The gross motor development of a typically developing infant is a dynamic process, the intra-individual variability of which can be investigated through longitudinal assessments. Changes in gross motor development vary, according to the interaction of multiple sub-systems within the child, environment, task setting, and experience or practice of movement. At present, studies on environmental factors that influence gross motor development in full-term infants over time are limited. The main aim of this study was to investigate environmental factors affecting intra-individual variability from birth to 13 months. The gross motor development of 41 full-term infants was longitudinally assessed every month from the age of 15 days using the Alberta Infant Motor Scale. Parents were interviewed monthly about environmental factors during childcare. Infants showed fluctuations in the percentile of gross motor development, and no systematic pattern was detected. The total mean range of gross motor percentile was 65.95 (SD = 15.74; SEM = 2.28). The percentiles of gross motor skills over the 14 assessments ranged from 36 to 93 percentile points. Factors that were significantly associated with the gross motor development percentile were the use of a baby walker (Coef. = −8.83, p ≤ 0.0001) and a baby hammock (Coef. = 7.33, p = 0.04). The use of baby hammocks could increase the gross motor percentile by 7.33 points. Although the usage of a baby walker is common practice in childcare, it may cause a decrease in the gross motor percentile by 8.83 points according to this study. In conclusion, healthy full-term infants exhibited a natural variability in gross motor development. Placing infants in a baby walker during the first year of age should be approached with caution due to the risk of delayed gross motor development.

Spinal Cord is the official journal of the International Spinal Cord Society. It provides complete coverage of all aspects of spinal injury and disease.

(1) Objective: To investigate the effects of play in an upright position on intra-individual variability and to examine the relationship between the variability of gross motor and language development in institutionalized infants aged six to ten months. (2) Methods: Thirty infants were conveniently enrolled in either the experimental or control groups. The Alberta Infant Motor Scale (AIMS) and the Communication and Symbolic Behavior Scales Developmental Profile (CSBS-DP) Infant/Toddler Checklist were tested pre and post each monthly intervention for three months. Sixteen infants in the experimental group received an additional program of 45 min play in an upright position three times a week for a 3-month period. (3) Results: There were significant between-group differences in intra-individual variability of the AIMS percentiles (p-value = 0.042). In addition, there was a significant difference in the intra-individual variability of the language percentile between groups (p-value = 0.009). The intra-individual variability of gross motor development was significantly correlated (r_s = 0.541; p = 0.03) with language development. (4) Conclusions: Play in an upright position could be applied to improve intra-individual variability in gross motor and language development percentiles in institutionalized infants.

Background: Patients with incomplete spinal cord injury (iSCI) and lower extremity muscle weakness often fall while standing up from a chair. The sit-to-stand (STS) task primarily uses the strength of the knee extensor muscles. The five times sit-to-stand test (FTSST) is often applied to determine lower limb function and the results are related to lower extremity muscle strength. This study explored the cut-off point for knee extensor muscle strength in patients with iSCI to independently determine their FTSST results and the correlation between knee extensor muscle strength and FTSST results. Methods: Forty-four participants were assessed for knee extensor muscle strength using a hand-held dynamometer (HHD) and the FTSST. Results: The data indicated that knee extensor muscle strength ≥ 53.06 Newton was the best independent predictor of the FTSST results (sensitivity 72.7%, specificity 72.7%). Moreover, knee extensor muscle strength was significant and correlated with the FTSST results (r = ─0.45, P = 0.035). Conclusion: The findings offer a cut-off point for the knee extensor muscle strength measured while standing up from a chair that may help medical professionals set rehabilitation goals for patients with iSCI.

Background: Postural control is vital for independent sitting in infants. Those in orphanages face environmental limitations and biological factors that affect trunk control. This study aimed to compare segmental trunk control between full-term and preterm/low-birth-weight infants and examine the correlations with daily activities. Methods: Thirty-three infants (16 full-term, 17 preterm/low birth weight) were assessed using the Segmental Assessment of Trunk Control (SATCo), and 27 were observed with the Daily Activity of Infant Scale (DAIS) over three weekdays and two weekends. Results: A slight significant difference (p < 0.05) in SATCo scores was found, with full-term infants scoring higher. Results found that both prenatal exposure and environmental factors could influence trunk control. A significant correlation (r_s = 0.771, p < 0.001) between trunk control and daily activities underscores the importance of upright and antigravity activities for postural development. A small-to-medium effect size suggested limited practical significance due to being conducted in a single orphanage with a homogeneous sample. Conclusions: The findings emphasize enhancing the orphanage environment and child-rearing practices to support trunk control development through upright posture, movement exploration, and high-quality caregiver interactions.