Motor competence (MC) is the ability to execute different motor tasks, and reflects the degree of mastery of fine and gross motor skills , . MC is a key component in children and adolescents in developing a healthy, active lifestyle and is a predictor of physical fitness [1-3]. Previous literature suggested that MC is expected to improve linearly with physical fitness as children develop, and that higher levels of MC allow for greater participation in physical activities, whereas low MC is associated with less physical activity , . Most studies focused on the external factors affecting MC, such as physical education classes and environmental interplay, but little is known about the association between MC and intrinsic factors, such as proprioception.
Proprioception is the conscious awareness of relative body limb position and motion, and plays a crucial role in limb coordination, kinematic control, and motor planning [4, 5].. Afferent proprioceptive signals to the brain originate from muscle spindles, Golgi tendon organs, ligaments, and joint capsules [7, 8]. Typical growth and development demonstrates an age-related pattern of improved proprioception within the elbow joints, where Typically Developed (TD) children show a larger error [9, 10] and variability compared to TD adults . Proprioceptive feedback is important in early skill development, especially when learning a motor sequence . However, little is known about the relationship between proprioception and MC. A better understanding of the influence of MC and proprioception on motor skill development is essential for fostering greater physical activity across the lifespan, especially in those with Developmental Coordination Disorder.
Developmental Coordination Disorder (DCD) is characterized by clumsy movement and poor motor skill learning [13-15]. The exact cause of DCD is unknown, but is often thought to be multifactorial . It has been partially linked with atypical brain development , sensorimotor dysfunction in the central nervous system , and environmental factors . Therefore, diagnosis of DCD entails a complex developmental and medical history, physical examination, school or workplace report, and motor competence assessment . The Movement Assessment Battery for Children 2nd Edition (mABC-2) assesses motor skill levels in children aged 3 to 16 years. Children with DCD generally show a lower total standard score on the mABC-2, indicating a lower level of motor skills compared to TD children . In school-aged children and adolescents, the estimated prevalence of DCD is 5-6% [22, 23]. This population showed decreased physical activity, difficulties with activities of daily living, and reduced academic performance and social participation [22, 24, 25]. Decreased MC in the DCD population have significant effects on health and quality of life, as DCD children have been found to be less physically active than their TD peers, and are unable to meet the global physical activity guidelines .
The DCD population shows impairments that affect the acquisition and execution of motor-related activities . Previous studies revealed that DCD children performed with poorer kinematic control of the upper limbs compared to TD children . Kinematic control is the ability to initiate and produce purposeful, precise movements. Common kinematic measures include movement trajectory, time, velocity, and normalized jerk [28-30]. Previous studies showed that DCD children performed with slower reaction times, larger endpoint errors, longer movement and/or deceleration times with more curved trajectories, and showed greater variability in movement speed compared to TD children in upper limb tasks [27, 31]. Normalized jerk (NJ), which is often used to measure movement smoothness [30, 32, 33], was found in children with and without DCD to have the same developmental trajectory; however, when controlled for age, children with DCD exhibited greater NJ in upper limb movement .
It has been speculated that decreased MC is associated with poor proprioception; however, previous literature on the proprioceptive deficits in the DCD population have been controversial [35-37]. Some studies indicated poorer proprioceptive function in DCD compared to TD adolescents [36, 38-40], whereas other studies showed no differences between the two populations [41-44]. In one research, DCD children were found to require more time in detecting passive elbow joint movement compared to TD children , but another study found no differences between the two groups in absolute error . Other evidence indicated low correlation between mABC-2 scores (representing MC) and proprioception of the upper extremities in TD and DCD children [37, 40, 41]. These studies, however, focused mainly on upper extremity proprioception in younger children. Little is known about lower extremity performance in adolescents. For adolescents aged 13 to 14, who are at a critical stage of development where they experience changes in motor abilities and develop new motor skills, lower limb performance is a crucial aspect that affects development of complex skills into their teenage and adult years .
Testing of proprioceptive ability, however, remains difficult, as there are very few objective tools to measure proprioception. Previous studies estimated proprioception using a kinesthetic sensitivity test (KST) and kinesthetic acuity test (KAT) in children with[36, 37] and without[35, 37, 48] DCD, but the accuracy of these methods have been criticized [45, 49]. Joint position sense is a simpler method than measuring movement sense , and a variety of tools, including goniometers  and other customized apparatuses [7, 9, 11, 49], have been used, however, mainly to assess proprioception of the upper extremity. Only one study assessed lower extremity joint position sense using a Biodex isokinetic dynamometer, which is limited to the laboratory setting . To our knowledge, there is currently no valid evidence of an objective assessment for proprioception that can be used for the lower extremities in adolescents.
Thus, our research set out to estimate joint position sense and kinematic control using a single inertial measurement unit (IMU) in a cross-sectional cohort of children, and to explore the extent to which these measures are associated with motor competence in adolescents aged 13 to 14 years.