

An update of the development of motor behavior

This primer describes research on the development of motor behavior. We focus on infancy when basic action systems are acquired-posture, locomotion, manual actions, and facial actions-and we adopt a developmental systems perspective to understand the causes and consequences of developmental change. Experience facilitates improvements in motor behavior and infants accumulate immense amounts of varied everyday experience with all the basic action systems. At every point in development, perception guides behavior by providing feedback about the results of just prior movements and information about what to do next. Across development, new motor behaviors provide new inputs for perception. Thus, motor development opens up new opportunities for acquiring knowledge and acting on the world, instigating cascades of developmental changes in perceptual, cognitive, and social domains. This article is categorized under: Cognitive Biology > Cognitive Development Psychology > Motor Skill and Performance Neuroscience > Development.

The development of gait and mobility: Form and function in infant locomotion

The development of locomotion can be described by its form (i.e., gait) and its function (i.e., mobility). Both aspects of locomotion improve with experience. Traditional treatises on infant locomotion focus on form by describing an orderly progression of postural and locomotor milestones en route to characteristic patterns of crawling and walking gait. We provide a traditional treatment of gait by describing developmental antecedents of and improvements in characteristic gait patterns, but we highlight important misconceptions inherent in the notion of "milestones". Most critically, we argue that the prevailing focus on gait and milestones fails to capture the true essence of locomotion-functional mobility to engage with the world. Thus, we also describe the development of mobility, including the use of mobility aids for support and propulsion. We illustrate how infants find individual solutions for mobility and how the ability to move cascades into other domains of development. Finally, we show how an integration of gait and mobility provides insights into the psychological processes that make locomotion functional. This article is categorized under: Psychology > Motor Skill and Performance Psychology > Development and Aging.

Effects of crawling exercises at home on improving young children's behavioral performance during the COVID-19 outbreak

PURPOSE

The aim of the present study was to investigate the effects of crawling exercises at home on improving young children's behavioral performance, thereby providing a reference for the role of physical activity in protecting and promoting behavioral development during the COVID-19 outbreak.

DESIGN AND METHODS

In total, 106 young children were included and randomly divided into the control group (51) and the experimental group (55). A 10-week exercise intervention was implemented, during which the control group engaged in rhythmic exercises, while the experimental group performed crawling exercises. The behavioral performance of young children was assessed using the Child Behavior Checklist before and after the intervention period.

RESULTS

Compared with before intervention, the behavior scores in the control group and the experimental group after intervention declined. In the control group, the internalizing behavior score, the externalizing behavior score, and the total behavioral score decreased by 1.12, 0.23 and 1.35 points, while those in the experimental group decreased by 1.78, 0.88 and 2.65 points, respectively. After the intervention, the experimental group behaved significantly better than the control group with regard to anxiety-depression and total behavioral performance (P < 0.05).

CONCLUSIONS

Both crawling exercises and rhythmic exercises led to a statistically significant improvement in the behavioral performance of young children. However, owing to the inherent benefits of integrating diverse movement elements and offering adaptable levels of difficulty, crawling exercises demonstrated a more prominent influence on the behavior of young children as compared to rhythmic exercises. As such, crawling can be recommended as a form of physical exercise for young children at home when outdoor activities are not feasible due to weather changes or epidemic control measures.

Muscle synergy analysis of eight inter-limb coordination modes during human hands-knees crawling movement

In order to reveal in-depth the neuromuscular control mechanism of human crawling, this study carries out muscle synergy extraction and analysis on human hands-knees crawling under eight specific inter-limb coordination modes, which are defined according to the swing sequence of limbs and includes two-limb swing crawling modes and six single-limb swing crawling modes. Ten healthy adults participate in crawling data collection, and surface electromyography (sEMG) signals are recorded from 30 muscles of limbs and trunk. Non-negative matrix factorization (NNMF) algorithm is adopted for muscle synergy extraction, and a three-step muscle synergy analysis scheme is implemented by using the hierarchical clustering method. Based on results of muscle synergy extraction, 4 to 7 synergies are extracted from each participant in each inter-limb coordination mode, which supports the muscle synergy hypothesis to some extent, namely, central nervous system (CNS) controls the inter-limb coordination modes during crawling movement by recruiting a certain amount of muscle synergies, rather than a single muscle. In addition, when different participants crawl in the same inter-limb coordination mode, they share more temporal features in recruiting muscle synergies. Further, by extracting and analyzing intra-mode shared synergies among participants and inter-mode shared synergies among the eight inter-limb coordination modes, the CNS is found to realize single-limb swing crawling modes by recruiting the four inter-mode shared synergy structures related to the swing function of each limb in different orders, and realize the two-limb swing crawling modes by recruiting synchronously two intra-mode shared synergy structures. The research results of the muscle synergy analysis on the eight specific inter-limb coordination modes, on the one hand, provide a basis for muscle synergy hypothesis from the perspective of crawling motion, on the other hand, also provide a possible explanation for the choice of the inter-limb coordination mode in human crawling.

Locomotor learning in infants at high risk for cerebral palsy: A study protocol

Background

Physical disability in individuals with cerebral palsy (CP) creates lifelong mobility challenges and healthcare costs. Despite this, very little is known about how infants at high risk for CP learn to move and acquire early locomotor skills, which set the foundation for lifelong mobility. The objective of this project is to characterize the evolution of locomotor learning over the first 18 months of life in infants at high risk for CP. To characterize how locomotor skill is learned, we will use robotic and sensor technology to provide intervention and longitudinally study infant movement across three stages of the development of human motor control: early spontaneous movement, prone locomotion (crawling), and upright locomotion (walking).

Study design

This longitudinal observational/intervention cohort study (ClinicalTrials.gov Identifier: NCT04561232) will enroll sixty participants who are at risk for CP due to a brain injury by one month post-term age. Study participation will be completed by 18 months of age. Early spontaneous leg movements will be measured monthly from 1 to 4 months of age using inertial sensors worn on the ankles for two full days each month. Infants who remain at high risk for CP at 4 months of age, as determined from clinical assessments of motor function and movement quality, will continue through two locomotor training phases. Prone locomotor training will be delivered from 5 to 9 months of age using a robotic crawl training device that responds to infant behavior in real-time. Upright locomotor training will be delivered from 9 to 18 months of age using a dynamic weight support system to allow participants to practice skills beyond their current level of function. Repeated assessments of locomotor skill, training characteristics (such as movement error, variability, movement time and postural control), and variables that may mediate locomotor learning will be collected every two months during prone training and every three months during upright training.

Discussion

This study will develop predictive models of locomotor skill acquisition over time. We hypothesize that experiencing and correcting movement errors is critical to skill acquisition in infants at risk for CP and that locomotor learning is mediated by neurobehavioral factors outside of training.Project Number 1R01HD098364-01A1.ClinicalTrials.gov Identifier: NCT04561232.

Real-Time Assembly of Coordination Patterns in Human Infants

Flexibility and generativity are fundamental aspects of functional behavior that begin in infancy and improve with experience. How do infants learn to tailor their real-time solutions to variations in local conditions? On a nativist view, the developmental process begins with innate prescribed solutions, and experience elaborates on those solutions to suit variations in the body and the environment. On an emergentist view, infants begin by generating a variety of strategies indiscriminately, and experience teaches them to select solutions tailored to the current relations between their body and the environment. To disentangle these accounts, we observed coordination patterns in 11-month-old pre-walking infants with a range of cruising (moving sideways in an upright posture while holding onto a support) and crawling experience as they cruised over variable distances between two handrails they held for support. We identified infants' coordination patterns using a novel combination of computer-vision, machine-learning, and time-series analyses. As predicted by the emergentist view, the least experienced infants generated multiple coordination patterns inconsistently regardless of body size and handrail distance, whereas the most experienced infants tailored their coordination patterns to body-environment relations and switched solutions only when necessary. Moreover, the beneficial effects of experience were specific to cruising and not crawling, although both skills involve anti-phase coordination among the four limbs. Thus, findings support an emergentist view and suggest that everyday experience with the target skill may promote "learning to learn," where infants learn to assemble the appropriate solution for new problems on the fly.

What Does Prone Skateboarding in the Newborn Tell Us About the Ontogeny of Human Locomotion?

The crawling behavior of sixty 2-day-old newborns was studied while they were supported prone on a mini skateboard and on a pediatric mattress without additional support. Analyses of the number and types of limb movements and their characteristics, the coactivation of limb pairs, and the displacement across the surface, revealed that newborns can crawl with locomotor patterns similar to those documented during quadrupedal locomotion in animals and human adults. This was particularly apparent on the skateboard. This discovery suggests that locomotor circuitry underlying quadrupedal locomotion develops during fetal life. Drawing upon other evidence for a quadrupedal organization underlying bipedal gait, we argue that early quadrupedal training may enhance interventions designed to hasten the onset of independent walking.