The aim of this study is to investigate if ankle-foot orthoses affect changes in muscle activity of children with spastic unilateral cerebral palsy during walking.

To minimize investigator variability, the same orthotist CO, clinical gait analyst GA and physiotherapist PT will perform their designated functions for all participants.

Each subject will be required to attend three appointments.

First appointment: CO takes a lower leg cast of the involved side; the cast is taken with the ankle and hindfoot corrected to neutral position.

Second appointment: CO fits the tone-reducing ankle-foot orthosis which entails trimming the device to fit footwear, checking the orthotic device restricts plantarflexion and ensuring comfortable and functional fit. The device is modified with holes for electrode placement at locations for tibialis anterior and gastrocnemius identified by PT.

The child receives the tone-reducing ankle-foot orthosis and is instructed to use this orthotic device on a daily basis for the next four weeks to grow accustomed to the tone-reducing stimuli which may require some acclimatization.

Third appointment: A clinical examination is conducted by PT. Surface gel electrodes are then attached while the participant is instructed in individual muscle activation tests; SENIAM guidelines will be followed for electrode placement and skin preparation, aside from hamstrings and rectus femoris which will follow amended instructions in line with the scientific literature.

GA quality checks the raw electromyography (EMG) signals by visual inspection during the isolated muscle activation tests and during a dynamic trial for movement artefacts, cross-talk, baseline drift and good noise-to-signal ratio.

Reflective markers are then applied in accordance with Plug-in Gait lower body model by PT to collect kinematic and kinetic data.

A resting trial is collected to establish the baseline activity level for each muscle.

The participant is instructed to walk at a self-selected speed along the walkway. Dynamic trials continue until two clean strikes to the middle force plate are collected for the involved leg. Barefoot data is collected first while any additional modifications necessary for electrode placement are made to the ankle-foot orthoses. The order of the orthotic conditions is randomized.

Data will be recorded confidentially using reference codes for participants and stored on a secure server with designated space allocated by the hospital.

Inclusion criteria:

• Spastic unilateral cerebral palsy (hemiplegic)
• Use of an ankle-foot orthosis (AFO) during walking because of equinus in the ankle,
• Excessive plantarflexion during walking
• Gross Motor Function Classification System (GMFCS) I or II

Exclusion criteria:

• Orthopedic surgery on the involved lower limb during the previous 12 months
• Treated with BTX-a in muscles of the involved lower limb during the previous 6 months
• Operated with selective dorsal rhizotomy (SDR)
• Passive dorsiflexion in the ankle, passive extension of the knee and hip < 0 degrees (no fixed contractures)