Extended Abstract
1.    Introduction
Gait is a complex human movement that relies on the coordinated activation of multiple muscle groups across the ankle, knee, and hip joints (1). Beyond examining gait in healthy individuals, researchers also analyze gait under various neural conditions and external stimulations (3). Once initiated, gait emerges as a repetitive pattern of lower-limb movements that transitions naturally from standing to stepping with minimal attentional demand (3). Several factors, including gender, physical fitness, and age, can influence the execution and quality of these movement patterns (2). Balance control is a fundamental component of motor function and plays a crucial role in nearly all daily activities (4). Disruptions in balance can impair other motor abilities, such as sensory integration and neuromuscular coordination (5). The vestibular system—comprising structures of the inner ear and associated neural pathways—contributes significantly to postural control, eye–head coordination, and spatial orientation, thereby helping maintain overall body stability (6). Understanding factors that affect balance is critical for reducing fall risk across the lifespan. Muscle weakness, particularly with aging, can compromise mechanical muscle function and elevate the likelihood of falls. Key lower-limb muscles such as the quadriceps, hamstrings, and gastrocnemius contribute to knee-joint stability, and alterations in their activation patterns can modify joint loading and movement efficiency (11, 12, 13). Electromyographic (EMG) analysis is widely employed in gait research as it provides valuable insights into neuromuscular contributions to biomechanical events. Given the central role of the vestibular system in maintaining postural stability, the present study aims to examine the effects of vestibular stimulation on the electrical activity of selected lower-limb muscles in active children during the stance phase of gait.
2.    Methods
This study included 30 active children aged 7–11 years from Tehran who participated in sports at least three times per week. The sample size was determined using G*Power with a statistical power of 0.80, an alpha level of 0.05, and an effect size of 0.50. Participants were screened to ensure the absence of underlying medical conditions, postural abnormalities, or lower-limb injuries (26). All ethical requirements were fulfilled, and written informed consent was obtained from both the children and their parents or guardians (IR.SSRC.REC.1403.005). An 8-channel surface electromyography system (MEGADOWIN 6000ME, Finland) with a 1000 Hz sampling frequency was used to record muscle activity. Disposable electrodes were placed over the biceps femoris, rectus femoris, gastrocnemius, soleus, tibialis anterior, and peroneus longus muscles according to the SENIAM guidelines, with a 2-cm inter-electrode distance following standard skin preparation (17). The protocol began with a pre-test session during which participants performed three maximal voluntary isometric contractions for each muscle. They then walked along a designated pathway six times (three trials with eyes open and three with eyes closed). A post-test session was conducted one day later. In this session, participants again walked the same pathway six times (three with eyes open and three with eyes closed), but only after receiving vestibular perturbation induced by controlled rotation on a turntable (five clockwise rotations and five counterclockwise rotations) (18). EMG signals were processed using a 10–500 Hz band-pass filter and a 50 Hz notch filter. The data were smoothed and normalized using the root mean square (RMS) method. Statistical analyses included descriptive statistics, the Kolmogorov–Smirnov test, repeated-measures ANOVA, and MANOVA, performed in SPSS version 22. The significance level was set at p < 0.05.

 

3.    Results
The demographic characteristics of the children participating in this study are summarized in Table 1. The mean age of the participants was 8.9 ± 0.7 years, with an average body mass of 29.4 ± 2.2 kg and a mean height of 132.9 ± 4.3 cm. The mean BMI was 16.4 ± 1.54 kg/m², indicating that the children fell within a healthy range for their age group. This homogeneity in anthropometric characteristics ensured that differences in muscle activity were primarily attributable to sensory conditions rather than physical disparities among subjects. 
Patterns of muscle activation across the four sensory conditions are illustrated in Fig. 1. Vestibular perturbation clearly influenced the electrical activity of lower-limb muscles during the stance phase of gait. Among the four conditions examined, the eyes-closed with vestibular perturbation condition elicited the highest neuromuscular demand. This was reflected in substantial increases in muscle activation, particularly in muscles responsible for postural stabilization and maintenance of mediolateral balance. As shown in Fig. 1, the soleus muscle demonstrated the greatest response to vestibular challenges, reaching a mean activation of 0.7572 mV/s. This elevated activity suggests that children relied heavily on the ankle plantarflexors to compensate for the reduced reliability of vestibular and visual input. Increased activation was also observed in the biceps femoris and peroneus longus, indicating enhanced recruitment of both posterior-chain and lateral stabilizing muscles when balance became more challenging. Statistical analyses confirmed that the differences in muscle activity across the sensory conditions were significant at p < 0.01. This finding indicates that vestibular disturbances produced measurable and meaningful alterations in neuromuscular control during the stance phase of walking. The consistent rise in muscle activation under perturbed conditions—particularly in the absence of vision—reflects the increased postural difficulty imposed by reduced vestibular function. Overall, the findings depicted in Fig. 1 demonstrate that vestibular perturbation disrupts normal gait regulation, prompting children to increase activation in specific lower-limb muscles involved in stability, joint protection, and control of sway. These results highlight the essential contribution of vestibular input to maintaining coordinated muscle function during gait and underscore the susceptibility of children’s neuromuscular systems to balance-related challenges. 
4.    Discussion
This study investigated the influence of vestibular perturbations on lower-limb muscle activity in children during gait. The findings demonstrated significant increases in the activation of the biceps femoris, soleus, and peroneus longus muscles, indicating that the vestibular system plays a central role in dynamic balance regulation. When vestibular input becomes unreliable, the body activates compensatory neuromuscular mechanisms to maintain postural stability, leading to heightened muscle activity—an observation consistent with previous research (28).
Earlier studies have shown that targeted vestibular stimulation can enhance balance performance in children with vestibular dysfunction (28), and that visual input serves as a critical source of sensory information for postural control (29). As balance ability improves progressively between the ages of 3 and 19 years (30), the developmental stage of the children in this study may explain their pronounced reliance on multisensory integration during gait. Evidence also suggests that short-term vestibular-based interventions enhance motor performance in children with neurological conditions, such as cerebral palsy (31), while external noisy stimulation can modify muscle activation patterns (32). Such findings collectively emphasize the importance of accurate vestibular signaling for both cognitive and motor development (33). Interventions combining vestibular and neuromuscular training have been shown to benefit children with Down syndrome (34), and structured programs such as FIFA 11+ effectively improve balance and reduce musculoskeletal injuries (35). However, some studies have reported conflicting results, often due to differences in participant characteristics, methodological approaches, or the type and intensity of sensory challenges used (36, 37). In the present study, removing visual input alone produced minimal effects on muscle activity, whereas the combination of visual deprivation and vestibular disturbance led to substantial increases. This demonstrates the cumulative effect of multi-sensory disruption on neuromuscular responses. These results highlight the importance of strengthening sensory systems during childhood to support lifelong motor health and reduce the risk of functional decline later in life. Prior work suggests that vestibular inputs contribute not only to balance but also to spatial perception and cortical processing (38). Additionally, targeted vestibular exercises have been shown to improve balance and coordination in children with attention-deficit/hyperactivity disorder (39). Biomechanical research also indicates that disruptions in sensory feedback can alter muscle efficiency and movement patterns, influencing joint loading and gait stability (40–42). Given that balance is governed by the interaction of vestibular, visual, and proprioceptive inputs (43, 44), assessing vestibular function in children may reveal underlying motor control vulnerabilities and support early rehabilitation planning (45–48). Overall, the present findings demonstrate that vestibular perturbations significantly reshape muscle activation strategies during gait, reflecting the body’s adaptive attempts to preserve stability when sensory reliability is compromised.

Ethical Considerations
Compliance with ethical guidelines
This study was conducted in accordance with established ethical standards for research involving human participants. The study protocol was reviewed and approved by the Research Ethics Committee of the Sports Science Research Institute (IR.SSRC.REC.1403.005). In line with these guidelines, written informed consent was obtained from all participating children and their parents or legal guardians.
Funding
This research did not receive any grants from funding agencies in the public, commercial, or non-profit sectors. 
Authors' contributions
All authors contributed equally to the conception, design, data collection, analysis, and preparation of the manuscript.
Conflicts of interest
The authors declare that they have no conflicts of interest related to this study.