The goal of this observational study is to learn if trunk control (the ability to balance and stabilize the upper body while sitting or moving) links autism severity to functional exercise capacity in children aged 4-12 years with Autism Spectrum Disorder (ASD). The main questions it aims to answer are:

1. Does trunk control explain why children with more severe ASD have lower functional exercise capacity?
2. Do trunk control and functional exercise capacity differ across ASD severity levels (Level 1, 2, and 3)?

Participants will complete two assessments in a single 30-40 minute session during their routine clinic visit:

1. A trunk control test, where a trained physiotherapist observes seated balance and movement.
2. A 6-Minute Walk Test (6MWT), where the child moves along a flat hospital corridor for 6 minutes and the total distance covered is recorded as a measure of functional exercise capacity.

No treatment or intervention is involved. All assessments are safe, non-invasive, and conducted at a tertiary care children's hospital in Pakistan.

Autism Spectrum Disorder (ASD) is a complex neurodevelopmental condition characterized by decreased cardiorespiratory fitness and motor impairments that limit participation in daily activities. Children with ASD commonly show reduced postural stability and trunk motor control (the ability to maintain and adjust the position of the upper body during movement). These impairments are increasingly recognized as significant contributors to functional limitations in individuals with ASD, yet the precise mechanism linking autism severity to reduced functional exercise capacity has not been formally tested.

This cross-sectional study tests a mediation model: whether trunk motor control explains the relationship between ASD severity and functional exercise capacity. ASD severity is classified using DSM-5 levels (Level 1, 2, and 3) from existing clinical records. Trunk motor control is assessed using the Trunk Impairment Scale (TIS), a validated tool measuring static balance, dynamic balance, and trunk coordination. Functional exercise capacity is measured using the Six-Minute Walk Test (6MWT), conducted per American Thoracic Society guidelines.

Statistical analysis uses bootstrap mediation (PROCESS Model 4, 5,000 resamples), controlling for age, sex, and BMI. This is the first study to examine this mediation pathway in a paediatric hospital setting in Pakistan, where no motor profile has been described in the literature for children with ASD.

Inclusion Criteria:

• Children aged 4-12 years (inclusive) at the time of assessment
• Confirmed diagnosis of ASD according to DSM-5 criteria, documented in the hospital record by a licensed clinical psychologist or developmental paediatrician
• Classified at DSM-5 severity Level 1, 2, or 3 in the existing clinical file
• Currently attending physiotherapy or developmental rehabilitation outpatient services at the hospital
• Able to attempt the Six-Minute Walk Test (6MWT) with or without verbal prompting
• Written informed consent from parent or legal guardian; verbal assent from child where developmentally appropriate (aged 7 years and above)

Exclusion Criteria:

• Co-existing neurological condition independently affecting gait (e.g., cerebral palsy, uncontrolled epilepsy)
• Orthopaedic condition precluding walking or safe execution of the Trunk Impairment Scale
• Acute illness, fever, or significant behavioural crisis at the time of the scheduled assessment session
• Current enrolment in a structured physiotherapy or physical activity intervention programme
• Caregiver refusal of consent or participant non-cooperation with either assessment tool at the time of the visit

Participants will be recruited consecutively from the developmental and rehabilitation paediatric physiotherapy outpatient department of a tertiary care children's hospital in Pakistan.

Individual participant data will not be shared, as the study involves a vulnerable paediatric population. Participant confidentiality and privacy are protected under the study's ethical approval conditions and applicable national research regulations of Pakistan.