This study aimed to review previous studies on APAs in children, particularly focusing on muscle activation and center of pressure (COP) as key variables.
Databases searched included PubMed, Scopus, and Google scholar. Inclusion criteria encompassed studies investigating APAs in children aged 3 to 18 years. Data extraction focused on temporal and quantitative parameters from force-plate and electromyography (EMG) measurements. Assessment of study quality was using the Newcastle Ottawa Scale (NOS). Data were meta-analyzed if studies employed similar measurements; otherwise, the results were reviewed narratively.
Fifty studies were included, with 46 focusing on typical development (TD) children and 29 on children with special health need conditions, including cerebral palsy (CP) (15 studies), developmental coordination disorder (DCD) (5 studies), autism spectrum disorder (ASD) (5 studies) and others (4 studies). Most studies utilized force-plate (31 studies) and EMG (29 studies) measurements.
Although the APAs period's end was consistently defined as 50 ms after the initiation of focal movement, onset latencies varied by task. For example, APAs onset ranged from 100 ms before focal movement initiation during forearm reaching in sitting to 150 ms for a single-leg task.
Developmentally, muscle onset latencies begin around ages 3-4, with latencies occurring approximately 500 ms before gait initiation and single-leg stance. As age increases, onset latencies progressively occur earlier, but those aged 14-16 haven’t yet reached adult-like latencies.
Moreover, increased task difficulty corresponded with greater peak COP displacement and muscle activation amplitudes during APAs in TD children. For instance, in load lifting, COP peak displacement increased from 10.8% to 15.65% foot length under light and heavy conditions. Muscle activity also intensified, with medial hamstring activation rising from 700% to 1000% baseline under different loads.
Compared to TD children, the results show delayed postural muscle onsets in children with DCD in the contralateral external oblique in goal-directed reaching and single-leg tasks in standing (SMD = 1.77, 95% CI [0.82, 2.71]), and in children with CP in the erector spinae during standing task (load lifting, catching and bilateral arm flexion) (SMD = 0.77, 95% CI [0.19, 1.36]). In the bimanual load lifting task in sitting, delayed postural muscle inhibition onsets in children with DCD in the brachioradialis (SMD = 0.99, 95% CI [0.47, 1.52]) compared with TD children.
This review reconfirms APAs maturation is a gradual process extending into late adolescence, with children diagnosed with DCD, CP, and ASD experiencing significant delays However, the heterogeneity of the included studies limits the generalizability of these findings.
Despite differing underlying mechanisms, the large effect sizes shared challenges in APAs among these groups, suggesting potential for common therapeutic approaches, such as task-specific training, to address APAs deficits across diverse populations.
Children
Electromyography
