Developmental constraints of quadrupedal coordination across crawling styles in human infants

Abstract

Human infants can crawl using several very different styles; this diversity appears at first glance to contradict our previous findings from hands-and-knees crawling, which suggested that there were strict limitations on coordination, imposed either mechanically or by the developing nervous system. To determine whether coordination was similarly restricted across crawling styles, we studied free crawling overground in 22 infants who used a number of different locomotor strategies. Despite the wide variety in the use of individual limbs and even the number of limbs used, the duration of the stance phase increased with duration of cycle, whereas the duration of the swing phase remained more constant. Additionally, all infants showed organized, rhythmic interlimb coordination. Alternating patterns (e.g., trotlike) predominated (86% of infants). Alternatively, yet much less frequently, all limbs used could work in synchrony (14% of infants). Pacelike patterns were never observed, even in infants that crawled with the belly remaining in contact with the ground so that stability was not a factor. To explore the robustness of the interlimb coordination, a perturbation that prolonged swing of the leg was imposed on 14 additional infants crawling on hands and knees overground or on the treadmill. The perturbation led to a resetting of the crawling pattern, but never to a change in the coordination of the limbs. The findings concur with those regarding other infant animals, together suggesting that the nervous system itself limits the coordination patterns available at a young age.

Coupling of upper and lower limb pattern generators during human crawling at different arm/leg speed combinations

“…The current protocol required participants to crawl on their hands-and-feet with the purpose of making comparisons to quadrupedal locomotion. Human infants typically crawl on their hands-and-knees; however, hand-and-foot crawling is occasionally observed (Patrick et al 2012). If the current protocol was used in adults who crawled on hands-and-knees, this would lead to a decrease in the functional length in the lower limbs.…”

The development of motor behavior

“…They may log roll from place to place or pivot in circles using auditory information to calculate the shortest rotational distance to their caregivers . As shown in Figure , some infants belly crawl, using limbs, head, and belly in various combinations for support and propulsion . The belly rests continually on the floor or bumps up and down during each cycle.…”

A new twist on old ideas: how sitting reorients crawlers

“…Sitting needn't be stationary. Infants can locomote in a sitting posture by bum shuffling over flat ground, sliding down slopes, and scooting down steps and drop-offs (Adolph, 1997; Fox, Palmer, & Davies, 2002; Kretch & Adolph, 2013; Patrick, Noah, & Yang, 2012). Similarly, the hands-and-knees posture is not limited to active locomotion.…”