This study was designed to investigate the effect of three months of plyometric exercise training on the mechanical and morphological properties of the plantar flexor muscle-tendon unit in children with unilateral cerebral palsy (UCP). Thirty-eight children with UCP were randomly allocated to the plyometric exercise group (n = 19, underwent a plyometric training program) or the Control group (n =19, received usual physical rehabilitation alone). Both groups were assessed for the plantar flexors' morphological and mechanical properties before and after treatment.

Thirty-eight children with CP participated in the study. They were recruited from King Khalid Hospital and Physical Therapy Center of College of Applied Medical Sciences at Prince Sattam bin Abdulaziz University, Al-Kharj, Saudi Arabia. Their age ranged between 10 and 16 years, were functioning at levels I or II according to the Gross Motor Function Classification System, and had spasticity level 1 or 1+ per the Modified Ashworth Scale. Children were excluded if they had nonreducible structural deformities, received neurolytic agents such as BOTOX or Phenol injections in the past six months, underwent neuromuscular or orthopedic surgery in the last 12 months, or if they had cardiopulmonary problems preventing them from performing high-intense exercise training.

Outcome measures

1. Plantar Flexors' Morphological Properties: length of gastrocnemius muscle-tendon unit, gastrocnemius muscle belly, and achilles, in addition to fascicle length, pennation angle, and gastrocnemius muscle thickness were assessed using a standard high-resolution ultrasound imaging system.
2. Plantar Flexors' Mechanical Properties: Passive range of motion of the ankle joint and maximum isometric voluntary contraction were assessed using an isokinetic dynamometer.

The plyometric exercise group received a 12-week plyometric training program. Each session lasted 45 minutes and was repeated two times a week. The training was conducted in conformity with the National Strength and Conditioning Association guidelines and American Academy of Pediatrics safety standards. The plyometric exercise program consisted of ten unilateral and bilateral lower limb plyometrics in the form of hopping/bounding/jumping activities. The Iplyometric workout was proceeded by a 5-minute warm-up and ended up with a 5-minute cool-down. The control group received their usual physical rehabilitation program for 45 minutes, twice/week for 12 consecutive weeks. The program comprised advanced balance training, and gait training exercises, postural and flexibility exercises, strength training exercises.

Inclusion Criteria:

• Hemiparetic cerebral palsy
• Age between 10 to 16 years
• Spasticity level 1 or 1+ according to the Modified Ashworth Scale
• Gross motor function level I or II according to the Gross Motor Function Classification System

Exclusion Criteria:

• Structural deformities
• Musculoskeletal or neural surgery in the last year
• BOTOX injection in the last 6 months.
• Cardiopulmonary disorders limit the ability to engage in explosive exercise training
• Perceptual and behavioral disorders.

This was a single-blind protocol. The researcher who collected the data was blind to the allocation of treatment.