The goal of this clinical trial is to evaluate whether intensive sensory stimulation therapy can improve upper limb motor skills and sensory function in children aged 12-16 years with severe symptoms of Developmental Coordination Disorder (DCD). The main questions it aims to answer are:

1. Will children with DCD who undergo intensive sensory stimulation therapy show greater improvement in upper limb motor function compared to those receiving standard therapy?
2. Will intensive sensory stimulation therapy lead to better sensory function outcomes, including joint position sense, resistance sense, pressure sense, temperature perception, and two-point discrimination? Researchers will compare children receiving intensive sensory stimulation therapy to those receiving standard therapy without intensive sensory stimulation to see if the targeted intervention results in superior improvements in motor and sensory function.

Background Developmental Coordination Disorder (DCD) is a neurodevelopmental condition that affects the development of motor skills in children, impacting their ability to perform a range of daily activities (Missiuna et al., 2008; Zwicker et al., 2012). According to the Diagnostic and Statistical Manual of Mental Disorders (American Psychiatric Association, 2013), DCD is characterized by difficulties in acquiring and executing coordinated movements.

The diagnostic criteria for DCD include motor abilities that are significantly below what would be expected for the individual's chronological age and learning experiences. These motor challenges must interfere substantially with daily living activities, educational or professional achievements, and hobbies. Symptoms typically emerge in early childhood and cannot be better explained by intellectual disability, neurological conditions affecting movement, or visual impairments. Motor difficulties often present as clumsiness, slowness, and inaccuracy in executing movements (Lachambre et al., 2021).

Recent research highlights the high prevalence and significant impact of sensory processing impairments among children with DCD. Studies have identified notable differences across various sensory domains - including visual, tactile, proprioceptive, auditory, and vestibular processing - when compared to typically developing peers (Tran et al., 2022). Children with DCD, for instance, exhibit greater deficits in proprioceptive processing, such as difficulties with localizing single and double simultaneous stimuli, graphesthesia, finger identification (Elbasan et al., 2012; Malloy-Miller et al., 1995), and two-point discrimination under both dynamic and static conditions (Law et al., 2011).

Children with DCD experience pronounced sensory differences that significantly affect their daily functioning. These sensory differences may also signal the presence of additional neurodivergent traits. Furthermore, sensory processing impairments are closely associated with poor motor coordination and have a substantial impact on daily activities (Keating et al., 2024).

Design and hypotheses The planned study is a randomised controlled trial (RCT) aimed at evaluating the effectiveness of intensive sensory stimulation therapy on upper limb motor skills and sensory function in children with pronounced symptoms of DCD, as assessed by The Movement Assessment Battery for Children - Second Edition (MABC-2).

Main hypotheses:

H1: Children with DCD who undergo intensive therapy involving sensory stimulation will show a significant improvement in upper limb motor function compared to children in the control group after four weeks of intervention.

H2: Children with DCD receiving intensive sensory stimulation will demonstrate significant improvements in upper extremity sensory function compared to the control group.

Specific hypotheses:

H2a: After four weeks of intensive sensory stimulation, children in the experimental group will exhibit better joint position sense compared to children in the control group.

H2b: After four weeks of intensive sensory stimulation, children in the experimental group will show an improved sense of resistance in the upper limb compared to the control group.

H2c: Children in the experimental group will demonstrate better temperature perception than those in the control group.

H2d: Children in the experimental group will display enhanced sense of pressure compared to the control group.

H2e: Children in the experimental group will demonstrate better two-point discrimination sense compared to children in the control group.

General procedure Participant Recruitment and Screening Children aged 12-16 with pronounced symptoms of DCD, identified using The Movement Assessment Battery for Children - Second Edition (MABC-2), will be recruited from the local clinics, schools, and rehabilitation centres.

Inclusion and exclusion criteria are described elsewhere in this record. The M-ABC-2 is a standardized tool used to assess motor coordination and identify movement difficulties in children aged 3 to 16 years. The test version for the age band 11-16 years wil be used. The test's tasks are grouped into three core domains: Manual Dexterity, Aiming and Catching, and Balance. Manual Dexterity tasks evaluate fine motor skills through activities like threading beads or placing pegs. Aiming and Catching tasks focus on hand-eye coordination using items like balls and beanbags. Balance tasks test both static and dynamic balance, such as standing on one leg or walking heel-to-toe along a straight line. The assessment typically takes about 20 minutes. Standardized instructions and materials are used to ensure consistency. Each task is scored based on the accuracy or time taken to complete it. These raw scores are then converted into standard scores and percentile ranks using normative data for the child's age group. Children with scores ranging from 40 to 50 standard points (=pronounced DCD symptoms) will be included.

Based on data from our previous research, we estimated that a total sample size of 82 participants (i.e., 41 per group) is required to achieve sufficient statistical power to detect meaningful differences between the groups. Given the anticipated length and demands of the intervention, we expect an attrition rate of approximately 15% due to potential dropouts. To account for this, we adjusted our recruitment target accordingly (total required N~94).

Baseline Assessment Before the intervention begins, all participants will undergo a baseline assessment. This will include: evaluation of upper limb motor skills using standardised motor tasks from the The Jebsen-Taylor Hand Function Test (JTHFT; Jebbsen et al., 1969; Fabbri et al., 2021); assessment of joint position sense, sense of resistance, sense of temperature, sense of pressure, and two-point discrimination sense.

The JTHFT is a standardized assessment designed to evaluate hand function in relation to everyday tasks. It is commonly used in rehabilitation and clinical settings to measure both fine and gross motor skills in individuals with neurological or musculoskeletal impairments, such as DCD. The test is appropriate for children over the age of five and provides normative data to allow comparison across age and gender groups. The JTHFT includes seven timed subtests, each simulating a daily activity involving the hands. These tasks are: writing a short sentence, turning over cards, picking up and placing small common objects, simulating feeding with a spoon, stacking checkers, moving light cans, and moving heavy cans. These subtests are performed individually, and each is timed in seconds, with shorter completion times indicating better hand function. The test is administered separately for each hand, typically beginning with the non-dominant hand, and it takes approximately 15 minutes.

To ensure consistency, the JTHFT is administered using a standardized protocol that includes specific instructions for each task, standardized materials, and defined starting positions.

Assessments will be conducted by trained evaluators who are blinded to group allocation.

Randomisation Participants will be randomly assigned to either: experimental group (with intensified sensory stimulation), or control group (without intensified sensory stimulation).

To ensure unbiased allocation of participants and equal group sizes, randomisation will be carried out using a computer-generated random number method. Participants will be randomised into either the experimental or control group using a simple randomisation method with allocation concealment, designed for continuous recruitment. Because the full list of participants is not available in advance, each participant will be randomised individually upon enrolment. To ensure equal group sizes over time, an adaptive control mechanism will be used once the halfway point of recruitment is approached. If a group begins to exceed its target number, subsequent participants will be automatically allocated to the underfilled group to maintain balance.

Intervention Phase (4 weeks) Experimental group: Participants will engage in a structured therapy programme focusing on intensive sensory stimulation of the upper limbs. Control group: Participants will receive an equivalent volume therapy programme without intensive sensory stimulation. Therapists administering interventions will follow a standardised protocol to ensure consistency (described esewhere in this record). All physiotherapists delivering the intervention in this study have undergone comprehensive training to ensure high-quality implementation of the intervention protocol. Prior to the start of the study, each physiotherapist will complete a structured training program, including both theoretical instruction and practical application of all intervention components. Their competence will be verified through supervised practice sessions and fidelity assessments, during which they demonstrated a high level of proficiency and adherence to the protocol. The intervention procedures have been developed and refined based on previous experiences. All procedures are non-invasive and have been designed to minimise any physical or psychological burden on participants. While participants may experience temporary fatigue, particularly during physical activity components, no significant risks are anticipated. The physiotherapists are trained to monitor participants closely throughout the intervention sessions and to respond appropriately to any signs of distress or adverse events.

Post-Intervention Assessment Immediately after completing the 4-week intervention, all participants will undergo a second assessment identical to the baseline assessment.

Evaluators will again be blinded to group assignments to minimise bias. Data Analysis Statistical analysis will compare pre- and post-intervention results between the experimental and control groups. Differences in motor performance and sensory function outcomes will be analysed using appropriate statistical tests (e.g., repeated-measures ANOVA, t-tests, non-parametric statistics), depending on data distribution.

Ethical Considerations The study protocol will be approved by an appropriate Research Ethics Committee. All procedures will adhere to ethical standards for research involving human participants, including confidentiality, the right to withdraw, and risk minimisation.

Outcome measures All outcome measures are described in detail elsewhere in this record. All assessors conducting the outcome measurements have undergone rigorous training and demonstrated excellent proficiency in administering the assessment tools. All outcome measures utilised in this study have been previously tested in pilot studies across diverse participant groups and have shown reliability ranging from good to excellent, with intraclass correlation coefficients (ICC) exceeding 0.8. All procedures employed in the study are considered safe. Participants may experience only minimal discomfort during certain assessments, such as pressure sensation testing. However, no significant risks are anticipated. The study protocol has been designed to prioritise participant safety and to ensure that any potential discomfort is transient and within ethically acceptable limits.

Inclusion Criteria:

• between 12-16 years of age
• diagnosed severe symptoms of the developmental coordination disorder based on The Movement Assessment Battery for Children 2nd Edition (M-ABC 2), with scores ranging from 40 to 50
• typical intellectual development (i.e., children attending mainstream education)
• voluntary participation and informed consent signed by parents or legal guardians

Exclusion Criteria:

• current or previous diagnosis of serious orthopaedic or neurological conditions (e.g. fractures, congenital deformities, cerebral palsy, etc.)
• history of any surgical procedures
• history of significant musculoskeletal pain or dysfunction lasting more than two weeks and requiring medical or physiotherapeutic intervention, or any such symptoms occurring within one month prior to the study
• any current musculoskeletal dysfunction and/or pain
• body mass index exceeding 22 kg/m³

Because of the international character of the project, legal considerations may be an issue. If this is not the case, the data may be available on request.

Statisticians responible for data processing and analysis