Abstract
This study aimed to investigate the inter-limb coordination pattern and the stability, intensity, and complexity of the trunk and limbs motions in human crawling under different speeds. Thirty healthy human adults finished hands-knees crawling trials on a treadmill at six different speeds (from 1 km/h to 2.5 km/h). A home-made multi-channel acquisition system consisting of five 3-axis accelerometers (ACC) and four force sensors was used for the data collection. Ipsilateral phase lag was used to represent inter-limb coordination pattern during crawling and power, harmonic ratio, and sample entropy of acceleration signals were adopted to depict the motion intensity, stability, and complexity of trunk and limbs respectively. Our results revealed some relationships between inter-limb coordination patterns and the stability and complexity of trunk movement. Trot-like crawling pattern was found to be the most stable and regular one at low speed in the view of trunk movement, and no-limb-pairing pattern showed the lowest stability and the greatest complexity at high speed. These relationships could be used to explain why subjects tended to avoid no-limb-pairing pattern when speed was over 2 km/h no matter which coordination type they used at low speeds. This also provided the evidence that the central nervous system (CNS) chose a stable inter-limb coordination pattern to keep the body safe and avoid tumbling. Although considerable progress has been made in the study of four-limb locomotion, much less is known about the reasons for the variety of inter-limb coordination. The research results of the exploration on the inter-limb coordination pattern choice during crawling from the standpoint of the motion stability, intensity, and complexity of trunk and limbs sheds light on the underlying motor control strategy of the human CNS and has important significance in the fields of clinical diagnosis, rehabilitation engineering, and kinematics research.
Highlights
Normal crawling is often regarded as a sign of the normal development of infants and young children [1]
Taking human adults and hands-knees crawling as research objects, this study aimed to investigate the inter-limb coordination pattern choice under different speeds from aspects of the motion stability, intensity and complexity of trunk and limbs
It can be seen that adults show a wide range of ipsilateral phase lag (IPL) values and most subjects crawl in trot-like pattern and no-limb-pairing pattern (IPL > 0.15) at low speed
Summary
Normal crawling is often regarded as a sign of the normal development of infants and young children [1]. Crawling can be divided into hand-knee type, hand-foot type, scooting type, creeping type, and mixed type, etc. The development situation of infants and young children can be evaluated by analyzing their crawling function. In the field of cerebral palsy (CP) rehabilitation [4,5], crawling is an excellent training item because it requires the patients to coordinate their multiple body parts and utilize audio and visual aids as their motion guide. In the field of neuroscience, crawling is Sensors 2017, 17, 692; doi:10.3390/s17040692 www.mdpi.com/journal/sensors
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